Flood-irrigated
Tropical Timber
Trials in the North of
Western Australia
NOVEMBER 2012
RIRDC Publication No. 12/044
Flood-irrigated Tropical Timber
Trials in the North of Western
Australia
1,2
2
by Dr Liz Barbour , Professor Julie Plummer and Len Norris
November 2012
RIRDC Publication No. 12/044
RIRDC Project No. PRJ-002676
1,3
© 2012 Rural Industries Research and Development Corporation.
All rights reserved.
ISBN 978-1-74254-493-9
ISSN 1440-6845
Flood-irrigated Tropical Timber Trials in the North of Western Australia
Publication No. 12/044
Project No. PRJ-002676
The information contained in this publication is intended for general use to assist public knowledge and
discussion and to help improve the development of sustainable regions. You must not rely on any information
contained in this publication without taking specialist advice relevant to your particular circumstances.
While reasonable care has been taken in preparing this publication to ensure that information is true and correct,
the Commonwealth of Australia gives no assurance as to the accuracy of any information in this publication.
The Commonwealth of Australia, the Rural Industries Research and Development Corporation (RIRDC), the
authors or contributors expressly disclaim, to the maximum extent permitted by law, all responsibility and liability
to any person, arising directly or indirectly from any act or omission, or for any consequences of any such act or
omission, made in reliance on the contents of this publication, whether or not caused by any negligence on the
part of the Commonwealth of Australia, RIRDC, the authors or contributors.
The Commonwealth of Australia does not necessarily endorse the views in this publication.
This publication is copyright. Apart from any use as permitted under the Copyright Act 1968, all other rights are
reserved. However, wide dissemination is encouraged. Requests and inquiries concerning reproduction and
rights should be addressed to the RIRDC Publications Manager on phone 02 6271 4165.
Researcher Contact Details
1
Dr Liz Barbour and Len Norris
Forest Products Commission
Locked Bag 888
Perth BC WA 6849
2
Dr Liz Barbour and Prof Julie Plummer
University of Western Australia
35 Stirling Highway
Crawley WA 6009
3
Email: [email protected]
Email: [email protected]
Email: [email protected]
Len Norris
Dept Agriculture and Food WA
Locked Bag 4
Bentley delivery centre WA 6983
In submitting this report, the researcher has agreed to RIRDC publishing this material in its edited form.
RIRDC Contact Details
Rural Industries Research and Development Corporation
Level 2, 15 National Circuit
BARTON ACT 2600
PO Box 4776
KINGSTON ACT 2604
Phone:
Fax:
Email:
Web:
02 6271 4100
02 6271 4199
[email protected].
http://www.rirdc.gov.au
Electronically published by RIRDC in November 2012
Print-on-demand by Union Offset Printing, Canberra at www.rirdc.gov.au
or phone 1300 634 313
ii
Foreword
This report records a joint project between the Rural Industries Research and Development
Corporation (RIRDC), the Forest Products Commission of Western Australia, Elders Forestry and the
University of Western Australia to ensure that the original plantation trials and plantings of tropical
tree species in the Ord River Irrigation Scheme (ORIS) on the Frank Wise Institute site were assessed
and published. Sixteen trials were selected to provide scientific information on:
•
sandalwood (Santalum album) growth rates, heartwood and oil production, and product
definition
•
African mahogany (Khaya senagalensis) growth rates
•
teak (Tectona grandis) growth rates
•
pongamia (Millettia pinnata) growth rates, seed production and seed oil quality
•
identification of other tropical species that could either be used as a long-term host for
sandalwood or as a tropical timber project for the north of Australia.
This set of trials holds valuable information which has and will assist in all aspects of the developing
essential oil and plantation industry in the north of Western Australia and similar developing tropical
forestry industries in Queensland and Northern Territory. The report provides a perspective of
different tree systems and their performance in flood-irrigated systems.
The sandalwood trials selected demonstrate a variety of silviculture systems. Outstanding trees, far
beyond expectations, were found within these trials. As with any plantation program, the aim of
breeders and silviculturalists alike is to uniformly repeat this exceptional performance in every tree
across each hectare of plantation. Tree distribution required to optimise a site for sandalwood
performance was investigated and discussed. Prior to this report, sandalwood growth analyses were
either on young plantations where inter-tree competition had not emerged as a parameter or on
singled-out older trees. The analysis of each of these trials explores the average expected performance
with different silviculture management systems.
New crop development is not encouraged when land valuation is as high as is presently being
experienced in the ORIS. Whereas annual crops can be manipulated to produce multiple generations
within a year, the first full-rotation commercial harvest of sandalwood will only occur in 2016 (a 15year rotation) and similarly with other tropical species. Sandalwood oil, at present, has a high
commercial potential that can support this slow development cycle. However, other tropical timber
species need to confront a range of issues before being considered viable.
This report is an addition to RIRDC’s diverse range of over 2100 research publications and it forms
part of our Essential Oils and Plant Extracts R&D program. RIRDC's vision for this program is of a
profitable and sustainable industry producing essential oils and plant extracts of the quality and
content that meets customers' evolving demands.
Most of RIRDC’s publications are available for viewing, free downloading or purchasing online at
www.rirdc.gov.au. Purchases can also be made by phoning 1300 634 313.
Craig Burns
Managing Director
Rural Industries Research and Development Corporation
iii
About the Authors
The Forest Products Commission is a Western Australian state agency that was formed out of the
Department of Conservation and Land Management in 2000. A number of researchers and technicians
have been responsible at various stages for the establishment and management of a series of tropical
tree trials at the Frank Wise Institute in the Ord River Irrigation Area. It is through this commitment
by the West Australian State Government that demonstration trails, research information and
germplasm has been made available to establish three budding tropical forestry industries: tropical
sandalwood (Santalum album), African mahogany (Khaya senegalensis) and teak (Tectona grandis).
The management and research associated with these trials provides continued support for these
fledgling industries.
Dr Liz Barbour and Len Norris were the two researchers from the Forests Products Commission
responsible for management and research program development during the period of this RIRDCsupported project. Dr Barbour is now with the University of Western Australia and Len Norris is
seconded to the Department of Agriculture and Food in Western Australia.
Professor Julie Plummer is a plant scientist from the University of Western Australia. She has been
studying production of tropical timbers and oil biosynthesis in sandalwood for most of the last decade.
She is the chief investigator on the Australian Research Council Linkage Project (LP0882690)
‘Elucidation of genetic and physiological factors controlling biosynthesis of sesquiterpenoids in
sandalwood, Santalum spp’, and the ARC Linkage Project LP100200016 ‘Molecular characterisation
of the fungal disease defence response in tropical sandalwood (Santalum album)’.
iv
Acknowledgments
We acknowledge and are grateful for the assistance provided by the following:
•
Rural Industries Research and Development Corporation, especially Dr Ros Prinsley (former
employee) and Ms Alison Saunders, for supporting this project so that these trials could be
documented
•
Forest Products Commission, especially Gavin Butcher, Peter Jones (former employee) and Grant
Pronk (former employee), for ensuring the management of the site so that this work could be
undertaken. John Streatfield (former employee) managed the site and assisted with the harvesting
during the period of this project. Dr Andrew Lyon completed the acoustic time-of-flight
measurement on sandalwood
•
Elders Forestry for their financial and in-kind support for the project. This project was initiated
with Dr Andrew Callister (former employee) and passed over to Dr Marie Connett
•
PhD students at the University of Western Australia: Jessie Moniodis (University of Western
Australia) for her technical assistance with the sandalwood oil analyses and Ni Luh Arpiwi for
completing the seed oil analyses for Millettia
•
Dr Chris Jones (University of Western Australia), Professor Joerg Bohlmann (University of
British Columbia, Canada) and Dr Katherine Zulak (formerly University of British Columbia,
Canada) for their thoughtful suggestions regarding aspects of sesquiterpene oil synthesis in this
project and during its development and analysis
•
Dr Andrew Callister of Treehouse Consulting who developed the individual tree-competition
indices and undertook the analysis
•
Craig Hallam of Enspec for undertaking the electrical impedance tomography.
v
Abbreviations
Institutions/Organisations
ACIAR
Australian Centre for International Agricultural Research
CALM
Conservation and Land Management with was formed from an amalgamation of
the Forests Department, the wildlife section of the Department of Fisheries and
Wildlife and the National Parks Authority. In 1990 it was split into the
Department of Environment and Conservation and the Forest Products
Commission.
DAFWA
Department of Agriculture and Food, Western Australia
DEC
Department of Environment and Conservation, Western Australia
FPC
Forest Products Commission, Western Australia
Elders Forestry
Integrated Tree Cropping Limited renamed Elders Forestry Limited
MU
Murdoch University
ORIS
Ord River Irrigation Scheme
ORIA
Ord River Irrigation Area
TFS
Tropical Forestry Services
UBC
The University of British Columbia, Vancover, Canada
UWA
The University of Western Australia, Perth, Western Australia
Parameters
BD
Basal diameter
HVT
High-value timber
BR
Basal radius
LEA
Large end area
CBD
Crown break diameter
LED
Large end diameter
CSV
Canopy stem volume
LER
Large end radius
DBH
Diameter at breast height (130 cm
above ground)
MAI
Mean annual increment
EBV
Estimated bole volume
SEA
Small end area
ESV
Estimated stem volume
SED
Small end diameter
HCI
Host count index
SER
Small end radius
HSDI
Host size-distance index
SPH
Stems per hectare
vi
Contents
Foreword ............................................................................................................................................... iii
About the Authors ................................................................................................................................ iv
Acknowledgments.................................................................................................................................. v
Abbreviations ........................................................................................................................................ vi
Executive Summary ............................................................................................................................. xi
1
Introduction ............................................................................................................................ 1
1.1 Background .............................................................................................................................. 1
1.2 Tropical forestry history in the Ord River Irrigation Scheme ................................................. 3
1.3 Sandalwood as a crop ............................................................................................................ 12
2
Objectives ............................................................................................................................. 16
3
Methodology ......................................................................................................................... 16
3.1 General methods and formula ................................................................................................ 17
3.2 Main species .......................................................................................................................... 18
4
Sandalwood (Santalum album) trials ................................................................................. 20
Sandalwood host selection demonstration plots .................................................................... 20
Sandalwood growth with Cathormion umbellatum ............................................................... 27
Investigation of spatial competition analysis ......................................................................... 39
Sandalwood heartwood and oil development ........................................................................ 54
4.1
4.2
4.3
4.4
5
5.1
5.2.
5.3
5.4.
5.5
High-value timber trials ...................................................................................................... 79
A summary of Khaya senegalensis growth within trials of different age and
silviculture, Trials 5, 7, 11, 12 and 15 ................................................................................... 79
Comparison of the growth of eleven high-value timber species, Trial 12 ............................. 83
Growth assessment of high-value timber demonstration plots, Trials 10, 11, 13 and
15............................................................................................................................................ 88
The growth of teak (Tectona grandis) on levee soil, Trial 14 ............................................... 91
Growth, seed yield and oil characteristics of Millettia pinnata, Trial 16 .............................. 96
6
Implications ........................................................................................................................ 100
6.1 Sandalwood trials ................................................................................................................. 100
6.2 High-value timber trials ....................................................................................................... 101
7
Recommendations .............................................................................................................. 103
Appendix A ........................................................................................................................................ 104
References .......................................................................................................................................... 106
vii
Tables
Table 4.1
Table 4.2
Table 4.3
Table 4.4
Table 4.5
Table 4.6
Table 4.7
Table 4.8
Table 4.9
Table 4.10
Table 4.11
Table 4.12
Table 4.13
Table 4.14
Table 4.15
Table 4.16
Table 4.17
Table 4.18
Table 4.19
Table 4.20
Table 4.21
Table 4.22
Table 4.23
Table 4.24
Table 4.25
Table 4.26
Table 4.27
Growth parameters of sandalwood and hosts in Trial 5 when they were 11 years old .....................21
Measured and estimated growth parameters of 15-year-old Peltophorum and Cassia as
sandalwood hosts in Trial 3 .............................................................................................................23
Measured and estimated growth parameters of 15-year-old sandalwood with host species
Peltophorum and Cassia in Trial 3 ..................................................................................................23
Growth parameters of 18-year-old and 17-year-old sandalwood established in 1990 (Trial 1)
and 1991 (Trial 2) respectively ........................................................................................................25
Growth parameters of sandalwood in 1991 (Trial 2) when planted in dual host configurations ......25
Growth parameters measured at 18 years and 17 years for host species established in 1990
(Trial 1) and 1991 (Trial 2) respectively .........................................................................................26
Sandalwood (S) and host (H) spacing and stocking for the six ratio treatments in the original
planting design of Trial 9 .................................................................................................................28
Trial 9 host (H) and sandalwood (S) stocking rates after culling of plots in 2003 ...........................29
The within column spacing and stems per hectare (SPH) for the six stocking treatments of
sandalwood and Cathormion umbellatum hosts in Trial 6...............................................................33
Age and planting details of Cathormion host trials..........................................................................37
P-values for model effects on sandalwood basal diameter using host count indices (HCI) in
Trial 7 ..............................................................................................................................................42
Estimates for significant effects of host count index (HCI) on sandalwood basal diameter in
Trial 7 ..............................................................................................................................................43
P-values for model effects on sandalwood basal diameter using host size-distance indices
(HSDIs) in Trial 7 ............................................................................................................................44
Estimates for significant effects of host size-distance index (HSDI) on sandalwood basal
diameter in Trial 7 ...........................................................................................................................45
Summary of selected significant linear models explaining the relative growth of sandalwood
with Peltophorum and Cassia hosts between 2001 and 2008 in Trial 3 ..........................................50
Summary of selected significant linear models explaining sandalwood stem volume with
Peltophorum and Cassia hosts in Trial 3 .........................................................................................52
Summary of selected significant linear models explaining the stem volume of Peltophorum
and Cassia in Trial 3 ........................................................................................................................53
Growth parameters for 30 trees destructively harvested
after 8 years from Trial 8 .................................................................................................................57
Total disc area and the area and percentage of heartwood and rot with discs located along
the bole of 30 sample trees in Trial 8 ...............................................................................................58
Field-determined parameters for the 40 trees sampled from Trial 4 ................................................63
Parameters calculated from photographic analysis of the four discs along the boles from trees
in Trial 4 ..........................................................................................................................................63
Mean estimated under-bark volume and heartwood volume and the percentage heartwood
(± s.d.) for bole sections, canopy stem and total above-ground volume ..........................................63
Total oil yield (g/kg) and santalol composition of the five sample locations in 20 trees
subsampled from Trial 4 ..................................................................................................................64
Proportion of alpha and beta-santalol in oil from the five sample locations in 20 trees
subsampled from Trial 4 ..................................................................................................................64
Over-bark measurements for sandalwood trees growing with the three host treatments in
Trial 7 ..............................................................................................................................................69
Core and cross-sectional parameters for sandalwood grown with the three host treatments in
Trial 7 ..............................................................................................................................................69
Proportion and yield (g/kg) of alpha-santalol, beta-santalol and total oil from cores sampled
at 30 cm from sandalwood with Cathormion, Dalbergia and Millettia hosts ..................................72
viii
Table 5.1
Table 5.2
Table 5.3
Table 5.4
Table 5.5
Table 5.6
Table 5.7
Table 5.8
Table 5.9
Table 5.10
Summary description of trial plots in which Khaya senegalensis was planted ................................80
Khaya senegalensis growth measurements across Trials 5, 7, 11, 12 and 15. Results at the
hectare level were calculated using surviving number of Khaya stems per hectare .........................81
Estimated parameters assessed for the nine high-value timber species surviving after 12
years (2008) in Trial 12 ...................................................................................................................87
Description of high-value timber demonstration plots in Trials 10, 11 and 15 ................................89
High-value timber growth measurements in Trials 10, 11, 13 and 15. ............................................90
Growth parameters for teak aged 3, 8 and 10 years at Kununurra in Trial 14 .................................94
Proportion of teak trees infected with termites assessed 10 months after planting in Trial 14,
DBH per pesticide treatment at 3 years of age and DBH with
outliers/runts removed .....................................................................................................................95
Seed traits of Millettia pinnata ........................................................................................................97
Correlations between measured seed variables of Millettia pinnata ................................................98
Composition of fatty acids within oil derived from seed of Millettia pinnata .................................98
Figures
Figure 1.1
Figure 4.1
Figure 4.2
Figure 4.3
Figure 4.4
Figure 4.5
Figure 4.6
Figure 4.7
Figure 4.8
Figure 4.9
Figure 4.10
Figure 4.11
Figure 4.12
Figure 4.13
Figure 4.14
Figure 4.15
Figure 4.16
Location of the ORIS, Kununurra (blue dot) in the north of Western Australia in relation to
the state capital, Perth (red dot) .........................................................................................................2
Trial 5 layout showing within and between row spacing (distance across plot from corner) for
sandalwood and hosts. .....................................................................................................................21
Trial 9 planting layout of sandalwood (S) and Cathormion host (H), for the six ratio treatments. ..29
Sandalwood tree height (cm), bole height (cm) and basal diameter (mm) within ratio treatments
of sandalwood (S) with a Cathormion host (H) when Trial 9 was 1 year old (2001) ......................30
Sandalwood (S) and Cathormion host (H) growth parameters in Trial 9 post culling (in 2003)
measured in 2008 .............................................................................................................................31
Trial 9 sandalwood (S) growth parameters measured in 2008 (8 years) of post culling treatments
without hosts (H) based on original treatments (Table 4.7) .............................................................31
Estimated stem volume (m3) of sandalwood for long-term host stocking treatments and
intermediate host types within treatments after 9 years in Trial 6 ....................................................34
Height (cm) of Cathormion umbellatum and sandalwood within the six stocking treatments
after 9 years in Trial 6 ......................................................................................................................34
Estimated sandalwood stem volume per hectare after 9 years in Trial 6 .........................................35
Relationship between the number of sandalwood per hectare and the mean individual tree
estimated stem volume (ESV), and the mean estimated stem volume per hectare (ESVha) in
Trial 6 after 9 years ..........................................................................................................................35
Basal diameter (cm) and estimated basal area per hectare (m2 ha-1) for Cathormion umbellatum
within stocking treatments in Trial 6 after 9 years ...........................................................................36
Diameter (a) and height (b) of sandalwood grown with Cathormion hosts generally at a 1:1
ratio with 462 sandalwood stems per hectare...................................................................................38
Mean basal diameter of 8-year-old sandalwood trees estimated on an internal and whole-plot
basis in Trial 7 .................................................................................................................................41
Spatial representation of a subject sandalwood tree (solid star) surrounded by four neighbouring
host trees (A–D: solid diamonds) within qualifying distance ..........................................................49
Stylistic representation of mean heartwood and rot areas within discs along the bole (a), and
an example of non-uniform heartwood production with rot in the centre (b) from Trial 8 ..............59
Relationships between the percentage of rot and aromatic wood within (a) all discs and (b) a
comparison of discs with rot originating in the centre and other sites in boles from Trial 8............59
Basal diameter class distribution of the 40 trees sampled in Trial 4 ................................................62
ix
Figure 4.17
Figure 4.18
Figure 4.19
Figure 4.20
Figure 4.21
Figure 4.22
Figure 4.23
Figure 5.1
Figure 5.2
Figure 5.3
Figure 5.4
Relationship between the height of the sampled disc within the tree (m) and (a) the total oil
yield, and (b) the percentage composition of total santalol within the oil in 20 trees subsampled
from Trial 4 ......................................................................................................................................65
Relationship between total oil yield (g/kg) of individual samples and (a) the cross-sectional
disc and heartwood area (cm2), and (b) the percentage of heartwood in 20 trees subsampled
from Trial 4 ......................................................................................................................................66
Estimated oil yield (g) for each of 20 subsampled trees in Trial 4, indicating the contribution
of the root stump, lower third, middle third and upper third of the bole ..........................................66
Relationships between sandalwood cross-sectional disc area (cm2) and (A) cross-sectional
heartwood area, and (B) cross-sectional heartwood proportion (%) in trees from Trial 7 ...............70
Relationships between heartwood % and (A) host size-distance index (HSDI) and, (B) host
count index (HCI) in trees from Trial 7. ..........................................................................................71
The electrical impedance tomograms for the 8-year-old tree (Tree 1, left), and the extrapolated
3-D tomogram and extracted discs for the 8-year-old (centre) and 15-year-old tree (Tree 2,
right) respectively ............................................................................................................................75
Relationships between IML readings and (a) heartwood area with discs for 9-year-old trees
from Trial 8 and (b) 15-year-old trees from Trial 4, heartwood diameter within discs for (c)
9-year-old and (d) 15-year-old trees, and percentage heartwood within discs for (e) 9-year-old
and (f) 15-year-old trees ..................................................................................................................77
Tree survival (%) for high-value timber species in Trial 12 from 1998 to 2008 .............................84
Height (a) and DBH (b) for high-value timber species in Trial 12
from 1998 to 2008 ...........................................................................................................................85
(A) Survival-adjusted estimated stem volume per hectare (m3), and (B) mean annual increment
for estimated stem volume of high-value timber species in Trial 12 between 1998 and 2008 .........86
Frequency (%) of high-value trees in Trials 10, 11 and 12 with one, two and three stems at
breast height .....................................................................................................................................90
Plates
Plate 1.1
Plate 1.2
Plate 1.3
Plate 1.4
Plate 1.5
Plate 1.6
Plate 4.1
Plate 4.2
Plate 4.3
Plate 4.4
Plate 4.5
Plate 5.1
Plate 5.2
Cununurra clay showing the cracking ability of this clay soil ............................................................2
Drilling a core from a sandalwood tree ..............................................................................................8
Santalum album tissue cultured shoots from juvenile tissue (The Tree Lab) ..................................11
Santalum album clonal plants used in the trial established in the ORIS (Nippon Paper) ................11
Testing the concept of Millettia pinnata hedges by directly sowing the seed. .................................14
One lay-out for flood-irrigated sandalwood plantation establishment. ............................................15
Trial 1 showing the planting arrangement with the sandalwood and Cathormium ..........................24
The sandalwood block in Trial 2 showing the edge effect together with Cathormion .....................26
Typical 8-year-old tree from this trial ..............................................................................................56
A sample of the 8-year-old wood assessed after the destructive harvest..........................................56
The plot combining sandalwood with the long-term host Dalbergia ...............................................68
Examples of wind-swept boles (top left), crooked boles (top right), and a tree displaying
favourable phenotype (bottom left), in a 9-year-old African mahogany plantation .........................82
The teak trial showing the variability in performance......................................................................93
Plate 5.3
The Millettia pinnata plot at the time the seed harvesting was completed for this report ........... 96
x
Executive Summary
What the report is about
This report records a joint project between the Rural Industries Research and Development
Corporation (RIRDC), the Forest Products Commission (FPC) of Western Australia, Elders Forestry
and the University of Western Australia (UWA) to ensure that 16 of the original plantation trials and
plantings of tropical species established in the Ord River Irrigation Scheme (ORIS) by the Western
Australian Government were assessed and published.
Who is the report targeted at?
The main target groups of this research are researchers and managers, especially within the Western
Australian Government system, non-governmental organisations and commercial and private
companies actively growing sandalwood in the ORIS. The included information on growth rates and
essential oil production will be of interest to investors and consultants.
Where are the relevant industries located in Australia?
The tropical sandalwood industry is presently focused in the ORIS on the outskirts of Kununurra in
the north of Western Australia. The biggest company in this sector is Tropical Forestry Services
(TFS). Elders Forestry and TFS have experimented with sandalwood plantations in Queensland and
there has been discussion of plantations starting in the Northern Territory. In addition there are private
growers who have attracted private investment. A number of Aboriginal communities have considered
tropical sandalwood as an enterprise. The tropical hardwood industry has been mainly developing in
Queensland and the Northern Territory and includes both teak and African mahogany.
The focus FPC has requested of UWA is to transfer tropical sandalwood knowledge to the more
ancient species, Australian sandalwood (Santalum spicatum). The ownership of these plantations
covers a wider spectrum of land and investment options and ranges from the private farmer to foreignowned managed investment schemes.
Background
Sandalwood, an otherwise insignificant hemi-parasitic tree, forms heartwood within its trunk that
contains one of the most sought-after essential oils, sandalwood oil. The sesquiterpene components
that make up the oil protect the tree’s core from fungal and insect attack. The oils are extracted and
used in a number of niche products, such as the base note for the most expensive perfumes. There are
also many products being discovered that address an increasing number of human health benefits.
In Western Australia in the 1980s, the concept of cultivating sandalwood was first considered in 1988.
An agreement between the Department of Conservation and Land Management (CALM, formerly the
Forests Department) and Department of Agriculture and Food Western Australia (DAFWA) was
reached and a series of plantings looking at different host combinations were established at the Frank
Wise Institute.
In 2000 the Forest Products Commission (FPC) was formed from the commercial activities within
CALM. The Tropical Forestry project at Kununurra based at the Frank Wise Institute became the
responsibility of FPC and was to work on a number of issues to do with sandalwood research,
including understanding and recording each planting/trial at the Frank Wise Institute.
xi
Aims/objectives
The 16 trials selected aimed to highlight information on: sandalwood (Santalum album) growth rates,
heartwood and oil production and product definition; African mahogany (Khaya senagalensis) growth
rates; teak (Tectona grandis) growth rates; pongamia (Millettia pinnata) growth rates, seed production
and seed oil quality; and the identification of other tropical species that could either be used as a longterm host for sandalwood or as a tropical-timber project for the north of Australia.
Methods used
There are two main groups of trials: those concerned with sandalwood and its hosts; and those related
to high-value timber species. Where possible, statistical analyses were completed using the original
design elements of the trials; however, where trials were of a demonstrational nature or no longer
conformed to the original design due to high mortality, only comparisons of descriptive results have
been made. In addition to trial measurements, destructive harvesting of sandalwood was undertaken,
and two non-invasive techniques were evaluated for their potential use in determining aromatic wood.
Results/key findings
Barbour (2008) indicated that the best hosts for tropical sandalwood were Cathormion umbellatum,
Dalbertgia latifolia and Millettia pinnata and this was further supported by the analyses of these
additional trials. Hosts producing lower sandalwood growth rates were Cassia siamea, Khaya
senegalensis, Peltophorum pterocarpum and Swietenia mahogani.
Poor host performance was related to a fast-growing nature and spreading canopy that enabled
dominant host occupation of the site and spatial competition with the sandalwood. An unexpected
finding was that even when tropical sandalwood was growing with favourable hosts, spatial
competition could negatively influence sandalwood growth. A specific trial designed to explore this
aspect showed that 9-year-old sandalwood growing with Cathormion displayed a growth decline when
sandalwood stocking rates were increased and when planted in different host-to-sandalwood ratios.
Trial analysis using spatial competition indices indicated that increasing host and sandalwood
stocking could produce a situation of negative competition effects on sandalwood growth rate. What
was of importance was how the nature of these competition interactions varied between hosts.
Heartwood formation was found within 8-year-old sandalwood; however, the amount and
development along the stem was generally low and highly variable between trees. In 15-year-old trees,
heartwood development was more reliable, and in some cases extended as far as 3.5 m up the tree
compared to a maximum of up to 1.8 m in 8-year-old trees. The calculated heartwood volume for 15year-old trees was approximately 6.3 kg, with the majority (4.4 kg) occurring in the bole.
Oil extracted from 11-year-old and 15-year-old sandalwood samples was of high quality, as indicated
by the alpha and beta-santalol composition standards required for S. album oil (ISO 3518:300E). Oil
yields from a single core that included heartwood and sapwood taken at 30 cm above the ground were
typically low (average of 1.3 per cent); however, after adjusting yield to reflect the sapwood-toheartwood ratio within cores, the average yield of heartwood was approximately 3.8 per cent.
Heartwood samples from 15-year-old sandalwood taken at five locations along the stem (from root
stump to bole top), had an average oil yield of 5.5 per cent. The average estimated oil yield from 15year-old sandalwood was approximately 300 g; however, it was noted that individual tree oil estimates
were wide ranging (between 18 to 780 g).
African mahogany (Khaya senegalensis) displayed superior growth rates in comparison to other highvalue timber species in the trials. The mean annual increment (MAI) for diameter at breast height
(DBH) across trials aged 9 to 12 years ranged from 1.9 to 2.7 cm per year. Other species that
demonstrated favourable growth rates included: teak (Tectona grandis), with an MAI of 2 cm per year
at 10 years old; and mahogany (Swietenia macrophylla) with an MAI of 2.0 at 12 years old. The
xii
growth rate of Indian rosewood (Dalbergia latifolia) was moderate, but it was the only high-value
timber species trialled that was able to promote good sandalwood growth.
In general, the observed stem form of all timber species was largely unfavourable for sawlog
production, with stems often crooked or having short bole lengths and large branches. Given this, the
recovery rates for sawlogs would be low and thus the concept of multiple products needs time to
develop scientifically. Poor form was largely believed to be a result of poor genetics, lack of
management and/or inappropriate silviculture. With inadequate silviculture records on the trials the
cause could not be isolated.
Compared to other high-value timber species, Millettia pinnata (pongamia) fits into a different
performance group, with its high-value product being seed (which is then used for producing
biodiesel) not sawlogs. The concept of hedges of economically viable pongamia supporting tropical
sandalwood growth is possible; however, whist Millettia pinnata seed oil has broadly been recognised
as suitable for biodiesel production, the viability of the undertaking will largely depend upon oil
quality and seed yield of the genetic resources used in a given environment.
Implications for relevant stakeholders
Industry
Sandalwood
The projected rotation length for commercial plantations of tropical sandalwood in the ORIS is 15
years. Trees assessed at this age under various silviculture treatments showed that Santalum album
has converted 30 per cent of its bole to heartwood. This amount of sandalwood heartwood would not
make the standard of a carving log (the highest-valued product from sandalwood); however, on oil
alone and based on current sandalwood prices, the potential of the industry has not been over-stated.
Most of the trials assessed were planted prior to the commercialisation of tropical sandalwood in the
ORIS and used silviculture systems and hosts that are different from what is seen in company
plantations today. The two biggest differences are: the past use of the primary host Acacia
trachycarpa which has been superceded by the dominant species Sesbania formosa; and the
separation of sandalwood and primary host in one row from the secondary host in a separate row. The
change in primary host had far greater implications on the choice and performance of the secondary
host (long-term host) than was originally appreciated. The shading effect of Sesbania and the different
management methods used to reduce the shading brought disease into the plantation as well as
suppressing secondary-host growth of some species. Whereas Cathormium was an exemplary host
with Acacia trachycarpa (producing the biggest trees on the Frank Wise Institute site), when the
primary host was changed to Sesbania, all benefits of Cathormium as the secondary host were lost.
This indicates that spatial host relationships need to be revisited and data from these trials infers that
the density of secondary hosts is too high.
A plantation project has two major factors to consider for economic sustainability: product market
value; and production per hectare. When entering high-value markets, the challenge of producing a
standard product needs to be met. The sandalwood oil profile has been shown to be stable between
trees and sites; a quality product can be extracted and sold that meets the ISO standard.
The second factor, production (either as tree wood volume or heartwood volume) per hectare, has
been shown to have wide variation across each trial and indeed to vary excessively across a site. The
challenge is to understand the key factors that control this variation and this report begins to look at
optimising spatial relationships for maximum sandalwood growth. Heartwood formation, whilst
related to growth, is regarded as a separate process. This is being explored through an Australian
Research Council award and the outcomes of that research, as background knowledge, are referred to
in this report.
xiii
High-value timber species
African mahogany (Khaya senegalensis) is impressive both in its ability to survive and its growth rate
in the ORIS. An intensive selection program is required to improve tree form and thus timber
recovery. This could also be the case with teak (Tectona grandis) but growth rates are lower and teak
is not as resistant to pests, particularly termites. The tree of most interest is rosewood (Dalbergia
latifolia) as it is an excellent host for tropical sandalwood. Whilst it is highly sought after, the form of
trees at the Frank Wise Institute does not make it a desirable timber tree and there are also problems
with raising this species in present nursery systems.
Communities
Sandalwood provides an opportunity where forestry and agriculture can closely combine. The hemiparasitic nature of sandalwood and competition indices indicate that intercropping with other valuable
horticulture or agriculture crops may be a way to optimise sandalwood growth and meet food needs.
However, sandalwood is a perennial plant, harvested after 15 years, and so for communities it is quite
different from annual harvest agricultural systems. With companies managing plantations for
investors, and local landowners either selling or leasing their land, the nature of the business is also
unfamiliar in the ORIS.
Sandalwood will create an industry in which the product will be grown and processed in the ORIS
before export. Sandalwood waste from harvesting, together with host biomass that will be removed at
the site, may be a product itself and needs to further exploration. Like the rum industry, sandalwood
could also attract a tourist trade. The industry will thus provide work for a varied range of skills.
Recommendations
The first outcome from this project was the discovery of heartwood rot within Santalum album at the
Frank Wise Institute. The first recommendation to RIRDC was to further investigate the heartwood rot
and this culminated in the RIRDC report Heartwood Rot Identification and Impact in Sandalwood
(Santalum album) (Barbour et al. 2010).
This project additionally recommends that:
•
Time-course studies of different planting designs are undertaken to quantify changing spatial
relationships between hosts and sandalwood so that silviculture recommendations over the full 15year rotation can be made.
•
The exploration of new secondary hosts is continued; including the concepts of a hedge of
Millettia pinnata and/or horticultural and/or agricultural inter-row integration.
•
Studies are undertaken to understand heartwood formation.
•
A selection program is initiated for the development of a timber product from African mahogany,
teak and Dalbergia.
•
Mechanical systems are developed for the selective harvest of sandalwood, the removal of clay,
and the separation of heartwood and sapwood.
•
The possibility of products from the non-sandalwood biomass at harvest is explored.
xiv
1
Introduction
Sixteen trials/plantings established at the Frank Wise Institute in the Ord River Irrigation Scheme
(ORIS) on behalf of the Western Australian Government were measured and analysed. These trials
contributed a good portion of the information used by industry to develop the first tropical forestry
plantation projects in the north with sandalwood, followed by teak and African mahogany.
1.1
Background
1.1.1 Ord River Irrigation Scheme history
The Ord River is 320 km long and located in the Kimberley region of Western Australia. The
headwaters of the Ord River are located below Mount Wells and it initially flows east around the edge
of Purnululu National Park before heading north through Lake Argyle. The river then passes west of
Kununurra and discharges into the Indian Ocean in Cambridge Gulf.
The ORIS was constructed on the river in 1963 and opened on 30 June 1972. The scheme created
Lake Argyle, which is Australia’s largest dam, covering an area of 741 km², and it generates power for
the local community as well as providing a constant source of irrigation water. Lake Kununurra was
also constructed as part of the project.
Allocation of the first 14 000 ha of farming land during Stage 1 of the project was completed in 1966.
The 30 farms produced mostly cotton; however, pest problems soon became apparent. The early
1970s saw the application of large amounts of pesticides; mainly to control the Helicoverpa armigera
caterpillar which then developed pesticide resistance. Pressure from pests resulting in low crop yields
combined with a drop in world cotton prices and led to the suspension of the commercial cotton
industry. In the 1990s the ORIS converted to sugar cane and a sugar mill was built on the outskirts of
Kununurra to support the growing industry, based on plans for the scheme’s expansion to 30 000 ha.
This land expansion did not occur and coupled with fluctuating market prices for sugar, the sugar mill
closed in 2007. Whilst other crops were being experimented with, tropical sandalwood which was a
fledgling industry, became the new dominant crop in the ORIS.
1.1.2 The challenges of the Ord River Irrigation Scheme
Remote north of Western Australia
The ORIS is located in a remote part of Australia with large distances to the main markets in the rest
of the continent (see Figure 1.1). Kununurra is 3228 km north of Perth and 780 km south-west of
Darwin. It is 1042 km north of Broome, which is the closest Western Australian town to Kununurra.
Crops grown in the ORIS thus need to be partially processed into an easily transportable form and be
of high value or grown in economically large quantities.
1
Figure 1.1 Location of the ORIS, Kununurra (blue dot) in the north of Western Australia in
relation to the state capital, Perth (red dot)
Soil
The soils in the first ORIS land release are known as cracking clays, mainly made up of Cununurra
clays (see Plate 1.1) and Aquitaine clays. The Aquitaine clays have higher clay content and while they
can be very productive, require careful management and irrigation practices. Smaller areas of redbrown earths, red earths, brownish cracking clays, colluvial outwash slopes, rock outcrops and other
soils also occur.
Cracking clay soils are often described as black soils or vertisols. They exhibit substantial shrinking
and swelling properties; resulting in deep, open desiccation cracks into which vegetation will often
fall. This vegetation then becomes incorporated into the soil mass, giving the dark grey or black
colouration. Continuous movement due to moisture variations can result in slicken sides or polished
surfaces within the soil profile.
Plate 1.1 Cununurra clay showing the cracking ability of this clay soil
2
Unless these cracking clays are continuously moistened, drying can cause cracks in the soil surface
that are able to rip roots. Furthermore, the ‘sticking’ properties of the clay make any commodity
harvested from the ground extremely difficult to extract and clean. All crops to date developed in the
ORIS have been above-ground crops. Tropical sandalwood will be the first commodity harvested from
below ground (i.e. the sandalwood roots) and it thus will have engineering challenges to overcome to
be economically viable in an area where labour is at its most expensive in Australia.
The soil pH is generally above 7, indicating that alkaline soils are typical. This may not have a direct
impact on tropical sandalwood as it is a hemi-parasite, but it may influence nutrient uptake and growth
of other tropical trees investigated individually and as hosts.
Furthermore, the electrical conductivities of the subsoils are very high so there is a strong possibility
of soil salting if groundwater is allowed to rise. Aquitaine clays in the northern part of the Weaber
Plains are known to have high salt content at depth and irrigation must be carefully planned to prevent
water seepage and subsequent water table elevation. Consequently, it is proposed that control be
exercised over water application and that this is combined with groundwater monitoring and
management. In this situation, tree crops have many advantages.
Climate
The climate is sub-tropical with two dominant seasons: the wet (monsoon or cyclone) season usually
extends from November to April, while the dry season can be taken as May to October. During the
wet season, temperatures and rainfall are relatively high with much of the rain activity coming from
thunderstorms and cyclones formed in subtropical low-pressure systems off the coast. The average
rainfall is 776 mm with around 90 per cent falling during the wet season. In contrast, the dry season is
characterised by lower temperatures, low rainfall and lower humidity. Net evaporation rates are
generally high, of the order of 2100 mm per annum and, during most months, evaporation exceeds
precipitation.
The sub-tropical climate in northern Western Australia could provide market advantages for crops
grown in the ORIS. Tropical fruits could use counter-seasonal marketing for improved profit, whereas
annual crops grown in the dry season with irrigation would be relatively free of major pests and
diseases as encountered in other parts of Australia and the world. A regional biosecurity plan is in
place to further reduce the risk of incursions. Recent evidence indicates that for tropical sandalwood,
infection by endemic fungi from surrounding bush is an additional threat to sustainability (Barbour et
al. 2010).
1.2
Tropical forestry history in the Ord River Irrigation Scheme
There are a number of reviews of the development of the tropical sandalwood industry in the ORIS
(Radomiljac 1993; Radomiljac et al. 1998b; Shea et al. 1998; Vernes and Robson 2002; Done et al.
2004; Barbour 2008; Barbour et al. 2010; Plummer et al. 2011).
1.2.1 A brief overview
Sandalwood once played an important role in the history of Western Australia, particularly in the
south-west. With tropical sandalwood now dominating in the ORIS, the question is whether the crop
is poised to tame the last frontier of the north for agriculture and forestry.
This otherwise insignificant hemi-parasitic tree forms heartwood within its trunk that contains one of
the most sought-after essential oils, sandalwood oil. The sesquiterpene components that make up the
oil protect the tree’s core from fungal and insect attack. The oils are extracted and utilised in a number
of niche products, such as the base note for the most expensive perfumes. There are also many
products being discovered that address an increasing number of human health benefits.
3
Prior to gold being discovered in Western Australia, it was the harvest and export of Australian
sandalwood (Santalum spicatum) that kept the colony solvent. The demand for tea from China was
compensated for by the sandalwood trade from Western Australia. This led to mass clearing of
Australian sandalwood and the eventual introduction of legislative control to temper this destruction.
Santalum spicatum regeneration has a unique aspect which, with increased human occupation, has
become its Achilles heel. The seed has to be buried for it to successfully establish. A sequence of wet
and hot dry days cracks the seed shell, allowing for germination; but if the emerging seedling is not
covered, it desiccates and soon dies. Seed dispersal is cleverly undertaken by a native marsupial, the
woylie which buries the seed as a later food store. The introduction of foxes and cats has played havoc
with woylie populations and even populations protected from these carnivores have mysteriously
declined in recent drought years. Successful regeneration is also threatened by increasing numbers of
goats on pastoral leases. Unless major human intervention occurs, the accumulating evidence points to
extinction as the natural seed dispersal and regeneration cycle has been destroyed. The present age
structure of the population certainly indicates an extinction trend.
Australia is no different from any other Pacific Rim country when it comes to exploitation of valuable
trees. The story of over-extraction also was felt in India and was exasperated by the spread of
sandalwood spike disease. The regulation of sandalwood sales from India caused a world shortage and
prices ultimately doubled. To date, this shortage has been compensated for by the harvest of Osyris
tenuifolia, East African sandalwood, as well as S. album from Indonesia, S. austrocaledonicum from
Vanuatu and S. yasi from Fiji, but all these countries are putting conservation strategies in place.
The first thoughts of plantation forestry in Kununurra focused on firewood production. CSIRO
planted two Eucalyptus camaldulensis trials at the Frank Wise Institute between 1976 and 1978.
Whilst trial measurements were published, it was never followed up.
In the 1980s the concept of cultivating sandalwood was first considered and the Forest Department of
Western Australia and the Australian Sandalwood Company sent a party to India to observe their
sandalwood industry. From this trip, the first sandalwood seed was imported into Australia and thirty
trees of sandalwood were established in Kununurra. This was followed by the planting of a series of
small plots when seed could be attained. In 1988 an agreement between the Department of
Conservation and Land Management (CALM formerly the Forests Department) and Department of
Agriculture and Food Western Australia (DAFWA) was reached and a series of plantings looking at
different host combinations were established at the Frank Wise Institute.
In this same period, Ian Richmond was awarded a Churchill Scholarship to go to India and learn more
about sandalwood, especially the tissue culture systems. When he returned, he collaborated with
Murdoch University to plant a series of three trials covering three different soil types, with a variety
of hosts and using newly imported genetic material from India.
The concept of tropical sandalwood plantations as a solution to meet the growing demand for
sandalwood wood and oil products was taking hold at this time. CALM invested in a dedicated
research scientist, Andrew Radomiljac, and through his PhD studies at Murdoch University, produced
the first solid research work on Santalum album in the ORIS. By the mid 1990s, promoters of a
managed investment scheme to sell woodlots of S. album to investors approached CALM for technical
support.
At this time negotiations for an Australian Centre for International Agricultural Research (ACIAR)
project between CALM and the Forest Department in India were progressing. The collapse of this
project and the loss of the research scientist from Kununurra left the research work at the Frank Wise
Institute in limbo. Fortuitously, a partnership of Tanya Vernes and Pat Ryan in subsequent years
established a few of the trials that were planned for the ACIAR project but the research aspect of the
project began to flounder.
4
During this same period, the first managed investment scheme failed. This was blamed on a number of
reasons including the rate of expansion in relation to system knowledge, use of the wrong hosts, and
the many aspects of management that still needed to be investigated and understood for reliable tree
growth and oil production.
Tropical sandalwood needs to be established successfully in a single pass. In-filling in the following
seasons, a common forestry practice in the south-west, cannot be done in the tropical environment of
the north due to the growth rates of hosts. Thus the key reason for the initial failure appeared to be the
lack of appropriate nursery practices and the low quality of plants produced for establishment.
A number of different types of growers came onto the scene. The failed first plantings from the initial
managed investment schemes (MIS) were purchased and managed for their African mahogany (which
was the dominant host that suppressed tropical sandalwood). This approach created an interest in
plantation African mahogany that spread across to the Northern Territory where land was cheaper
than in the ORIS. This was the beginning of MIS’s in African mahogany.
Teak was another tree crop initiated in the ORIS that was adopted by managed investment scheme
companies. Two trials were established in the ORIS, one by CALM at the Frank Wise Institute and
the other by Elders Forestry. These were the basis of the industry which then moved across to
Queensland, once again due to land prices.
New managed investment schemes for sandalwood came into the ORIS and eventually the market was
dominated by Elders Forestry and Tropical Forestry Services (TFS). A number of private growers in
the ORIS started growing tropical sandalwood and most of these plantations became private
investment schemes. A combination of the collapse of the sugar industry, the sandalwood investment
strategy and a gradual improvement of establishment systems has meant that the ORIS is now
dominated by tropical sandalwood. In the single year of 2010, 4667 ha of tropical sandalwood was
established.
In 2000 the Forest Products Commission (FPC) was formed from the commercial activities within
CALM. The remainder of CALM was renamed the Department of Environment and Conservation
(DEC). The Tropical Forestry project at Kununurra based at the Frank Wise Institute became the
responsibility of FPC under Peter Jones. For a few years, the research program was subcontracted to
DEC under Dr John McGrath but this changed with a review of the project by Richard Mazanec (Tree
Breeder, DEC) and was transferred to Dr Liz Barbour (Seed Technologies) within FPC.
The research program on tropical forestry in FPC was to work on these issues:
•
understand and capture the genetic diversity of Santalum album as it is difficult to get further
accessions from other native populations
•
find a non-destructive system of oil sampling that correlates with the whole tree so that genetic
origins can be correlated to heartwood oil production for selection
•
transfer the benefits discovered with S. album to S. spicatum
•
develop a seed orchard system for out-crossed seed of the best selections captured through
grafting
•
develop a tissue culture system so that the best selections can be cloned and made available to the
industry
•
understand and record each planting/trial at the Frank Wise Institute.
5
1.2.2 Meeting the FPC research objectives
To meet these objectives, a number of collaborations were developed with industry, universities and
federal funding bodies. This project, which started in July 2007, has provided background information
for the projects numbered 4 onwards.
1. FPC-UWA: Chris Jones Honours Project (2004): ‘An accurate method for estimating the oil
content and quality of Australian Grown Plantation East Indian Sandalwood, (Santalum
album)’. Supervisors: A/Prof JA Plummer and A/Prof EL Ghisalberti (UWA).
2. UWA-FPC-DEC-ARC-Linkage Project (LP045191) (2005–2007): ‘Indian sandalwood: Genetic
and oil diversity, and biochemistry of the Australian germplasm collection’. CIs: A/Prof JA
Plummer and A/Prof EL Ghisalberti (UWA). PIs: Dr L Barbour (FPC) and Dr M Byrne (DEC).
PhD: Chris Jones.
3. FPC-RIRDC No 08/138 (2007–2008): ‘Analysis of plant-host relationships in tropical
sandalwood (Santalum album)’ (see Barbour, 2008).
4. UWA-FPC-UBC-ARC Linkage Project (LP0882690) (2007-2011): ‘Elucidation of genetic and
physiological factors controlling sesquiterpenoid biosynthesis in Sandalwood, Santalum sp.’.
CIs: A/Prof JA Plummer and A/Prof EL Ghisalberti (UWA). PIs: Dr L Barbour (FPC) and
A/Prof J Bohlmann (UBC). Post Doc: Dr Chris Jones. PhD: Jessie Moniodis.
5. FPC-RIRDC No 10/179 (2008–2009): ‘Heartwood rot identification and impact in Sandalwood
(Santalum album)’. (see Barbour et al. 2010).
6. UWA-RIRDC PRJ0068221 (2011): Workshop hosted by UWA ‘Sandalwood oil: genetic
solutions developed to improve quantity and quality’ (see Plummer et al. 2011).
7. FPC-MU-Elders Forestry-RIRDC PRJ-4786 (2010–2013): ‘Tropical sandalwood silviculture
management to minimise fungal attack’.
8. UWA-FPC-UBC-MU-Elders Forestry-ARC Linkage Project (LP100200016) (2011-2014):
‘Molecular characterisation of the fungal disease response in tropical sandalwood (Santalum
album)’. CIs: A/Prof JA Plummer, A/Prof EL Ghisalberti, Dr L Barbour (UWA), Dr T Burgess
(MU). PIs: G. Butcher (FPC) and A/Prof J Bohlmann (UBC). Post Doc: Kesserin Tungngoen,
PhD.
9. UWA-FPC: Ni Luh Arpiwi PhD ‘Optimising Millettia pinnata seed production’. Supervisors:
A/Prof JA Plummer, A/Prof G Yan and Dr L Barbour (UWA).
Other researchers involved:
•
Dr Katherine Zulak (UBC), to investigate oil synthesis in S. austrocaledonicum, a sandalwood
species from Vanuatu
•
Dr Margaret Byrne (DEC) with Dr Melissa Millar, to develop microsatellites for DNA analysis
•
Dr Liz Watkin (Curtin University), to screen and identify superior soil rhizobia for host nitrogen
fixation.
Research outcomes
Below is a short discussion of the research outcomes for each of the objectives listed above. At times
the outcomes didn’t follow the expected paths.
6
Understand and capture genetic diversity of Santalum album as it is difficult to get further
accessions from other native populations
The genetic diversity of Santalum album was initially assessed using a reliable restriction fragment
length polymorphism method (Jones et al. 2009). Surprisingly low levels of genetic diversity were
present among the trees established at the Frank Wise Institute and the CALM arboretum.
Reassuringly, the Timor-sourced sandalwood trees were distinct from the Indian-sourced trees, and
exhibited a more ancestral genotype, indicating that the prehistoric source of S. album was indeed
Timor. Thus, the common name ‘tropical sandalwood’, and not ‘Indian sandalwood’ is being used in
this report. It was also noted that there were many trees within the plantings that were very closely
related and genetically indistinguishable from each other.
The entire sandalwood genus appears to have originated in Australia (Harbaugh and Baldwin 2007;
Jones et al. 2009). Santalum spicatum is one of the most ancestral species of the genus. Its
confinement to the south-west of Western Australia is likely due to climatic cycling through the
Pleistocene. Sandalwood isolated to the north became a melting pot of sandalwood diversification.
Speciation is thought to have occurred through long-range dispersals to the Pacific and a small
founder population north to Timor. Limited initial genetic diversity, a propensity to asexually
propagate and a high occurrence of self-pollination are likely to be the main reasons for such low
diversity. Most probably, humans transported S. album from Timor to India. Perhaps it was also this
human selection pressure that has made the genetic diversity of S. album so narrow, with its static oil
profile and high santalol content (Jones et al. 2006; Jones et al. 2007). In comparison, most other
sandalwood species, including S. spicatum (Byrne et al. 2003), have greater genetic diversity and
wide-ranging oil profiles, often accumulating less-favoured sesquiterpenes for commercialisation.
This information showed ORIS industry members that they needed to know the diversity of their
tropical sandalwood plantings. This was for a number of reasons: (i) for the establishment of seed
orchards (to maximise out-crossing); (ii) to understand the make-up of present plantations for disease
susceptibility/resistance; (iii) for future security against disease and pest resistance; and (iv) for future
product development (alternate genes) and for other products (for example, bark, seed pulp or
kernels).
An alternate DNA technology for assessing genetic diversity using simple sequence repeats, or
microsatellites was developed (Millar et al. 2011). This provided a service to industry and allowed the
flexibility of adding further different selections into the FPC study. The microsatellite method
permitted a few selections at a time to be added to the knowledge pool. This second screening showed
somewhat higher diversity within the population, but compared to other tree species the diversity
remains remarkably low.
Find a non-destructive system of oil sampling that correlates with the whole tree so that
genetic origins can be correlated to heartwood oil production for selection
To select for high sandalwood-oil producing trees, a system of non-destructive sampling was required.
The system needed to be relatively quick and inexpensive and also give a high correlation to wholetree oil assessment. A system that had been developed for eucalypts to correlate density and pulp yield
(Downes et al. 1997) was employed and involved extracting cores at breast-height diameter from the
tree bole using a chainsaw-driven drill (see Plate 1.2).
7
Plate 1.2 Drilling a core from a sandalwood tree
Twenty-two 10-year-old sandalwood trees were used in this study; all were cored at 30 and 100 cm
above the ground but only 10 trees destructively harvested. The oil quantity results were so diverse
that no strong relationship between cored sub-samples and whole-tree oil content could be found
(Jones et al. 2007). The oil profiles from these trees were surprisingly stable but, at this stage, this
information could not be correlated to genetic diversity. It was further observed that a number of trees
had no sign of heartwood production and related oil production. All trees selected were similar in
external appearance and hence the quest to understand why there was this large variation in oil
production (Jones et al. 2007).
Extending the oil sampling from different trees across a known genetic diversity, it was realised that
S. album was producing the main sesquiterpene constituents in precisely the same proportions. Cooccurrence patterns indicated that several groups of sesquiterpenes might be synthesised by the same
enzyme. Santalenes and santalols are the most valuable components of the sesquiterpene oils
produced by S. album, and from this analysis a pathway for their biosynthesis was hypothesised and
published in a key paper (Jones et al. 2006). Put simply, the biosynthetic pathway has two main steps:
the conversion of farnesyl diphosphate into santalenes by santalene synthase; and the conversion of
the santalenes to santalols by cytochrome P450 oxidase.
A bisabolene synthase and a germacrene D-4-ol synthase were the first terpene synthase genes from
sandalwood to be cloned and biochemically characterised (Jones et al. 2008). As hypothesised earlier
(Jones et al. 2006), the enzymes were multifunctional and produced mixtures of sesquiterpenes in
unique, but consistent proportions. To further this path of gene discovery, a cDNA library from the
RNA of an oil-producing sandalwood tree in the FPC plantings was made and this was
comprehensively sequenced using conventional and massively parallel technologies. From this library,
candidate genes in the oil biosynthetic pathway were selected, expressed and tested. On 1 April 2010,
the santalene synthase from S. album was isolated and shown to convert the universal sesquiterpene
precursor, farnesyl diphosphate into the three santalenes and bergamotene in exactly the same
proportions as predicted (Jones et al. 2006).
8
Plate 1.2 Drilling a core from a sandalwood tree
Twenty-two 10-year-old sandalwood trees were used in this study; all were cored at 30 and 100 cm
above the ground but only 10 trees destructively harvested. The oil quantity results were so diverse
that no strong relationship between cored sub-samples and whole-tree oil content could be found
(Jones et al. 2007). The oil profiles from these trees were surprisingly stable but, at this stage, this
information could not be correlated to genetic diversity. It was further observed that a number of trees
had no sign of heartwood production and related oil production. All trees selected were similar in
external appearance and hence the quest to understand why there was this large variation in oil
production (Jones et al. 2007).
Extending the oil sampling from different trees across a known genetic diversity, it was realised that
S. album was producing the main sesquiterpene constituents in precisely the same proportions. Cooccurrence patterns indicated that several groups of sesquiterpenes might be synthesised by the same
enzyme. Santalenes and santalols are the most valuable components of the sesquiterpene oils
produced by S. album, and from this analysis a pathway for their biosynthesis was hypothesised and
published in a key paper (Jones et al. 2006). Put simply, the biosynthetic pathway has two main steps:
the conversion of farnesyl diphosphate into santalenes by santalene synthase; and the conversion of
the santalenes to santalols by cytochrome P450 oxidase.
A bisabolene synthase and a germacrene D-4-ol synthase were the first terpene synthase genes from
sandalwood to be cloned and biochemically characterised (Jones et al. 2008). As hypothesised earlier
(Jones et al. 2006), the enzymes were multifunctional and produced mixtures of sesquiterpenes in
unique, but consistent proportions. To further this path of gene discovery, a cDNA library from the
RNA of an oil-producing sandalwood tree in the FPC plantings was made and this was
comprehensively sequenced using conventional and massively parallel technologies. From this library,
candidate genes in the oil biosynthetic pathway were selected, expressed and tested. On 1 April 2010,
the santalene synthase from S. album was isolated and shown to convert the universal sesquiterpene
precursor, farnesyl diphosphate into the three santalenes and bergamotene in exactly the same
proportions as predicted (Jones et al. 2006).
8
A provisional patent was lodged for the santalene synthase gene and along with the kinetic parameters
of the recombinant enzyme in the three main sandalwood species, S. album, S. spicatum and S.
austrocaledonicum. Firmenich SA was first to patent the S. album santalene synthase (WO
2010/067309 A I (FIRMENICH SA)). Jones et al. (2011) showed that by exploring multiple species,
the unique, highly conserved nature of santalene synthase in the genus can be recognised; and this has
many evolutionary ramifications. The enzyme is a sequence of amino acids and less than 2 per cent of
this amino acid sequence differs between the enzymes of the most advanced and the enzymes of the
most ancestral of sandalwood species.
The conversion of santalenes to santalols can be done chemically but with poor efficiency. The ideal
would to be to identify and isolate the cytochrome P450 oxidase gene, which is responsible for the
conversion of santalenes to santalols.
These gene discoveries open doors to new technologies which enable the in vivo production of
sandalwood oil in engineered microorganisms. Due of the shortage of sandalwood oil, some of the
world’s largest fragrance and flavour companies have been searching for chemically synthesised
compounds with similar organoleptic properties to those of the authentic oil. A number of synthesised
compounds have been introduced to the market and they occupy a new niche of single, pure
compounds that can be accurately included into a formula for reliable product repeatability.
The biosynthetic production of sesquiterpenes (santalenes and santalols) using the sandalwood genes
in yeast constructs produces exactly the same sesquiterpenes as produced in sandalwood heartwood.
Individually, these compounds are not dissimilar from the natural sesquiterpenes. The singular
difference between biosynthetic sesquiterpenes and natural sandalwood oil is the overall composition.
Natural sandalwood oil may contain up to 100 different components and, as a result, biosynthetic
sesquiterpenes and natural sandalwood oil will occupy different markets.
Convert the benefits discovered with S. album to S. spicatum
50
45
40
35
30
25
20
15
10
5
0
S.spicatum
S.album
al
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Composition (%)
The quality difference between S. album and S. spicatum is the frequent presence of the oil
component farnesol in the latter species (see Figure 1.2). Analyses indicate that when levels of
farnesol are high, santalols are typically low (Moniodis,pers. comm.). Farnesol is regarded as an
irritant and thus S. spicatum oil does not make the ISO standard and cannot be mixed into products
above a certain proportion. Farnesol separation from the essential oil is an expensive and inefficient
process so selection and breeding may be a solution to select for oil profiles with low farnesol in S.
spicatum.
Figure 1.2 Typical sandalwood oil profile of Santalum album and Santalum spicatum
9
Develop a seed-orchard system for out-crossed seed of the best selections captured through
grafting
To establish an S. album breeding population to enable deployment of seed orchards, the genetic
diversity of the species needed to be understood. Because of poor accession records, DNA
technologies were relied upon to unravel the relatedness of selections.
Two progeny trials had been established at the Frank Wise Institute. The first trial, established in
1996, captured a diverse range of S. album material which included selections from the Indian
Forestry seed orchards (from their breeding program), selections of plus-trees from the Frank Wise
Institute, Northern Territory trees and some selections from Timor. Whilst rigorously designed, the
trial had no buffer and the host combination did not remain constant. The one common host, African
mahogany has suppressed the sandalwood growth as well as other host trees and this trial is now lost.
The second trial, established in 2004, was from plus-tree selections from the Frank Wise Institute. The
long-term host, Cathormium umbellatum, was planted over a 2-year period and it was also used as the
buffer row. Initial sandalwood growth was exceptional and it was realised that the nursery technique
used in Perth (of growing the seedlings in an organic medium, mainly composted bark, and using
water that was of near neutral pH) enabled the seedlings to grow to a stem thickness not observed in
Kununurra nurseries. Sandalwood growth was excellent until the Sesbania formosa started to die and
adjacent sandalwood appeared stressed, aborting their leaves. A theory mooted was Sesbania may
become allelopathic and kill surrounding trees as it dies to ensure seed propagation success. The
removal of the Sesbania that were within the same row as the sandalwood forced the sandalwood trees
into host-shock and it took 3 years before the sandalwood recovered through the eventual connection
with the long-term host.
Clonal capture of mature selections was successfully achieved using the mango-grafting technique.
This grafting method used scion material about 10 cm long with all the leaves removed. Success was
attained when the stem was green to woody and the diameter matched that of the rootstock for
cambium fusion. The cleft join was bound with grafting tape and the scion covered with a plastic bag
left open at the base to ensure appropriate humidity. Once the shoots extended from the lateral buds,
the plastic bag was removed. The removal of this bag had to occur in a high humidity environment or
the young leaves had to be sprayed with an anti-transpirant to prevent leaf desiccation and abortion.
Enough grafts were successful to start establishing an archive and an area was cleared to extend this
planting as more selections were captured. The industry also became successful in genetic capture
using grafting and extensive seed production areas have been established.
Develop a tissue culture system so that the best selections can be cloned and made
available to the industry
Tropical sandalwood has two aspects that favour tissue culture success: the seedling price is high and
the species lends itself to somatic embryogenesis. Whilst the understanding of the regulation of the
biosynthetic pathway for santalol is unraveling, the concept of cloning genotypes that have superior
performance in ORIS conditions is attractive.
FPC did not have the facilities to undertake tissue culture on a commercial basis. However, it was able
to capture material in sterile cultures and hence relationships were developed with The Tree Lab
(New Zealand) and NIPPON Paper (Collie, Western Australia) to explore the commercial tissue
culture option (see Plates 1.3 and 1.4). Both companies came to the conclusion that only S. album
material sourced from seed (juvenile) could be propagated through to rooting. Clones initiated, either
through micropropagation or somatic embryogenesis, from mature tissues could not be rooted reliably.
So whilst initiation, multiplication and shoot production are well-developed, the final stage of rooting
remains a challenge.
10
Plate 1.3 Santalum album tissue cultured shoots from juvenile tissue (The Tree Lab)
A clonal trial was established with the clonal material produced by Nippon Paper which will be of
value in future years.
Plate 1.4 Santalum album clonal plants used in the trial established in the ORIS (Nippon Paper)
Clones could be initiated from seedling material and the callus material cryo-preserved whilst the
clones are being field-tested, as is the case with Pinus radiata. This would provide an opportunity to
mass produce high-performing clonal lines for the ORIS.
Understand and record each planting/trial at the Frank Wise Institute
This RIRDC project and Barbour (2008) began the recording of each of the trials/plantings that were
established in the ORIS over the last 20 years. Management of the Frank Wise Institute Tropical
11
Forestry project has been transferred between three different organisations and locations, and
unfortunately many of the records were misplaced. The first challenge for this research objective was
to review the information available so that a history of each trial could be collated.
The trials are split into two broad types: general silviculture trials and genetic conservation trials. The
trials presented in this report are the silviculture trials, which are either monoculture trials of different
species or combination trials to understand and optimise the sandalwood–host relationships.
1.3
Sandalwood as a crop
1.3.1 The hemi-parasitic nature of sandalwood
Tropical sandalwood (Santalum album) is a small tropical tree from the Santalaceae family. The
species occurs from India through to the South Pacific and to the northern coast of Australia. These
evergreen trees reach a height of between 4 and 10 m and can live for 100 years. They can flower
from the first year producing very small, blood-red flowers that attract a variety of pollinators such as
bees, flies and butterflies. Once pollinated, flowers produce a berry which attracts and is eaten by
birds or alternatively falls to the ground. The berry pulp inhibits germination and so must rot off, be
consumed by a bird, or be abrasively removed by soil or manually before the seed can germinate
within accumulated mulch.
The ability of sandalwood trees to re-sprout from roots left in the ground after a tree has been
removed may contribute to the observed lack of genetic diversity. The thicket of sprouts eventually
thins to two or three trees which, if there are enough hosts nearby, successfully continue their growth
through to mature trees. An out-crossing study with S. spicatum indicated that this species
preferentially out-crosses (Muir et al. 2004) but if there was no choice, as in a case where clonal
material dominates, inbreeding would be the only reproductive strategy available.
With this reproductive plasticity, the need for sandalwood to be a hemi-parasite is a prominent
question. The definition of a hemi-parasitic tree implies that sandalwood is photosynthetic but that
additional water, mineral nutrients and organic substances are acquired via the host plant (Radomiljac
et al. 1998c, Radomiljac et al. 1999b). It does this by parasitising other trees by connecting with their
roots by means of haustoria from its own roots. So aggressive is sandalwood in finding hosts to
connect with that within 30 days from germination 70 per cent of seedlings have generated haustoria
(Nagavai and Srimathi 1985).
There are a number of common factors that determine the distribution of tropical sandalwood. One of
these relates to the ability of trees to adapt to alkaline soils. The Cununurra clays are alkaline and this
is also common to Timor soils and the red soils of India where sandalwood is dominant. A high pH
affects nutrient availability, making some micro-nutrients inaccessible to plants. The red soils in India
have high iron levels but lack nitrogen, phosphorous and potassium. The ORIS soil is poor in nitrogen
and phosphorous and the micro-nutrients iron, copper and zinc are present only in marginal
concentrations. Soil composition and variation in tolerance of the host species will affect what is
made available to sandalwood and hence it is not surprising that a range of nutrients have been found
to be supplied by a variety of hosts to sandalwood: calcium and iron (Sreenivasan Rao 1933); nitrogen
and phosphate (Iyengar 1960): and potassium, phosphate and magnesium (Rangaswamy et al. 1986).
The classic definition of a hemi-parasite neglects to acknowledge the structural benefits hosts can
provide. In the harsh climates of the Kimberley, India and Timor, being amongst other trees that
provide sun, wind and grazing protection would certainly be a survival advantage. The need for sun
protection on the juvenile sandalwood stem is a key factor highlighted in Barbour et al. (2010). When
bark is damaged via sun-scorch, it provides a heartwood rot entry point that sandalwood has difficulty
in defending. A balance between protection of the tree bole from the sun and access to sunlight for
12
photosynthesis is required for optimum sandalwood growth and survival (Barbour 2008). The
compatibility of the host structure in relation to sandalwood growth is a key factor contributing to the
success of the hemi-parasitic relationship. If sandalwood is grown with a host that dominates this
spatial balance preventing photosynthesis, either an intervention is needed (pruning or culling of the
host) or the sandalwood will cease growing and eventually die. The concept of defining this
relationship is a dominant theme throughout this report.
The silviculture system devised in the ORIS utilises three hosts: a pot host, a short-term host and a
long-term host. The first, the pot host, is a prostrate herbaceous plant introduced to the containergrown sandalwood 1 month prior to field planting. Early research (Barbour and Broadbent, pers.
comm.) showed that the success of this pot host is proportionally based to its vigour. The vigour of the
most popular pot host, Alternanthera nana, needs to be balanced with the timing of its introduction
into the pot so that it does not over-grow and suppress the sandalwood seedling (Radomiljac 1998;
Radomiljac and McComb 1998a; Radomiljac et al. 1998a). If Alternanthera is introduced too early
and dominates the sandalwood seedling, expensive manual pruning has to occur.
The short-term host enables rapid sandalwood growth, and hosts selected to date die 2–4 years after
establishment leaving the long-term host to grow and support the sandalwood over its production life.
In the ORIS, the most successful short-term hosts have been legumes that fix nitrogen and with the
ORIS soils lacking nitrogen this should be expected. Radomiljac et al. (1998c) demonstrated the
successful translocation of nitrogenous compounds between host and sandalwood.
Short and long-term hosts are planted at the same time as the sandalwood, with plantation
establishment usually occurring in May–June, or at least before summer temperatures escalate. The
growth rate of the short-term host demands a one-pass establishment with no in-filling.
Similar to the pot host, short-term host success is related to its vigour. Two host species have
dominated ORIS plantings, Acacia trachycarpa and Sesbania formosa. Both species are native to the
region and are short-lived legumes. Sesbania formosa is the species that now prevails for a number of
reasons: it is the more vigorous, it is a prolific seeder and it is easy to propagate in the nursery system
in Kununurra. The downside is that, due to its vigour, its introduction has suppressed the growth of
some secondary hosts. Cathormion umbellatum is notable example of this. In the first trials in the
ORIS which used Acacia trachycarpa as the short-term host, the growth of both sandalwood and
secondary-host Cathormion was magnificent. Later trials that used Sesbania with Cathormium were
not as successful; the fast-overshadowing, vertical growth of Sesbania suppressed Cathormion growth
and hence the Cathormion was not of sufficient size to support the sandalwood when the Sesbania
died. The initial response to maintaining the use of Sesbania as a short-term host and Cathormion as
the long-term host was to prune Sesbania. Due to the extent of the sandalwood plantations,
mechanical vertical and horizontal pruning occurred which appeared to extend the life of the tree; but
a build up of fungal disease over time increased Sesbania death, and this practice has since been
discontinued.
The long-term host trials require a full-rotation for the relationship between host and sandalwood to
be assessed. This was highlighted in Barbour (2008) and the discussion will continue with further
trials being assessed in this report.
Present knowledge highlights that the success of a host–sandalwood relationship starts with the soil. It
is the interaction between host and soil that determines what is passed from host to sandalwood in
terms of water and nutrients, and in the case of the ORIS, nitrogen. The sandalwood itself needs to
photosynthesise but this demand is complicated by the need for sun protection of the bark, as the bark
is the critical pest and disease barrier for the tree. The analysis of these trials will show how these
relationships unravel and their influence on sandalwood growth and ultimately on heartwood oil
production.
13
1.3.2 Adding value to the long-term host
Many of the trials at the Frank Wise Institute were established to identify and develop a valuable
secondary host. The hypothesis was that if additional worth could be attained from the secondary host,
the productivity and profitability of the plantation would be greatly increased or hedged when
sandalwood prices fluctuate.
Long-term host species selection was based upon a high-value sawlog product. The ORIS’s unusual
soils, temperatures and flood irrigation meant that the selection process needed to start with species
that had both potential economic value and good survival under these conditions. The classic forestry
approach is to establish provenance trials of each species and then when species and superior
provenances were identified, initiate a breeding program. This has certainly been true of the
successful plantation species across Australia (Pinus pinaster, P. radiata, Eucalyptus globulus, E.
nitens and the RIRDC-funded Australian Low Rainfall Tree Improvement Group). Poor accession
records did not allow this methodical process in the ORIS. Two species, African mahogany and teak,
were identified early in their plantation cycle; both survived the harsh conditions and showed
exemplary initial growth that was recognised as being worthy of further development.
The inclusion of African mahogany and teak in sandalwood plantations as secondary hosts was a
disaster. African mahogany clearly suppressed sandalwood growth (Barbour, 2008) and was the main
cause of the collapse of the first managed investment scheme. Teak was used by Elders Forestry and
when its negative impact was realised, the trees were removed from sandalwood plantations. Fastgrowing, dominant sawlog species appear to be unsuitable long-term hosts in a sandalwood plantation
system.
Silviculture management of a sawlog species in a multi-species plantation would have to be
developed. Silviculture regimes in a monoculture plantation are severe and include a cull of
approximately 6:1 selection pressure. This enables the use of lower-level genetics compared to when
plantations are established for final stocking. In a multi-species plantation, the risk of damage to the
sandalwood if the host species was thinned would be high. This suggests that for a reasonable return
from a sawlog species within a sandalwood plantation system, a clonal system should be considered.
Plate 1.5 Testing the concept of Millettia pinnata hedges by directly sowing the seed.
14
Another option is that secondary hosts do not have to be tall, solid trees. The introduction of
pongamia (Millettia pinnata), the biodiesel tree, has opened a new way of thinking (see Plate 1.5).
This species was identified as a successful host of sandalwood (Barbour 2008). A hedge of pongamia
producing easy-to-harvest seed pods may be just as effective as a secondary host for sandalwood as
uniformly spaced trees.
Sandalwood is in focus at present but the woody biomass that will need to be removed from the site at
harvest may have value as a quite different product than the first envisaged sawlog. With wood
chemistry reaching new levels that crosses boundaries into food and fibre products, this may well
become the high-value secondary product that cements trees again as a new frontier industry in
Australia.
1.3.3 Tropical sandalwood plantations after 15-years growth
The most pertinent question for the developing tropical forestry industry in the ORIS is the quantity
and quality of trees in sandalwood plantations when they are 15 years old. There are not many
examples of trees this old in the ORIS, and those plantings that are this age were undertaken with
quite different silviculture systems than what the valley is presently experimenting with. Nevertheless,
knowing how much sandalwood and other biomass produced from each hectare in the ORIS will help
with planning.
The standard layout of sandalwood plantations in the ORIS is with rows 3.6 m wide and this is due to
an historic development from agriculture and the flood and drain system. Normally sandalwood is
planted 3 m apart down every second row with a Sesbania planted between the sandalwood. Thus
sandalwood is planted at approximately 460 stems per hectare (SPH). The secondary host is planted in
the alternate row and normally 6 m apart. In some cases two sandalwood rows are planted at 1.8 apart
with only one secondary host row (see Plate 1.6). A present overview of the ORIS would show many
computations of these planting models. Understanding the trials in this report may identify the final
parameters of sandalwood and its possible hosts in the establishment of a hectare of plantation in the
ORIS.
Plate 1.6 One lay-out for flood-irrigated sandalwood plantation establishment.
Mounds are formed every 1.8 m but only the second row planted.
15
2
Objectives
The project involves the measurement and analysis of 16 trial plots (Appendix A) at the Frank Wise
Institute, in the Ord River Irrigation Area near Kununurra, Western Australia. The over-arching
objectives were to provide information and outcomes for the following:
•
sandalwood (Santalum album) growth rates, heartwood and oil production and product definition
•
African mahogany (Khaya senegalensis) growth rates
•
teak (Tectona grandis) growth rates
•
pongamia (Millettia pinnata) growth rates, seed production and seed oil quality
•
identification of other tropical species that could either be used as a long-term host for
sandalwood or as a tropical timber project for the north.
3
Methodology
There are two main groups of trials, those concerned with sandalwood and its hosts (Chapter 4), and
those related to high-value timber species (Chapter 5). Where possible, statistical analyses were
completed using the original design elements of the trials, however, where trials were of a
demonstrational nature or no longer conformed to the original design due to high mortality, only
comparisons of descriptive results have been made. In addition to trial measurements, destructive
harvesting of sandalwood was undertaken, and two non-invasive techniques were evaluated for their
potential use in determining aromatic wood.
During project planning, the only methods to be used were basic tree allometry together with tree
coring to non-destructively assess heartwood formation and oil quantity and quality. Minimal
destructive harvest was to occur so that trials could be preserved.
Basic growth analysis indicted that competition relationships occurred between the trees; and
competition indices, a statistical technique never before used on hemi-parasites, was explored for
greater spatial understanding.
Furthermore, the FPC’s need to remove some plantings provided the opportunity for greater
destructive harvesting than was initially planned. Destructive harvests of 8-year-old and 15-year-old
sandalwood was completed and revealed the presence of a fungal heartwood rot. This became a
separate study published by RIRDC (Barbour et al. 2010). Understanding that this heartwood rot was
mainly caused through the breaking of the bark (as would occur with coring), the coring aspect of the
project was stopped. Alternate methods of non-destructive assessment of heartwood oil were then
explored. This introduced experimenting with acoustic time-of-flight measurement as well as
electrical impedance to detect heartwood and heartwood rot formation.
As fungal infection changed the internal heartwood core profile from circular to a multitude of shapes,
a photographic system was developed to estimate heartwood production.
All sandalwood oil analyses were done with a hexane extraction and assessed using gas
chromatography methodologies.
16
3.1
General methods and formula
A number of standard measurements and calculations were used in the assessment and analysis of
sandalwood and high-value timber trials and these are explained below.
•
basal diameter (BD): the diameter at the base of the stem, approximately 10 cm from ground level
•
basal area: the cross-sectional area at the base of the stem, calculated from basal diameter as:
Basal area (m2) = π x (BD/200)2
•
diameter at breast height (DBH): the diameter of the stem, over bark, measured at 1.3 metres.
Where more than one stem was present a combined DBH was calculated using the following
formula:
Combined DBH = ∑(DBH12 + DBH22 + DBHi2)
•
crown break diameter (CBD): the diameter of the stem where it separated into multiple branches.
Where there were multiple stems from the base of the tree, CBD was equal to basal diameter
•
bole length: the length (or height) of the stem from ground level to where it separated into
multiple branches
•
tree height: height of tree from ground to highest visible leader or branch, measured with either a
height pole or Vertex III (Haglöf, Sweden)
•
bole volume: unless otherwise specified, bole volume was calculated using Smalian’s formula,
using a basal radius (BR) and crown break radius (CBR) taken from the respective diameter
measurements:
Bole volume = (π BR2 + π CBR2) x bole length
2
Estimated stem volume (ESV) differed for high-value timber species and sandalwood:
•
unless otherwise stated, high-value timber (HVT) volume was estimated using a single conical
volume calculation:
HVT ESV (m3) = π (DBH/200)2 x tree height
3
•
unless otherwise stated, sandalwood volume was estimated as the sum of bole volume and the
above bole conical volume to the top of the tree:
Sandal ESV (m3) = bole vol + (π (CBD/200)2 x (tree height-bole length))
3
17
3.2
Main species
3.2.1 Primary hosts
Acacia trachycarpa E.Pritz. Fabacaea subfamily Mimosoideae: Known as Sweet-scented
Minnieritchie, the species is an arid-to-tropical Australian shrub or small tree ideal for planting in
frost-free regions. It grows in neutral to alkaline soils in 120–400 mm rainfall zones but in the drier
parts of its distribution it becomes riverine, growing in dry creeks. The tree can reach 15 m in height
with a spreading crown of up to 10 m in diameter. The trunk has a curling, ‘minni ritchi’ bark texture
with a pine scent which is unique and interesting for an arid tree. The leaf is made up of soft, pineneedle-like, narrow phyllodes, 12–50 mm long. It produces yellow, rod-shaped flowers in spring. It
propagates by seed and its coppicing is assumed weak.
Sesbania formosa (F.Muell.) N.T.Burb.: Very-fast-growing, a native Western Australian tree that is
distributed from Karratha up north to Broome and across to Halls Creek. The tree is 2.5–13 metres tall
with white to cream pea-shaped flowers which appear between May to September. It is commonly
known as the White Dragon Tree with pale-grey bark which is furrowed and corky. The leaves are
pinnate 15–40 cm long with 5–20 or more pairs of leaflets. The trees can grow in a variety of
environments. The species tolerates saline and waterlogged conditions. They are short-lived, lasting
from between 3 and 5 years.
3.2.2 Secondary hosts or timber species
Cathormium umbellatum (Vahl.). Fabaceae subfamily Mimosoideae: A native species distributed
in the most northern areas of Western Australia around Kununurra through to the Northern Territory.
The species grows in alluvial soils, wet river sites, mangroves, dune swales, sandstone screes and
rainforest and is described as a tree or shrub 3–24 m high. Leaves are bipinnate with opposite leaflets.
The tree produces cream flowers between September and October, which develop into a pod with one
seed.
Cedrela odorata L. Meliaceae: Known as Cedro Hembra or Spanish, Mexican or Cigar-box cedar,
the species is one of the world’s most important timber species and occurs naturally from the Mexican
Pacific coast, through Central America and the West Indies to its southern limit in Argentina. The
species prefers well-drained soils, occasionally limestone and is able to tolerate a long dry season. It
does not flourish in areas of rainfall greater than 3000 mm or on sites with water-logged soils. The
species is a monoecious, semi-deciduous tree ranging in height from 10 to 30 m with pinnate
compound leaves grouped towards the end of the branches.
Dalbergia latifolia Roxb. Fabaceae subfamily Faboideae: Dalbergia is a large genus of
approximately 500 species from small to medium-sized trees, shrubs and lianas with a wide
distribution. It is native to the tropical regions of Central and South America, Africa, Madagascar and
southern Asia. Dalbergia latifolia is known as (East) Indian rosewood or sonokeling and can be found
in India, Nepal and Malaysia. Naturally, the species can receive a rainfall between 750 and 5000 mm
and survive maximum temperatures of 37–50°C. The species grows best on deep loams or clays
containing lime; poor drainage causes stunting of tree growth. The tree is predominantly a singlestemmed deciduous tree with a dome-shaped crown of lush, green foliage. The bark is grey, thin with
irregular short cracks, and it has a root system that will produce suckers when near the surface. The
trees can reach a height of 20–40 m and a girth of 1.5–2 m.
Khaya senagalensis Meliaceae: Khaya is a genus of seven species of trees in the mahogany family
Meliaceae, native to tropical Africa and Madagascar. K. senegalensis is known as the Dry Zone
Mahogany and is distributed from the Congo across to Senegal. A deciduous tree, usually 15–20 m
tall with a diameter up to 1.5 m, it can have 8–16 m of clean bole and often is buttressed at the base.
18
The leaves are pinnate, with 4–6 pairs of leaflets and the terminal leaflet absent; each leaflet is 10–15
cm long and is abruptly rounded toward the apex but often with an acuminate tip. The flowers are
produced in loose inflorescences, each flower small, with four or five yellowish petals and ten
stamens. The fruit is a globose four or five-valved capsule 50–80 mm diameter, containing numerous
winged seeds.
Pongamia pinnata (L.). Fabaceae (recently renamed Millettia pinnata): Indian Beech is an IndoMalaysian species common on alluvial and coastal situations to 1200 m altitude from India to Fiji.
The species can withstand temperatures from slightly below 0°C to as high as 50°C and an annual
rainfall of 500–2500 mm. The tree grows wild on sandy and rocky soils including oolitic limestone,
but will grow in most soil types even with its roots in salt water.
The tree is described as a fast-growing deciduous tree up to 25 m tall. The trunk can reach 60 cm in
diameter with smooth grey bark. Leaves are imparipinnate, with young leaves showing a pinkish-red
tinge which matures into a glossy, deep green and grouped into 5–9 leaflets with the terminal leaf
larger than the others. Flowers are fragrant, white to pinkish, paired along a rachis in axillary,
pendent, long racemes of panicles reminiscent of wisteria. The pod is stalked, oblique-oblong, flat,
smooth, thickly leathery to sub-woody, indehiscent with one reinform seed per pod.
The wood is yellowish-white, coarse, hard and beautifully grained but is not durable; limiting its use
to cabinet-making and fuel. The wood has a calorific value of 4600 kcal per kg. The tree has been
used extensively in folk medicine with both the oil and residues being toxic; containing a high level of
alkaloids. The seed contains pongam oil, a bitter red-brown, thick, non-drying oil which lends itself
for use in the leather tanning process, in soap, as a linament for treatment for scabes, herpes and
rheumatism and as an illuminating oil. Recently it has been recognised for its bio-diesel potential.
Trees reach seed bearing at the age of 4–7 years with a single tree able to yield between 9 to 90 kg
seed per tree of which approximately 25 per cent of this weight is pongam oil.
Pterocarpus indicus (Willd.). Fabacaea: This species comes from the western limit of southern
Burma, extending eastwards through to Solomon Islands and can tolerate an annual precipitation of
960–2180 mm and a pH range of 4.0–7.5. It is able to tolerate water-logging but cannot tolerate
shallow soils and stiff clays.
The tree is a large deciduous tree, 30 m or more high with large and high buttresses. Leaves are 12–22
cm long in all with 5–13 leaflets and greyish brown to green in colour. Seeds are winged with the
seed-bearing part covered by a woody protection. The seed is dark brown and smooth in appearance
and ripens within 4–6 months. The wood harvested from these trees is regarded as one of the best
furniture timbers; it has a density of 625 kg per m3 and can be air-dried with no difficulty.
Tectona grandis. This is one of the three species in the genus Tectona. The other two species,
T. hamiltoniana and T. philippinensis, are endemics with relatively small native distributions in
Myanmar and the Philippines respectively. Tectona grandis is native to India, Indonesia, Malaysia,
Myanmar, northern Thailand, and northwestern Laos but is naturalised and cultivated in many
countries, including those in Africa and the Caribbean. Tectona grandis is a large, deciduous tree that
is dominant in mixed-hardwood forests. It has small, fragrant, white flowers and papery leaves that are
often hairy on the lower surface.
19
4
Sandalwood (Santalum album) trials
4.1
Sandalwood host selection demonstration plots
The trials detailed below are those that did not have experimental designs. It is possible that these
trials formed part of plantation-establishment research or were done for other experimental purposes,
but there were no adequate extant records to indicate objectives. These trials provided an established
resource to examine the growth of sandalwood up to 18 years of age in combination with various host
species and different planting patterns. Given the close proximity of all trials within the Frank Wise
Institute, the soil type and climate experienced by each trial was largely similar, and it is likely the
irrigation regime did not differ considerably across trials. It is suggested that indirect comparisons of
growth results across trials could be made with some confidence regarding the utility of particular
host species or planting designs.
4.1.1 Sandalwood aged 11 years (1997), Trial 5
Method
Trial description
The trial was established to demonstrate sandalwood growth in a multi-species plantation with highvalue timber hosts. Host species used were Khaya senegalensis, Cathormion umbellatum, Swietenia
mahogani and Cassia siamea. A total of 15 rows were planted in an area of 0.89 ha, with the planting
design used shown in Figure 4.1. The middle row of each 3-row group was a host-only row where
species were planted in the same repeated order along the length of each row. This planting was not
established with a short-term host species and instead Cathormion was planted within the sandalwood
rows. Initial stocking was equivalent to 470 sandalwood stems per hectare, 480 Cathormion, 150
Khaya, 125 Swietenia and 235 Cassia with a total of 1460 SPH. The sandalwood-to-host ratio at
establishment was approximately 1:2.
Measurement
In 2001 records were found where only the BD, DBH and height of only the sandalwood were
measured. In 2008 when the trees were 11 years old, measurements included both sandalwood and
hosts, with BD, DBH, bole height, CBD and tree height recorded.
Results
Between 5 and 11 years from planting, 15 sandalwood plants died, reducing survival from 79 to 75
per cent or 352 SPH. The total number of host and sandalwood stems surviving at 11 years was
equivalent to 806 SPH, or 55 per cent of the original planted trees. The ratio of sandalwood to host at
11 years of age had changed to 1: 1.3.
20
Rows
18
S
SWE
S
15
C
CAS
12
S
9
Guard
S
SWE
S
C
C
CAS
K
S
S
C
CAS
C
6
S
SWE
3
C
0
Meters
S
SWE
S
C
C
CAS
C
K
S
S
K
S
C
CAS
C
C
CAS
C
S
S
SWE
S
S
SWE
S
K
C
C
K
C
C
K
C
1
2
3
4
5
6
4
5
6
0
1.8
3.6
7.2
9
10.8
14.4
16.2
18
5.4
Guard
12.6
Figure 4.1 Trial 5 layout showing within and between row spacing (distance across plot from
corner) for sandalwood and hosts. C = Cathormion, K = Khaya, SWE = Swietenia, CAS
= Cassia, S = sandalwood, and guard rows were vacant.
At 5 years of age this sandalwood had a BD of 6.1 ± 1.8 cm, DBH of 3.6 ± 1.3 cm and trees were 4.2
m tall. Mean growth parameters (Table 1.1) indicated that sandalwood growth rates up to 11 years of
age were low. The average basal diameter of sandalwood increased by 2.8 cm, a rate of less than 0.5
cm per year between age 5 years and 11 years. The stem basal area occupied by all species on the site
was equivalent to 26.9 m2 per hectare, of which 8 per cent was attributed to sandalwood. Khaya was
the dominant species on the site and contributed 53 per cent of total stem basal area and 69 per cent of
the total estimated stem wood production for the site, despite only accounting for 10 per cent of stems
initially established.
The largest parameters recorded for an individual sandalwood plant at 11 years of age were 20.6 cm
for basal diameter, 12.9 cm for DBH, 5.5 m bole height, 9.5 m tree height and maximum calculated
bole and estimated stem volumes for individual trees were 0.050 m3 and 0.079 m3 respectively.
Table 4.1 Growth parameters of sandalwood and hosts in Trial 5 when they were 11 years old
(mean ± s.d.)
Santalum
album
Parameter
Cathormion
umbellatum
Cassia
siamea
Khaya
senegalensis
Swietenia
mahogani
No. observations
314
71
111
130
91
Survival (%)
75.1
16.5
52.9
96.3
82.7
8.9 ± 3.1
7.1 ± 3.3
26.1 ± 6.2
35.4 ± 5.6
9.8 ± 3.0
Basal diameter (cm)
DBH (cm)
6.4 ± 3.0
4.8 ± 2.8
18.9 ± 4.6
26.4 ± 5.6
6.8 ± 2.7
0.92 ± 0.70
0.71 ± 0.65
0.88 ± 0.78
2.7 ± 1.3
1.1 ± 0.64
5.2 ± 1.4
3.3 ± 1.4
9.3 ± 2.3
13.6 ± 2.4
5.4 ± 1.7
2.20
0.32
6.67
14.38
0.77
0.006 ± 0.006
0.003 ± 0.004
0.037 ± 0.039
0.114 ± 0.062
0.007 ± 0.006
0.014 ± 0.012
0.008 ± 0.013
0.172 ± 0.113
0.312 ± 0.175
0.016 ± 0.014
ESV/ha (m ha )
2.1
0.2
4.6
16.7
0.7
Surviving SPH
353
80
125
146
102
Bole height (m)
Tree height (m)
2
Basal area/ha (m ha )
3
Bole vol (m )
3
ESV (m )
3
-1
-1
DBH = diameter at breast height, ESV = estimated stem volume, SPH = stems per hectare.
21
Discussion
The combination of host species used here produced low sandalwood growth at age 11. Two of the
host species, Khaya and Swietenia, belong to the Meliaceae family, which has been broadly indicated
as providing poor long-term hosts (Barbour 2008). Leguminous species often make better hosts in the
Cununurra clays (Barbour 2008; Radomiljac and McComb 1998b; Radomiljac et al. 1999a;
Radomiljac et al. 1999b) probably because symbiotic relationships with rhizobia enable legumes to fix
atmospheric nitrogen and nitrogen-containing compounds are transferred to sandalwood (Radomiljac
et al. 1998c). The potential nutritional benefit gained from the two legume species used, Cassia and
Cathormion, was insufficient to allow the slower-growing sandalwood to compete for resources,
particularly against Khaya which dominated the site in terms of basal area production. The tree size
and the proportion of the site occupied by Cassia suggest it could also have negative competition
effects on sandalwood growth. Both Cassia and Khaya were nearly or more than double the height of
sandalwood and dense shading by these trees, especially Khaya, appeared to be a major factor. The
effects of competition on sandalwood growth are more thoroughly discussed in Section 4.3.
4.1.2 Sandalwood aged 16 years (1993), Trial 3
Method
Trial description
The planting consists of separate host species blocks with no experimental design applied. Long-term
host species used for this trial were Peltophorum and Cassia. The Peltophorum block had four rows
with hosts at 9 m spacing and sandalwood planted at 3 m either side of each host within the row. The
sandalwood-to-host ratio at establishment was 2:1 with stocking of 1235 SPH for sandalwood and 617
SPH for hosts. The area of this block was 0.13 ha. The Cassia block contained 10 rows, oddnumbered rows had alternate positions of host and sandalwood at 3 m spacing, and even-numbered
rows were planted only with sandalwood spaced at 3 m. The planting ratio of sandalwood to host was
3:1 with sandalwood stocked at 929 SPH and hosts at 309 SPH. The area of this block was 0.41 ha.
Measurement
In 2001 (8 years old) sandalwood DBH, basal diameter, bole height and tree height were measured.
Measurements in 2008 (15 years old) recorded sandalwood DBH, basal diameter, bole height, crown
break diameter (CBD) and tree height for both sandalwood and host. Calculated parameters of basal
area, bole volume and estimated stem volume (ESV) were done on an individual tree and per hectare
basis.
Results
At 15 years of age, sandalwood survival was very poor with Peltophorum as a host. There was better
survival with Cassia but sandalwood survival was still low. Within the Peltophorum block, two thirds
of hosts survived (67.3 per cent) but few sandalwood (6.9 per cent). In the Cassia block, most hosts
survived (92.1 per cent) and only a quarter of sandalwood trees (25.2 per cent).
Cassia trees were considerably larger than Peltophorum after 15 years (Table 4.2). Cassia trees were
taller with wider trunks and the estimated stem volume was four times greater. Combined with greater
survival rates of Cassia, the estimates of stem volume per hectare were seven times greater than for
Peltophorum.
Sandalwood trees were much smaller than their associated hosts (Table 4.3). Differences in growth
parameters between sandalwood in association with the two hosts were relatively small, however
because of more favourable sandalwood survival in association with Cassia the estimated stem
volume per hectare was close to four times that with Peltophorum as the host. Despite sandalwood
22
having an initial stocking two and three times higher than Peltophorum and Cassia respectively, the
proportion occupied (basal diameter) per hectare was less than 13 per cent of the area occupied by the
hosts.
Table 4.2 Measured and estimated growth parameters of 15-year-old Peltophorum and Cassia
as sandalwood hosts in Trial 3 (mean ± s.d.)
Peltophorum block
Parameter
DBH (cm)
Basal diameter (cm)
2
Basal area (m )
Basal area/ha (m2 ha-1)
Tree height (m)
Cassia block
18.44
±
4.65
28.61
±
9.07
25.49
±
5.61
43.86
±
13.18
0.0535
±
0.0216
0.1645
±
0.0917
12.52
68.27
8.96
±
1.74
12.90
±
2.74
Bole height (cm)
181.52
±
66.51
119.22
±
125.91
3
Bole volume (m )
0.0690
±
0.0356
0.1199
±
0.0976
3
0.1360
±
0.0819
0.5803
±
0.3905
ESV (m )
3
ESV/ha (m ha )
-1
Surviving stems (SPH)
31.82
240.82
234
415
DBH = diameter at breast height, ESV = estimated stem volume, SPH = stems per hectare.
Table 4.3 Measured and estimated growth parameters of 15-year-old sandalwood with host
species Peltophorum and Cassia in Trial 3 (mean ± s.d.)
Peltophorum block
Parameter
DBH (cm)
Basal diameter (cm)
2
Basal area (m )
Cassia block
10.84
±
3.75
11.95
±
3.10
14.47
±
4.82
18.15
±
5.72
0.0181
±
0.013
0.0284
±
0.0193
7.35
±
1.37
Basal area/ha (m2 ha-1)
1.54
Tree height (m)
6.18
±
2.69
Bole height (cm)
168.18
±
95.58
120.29
±
98.70
3
Bole volume (m )
0.0229
±
0.019
0.0237
±
0.0252
3
0.0433
±
0.041
0.0598
±
0.0468
ESV (m )
3
ESV/ha (m ha )
-1
Surviving stems (SPH)
6.65
3.68
13.99
85
234
DBH = diameter at breast height, ESV = estimated stem volume, SPH = stems per hectare.
Discussion
In the planting arrangements used here, Peltophorum and Cassia performed poorly as hosts for
sandalwood based on survival, and at best produced moderate growth rates. To put the growth in
perspective Barbour (2008) indicated that the average sandalwood DBH for moderate to good hosts
ranged from 9 to 10.8 cm at 9 years, compared to only 10.8 to 11.95 cm at 15 years achieved here.
With the absence of comparable experimental treatments it was difficult to identify the degree to
which the poor sandalwood performance was contributed to by species or planting design. In seedling
trials, sandalwood grown with Cassia siamea produced similar growth to those with Dalbergia
latifolia and Millettia pinnata (Rai 1990), which have been identified as good hosts in plantation trials
(Barbour 2008). This suggests Cassia was functionally capable of providing requirements for
sandalwood growth, but over time its growth rate and size produced negative competition effects. The
planting design had sandalwood initially stocked at 1235 stems per hectare and hosts at 617 stems per
23
hectare giving a 2:1 ratio, so that there were substantially fewer hosts for each sandalwood tree than
the trial used by Barbour (2008) where sandalwood and hosts were in a 1:1 ratio and stocked at 462
stems per hectare. The higher stocking of sandalwood and lower host ratios would elevate intraspecific competition and potentially the level of parasitism between individual sandalwood, and these
factors were likely to contribute to the low survival and growth rates. Further examination of
competition within this trial is detailed Section 4.3.
4.1.3 Sandalwood aged 17 years and 18 years, Trials 1 (1990) and 2 (1991)
Methods
Trial establishment
Both Trial 1 and Trial 2 were located in the same block at the Frank Wise Institute with Trial 1
positioned about 85 m to the south of Trial 2. The trials were established on Cununurra clay, using
land preparation for flood irrigation with mounded rows and with a long-term host-to-sandalwood
ratio of approximately 1:1. The sandalwood and long-term hosts were spaced at 3 m within alternating
rows. Planting density of sandalwood and host together was approximately 460 SPH.
Trial 1 included the long-term host Cathormion umbellatum, and covered an area of around 0.4 ha
with only three rows of both sandalwood and hosts remaining. It appeared as though it was a remnant
from a larger trial. There was a gap of 10–15 m between this trial and the next trees (see Plate 4.1).
Plate 4.1 Trial 1 showing the planting arrangement with the sandalwood and Cathormium
Trial 2 was planted over 1.3 ha and tested three long-term host species: Acacia aneura, Bauhinia
cunninghamii and Cathormion umbellatum. The trial was split longitudinally into three blocks
approximately 70 m long, with each host represented once within a row in a randomised pattern. Poor
sandalwood survival with the Acacia and Bauhinia hosts made statistical analysis using the original
design impossible.
Measurement
Both trials were assessed in 2008 at ages 18 years and 17 years for the 1990 and 1991 trials
respectively. Sandalwood diameter at the base, breast height and bole break were measured, as were
the bole height and tree height. The host basal diameters and tree height were measured.
Results
Sandalwood survival in Trial 1 was 30 per cent (139 SHP) and Cathormion umbellatum 51 per cent.
There was one row in which only one sandalwood survived, compared to approximately 30
24
sandalwood in the each of the other two rows, and it is not known whether this mortality occurred
naturally or by design to benefit the remaining sandalwood. With this row excluded in the analysis,
sandalwood survival increases to 43 per cent.
Sandalwood survival in Trial 2 was 35 per cent (162 SPH). When the sandalwood was planted
alongside one row of Cathormion, sandalwood survival was 50 per cent compared to 33 per cent with
Acacia and Bauhinia. In this mixed host planting, 56 per cent of sandalwood survived when planted
with Bauhinia and Cathormion combination. Only 11 per cent of planted Acacia aneura were
surviving at 17 years of age, compared to 73 per cent of Bauhinia cunninghamii and 83 per cent of
Cathormion umbellatum.
The sandalwood in Trial 1 was larger than those in Trial 2 (Table 4.4), and had a basal diameter of 1.4
compared to 1.1 MAI (cm per year). The mean growth of sandalwood in combination with different
hosts in Trial 2 varied (Table 4.5) and those growing next to at least one row of Cathormion were
superior to those without Cathormion. The mean over-bark estimated stem volume, adjusted for
survival, of sandalwood in Trial 1 was 27.2 m3 per hectare compared to 9.9 m3 per hectare for Trial 2.
The best performing host combination in Trial 2, Bauhinia and Cathormion, had an estimated stem
volume of 17.3 m3 per hectare.
Cathormion in Trial 1 had basal diameter MAI of 1.5 cm per year compared to 1.2 cm per year in
Trial 2 (Table 4.6). The surviving Acacia hosts in Trial 2 were smaller compared to Bauhinia and
Cathormion, which on average had grown to a similar size.
Table 4.4 Growth parameters of 18-year-old and 17-year-old sandalwood established in 1990
(Trial 1) and 1991 (Trial 2) respectively (mean ± s.d.)
Trial 1 (1990)
Parameter
Trial 2 (1991)
Mean
Min
Max
Mean
Min
Max
Basal diameter (cm)
25.6 ± 8.1
11
58
17.9 ± 4.9
6.5
35.2
DBH (cm)
18.7 ± 5.7
7.2
33.1
13.8 ± 4.2
4.8
28.6
Crown break diam. (cm)
22.9 ± 9.1
8.3
58
14.7 ± 4.9
4.5
32.1
Bole height (cm)
195.2 ± 78.3
0
480
148.6 ± 58.5
0
420
Tree height (cm)
767.9 ± 146.5
441
1100
549.6 ± 118.5
300
950
3
0.089 ± 0.061
0
0.378
0.033 ± 0.025
0
0.212
3
0.196 ± 0.155
0.015
0.812
0.061 ± 0.048
0.003
0.309
Bole volume (m )
Stem volume (m )
Table 4.5 Growth parameters of sandalwood in 1991 (Trial 2) when planted in dual host
configurations (mean ± s.d.)
Hosts
n
Basal diam.
(cm)
DBH
(cm)
Height
(cm)
Bole volume
(m3)
Stem volume
(m3)
A/A
4
17.6 ± 2.6
14.7 ± 3.8
500.0 ± 40.8
0.033 ± 0.008
0.060 ± 0.024
A/B
51
16.1 ± 4.4
12.3 ± 3.7
503.9 ± 116.6
0.028 ± 0.021
0.048 ± 0.039
A/C
36
18.5 ± 4.4
14.7 ± 4.4
556.9 ± 119.0
0.034 ± 0.019
0.067 ± 0.043
B/B
8
15.9 ± 3.8
11.8 ± 3.8
500.0 ± 116.5
0.019 ± 0.018
0.039 ± 0.026
B/C
52
18.8 ± 4.7
14.7 ± 4.2
570.2 ± 79.4
0.037 ± 0.020
0.066 ± 0.039
C/C
43
18.0 ± 3.9
13.6 ± 3.2
617.4 ± 110.7
0.038 ± 0.032
0.062 ± 0.041
Hosts: Acacia aneura (A), Bauhinia cunninghamii (B) and Cathormion umbellatum (C).
25
Table 4.6 Growth parameters measured at 18 years and 17 years for host species established in
1990 (Trial 1) and 1991 (Trial 2) respectively (mean ± s.d.)
Established
Trial 1
Trial 2
Host
Survival (%)
Basal diameter (cm)
Tree height (cm)
Cathormion umbellatum
51
26.7 ± 11.5
704.0 ±166.2
Acacia aneura
11
12.7 ± 3.8
482.4 ± 95.1
Bauhinia cunninghamii
73
19.6 ± 6.4
592.7 ± 132.6
Cathormion umbellatum
83
20.3 ± 6.1
529.2 ± 138.9
Discussion
Survival of sandalwood varied with host combinations and indicated that neither Bauhinia
cunninghamii nor Acacia aneura were suitable as sole long-term hosts. At 17 and 18 years of age,
Cathormion umbellatum was able to sustain between 40 and 50 per cent of sandalwood trees when
established at an initial density of 463 stems per hectare at a 1:1 host-to-sandalwood ratio.
Sandalwood survival was lower than desirable for a commercial plantation and may be related to the
less-than-optimised nature of the silviculture and management practices applied across the trials. It
could also be that the initial 1:1 host-to-sandalwood ratio was inadequate for long-term sandalwood
survival and resource competition contributed to high mortality. Unfortunately early survival data was
not available and the timing of the mortality undetermined, which may have elucidated causal factors.
The differences in growth parameters between the 17-year-old and 18-year-old sandalwood were
considerably larger than what would be expected of one year’s growth. Even when sandalwoods
grown with Cathormion hosts were compared between Trial 1 and Trial 2, the large difference could
not be accounted for. Trial 1 was only six rows wide and sandalwood trees would therefore benefit
from strong edge effects. The positive impact of edge effects on sandalwood growth was also
displayed in Trail 2 (see Plate 4.2). The 35 surviving sandalwood in the first two edge rows planted
adjacent to least one row of Cathormion had an estimated stem volume of 23.8 m3 per hectare. This
closely resembled the estimated 27.2 m3 per hectare for sandalwood in Trial 1. This space requirement
for sandalwood when grown with Cathormion is further confirmed later in this report (Section 4.2.2,
Trial 6). The strong influence of planting density reinforces the understanding required to achieve the
correct balance between host and sandalwood stocking and their spatial arrangement to obtain optimal
sandalwood growth in a plantation system.
Plate 4.2 The sandalwood block in Trial 2 showing the edge effect together with Cathormion
26
This is the first report on the growth performance of plantation-grown 17-year-old and 18-year-old
sandalwood. Taking into account the unknown history of the Trials as well as their final stocking rate,
it is questioned whether they are representative of future plantations of a similar age. The growth
rates, as indicated by basal diameter MAIs of 1.4 cm in Trial 1 and 1.0 cm for Trial 2, were not
dissimilar to those reported for younger sandalwood. Barbour (2008) reported mean basal areas for
sandalwood equivalent to basal diameters of 14.4 cm (1.6 MAI) when grown with Cathormion, and up
15.8 cm (1.8 MAI) with the best host species after 9 years at an established density of 463 stems per
hectare. At 14 years, sandalwood has an average basal diameter of 13.3 cm (~1.0 MAI) when grown
with Acacia mangium at the Frank Wise Institute, and up to 18.1 cm (1.3 MAI) at Carnarvon (24°532
S 113°39’39 E) when grown with Azaderachta indica (neem) (McComb 2009). This previous work
indicates that single-tree sandalwood growth performance in Trial 1 is higher than expected when
using Cathormion as a long-term host. Survival could be greatly enhanced with silviculture
improvements but whether this would correlate to increased total wood yield per hectare is
questionable knowing there are sandalwood growth limitations based on its spatial requirements,
especially with Cathormion as a host.
Trial 2 demonstrated that there was a sandalwood growth benefit when grown with dual host species
compared to growth with a single host species. Sandalwood grown with a combination that included
Cathormion with another species was better than Cathormion on its own, even when the other species
was Bauhinia cunninghamii and/or Acacia aneura which are singularly poor performing hosts. This
finding is supported in other trials (Section 4.3.1, Trial 7). The additive effect on sandalwood growth
of these mixed-host environments is unclear. It is hypothesised that as the composition of sandalwood
sap flow varies with different host species (Radomiljac et al. 1998c), it is possible that in a mixed-host
environment sandalwood takes up a broader range of host organic and mineral solutes which
ultimately better satisfies growth requirements. Many commercial plantations are currently being
established with mixed-host combinations. This spreads the risk of host loss by insect pests and
disease and natural ageing, which in turn lowers the risk of reduced sandalwood growth due to
inadequate nutrients from hosts. Further research is required to understand the dynamics of the
interactions in mixed-host sandalwood plantations and to quantify the improvements to sandalwood
growth.
4.2
Sandalwood growth with Cathormion umbellatum
Cathormion umbellatum Fabaceae is a shrub to small tree native to northern Australia (Florabase
2011), and it was identified as a candidate host because of its ability to fix nitrogen. During the initial
stages of research into sandalwood cultivation in the Ord River Irrigation Area (ORIA) in the early
1990s, Cathormion was classified as a ‘satisfactory’ intermediate host compared to other species, such
as Albizzia and Khaya (Done et al. 2004). Subsequently Cathormion was broadly utilised as a longterm host species in a large number of the initial commercial plantations. More recently, plantation
systems have incorporated multiple host species, yet Cathormion remains an important species in the
host mix and could be considered somewhat of a ‘benchmark’ against which the effectiveness of other
hosts is judged. This section examines the impact of different host ratios and spatial configurations on
sandalwood grown with Cathormion.
4.2.1 Effect of host ratio on sandalwood growth with Cathormion umbellatum as
the primary host, Trial 9
Methods
Trial establishment and design
Planted in 2000 with sandalwood and long-term host, Cathormion umbellatum in six ratio treatments
(Table 4.7) with Sesbania formosa as the short-term host (Radomiljac et al. 1999a). Land was
27
prepared for flood irrigation and mounds made 1.8 m apart. Ratio treatments were allocated randomly
to plots 18 m wide by 36 m long, with six replicates. Planting configurations varied according to ratio
treatment (Figure 4.2), however each plot was planted in three ‘columns’ each of three rows, with a
constant 1.8 m between rows and 3.6 m between ‘columns’. In 2003, when trees were aged 3 years,
the original planting design was considered overcrowded and rows 2, 5 and 8 in each block were
removed thus altering the sandal treatment ratios (Table 4.8).
Table 4.7 Sandalwood (S) and host (H) spacing and stocking for the six ratio treatments in the
original planting design of Trial 9
Sandal
SPH
Host
spacing
in row
(m)
Host/
plot
Total host/
treatment
Host
SPH
Treat.
Ratio
(S:H)
Sandal
spacing in
row (m)
1
1:8
9
12
48
185
3
96
384
1481
2
1:4
6
18
72
278
3
72
288
1111
3
1:2
3
36
144
556
3
72
288
1111
4
1:1
6
54
216
833
6
54
216
833
5
2:1
3
72
288
1111
3
36
144
556
6
4:1
3
72
288
1111
6
18
72
278
Sandalwood/
plot
Total
sandal/
treatment
Measurement
Sandalwood trees were first measured in 2001 (1 year old), with a second measurement of host and
sandalwood in November 2008 (8 years old). In 2008 only the internal blocks were measured to avoid
edge effects from surrounding plots. Only Treatments 1, 4, 5 and 6 were measured because of the
repetitive nature of treatments existing post-culling (Table 4.8). Basal diameter and height were
measured for sandalwood and host, with DBH, crown break diameter and bole height, measured for
sandalwood only. Sandalwood growth data from 2001 was subjected to an analysis of variance. Only
descriptive means were computed for the 2008 data because the host culling in 2003 changed planting
arrangements, resulting in an imbalance in the original experimental design.
28
H
H
H
H
H
H
H
H
H
H
H
S
H
H
S
H
H
S
H
H
H
H
H
H
H
H
S
H
H
S
H
H
S
H
H
H
S
H
H
S
H
H
S
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
S
H
H
S
H
H
S
H
H
H
H
H
H
H
H
H
H
H
H
S
H
H
S
H
H
S
H
H
H
H
H
H
H
H
S
H
H
S
H
H
S
H
H
H
S
H
H
S
H
H
S
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
S
H
H
S
H
H
S
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
S
H
H
S
H
H
S
H
S
H
H
S
H
H
S
H
H
H
H
H
H
H
S
H
H
S
H
H
S
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
S
H
H
S
H
H
S
H
H
H
S
H
H
S
H
H
S
H
S
H
H
S
H
H
S
H
H
H
H
H
H
H
S
H
H
S
H
H
S
H
H
H
H
H
H
H
H
H
H
S
H
H
H
S
H
H
S
H
H
S
H
H
S
H
H
S
H
H
S
H
H
S
H
S
H
S
S
H
S
S
H
S
S
S
H
S
S
H
S
S
H
H
S
H
H
S
H
H
S
S
S
H
S
S
H
H
S
H
S
S
H
S
S
H
S
S
S
S
H
S
S
S
H
S
S
H
S
S
H
S
S
H
S
S
H
S
S
H
S
S
H
S
H
H
S
H
H
S
H
S
H
S
S
H
S
S
H
S
S
S
H
S
S
H
S
S
H
S
S
H
S
S
H
S
S
H
S
S
H
S
H
H
S
H
H
S
H
S
H
S
S
H
S
S
H
S
S
S
H
S
H
S
H
S
H
S
S
H
S
H
S
H
H
S
H
S
H
S
S
H
S
S
H
S
S
S
H
S
S
H
S
S
H
S
S
S
H
S
S
H
S
S
H
S
S
H
S
S
H
S
S
H
S
S
H
S
H
H
S
H
H
S
H
S
H
S
S
H
S
S
H
S
S
S
H
S
S
H
S
S
H
S
S
H
S
S
H
S
S
H
S
S
S
S
S
S
S
Treatment 1 (1:8)
S
S
S
S
S
S
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
S
S
S
S
S
Treatment 2 (1:4)
Treatment 4 (1:1)
Treatment 3 (1:2)
Treatment 5 (2:1)
H
H
H
H
H
H
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
H
H
H
H
H
H
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
H
S
H
S
S
H
S
S
H
S
S
H
S
S
H
Treatment 6 (4:1)
Figure 4.2 Trial 9 planting layout of sandalwood (S) and Cathormion host (H), for the six ratio
treatments. Intermediate hosts were planted at 1.5 m either side of each sandalwood.
Table 4.8 Trial 9 host (H) and sandalwood (S) stocking rates after culling of plots in 2003
Post-culling of hosts in 2003
Treat.
Original
ratio
(S:H)
Sandal/
plot
Total
sandal/
treatment
Sandal
SPH
Host/
plot
Total
host/
treatment
Host
SPH
Current
treatment
2008
measure
1
1:8
0
0
0
72
288
1111
All host
Yes
2
1:4
0
0
0
72
288
1111
All host
No
3
1:2
0
0
0
72
288
1111
All host
No
4
1:1
36
144
556
36
144
556
1:1
Yes
5
2:1
72
288
1111
0
0
0
All sandal
Yes
6
4:1
72
288
1111
0
0
0
All sandal
Yes
Results
At 1 year, the trial showed no difference in the mean sandalwood basal diameters between ratio
treatments (P = 0.146) (Figure 4.3). There were however differences between sandalwood tree height
(P <0.001) and bole height (P <0.001) between treatments. Generally sandalwood trees in treatments
29
S
S
with a higher proportion of hosts were shorter than with those with higher proportion of sandalwood
(i.e. lower proportion of hosts). More specifically sandalwood were shortest under a sandalwood-tohost ratio of 1:8 (Treatment 1) compared to all other treatments, except where sandalwood was in a 1:
4 ratio with Cathormion (Treatment 2). The tallest sandalwood were in treatments where there were
more sandalwood (S) than hosts (H) such as Treatments 5 (1S:1H) and 6 (4S:1H). Bole height under
the 1:8 ratio of sandalwood to Cathormion (Treatment 1) was also shorter than most other ratios
(Treatments 4, 5 and 6). Sandalwood basal diameter followed a similar trend to tree height and it
increased as the ratio shifted from many hosts per sandalwood to many sandalwood per host.
40
250
35
30
25
150
20
100
15
Diameter (mm)
Height (cm)
200
10
50
5
0
0
T1 1S:8H
Tree Ht
Bole Ht
T2 1S:4H
Basal dia
T3 1S:2H
T4 1S:1H
Treatment
T5 2S:1H
T6 4S:1H
Figure 4.3 Sandalwood tree height (cm), bole height (cm) and basal diameter (mm) within ratio
treatments of sandalwood (S) with a Cathormion host (H) when Trial 9 was 1 year
old (2001) (mean ± s.d.)
When Trial 9 was measured after 8 years (2008), sandalwood in treatments with all hosts removed
(Treatments 5 and 6) were considerably smaller than those sandalwood where a 1:1 ratio with
Cathormion hosts remained (Treatment 4; Figure 4.4). All measured parameters were lower in these
treatments and this resulted in an estimated wood volume of 0.0127 ± 0.0061 m3 for sandalwood
without hosts compared to 0.0271 ± 0.0134 m3 for sandalwood with hosts at a 1:1 ratio. Cathormion
growth was similar with or without sandalwood. Where Cathormion was a host for sandalwood at a
1:1 ratio, there was on average less than less than 5 mm difference in basal diameter and 10 cm in tree
height, when growth with and without the parasite were compared.
There was little difference in sandalwood growth between Treatments 5 and 6, which had no hosts
since culling. There was a slight trend for smaller trees with the higher pre-culling sandalwood-to-host
ratio (4S:1H, Treatment 6) than with the lower ratio (2S:1H, Treatment 5) but basal diameter and
DBH were less than 1.5 cm apart and there was only 2.3 cm difference between bole and 7.5 cm in
tree height (Figure 4.5). Estimated stem volumes reflected this similarity and Treatment 5 was only
0.0257 m3 larger than Treatment 6. Presumably growth rates post culling would be similar for both
treatments and their similarity in 2008 reflects similar growth at one year (Figure 4.3) and probably at
3 years of age when culling occurred.
30
B 6
A 25
5
15
Height (m)
Diameter (cm)
20
10
5
4
3
2
1
0
0
S - 1S:1H Sandal only H - 1S:1H
Treatment
Basal dia
CBD
DBH
S - 1S:1H Sandal only H - 1S:1H
Treatment
Bole Ht
Host only
Host only
Tree Ht
Figure 4.4 Sandalwood (S) and Cathormion host (H) growth parameters in Trial 9 post culling
(in 2003) measured in 2008 (mean ± s.d., CBD = canopy break diameter)
A
B
5
4.5
12
4
10
3.5
Height (m)
Diameter (cm)
14
8
6
2
1.5
4
1
2
0.5
0
T5 2S:1H
Basal dia
3
2.5
DBH
0
T6 4S:1H
T5 2S:1H
Original Treatment
CBD
Tree Ht
Bole Ht
Original Treatment
T6 4S:1H
Figure 4.5 Trial 9 sandalwood (S) growth parameters measured in 2008 (8 years) of post culling
treatments without hosts (H) based on original treatments (Table 4.7) (note, all hosts
culled in Treatment 5 (2S:1H) and Treatment 6 (4S:1H) in 2003, Figure 4.2, Table 4.8,
mean ± s.d.)
Discussion
Successful sandalwood plantations will require a balance between the growth of sandalwood and
hosts. Achieving this balance is complicated by the parasitic interactions, via haustoria, but also by
competition for resources including water, nutrients and light for photosynthesis and shading, which
protects bark from damage by the sun. Here this was further complicated by the presence of the
intermediate host Sesbania formosa in addition to the long-term host Cathormion umbellatum and the
distances between sandalwood and hosts. During early establishment, increasing the Cathormion
umbellatum host ratio beyond four per sandalwood was detrimental. At this early stage it was unlikely
that Cathormion had any positive host effects, particularly in Treatments 2, 3, 5 and 6 that had
separate long-term host rows. Sandalwood haustoria were most likely to first intercept and parasitise
the roots of the intermediate host, Sesbania formosa, which was planted within rows at a constant
spacing of 1.5 m either side of sandalwood throughout the trial. Presumably haustorial connections
and resources for these intermediate hosts were relatively constant. Differences in growth must
31
therefore be a function of competition for resources between growth of the long-term host
(Cathormion) and sandalwood. Unfortunately without early host growth data this can not be further
investigated.
After culling, the sandalwood in no host plots (Treatments 5 and 6) would only have had weeds and
other sandalwood to parasitise because the intermediate host, S. formosa, that was planted within
sandalwood rows tends to die out after 3 years. This resulted in clear differences at 8 years and every
measured growth parameter was larger for sandalwood grown with long-term hosts at a 1:1 ratio
(Treatment 4) than for sandalwood grown without hosts. To highlight the differences between them,
the estimated wood volume per hectare, based on surviving stems, was 11.34 m3 for sandalwood with
hosts compared to 6.99 m3 for those without hosts, even though these treatments initially had twice as
many sandalwood plants.
The original planting ratios of 2S:1H and 4S:1H (Treatments 5 and 6 respectively) present during the
first 3 years before culling did not have a residual effect on sandalwood growth at 8 years. Both
treatments displayed very similar growth patterns between 1 and 8 years of age. These treatments
were both planted so that sandalwood and long-term hosts were in separate rows, and it is possible
that the similarity in growth patterns reflect the lack of early long-term host influence, and the
constant intermediate host (S. formosa) effect up to 3 years of age in this planting configuration. The
immediate availability of S. formosa roots along mounds, and intermittently waterlogged conditions
from irrigation water that flows between mounds, may provide an environment in which roots initially
grow along and not across rows, and thus connections to long-term host roots may not occur in the
first 3 years.
4.2.2 The effect of spacing and host-parasite ratio on sandalwood growth with
Cathormion umbellatum as the primary host, Trial 6
Methods
Trial establishment design
Trial 6 was planted in 1999. Six stocking treatments consisting of different spacing and two host-tosandalwood ratios (Table 4.9) were planted in blocks of five plots. The 2:1 ratio was planted in plots
consisting of paired columns with sandalwood and Cathormion umbellatum (long-term host) planted
in separate columns, and the 4:1 ratio was planted in plots consisting of three columns with long-term
hosts in the two outer columns and sandalwood in the middle column. Each column within a plot was
1.8 m apart and there was 3.6 m between plots. Within treatment blocks, intermediate hosts Sesbania
formosa and Acacia trachycarpa were planted in alternating sandalwood columns, midway between
the sandalwood, such that there were three columns with Sesbania and two columns of Acacia per
block. Treatments were arranged from one to six across the site with no true replication applied.
32
Table 4.9 The within column spacing and stems per hectare (SPH) for the six stocking
treatments of sandalwood and Cathormion umbellatum hosts in Trial 6
Treatment
No. of
Cathormion
columns
Host:sandal
ratio
Sandal
spacing
(m)
Sandal
stocking
(SPH)
Cathormion
spacing (m)
Cathormion
stocking
(SPH)
1
1
2:1
3
617
1.5
1234
2
1
2:1
4
462
2
924
3
1
2:1
6
308
3
616
4
2
4:1
3
462
1.5
1848
5
2
4:1
4
347
2
1388
6
2
4:1
6
231
3
924
Measurement
In 2008, when Trial 6 was 9 years old the six treatments were divided into four measurement areas, or
pseudo replicates, 25 m long. Only four of the five plots within each block were measured to maintain
a balanced number of primary host columns. Sandalwood height, basal diameter, DBH, crown break
diameter and bole height were measured. Values for stem basal area, crown break area, estimated bole
volume (EBV) and estimated stem volume (ESV) were calculated. Cathormion basal diameter and
height were measured. Intermediate host species were no longer living at the time of measurement.
Statistical analyses were carried out using the pseudo replication structure, and these examined the
fixed effects of treatments and intermediate hosts, along with their interaction. A linear mixed model
approach was used to accommodate the design of the study. All analyses were carried out for the
mean treatment at a tree level and the sums which gave output at the replicate level allowing
adjustments to be made for the number of surviving trees, and also percentage survival.
Results
After 9 years, overall sandalwood survival from the sampled area was 77.6 per cent. Intermediate
hosts influenced survival (p = 0.03) and more sandalwood survived with S. formosa (82.3 per cent)
than A. trachycarpa (72.9 per cent). There were no significant differences in sandalwood survival
between treatments, however for treatments with equivalent sandalwood spacing (1 and 4; 2 and 5; 3
and 6) the survival of the 4:1 ratio treatment was always equal to or higher than the 2:1 ratio
treatment. Survival of Cathormion was 73.1 per cent across all treatments and ranged from a low of
68.1 per cent for Treatment 1 to a high of 81.8 per cent for Treatment 2.
Stocking rates influenced (P = 0.001) sandalwood basal diameter, but there was no interaction with
treatments. Sandalwood in Treatment 3 had the largest basal area (16 ± 3 cm2) and Treatment 1 the
smallest (13.7 ± 3.2 cm). A significant effect of treatment was found (P = 0.0014) for sandalwood
DBH but not between intermediate hosts. Sandalwood DBH was larger in Treatment 6 (12.7 ± 2 cm)
compared with Treatments 1, 2 and 4, and Treatment 1 had the smallest DBH (9.85 ± 2.50 cm).
Intermediate host species did not influence sandalwood DBH at 9 years of age. Sandalwood were
generally 550–600 cm tall but were tallest in Treatment 6 (616 ± 73 cm; P = 0.02) and shortest in
Treatment 2 (549 ± 91 cm) (Figure 4.7).
Sandalwood bole volume was effected by treatment (P<0.0001), whilst the effect of intermediate host
was marginal (P = 0.06). Treatment 6 (0.033 ± 0.015 m3) and Treatment 3 (0.028 ± 0.013 m3) had the
greatest sandalwood bole volume and Treatment 1 the smallest bole volume (0.020 ± 0.016 m3).
Estimated wood volume of sandalwood varied between stocking rates (p<0.0001) (Figure 4.6), but
there was no intermediate host effect. Estimated sandalwood stem volume per hectare was greater in
33
Treatments 6 (0.049 ± 0.031 m3) and 3 (0.044 ± 0.019 m3) than all other treatments except Treatment
5, and Treatment 1 had the smallest mean wood volume (0.031 ± 0.016) (Figure 4.6). Sandalwood
grown in treatments with a 2:1 host ratio (see Table 4.9 for treatment descriptions) had lower
estimated stem volume than those grown in the equivalently spaced treatments with a 4:1 ratio (i.e.
Treatments 1 versus 4, 2 versus 5, 3 versus 6).
0.06
Est. stem volume (m3)
0.05
0.04
0.03
0.02
0.01
0
1
AT
SF
2
3
All Data
Treatment
4
5
6
3
Figure 4.6 Estimated stem volume (m ) of sandalwood for long-term host stocking treatments
and intermediate host types within treatments after 9 years in Trial 6 (mean ± s.e., AT
= Acacia trachycarpa, SF = Sesbania formosa, refer to Table 4.9 for treatment
descriptions)
700
600
Hieght (cm)
500
400
300
200
100
0
1
Cathormion
Sandalw ood
2
3
4
5
6
Treatment
Figure 4.7 Height (cm) of Cathormion umbellatum and sandalwood within the six stocking
treatments after 9 years in Trial 6 (mean ± s.e., refer to Table 4.9 for treatment
descriptions)
The difference between estimated sandalwood volume per hectare between the highest and lowest
stocking treatments of 617 SPH (Treatment 1) and 231 SPH (Treatment 6) was 4.58 m3 (Figure 4.8).
Despite producing the smallest trees on an individual basis, Treatments 1 and 4 had the highest
sandalwood stem wood productivity per hectare. Even though Treatment 6 produced the largest
individual trees, it had lower productivity per hectare than all other treatments as a result of the low
sandalwood stocking rate. Across all stocking treatments the estimated volume per hectare was lower
when sandalwood was grown with Acacia (Figure 4.8) compared to Sesbania, with the greatest
difference being 3.28 cm3 per hectare for Treatment 5.
34
There was an opposing trend of individual and block yield with the number of sandalwood stems per
hectare (Figure 4.9), such that as stocking rate increased the individual tree yield declined but block
yield increased. In both cases the relationships were most strongly described by logarithmic
regressions with R2 values of 0.986 and 0.725 for mean estimated stem volume and mean estimated
stem volume per hectare respectively (Figure 4.9).
Est. stem volume (m 3ha-1)
16.0
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
1
AT
SF
2
3
4
5
6
Treatment
All Data
Figure 4.8 Estimated sandalwood stem volume per hectare after 9 years in Trial 6 (note, Acacia
trachycarpa (AT) and Sesbania formosa (SF) were intermediate hosts within the six
Cathormion umbellatum stocking treatments, see Table 4.9 for treatment details)
16
0.060
Mean est stem vol (m3)
12
0.040
10
8
0.030
6
0.020
0.010
y ESV = -0.0181Ln(x) + 0.1472
R2 = 0.9864
0.000
200
ESV
ESV ha
250
300
350
400
y ESVha = 4.2603Ln(x) - 13.48
R2 = 0.7246
450
500
550
600
4
Est stem vol ha-1 (m3)
14
0.050
2
0
650
Established Sandalwood stems ha-1
Figure 4.9 Relationship between the number of sandalwood per hectare and the mean
individual tree estimated stem volume (ESV), and the mean estimated stem volume
per hectare (ESVha) in Trial 6 after 9 years
Cathormion basal diameters differed between treatments (P <0.001) and Treatment 3 (16 ± 5 cm) had
the largest diameter, and Treatments 4 (12 ± 4 cm) and 5 (13 ± 4 cm) the lowest (Figure 4.10).
Cathormion basal diameters were larger for 2:1 host-to-sandalwood ratio treatments (see Table 4.9 for
treatment descriptions), compared with the equivalently spaced treatments with a 4:1 ratio. This trend
was reversed when examined on a per hectare basis, where the higher host stocking rate in the 4:1
treatments resulted in a larger basal area compared to the equivalently spaced 2:1 configurations
35
18.0
18.0
16.0
16.0
14.0
14.0
12.0
12.0
10.0
10.0
8.0
8.0
6.0
6.0
4.0
4.0
2.0
2.0
0.0
Basal area (m2 ha-1)
Basal diameter (cm)
(Figure 4.10). Mean height of Cathormion was very uniform (Figure 4.7) and only varied by 22 cm
between treatments.
0.0
1
Basal diameter
2
Basal area
3
4
5
6
Treatment
2
-1
Figure 4.10 Basal diameter (cm) and estimated basal area per hectare (m ha ) for Cathormion
umbellatum within stocking treatments in Trial 6 after 9 years (see Table 4.9 for
treatment descriptions)
Discussion
Sandalwood survival was higher where Sesbania formosa was used as the intermediate host. Growth
of sandalwood was similar with either of the intermediate hosts, S. formosa or Acacia trachycarpa.
Thus sandalwood planted with S. formosa would have greater yield per hectare compared to A.
trachycarpa within this trial.
Sandalwood were consistently larger on an individual basis when planted in treatments with a 4:1
host-to-sandalwood ratio (Treatments 4, 5, 6) compared to the equivalently spaced 2:1 ratio treatments
(Treatments 1, 2, 3). This may be due to greater availability of host roots, which presumably increased
the frequency of haustorial connections, and an associated rise in solute uptake which could improve
sandalwood growth. Whilst higher host availability improved sandalwood growth, the results within
sandalwood-to-host ratio treatments indicated a trend of increased sandalwood growth when spacing
between trees was further apart. So even ‘good’ hosts acted as competitors within the plantation
environment and could be detrimental to growth with increasing planting density. Further to this, the
short distance between sandalwood within high stocking treatments increased the direct competition
and parasitism between sandalwood trees, and this may have contributed to the reduced individual
sandalwood growth in these treatments.
Total sandalwood productivity at the stand level ran counter to the individual tree productivity for
equivalently spaced treatments, as sandalwood grown under high stocking rates outweighed the yield
of fewer, but larger trees. In terms of maximising total wood yield, Treatments 1 and 4, with
sandalwood stocking rates of 617 and 462 SPH respectively, were the preferred planting design.
However, ultimately the commercial value of sandalwood lies in heartwood production and oil yield
and thus plantation design should be aimed at optimising this component. Clearly external
sandalwood size can be manipulated by altering stocking rates and host ratios when sandalwood is
planted with C. umbellatum as the primary host, however the impact, if any, of the treatments on
heartwood remains unclear. In the future, monitoring aromatic wood yield in addition to growth data
should allow for a more precise economic evaluation of the different planting designs.
Cathormion growth was not reduced by increasing parasitic load from a 4:1 ratio to equivalently
spaced 2:1 ratio treatments. Indeed Cathormion trees planted at 2:1 were wider and taller than in the
36
equivalent 4:1 treatments, indicating that the effects of competition between hosts for environmental
resources were potentially greater than any detrimental parasitic effects.
4.2.3 Compilation of sandalwood growth with Cathormion umbellatum as
primary host
Methods
Mean height and basal diameter data was compiled from the Cathormion host trials presented within
this report, except for Trial 7 age 3, which used the data presented by Barbour (2008). Trials and
treatments within trials were selected based upon the most common stocking arrangement where
sandalwood and Cathormion were planted at a 1:1 ratio, with 462 stems per hectare of each (Table
4.10). Where trials contained multiple treatments, the treatment with the closest parameters to these
was chosen. All the trials, except Trial 7, had sandalwood and Cathormion planted in separate and
alternate rows. Scatter plots were used to graphically represent the growth curve of sandalwood basal
diameter and height between 2 and 18 years old, with relationships determined by the Excel trendline
function.
Table 4.10 Age and planting details of Cathormion host trials
Tree age
Host: sandal
ratio
Established
sandalwood
SPH
Surviving
sandalwood
SPH
Surviving host
SPH
Trial #
(years)
Number of
samples
9
1
208
1:1
556
533
-
7
3
209
1:1
462
402
420
9
8
60
1:1
556
417
403
6
9
66
2:1
462
319
378
2
10
143
1:1
462
231
-
7
11
45
1:1
462
370
322
2
17
143
1:1
462
217
383
1
18
61
1:1
462
199
236
Results
Sandalwood basal diameter and height increased with age (Figure 4.11). Log functions fitted to the
data accounted for approximately 90 per cent of the variation in basal diameter and height. Growth
was rapid between 1 and 7 years after which thegrowth rate slowed. The lack of data for trees aged 4
to 7 years reduced confidence in the growth curve during this period. However, despite gaps in the
data, there was a consistent growth pattern between age 8 years and 11 years suggesting that
conditions in the selected trials generally promoted similar sandalwood growth rates, and potentially
similar growth curves. The exception was a substantial difference in size between sandalwood at 17
and 18 years of age and with limited data after 11 years it is difficult to know which curve is more
representative of growth. This is further complicated by a potential edge effect in Trial 1 (age 18
years), and as such a more conservative trend should be considered normal.
For both basal diameter and height the power trendline function provided a stronger fit, 0.98 and 0.96
respectively, compared to the log relationships (Figure 4.11). However the trend lines of power
functions at 18 years were closer to the upper data point of Trial 1 and this was considered unusually
high due to edge effects and so the more-conservative log relationships were presented. At harvestable
age (15 years) the difference between log and power function was less than 2 cm for basal diameter
and 30 cm for height, however differences in the log and power relationships were very apparent in
37
comparisons beyond the bounds of the available data. At 25 years the power function gives a basal
diameter of 31 cm compared to 23 cm for the log function. Accurate modelling of sandalwood growth
curves would require data across a longer time scale that encompassed the juvenile fast growth phase,
the mature steady growth phase and senescence.
b
30
9
8
25
7
Tree height (m)
Basal diameter (cm)
a
20
15
10
y = 7.038Ln(x) + 0.4005
R2 = 0.8972
5
5
10
15
5
4
3
2
y = 2.0374Ln(x) + 0.8263
R2 = 0.9027
1
0
0
6
0
20
0
Age
5
10
Age
15
20
Figure 4.11 Diameter (a) and height (b) of sandalwood grown with Cathormion hosts generally
at a 1:1 ratio with 462 sandalwood stems per hectare (see Table 4.10 for trial details)
Discussion
The parasitic nature of sandalwood means it is not plausible to establish a ‘standard’ free-growing
growth rate or growth curve that is applicable to plantation forestry. Hence, an alternative growth
standard is required so that performance of different host species, spacing and designs can be put into
context. We suggest that a 1:1 Cathormion host-to-sandalwood ratio, established at 462 sandalwood
stems per hectare with a spatial arrangement of 3 m within rows and 7.2 m between rows could
provide a benchmark for sandalwood plantation production.
For a benchmark to succeed good data is required, however, there are some inherent issues with the
dataset presented. The data was compiled across different trials established as much as 11 years apart
and so these growth curves may not accurately represent sandalwood growth through time with
Cathormion as the primary host. A complete time series of growth was not kept for these trials and a
maximum of two time points (approximately 7 years apart), were available for any one trial. Where
more age data was available, such as trees aged 8 to 11 years, growth rates were consistent, but
growth curves of individual trials may vary through time or at particular points in time. In addition,
mortality increased with trial age and thus reduced stocking of both Cathormion and sandalwood, was
inherently linked with growth rates in older trials, and it is possible larger trees with more extensive
root networks were more likely to survive, biasing the results. For all trials, active management
included pruning, weed and insect control, and irrigation; but inadequate records do not allow
accurate comparisons with current practices in commercial plantations. Declining survival of
sandalwood and Cathormion per hectare with age (Table 4.10) could be related to sub-optimal
management practices, as indeed these have improved with experience, and so these results represent
a baseline. Alternatively, the decline in survival could indicate increasing stress from competition, as
the demand on resources for survival and growth increase with the size of trees.
None-the-less, the growth curves presented for sandalwood planted at 462 stems per hectare in a 1:1
ratio with Cathormion in a 3 x 7.2 m spacing, represent the best available baseline data for plantation
production at this time. These generalised growth curves provide a dataset for comparing the relative
effectiveness of different hosts, spatial arrangements and plantation management over the expected
plantation rotation.
38
4.3
Investigation of spatial competition analysis
The hemi-parasitic nature of sandalwood dictates that the majority of plantations are by necessity
mixed-species environments. Standard sandalwood silviculture employs an herbaceous pot host, an
intermediate ‘woody’ host and a long-term host. Hosts may consist of multiple species, so at any one
time there can be between two and five tree species in a plantation. In mixed-species environments
there are three interactions resulting in different growth outcomes and these are: competition (where
one species exerts negative effects on another and reduces its growth); competition reduction (where
inter-specific competition is lower than intra-specific competition and results in improved growth for
all species); and facilitative production (where one species positively impacts another and improves
their growth) (Vandermeer 1989). The complexity of these interactions within mixed-species
plantations is highlighted in reviews by Forrester et al. (2006) and Kelty (2006), and it is foreseeable
that the parasitic nature of sandalwood would increase this complexity.
For sandalwood to grow successfully in plantations, positive facilitative production effects (primarily
via parasitism of hosts but also through environmental benefits) must outweigh the negative effects of
host competition for resources such as light, space, water and soil nutrition. In turn, the host must be
able to successfully withstand the parasitic draw of water and nutrients as well as the spatial and
environmental competition, to sustain sandalwood throughout the rotation. Variation in the
interactions between sandalwood and hosts will result from differences in the amount and constitution
of solute uptake (Radomiljac et al. 1998c), and the size and structure of hosts (Barbour 2008) and thus
it is likely that spatial requirements for successful sandalwood growth will vary between host species.
There is a lack of quantitative knowledge on variation in competitive interactions and the impact of
spatial parameters between sandalwood and its host species and how these may effect growth.
Decisions for plantation designs to date have been largely based on the best estimation or from trial
and error experimentation.
Competition indices can provide insight into spatial parameters and the impact on growth of inter- and
intra-specific interactions between trees in native forest (von Oheimb et al. 2011; Zhao et al. 2006)
and mixed-species plantation environments (Bristow 2006; Vanclay 2006b). Analysis of tree growth
using competition indices aims to account for the impact of relative size and/or density of
neighbouring trees, within a specific horizon of influence around target trees. The ability to account
for spatial effects as well as species differences simultaneously could provide a level of understanding
of host–sandalwood interactions within plantations not yet achieved. The analysis completed here
across two trials aimed to provide a preliminary examination of the utility of spatially explicit
competition indices to explain differences in sandalwood growth with different host species.
4.3.1 Spatially-dependent host effects on sandalwood size when grown with six
host species, Trial 7
Methods
Trial establishment and design
Trial 7 was established in 1999 to test sandalwood growth with six long-term hosts: Khaya
senegalensis and Cedrela odorata from the Meliaceae family; and Cathormion umbellatum,
Dalbergia latifolia, Millettia pinnata (syn. Pongamia pinnata) and Pterocarpus indicus from the
Fabaceae family. The short-term host was Acacia trachycarpa and Alternanthera was used as the pot
host. The six long-term host treatments were planted in a randomised complete block design
replicated five times. The ratio of sandal to intermediate host was 1:1, and the sandal to long-term
host ratio was initially established at 1:2; however, in 2003 hosts were removed from every second
row so that a ratio of 1:1 was achieved. Post-thinning treatment blocks were eight rows wide by 12
positions long with sandalwood and long-term hosts alternating at 3 m spacing within each row.
39
Measurement and statistical analysis
In January 2008, when trees were 8 years old, plots within the trial were measured and statistical
analysed (Barbour 2008). Individual tree data from these measurements was then used for further
analysis here. This approach, used in mixed-species analysis, was experimental in its application to
the complex interactions of spatial host relationships in sandalwood plantations. Two host
competition indices were calculated for individual sandalwood within five competition horizons (x);
6, 9, 12, 15, and 18 m (i.e. hosts within this distance from an individual sandalwood tree), using
Simile modelling environment software (Simulistics, Edinburgh). The indices were calculated as:
•
host count index (HCIx) = number of host trees within x metres (horizon) of the subject
sandalwood tree
•
host size-distance index (HSDIx) = ∑i BAi/Di, where BAi is the basal area of host tree i and Di is
the distance from host tree i to the subject sandalwood tree, for all host trees within x metres of
the subject sandalwood tree.
Host treatment plots were segregated into two areas: interior (the inner four rows x eight planting
positions); and periphery (outer two rows on each side and outer two planting positions on each end).
This division allowed for modelling interior sandalwood diameter as if they were growing with a
single host species, while considering peripheral trees as being under the potential influence of host
species in neighbouring treatment plots.
A mixed-model analysis using ASReml (VSN International, Hemel) was completed to determine the
effect of the indices on sandalwood basal diameter. Host treatments, plot interior host indices, plot
periphery host indices and treatment by interior index interaction were fitted as fixed effects in the
model. The row and position of individual trees and the plot column of the host treatment were fitted
as random effects to model environmental effects across the site.
Results
Host count indices
Host count indices (HCIs) were not significant determinants of the size of sandalwood in plot interiors
regardless of the horizon used, indicating that the type of host and not the number of hosts was more
influential within the single species environment of a plot interior. There were substantial differences
between hosts, and the predicted basal diameters of sandalwood grown in Dalbergia and Millettia
plots were slightly larger than those grown with Cathormion, and in turn, these were larger than
sandalwood grown with Pterocarpus or Cedrela, followed by Khaya (Figure 4.12). There were slight
differences to host species ranks when sandalwood basal diameter was estimated using whole plots or
only plot interiors. For all species except Cathormion, there was an increase in predicted diameter
suggesting positive edge effects or benefits of host diversity.
In the plot periphery, different host species appeared to have different horizons of influence (Table
4.11). Millettia appeared to have an influence when in close proximity (6 to 9 m), Pterocarpus when
further away (12 to 15 m) and Dalbergia and Khaya were influential across a wide range of distances
(6 to 18 m). The significant effects from the analysis (Table 4.11) were further fitted together in a
linear model, which was subsequently reduced to provide a final estimate of the most significant
effect of host count indices on sandalwood growth for each species (Table 4.12).
40
18
Predicted basal diameter (cm)
16
14
12
10
8
6
4
2
0
Dal
Internal plot
Cath
Mil
Pt
Ced
Kh
Whole plot
Figure 4.12 Mean basal diameter of 8-year-old sandalwood trees estimated on an internal and
whole-plot basis in Trial 7 (long-term hosts: Dal = Dalbergia, Cath = Cathormium, Mil =
Millettia, Pt = Pterocarpus, Ced = Cedrela, Kh = Khaya)
The effects of host count indices for each host in the periphery of their own plots were mostly
significant, and reflected the ranking of host treatments determined from the plot interiors. For
example, it was estimated that for each Dalbergia tree within 6 m, basal diameter of sandalwood
within Dalbergia plots was increased above the mean by 0.64 cm, whereas for each Khaya tree within
9 m, basal diameter of sandalwood within Khaya plots was reduced below the mean by 0.92 cm
(Table 4.12). These mirrored the host-treatment effects on sandalwood in the plot interiors, where for
Dalbergia this was estimated as 1.23 cm greater than the trial mean and estimated as 7.55 cm lower
than the trial mean for Khaya.
The positive effect of the plot periphery on sandalwood growth within plots of host species suggests a
positive influence of certain multi-host environments. For example, there appeared to be favourable
reciprocal interaction between Cedrela and Millettia on sandalwood basal diameter. Each Cedrela
tree within 12 m of sandalwood in a Millettia plot increased basal diameter by an estimated 1.2 ± 0.4
cm, and in the Cedrela plots each Millettia tree within 12 m of a sandalwood increased basal diameter
by an estimated 1.5 ± 0.4 cm. The predicted basal diameter of a sandalwood in the periphery of a
Millettia plot with 12 Millettia and 2 Cedrela available as hosts within 12 m was 17.5 cm. This was
substantially greater than the predicted treatment mean in the interior of Millettia plots (14.4 cm) or
Cedrela plots (9.5 cm). Cedrela and Dalbergia also appeared to have a strong positive interaction;
however, this was only significant for sandalwood with Cedrela present in the periphery of Dalbergia
plots.
There were also negative interactions between host species. For example sandalwood growth was
reduced when its host included a mix of Pterocarpus and Millettia. Each Millettia tree within 12 m of
a sandalwood in a Pterocarpus plot reduced the estimated basal diameter by 0.5 ± 0.2 cm. A
sandalwood in the periphery of a Pterocarpus plot with 20 Pterocarpus within 15 m and 4 Millettia
within 4 m was predicted to have a basal diameter of 10.4 cm, which is substantially smaller than the
predicted treatment mean for the interior of Pterocarpus (11.8 cm) or Millettia plots (14.4 cm).
41
Table 4.11 P-values for model effects on sandalwood basal diameter using host count indices
(HCI) in Trial 7
Effect
6m
horizon
9m
horizon
12 m
horizon
15 m
horizon
18 m
horizon
m (overall mean)
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
Effects on basal diameter of sandalwood in the plot interior
Treatment
0.008
0.075
0.233
0.015
0.003
HCI Cathormion
0.070
0.410
0.411
0.258
0.641
HCI Cedrela
0.789
0.132
0.869
0.824
0.735
HCI Dalbergia
0.142
0.196
0.250
0.087
0.250
HCI Khaya
0.544
0.913
0.825
0.972
0.821
HCI Millettia
0.808
0.475
0.867
0.957
0.734
HCI Pterocarpus
0.263
0.974
0.785
0.085
0.174
Effects on basal diameter of sandalwood in the plot periphery
HCI Cathormion
0.139
0.513
0.696
0.490
0.270
HCI Cedrela
0.490
0.474
0.252
0.063
0.395
HCI Dalbergia
< 0.001
< 0.001
0.051
0.197
0.015
HCI Khaya
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
HCI Millettia
< 0.001
0.021
0.113
0.613
0.257
0.458
0.079
0.036
0.013
0.120
HCI Pterocarpus
Effects on basal diameter of the host-species treatment by HCI interaction
Treatment x HCI Cathormion
0.857
0.314
0.477
0.68
Treatment x HCI Cedrela
0.701
0.080
0.028
0.078
0.019
Treatment x HCI Dalbergia
0.020
0.128
0.109
0.186
0.389
Treatment x HCI Khaya
0.129
< 0.001
< 0.001
< 0.001
0.003
Treatment x HCI Millettia
0.653
0.003
< 0.001
0.005
0.009
Treatment x HCI Pterocarpus
0.363
0.081
0.302
0.221
0.39
9.3
9
8.9
8.9
8.9
Error Variance
0.684
All effects were fitted simultaneously for each horizon, where data for plot interior was excluded because differences were
not significant. P-values < 0.05 are presented in bold. (Note Millettia pinnata syn. Pongamia pinnata.)
Host size-distance indices
Results from fitting the host size-distance indices (HSDIs) were generally similar to those from fitting
the host count indices, particularly within the plot periphery where Dalbergia, Khaya and Millettia
again had significant effects on sandalwood diameter across most horizons (Table 4.13). Also the
interaction effects of host species within the plot periphery had a similar pattern, with the exception
that Dalbergia interactions were significant up to 12 m for the HSDI compared to only 6 m for the
HCI. However, there was one important difference between the indices, in that the HSDI displayed
significant negative effects on sandalwood basal diameter within the plot interiors of two treatments,
Cathormion and Millettia (Table 4.14). This indicated that an increase in the relative size of the host
(as indicated by the HSDI) within the plot interior neighbourhoods, resulted in a decline in basal
diameter of sandalwood with Cathormion and Millettia hosts.
42
Final reduced models for each species treatment were again produced using only the most significant
horizons (Table 4.13), with the estimated effect on sandalwood diameter of the final model indicated
(Table 4.14).
Table 4.12 Estimates for significant effects of host count index (HCI) on sandalwood basal
diameter in Trial 7
Effect
mu (overall mean)
Level
Estimate
SE
na
13.96
0.51
Effects on basal diameter of sandalwood in the plot interior
Host-species treatment
Dalbergia
1.23
0.57
Pterocarpus
-2.16
0.58
Cedrela
-4.42
1.06
Khaya
-7.55
0.78
Effects on basal diameter of sandalwood in the plot periphery
Treatment-specific
Cedrela
-0.15
0.05
HCI Cedrela 12 m
Millettia
1.17
0.42
Treatment-specific
Cedrela
5.63
1.62
HCI Dalbergia 6 m
Dalbergia
0.64
0.19
Treatment-specific
Dalbergia
-0.48
0.19
HCI Khaya 9 m
Khaya
-0.92
0.08
Cedrela
1.46
0.4
Millettia
0.1
0.04
-0.46
0.18
Treatment-specific
HCI Millettia 12 m
Pterocarpus
Estimates are made using the final reduced model containing the most significant horizons displayed in Table 4.11.
43
Table 4.13 P-values for model effects on sandalwood basal diameter using host size-distance
indices (HSDIs) in Trial 7
Effect
6m
horizon
9m
horizon
12 m
horizon
15 m
horizon
18 m
horizon
Mu (overall mean)
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
Effects on basal diameter of sandalwood in the plot interior
Treatment
HSDI Cathormion
< 0.001
0.01
0.01
< 0.001
0.002
0.02
0.03
0.07
0.10
0.23
HSDI Cedrela
0.32
0.41
0.18
0.15
0.24
HSDI Dalbergia
0.18
0.26
0.14
0.06
0.09
HSDI Khaya
0.36
0.46
0.80
0.84
0.94
HSDI Millettia
0.04
0.48
0.42
0.22
0.24
HSDI Pterocarpus
0.33
0.65
0.79
0.37
0.28
Effects on basal diameter of sandalwood in the plot periphery
HSDI Cathormion
0.38
0.99
0.58
0.22
0.20
HSDI Cedrela
0.09
0.13
0.34
0.38
0.64
HSDI Dalbergia
< 0.001
< 0.001
0.001
0.002
0.001
HSDI Khaya
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
HSDI Millettia
0.003
0.05
0.03
0.06
0.06
HSDI Pterocarpus
0.06
0.02
0.11
0.23
0.29
Effects on basal diameter of the host-species treatment by HSDI interaction
Treatment x HSDI Cathormion
0.65
0.40
0.24
0.27
Treatment x HSDI Cedrela
0.52
0.98
0.15
0.08
0.04
Treatment x HSDI Dalbergia
0.04
0.04
0.03
0.08
0.16
Treatment x HSDI Khaya
0.08
0.002
0.002
< 0.001
0.001
Treatment x HSDI Millettia
0.47
0.003
0.003
0.004
0.01
Treatment x HSDI Pterocarpus
0.13
0.09
0.15
0.07
0.09
Error variance
9.3
9.1
8.9
8.8
8.8
0.28
All effects were fitted simultaneously for each horizon. P-values < 0.05 are presented in bold.
A positive interaction was again observed between Cedrela–Millettia and Cedrela–Dalbergia (Table
4.14). An increase in the relative size and density of Millettia trees within 12 m of sandalwood in
Cedrela plot increased basal sandalwood diameter by 1.77 ± 0.43 cm per HSDI unit, and by 2.16 ±
0.64 cm for each unit increase in HSDI of Dalbergia hosts within 9 m of a Cedrela plot. Unlike for
the HCI the benefit was not reciprocal and was only statistically significant when the subject
sandalwood was located in a Cedrela plot. A significant negative interaction was again observed
between Millettia and Pterocarpus.
44
Table 4.14 Estimates for significant effects of host size-distance index (HSDI) on sandalwood
basal diameter in Trial 7
Effect
Mu (overall mean)
Level
Estimate
SE
na
13.47
0.48
Effects on sandalwood basal diameter in plot interior positions
Cathormion
3.61
1.18
Cedrela
-3.64
1.05
Dalbergia
4.45
1.52
Khaya
-6.98
0.78
Millettia
3.48
1.30
Pterocarpus
-1.64
0.56
HSDI Cathormium 6m
-1.03
0.42
HSDI Millettia 6m
-0.49
0.24
Host treatment effects
Effects on sandalwood basal diameter in plot periphery positions
Treatment-specific
Cedrela
-0.19
0.06
Cedrela
1.77
0.43
Dalbergia
0.48
0.11
Khaya
1.11
0.45
Treatment-specific
Dalbergia
-0.29
0.10
HSDI Khaya 9 m
Khaya
-0.44
0.04
Cathormion
0.37
0.38
Treatment-specific
Cedrela
2.16
0.64
HSDI Millettia 12 m
Millettia
0.16
0.06
Pterocarpus
-0.69
0.29
HSDI Cedrela 12 m
Treatment-specific
HSDI Dalbergia 9 m
Estimates are made using the final reduced model containing the most significant horizons displayed in Table 4.13.
Discussion
Host species within plot interiors were more influential in determining sandalwood growth than the
effect of the number and relative size of hosts as indicated by the two competition indices used here.
The host-species effects displayed here were in general agreement with the analysis using the original
trial design elements completed by Barbour (2008) that indicated sandalwood was larger with
Dalbergia and Millettia followed by Cathormion. However, the analysis used here revealed more
about the nature of interactions between hosts in their support of sandalwood size within single and
multi-species environments that were not previously detected or confirmed. For example, the
resilience of Dalbergia as a host was highlighted by Barbour (2008), as it was able to promote
superior sandalwood growth even when lower host survival reduced the ratio of sandalwood to hosts
to 1:0.6, compared to a 1:1.2 ratio for Millettia. The analysis here further complements this finding by
indicating significant positive effects of the number and relative size of Dalbergia on sandalwood
growth in all plot periphery horizons (excluding 15 m HCI). Importantly, this confirms that
sandalwood size was improved by the presence of Dalbergia hosts, and not as a result of increased
availability of space and reduced host competition. As such, it could be predicted that sandalwood
growth would have been further improved if Dalbergia survival had been greater.
In contrast to Dalbergia, the HSDI, the sum of host relative basal diameters, of Millettia and
Cathormion had a significant negative effect on sandalwood size within a 6 m radius of sandalwood.
45
This indicated that these two species were more aggressive competitors than Dalbergia when in close
proximity to sandalwood. Interestingly, the number of hosts (HCI) did not display the same negative
effect at this proximity, which suggests suitable plantation management to increase sandalwood
growth with these two host species may be to retain host stocking but modify host structure, for
example by canopy pruning.
Another benefit of the analysis was the ability to determine sandalwood response in a multiple-host
environment that existed beyond the structured blocking used in the original experimental design.
Visual observation of sandalwood within the boundaries of Millettia and Dalbergia plots suggested
there could be a positive ‘combining effect’ of the two superior host species; however, somewhat
surprisingly, the analysis displayed a lack of significant growth response above that in single-host
environments. This is an example of the imbalance that can occur between observation and
quantitative results, and highlights the utility of the analysis technique in maximising information
gained from sandalwood trials. Other species combinations, notably Cedrela–Millettia and Cedrela–
Dalbergia, did display positive effects on sandalwood growth despite Cedrela being a very poor host
in a single-species environment. Using a low ratio of Cedrela within a host mix could be further
investigated.
The original trial design had trees positioned on a repeated rectangular grid with constant spacing
between hosts and sandalwood for all host species, where differentiation in spatial arrangement only
occurred through tree mortality. Competition indices improve the outcomes of analysis in trials where
mortality has modified the original design (Bristow et al. 2006), but Vanclay (2006a) warns common
forestry trial designs, such as that used here, rarely provide a good basis for maximising the
information gained from competition indices. In addition, basal area was used as the physical
parameter for the calculation of HSDI, but it may not be the optimal parameter of competition
evaluation in sandalwood plantations. Canopy parameters may provide a better indicator of
competition in sandalwood trials because they display a more ‘plastic’ response to competition (von
Oheimb et al. 2011). Further investigation using alternative trial designs (Vanclay 2006a), index
calculation, and methods for horizon calculation (von Oheimb et al. 2011; Rivas et al. 2005) should
improve the methodology. The goal of such work would be to provide a response surface of
sandalwood growth in relation to various host, stocking and spatial regimes to predict optimal
plantation arrangements, as demonstrated by Vanclay (2006b) for mixed Acacia and Eucalyptus
plantations. This approach would narrow plantation design and host species options so that more
efficient field testing could be completed, as opposed to a ‘trial and error’ approach.
The aim of this study was to provide a preliminary investigation of the utility of spatial competition
indices in providing insight into the effect of interactions between sandalwood and hosts on tree
growth at the individual tree level. The two indices used here, host count index (HCI) and host sizedistance index (HSDI) produced similar results and were able to show some differentiation in the
response of sandalwood to competition from different host species. Whilst not definitive, these results
offer reasons to suggest that considerable scope exists to improve the analysis technique for use in
sandalwood plantations.
4.3.2 Spatially-dependent host effects on sandalwood size within a trial without
an experimental design, Trial 3
Method
Trial description
Trial 3 was planted in 1993. The planting consists of separate host-species blocks with no
experimental design applied. The Peltophorum block had four rows with hosts at 9 m spacing and
sandalwood planted at 3 m either side of each host within the row. The sandalwood-to-host ratio at
establishment was 2:1 with stocking of 1235 SPH for sandalwood and 617 SPH for hosts. The area of
46
this block was 0.13 ha. The Cassia block contained 10 rows. Odd-numbered rows had alternate
positions of host and sandalwood at 3 m spacing, and even-numbered rows were planted only with
sandalwood spaced at 3 m. The planting ratio of sandalwood to hosts was 3:1 with sandalwood
stocked at 929 SPH and hosts at 309 SPH. The area of this block was 0.41 ha.
Measurement
In 2001 (8 years old) sandalwood DBH, basal diameter, bole height and tree height were measured.
Measurements in 2008 (15 years old) recorded sandalwood DBH, basal diameter, bole height, crown
break diameter (CBD) and tree height for both sandal and host. Calculated parameters of basal area,
bole volume and estimated stem volume (ESV) were done on an individual tree and per hectare basis.
Data preparation
Data from 2001, when only sandalwood parameters were measured, was used to determine relative
growth. Tree height, basal area and total stem volume were used as variables in the analysis. The
position of each tree in two-dimensional space was also recorded as the distance (meters) between
trees within and across rows.
The usual application of competition indices is to quantify the competition environment of subject
trees as a potential determinant of growth in the forthcoming period. Applying this would involve
using competition indices formulated with the 2001 data as potential determinants of growth from
2001 to 2008. However, because host size data was not available from the 2001 assessment, an
assumption was therefore made that tree height of each host tree in 2001 was 0.7 times tree height at
2008, and that basal area of each host tree in 2001 was 0.5 times basal area in 2008. These assumed
host data were only used for the calculation of interaction indices, not for analysis of host tree growth.
Relative growth in the period of 2001–2008 was estimated following Causton and Venus (1981):
Relative growth = ln(basal area in 2008) – ln(basal area in 2001)
Equation 1
Development of tree-tree interaction indices
The indices of tree-tree interaction between sandalwood and hosts cannot strictly be termed
competition indices because the parasitic nature of the relationship means that a host is a potential
resource as well as a competitor in the plantation environment. As such the indices between host trees
and sandalwood will be referred to as either ‘hosting indices’ or ‘parasitism indices’, as a measure of
the effect of hosts on sandalwood, and sandalwood on hosts respectively. The term competition
indices can refer to host-host and sandalwood-sandalwood interactions.
The indices used in the analysis can be characterised by three parameters which define the
relationship described by an index, these are:
•
distance, where indices can either be distant-independent or distant-dependent where the index
includes the distance between subject tree and interacting trees
•
competitor size, where indices are either size-independent or size-dependent if the index includes
a relative measure of the size of competitor (host) trees
•
subject size, where indices are either subject-independent or subject-dependent if the index
includes the size of the subject tree.
A critical aspect of competition analysis is correctly identifying which neighbouring trees are
interacting with the subject tree. Typically, neighbouring trees are considered to be interacting with a
subject tree if they are located within a specified distance. For the present analyses, the
neighbourhood distance has been defined as:
47
Ds = Ks*(subject tree height + neighbouring tree height)
Equation 2
where Ks is a variable coefficient between 0 and 1, used to modify the size of the neighbourhood
horizon. For example a Ks of 0.5 indicates a neighbourhood of half the sum height of the target tree
and neighbour.
The well-established Hegyi competition index was applied to the prediction of sandalwood relative
growth by tree-tree interactions in 2001:
IHegyi = ∑i BANi/BAs x Di
Equation 3
where BANi is the basal area of neighbouring tree i, BAS is the basal area of the subject tree and Di is
the distance from the subject tree to the neighbouring tree for all trees I, where Di<Ds. When applied
to host-host or sandalwood-sandalwood interactions, Hegyi’s index is distant-dependent, sizedependent and subject-dependent. Simpler subject-independent indices for competition, hosting and
parasitism were formulated for predicting the size of subject trees by their neighbourhood
interactions. These indices were:
ISIndep = ∑i BANi/Di
Equation 4
HIhost count = n(hosts)
Equation 5
HIhost ratio = ∑i 1/ns
Equation 6
where ISIndep is a subject-independent, size-dependent and distance-dependent index derived from the
Hegyi index. HIhostcount is a count of host trees within qualifying distance Ds to subject sandalwood
trees. HIhostratio is an index of the effective host-to-sandalwood ratio experienced by subject
sandalwood trees where ns is a count of the number of sandalwood trees within qualifying distance Ds
of host tree I, see Figure 4.13 in which host A has the subject sandalwood and two other sandalwood
trees (open stars) within qualifying distance Ds.
The program Simile (Simulistics, Edinburgh) was used for calculating interaction indices. Each index
was estimated with a range of Ks values to infer the effective distances over which tree-tree
interactions could be detected. ISIndep was analysed with respect to competition, hosting and parasitism,
whereas HIhostcount and HIhost ratio were only considered as hosting indices.
Statistical analysis
Interaction indices were treated as covariates in linear models to explain growth and stem volume
using S-Plus V.6.0. Dependent variables were transformed when necessary to satisfy normality of
residuals, and outliers were occasionally removed to ensure residuals were homoscedastic. Row
number and within-row position were included as covariates or factors when their effect was
significant.
48
Figure 4.13 Spatial representation of a subject sandalwood tree (solid star) surrounded by four
neighbouring host trees (A–D: solid diamonds) within qualifying distance
Results
Sandalwood relative growth
Only 11 sandalwood trees survived to 2008 in the Peltophorum block and the statistical power for
analyses of their growth or volume was accordingly weak. Nevertheless, tree-tree interactions
appeared to be more marked in this smaller block than in the Cassia block.
Hegyi competition indices (CIhegyi) with Ks between 0.6 and 0.8 explained significant variation in
sandalwood relative growth (Table 4.15). The growth response to competition indices was negative,
suggesting significant competition for resources between sandalwood up to an average distance of
10.8 m (equivalent to Ks = 0.8 in 2001). Hegyi hosting indices (HIhegyi) also displayed negative
relationships with sandalwood relative growth where indices with Ks were between 0.3 and 0.8 (Table
4.15). This suggests that sandalwood growth was reduced as the combined size of the Peltophorum
host trees in their neighbourhoods increased. Multiple regression models including CIhegyi and HI hegyi
indices explained more variation (up to R2 of 0.75) in relative growth than univariate regressions
(Table 4.15). The optimum Ks for CIHegyi in multiple regressions was 0.8 (average interaction limit
10.6 m) whereas the Ks for HIHegyi was optimised at either 0.3 (average 4.7 m) or 0.8 (average 12.5 m).
The size-independent index HIhostratio with Ks = 0.6 (average interaction limit 12.1 m) explained a
similar proportion of variance in sandalwood relative growth in the Peltophorum block to the best
multiple regression of Hegyi indices (Table 4.15). The host ratio index was superior to the Hegyi
indices in this comparison as the excluded outlier in the Hegyi regression was well-predicted by the
host ratio index. Unlike for the Hegyi indices, sandalwood growth from 2001 to 2008 was positively
related to HIhostratio. This suggests that subject sandalwood trees with greater numbers of available
Peltophorum hosts (i.e. hosts without or with few nearby sandalwood trees) were at a growth
advantage.
49
Table 4.15 Summary of selected significant linear models explaining the relative growth of
sandalwood with Peltophorum and Cassia hosts between 2001 and 2008 in Trial 3
Host
Independent
variable(s)
Ks
Outliers
Sign of
coefficient
Effect
P-value
Model
P-value
Model
R2
Peltophorum
CIHegyi
0.5
0
negative
0.06
0.058
0.35
0.6
0
negative
0.01
0.013
0.50
0.7
0
negative
0.01
0.013
0.50
0.8
0
negative
0.02
0.024
0.45
HIHegyi
0.3
1
negative
0.02
0.016
0.53
0.4
1
negative
0.04
0.035
0.45
0.5
1
negative
0.02
0.020
0.50
0.6
1
negative
0.03
0.029
0.46
0.7
1
negative
0.01
0.008
0.61
0.8
1
negative
0.01
0.006
0.62
CIHegyi
0.8
1
negative
0.04
0.008
0.75
HIHegyi
0.3
CIHegyi
0.8
0.008
0.75
HIHegyi
0.8
HIhost ratio
0.6
0.009
0.69
0.019
0.08
0.006
0.10
0.010
0.13
0.007
0.10
0.01
1
negative
0.02
0
positive
row (covariate)
Cassia
HIhost ratio
0.7
1
positive
0.8
1
positive
0.00
0.04
0.9
1
positive
row (covariate)
HIhost ratio
0.01
0.09
row (covariate)
HIhost ratio
0.00
0.15
row (covariate)
HIhost ratio
0.11
0.00
0.02
1
1
positive
row (covariate)
0.00
0.04
Where CI and HI indicate indices representing effects of sandalwood-sandalwood and host-sandalwood interactions
respectively.
Interaction indices provided less prediction of sandalwood growth in the Cassia block than in the
Peltophorum block. None of the Hegyi indices were statistically significant either singly or in
multiple regression combinations. Host ratio indices were significant with Ks values between 0.7 and
1.0 although they explained only 8 to 13 per cent of variation in sandalwood growth, which was
considerably less than in the Peltophorum block.
Sandalwood stem volume
It would be inappropriate to predict stem volume with subject-dependent indices, as the dependent
variable would be represented in the denominator of the predictive variables. Therefore, only subjectindependent indices were evaluated as explanatory variables for stem volume in 2008.
The subject-independent hosting index derived from the Hegyi index (HISIndep) was a significant
predictor of sandalwood volume in the Peltophorum block at two values of Ks: 0.4 and 0.5 (Table
4.16). This neighbourhood equates to an average tree-tree distance of 10.1 m. The relationship
between HISIndep and sandalwood volume was negative which supports the findings of the analysis of
50
sandalwood growth using the Hegyi hosting index that large Peltophorum host trees can negatively
impact sandalwood growth within a neighbourhood of 10 m.
The subject-independent competition index was not significant with Ks between 0.2 and 1.0. The host
count index (HIhostcount) was the simplest index used, derived from a count of hosts within the
neighbourhood; it proved to be the most powerful predictor of sandalwood stem volume in the
Peltophorum block. This index accounted for approximately 60 per cent of the variation in the data
when using Ks of 0.8 to 1.0 (Table 4.16). This relationship was positive, implying that increasing
numbers of Peltophorum hosts within the neighbourhood of sandalwood were beneficial in increasing
sandalwood stem volume. These results support the conclusion drawn from the growth analysis with
Hegyi indices; that the number rather than the size of nearby Peltophorum hosts was beneficial to
sandalwood.
The larger dataset of sandalwood stem volume in the Cassia block offered greater power to detect
significant effects of interaction indices. All HIhostcount and HIhostratio indices with Ks between 0.2 and
1.0 were statistically significant, although only the best models for each index type are presented
(Table 4.16). The index with best explanatory power was HIhostratio with Ks of 0.8 (R2 =0.36,
P<0.0001). Sandalwood volume was positively related to the presence of ‘available’ Cassia host trees
(i.e. those without other nearby sandalwood trees) within an average of 13 m, which is equivalent to
Ks of 0.8 for this index.
Size-dependent indices were only significant for sandalwood stem volume in the Cassia block when a
hosting index (HISIndep) and competition index (CISIndep) were combined in multiple regression. The
optimum Ks in such multiple regression models was 1.0 for HISIndep and 0.4 for CISIndep (Table 4.16),
which equate to an average Cassia-sandalwood interaction limit of 16.3 m and an average
sandalwood-sandalwood interaction limit of 6.5 m. The hosting index was positively related to
sandalwood volume and was more significant in this model than the competition index, which was
negatively related to sandalwood volume. These results support the conclusions drawn from
evaluation of the host ratio index, that sandalwood stem volume is increased when the number of
available hosts increases within the neighbourhood.
Host stem volume
Host tree volume could be reduced by parasitism from nearby sandalwood and by competition from
other nearby hosts. Both of these effects were statistically significant on Peltophorum as represented
by size-dependent parasitism indices and competition indices (Table 4.17). As univariate predictors of
Peltophorum stem volume, parasitism (PISIndep) and competition (CISIndep) indices were most significant
at Ks = 1.0 (Table 4.17). However, the best model of Peltophorum volume included both PISIndep and
CISIndep in multiple regression, explaining 45 per cent of variation in the data (Table 4.17). The average
neighbourhood limits for Peltophorum-sandalwood and Peltophorum-Peltophorum interactions
accounted in this model were 14.1 m and 25.8 m respectively.
51
Table 4.16 Summary of selected significant linear models explaining sandalwood stem volume
with Peltophorum and Cassia hosts in Trial 3
Host
Independent
variable(s)
Ks
Outliers
Sign of
coefficient
Effect
P-value
Model
P-value
Model
R2
Peltophorum
HISIndep
0.4
0
negative
0.00
0.001
0.36
0.5
0
negative
0.02
0.020
0.46
0.7
0
positive
0.01
0.013
0.51
0.8
0
positive
0.00
0.004
0.61
0.9
0
positive
0.00
0.004
0.63
1.0
0
positive
0.01
0.005
0.60
HIhost ratio
1.0
0
positive
0.04
0.040
0.39
HISIndep
1.0
1
positive
0.00
0.005
0.13
CISIndep
0.4
<0.001
0.22
<0.001
0.36
HIhost count
Cassia
0.04
row (covariate)
HIhost ratio
0.00
0.9
1
positive
0.00
row (covariate)
0.00
position
(covariate)
0.17
HIhost ratio
0.8
1
positive
0.00
row (factor)
0.01
position
(covariate)
0.01
Where CI and HI indicate indices representing effects of sandalwood-sandalwood and host-sandalwood interactions
respectively.
Variation in Cassia stem volume was best explained by positive effects of PISIndep and CISIndep in
multiple regression (Table 4.17). A possible explanation for positive correlations between the size of
subject trees their neighbours is that these indices were registering spatial autocorrelation due to
shared environment, rather than tree-tree competitive interactions. Alternatively, the positive sign of
these relationships for Cassia compared with the negative sign for Peltophorum may indicate that
Cassia stem volume is more resilient to the effects of parasitism and/or intra-specific competition.
However, lack of replication in the experimental design means that the parasitism, competition and
species effects could not be separated from the potential environmental effects within the trial.
52
Table 4.17 Summary of selected significant linear models explaining the stem volume of
Peltophorum and Cassia in Trial 3
Species
Independent
variable(s)
Ks
Outliers
Sign of
coefficient
Effect
P-value
Model
P-value
Model
R2
Peltophorum
PISIndep
0.4
0
negative
0.05
0.049
0.07
0.5
0
negative
0.04
0.037
0.08
0.6
0
negative
0.03
0.030
0.09
0.7
0
negative
0.02
0.016
0.20
0.8
0
negative
0.01
0.012
0.12
0.9
0
negative
0.01
0.008
0.13
1.0
0
negative
0.00
0.002
0.28
0.9
0
negative
0.05
0.047
0.07
1.0
0
negative
0.03
0.025
0.09
PISIndep
0.7
1
negative
0.04
<0.001
0.45
CISIndep
1.0
CISIndep
0.02
row (covariate)
Cassia
0.00
0.4
1
positive
0.04
0.036
0.04
0.5
1
positive
0.01
0.014
0.05
0.6
1
positive
0.01
0.009
0.06
0.7
1
positive
0.01
0.005
0.07
0.8
1
positive
0.01
0.005
0.07
0.9
1
positive
0.01
0.005
0.07
1.0
1
positive
0.01
0.007
0.06
0.3
1
positive
0.00
0.000
0.13
0.4
1
positive
0.00
0.000
0.11
0.5
1
positive
0.01
0.006
0.06
0.6
1
positive
0.00
0.004
0.07
0.7
1
positive
0.01
0.013
0.05
0.8
1
positive
0.04
0.042
0.04
PISIndep
0.8
1
positive
0.07
<0.001
0.38
CISIndep
0.4
PISIndep
CISIndep
0.00
row (factor)
0.00
CI and PI indicate indices representing effects of host-host effect and sandalwood–host effect (parasitic effect) respectively.
Discussion
The preliminary analysis using interaction indices has given an indication to their potential utility in
examining and comparing the nature of the intra-specific, parasitic and hosting relationships within
the sandalwood plantation environment. Notwithstanding the problems associated with lack of
replication at the species level and limited data available with the Peltophorum block, some
comparison can be made between Peltophorum and Cassia as hosts for sandalwood.
In both cases, sandalwood growth and volume were improved by proximity to host trees that had a
lower number of nearby sandalwood. This would seem to indicate that both species are functional
hosts and provide some facilitative effect that is beneficial to sandalwood growth. However,
sandalwood relative growth and volume in the Peltophorum block were negatively associated with
size-dependent hosting indices. This relationship indicates that where Peltophorum size increases the
53
facilitative benefits of the host, it is increasingly outweighed by an increase in the competition for
primary resources within the environment, which results in lower sandalwood growth. Despite Cassia
being considerably larger than Peltophorum, it did not appear to have the same size-dependent
detrimental effect on sandalwood relative growth or stem volume.
The sandalwood to sandalwood competition in the Peltophorum block appeared to have a stronger
negative effect on growth between 2001 and 2008 than within the Cassia block. This occurred despite
the number of sandalwood on a per hectare basis being over 2.5 greater in the Cassia block. Whilst
the data does not provide direct insight into the cause of such an anomaly, it does provide a stimulus
for further investigation as to why it may occur. For example it could be hypothesised that the Cassia
has a higher availability of roots within a compatible soil horizon which could increase the number of
sandalwood–host connections, potentially limiting sandalwood-sandalwood parasitism. Other
explanations relating to root physiology, differentiation in nutrient draw from hosts, and competition
for primary resources could be investigated to further the understanding of factors that contribute to a
successful host.
In the analysis presented here, neighbourhood areas were defined in terms of tree heights rather than
discrete distances. This should have the advantage of accounting for the asymmetrical nature of
above-ground competition, in that larger trees will have greater spheres of influence within the
environment. The spatial extent of tree-tree interaction limits revealed by the analysis was surprisingly
large, with few significant indices extending to less than an average of 10 m. For example the average
sandalwood-host interaction limited for the most significant relationship between the Peltophorum
count index and sandalwood volume was 18 m at a distance coefficient of 0.9 (Table 4.16). The
specific combination of the tallest Peltophorum and sandalwood trees within the analysis (18.7 m and
10.5 m respectively) equated to an interactive neighbourhood of over 26 m. Such observations have
important ramifications for the experimental design of sandalwood host trials and plantations. In
particular, large plots to separate out treatment effects are required if tree-tree interaction indices are
not used as part of the analysis.
4.4
Sandalwood heartwood and oil development
The commercial value of Santalum album is largely dependent on its fragrant heartwood. This
heartwood is used in joss sticks and carvings, and the sandalwood oil extracted from it is sought after
for a number of aromatic, flavour and health-based products. The majority of the oil is composed of
sesquiterpene alcohols, dominated by α (alpha) and β (beta)-santalol (Verghese et al. 1990; Jones et
al. 2006) which are the primary indicators of oil quality. Whilst the control of oil production at the
molecular level is starting to be uncovered (Jones et al. 2006; Jones et al. 2008; Jones et al. 2011), the
factors involved in initiation and regulation of heartwood and oil development are not well understood
but like most tree characteristics are likely to be the result of genetic and environmental interactions.
Although traditional estimates of the heritability of heartwood and oil have not been established, the
FPC sandalwood germplasm has relatively low levels of genetic diversity compared to natural stands
in India (Suma and Balasundaran 2003), yet it displays substantial phenotypic variation in heartwood
(Jones et al. 2009). Whilst there may well be genotypes with a predisposition for heartwood and oil
production, the environmental component is likely to be highly influential in the stimulation of
heartwood and oil deposition. It is possible that differences in heartwood and oil directly relate to
variation in uptake of assimilates between host species (Radomiljac et al. 1998c), as well as the
potential transfer of species-specific compounds between host and root hemi-parasites (Loveys et al.
2001). In addition, differences in host root and canopy structure and competition may indirectly affect
heartwood and oil content by modifying the immediate environment. This could result in differential
exposure to stress factors such as amount of sunlight and pathogens, which have been implicated, but
not confirmed, as contributors to heartwood initiation and/or development (Rai 1990; Barbour et al.
2010). To date host species selection has been conducted primarily on the basis of optimising growth
performance, and there is a need to complement this work with data on heartwood formation.
54
Heartwood occurrence in plantation trees has largely been monitored using non-destructive core
sampling at one or two heights within the stem (Brand et al. 2006; Brand et al. 2007; Jones et al.
2007). Some heartwood has formed in some 10-year-old trees in plantations (Rai 1990; Jones et al.
2007), with most trees producing heartwood by 14 years (Brand et al. 2006; McComb 2009).
Destructive harvesting from natural forests indicates heartwood formation can be delayed to 14-46
years and even in mature trees the amount and proportion of heartwood is highly variable (Rai 1990;
Haffner 1993; Venkatesan et al. 1995), Whilst non-destructive core sampling allows for the
assessment of the presence of heartwood and oil, it has not provided a clear assessment of the amount
(volume) and pattern of heartwood development and there is a need to better quantify the heartwood
and oil development within plantation-grown sandalwood trees. This will aid plantation managers in
estimating plantation yield and in decision making for host selection, planting designs, thinning
programs and rotation lengths.
Core sampling within the FPC trials has in some cases proved not entirely ‘non-destructive’. The
invasive nature of the method provides an entry point for pathogens that are damaging to wood
quality, and possibly long-term tree health (Barbour et al. 2010). The ability to confirm the presence
and estimate the volume of heartwood in standing trees is required to improve plantation management
and estimate harvest yield but to reduce the risk of tree damage, alternative techniques of heartwood
evaluation are necessary. Non-destructive methods to evaluate wood properties have been around
since the 1940s. Advances in technology have seen a suite of methods developed and some of these
may be adapted for use in analysis of standing trees (Bucur 2003). Two of these methods, electrical
impedance tomography and acoustic time-of-flight, utilise a portable device that, once calibrated to a
species and environment, would provide data capture at a rate similar to core sampling. The methods
are based on different signals to determine wood characteristics: electrical impedance uses electrical
current that responds to variations in chemical properties of wood, specifically moisture content; and
acoustics utilise sound waves that respond to the mechanical properties of wood. The ability of these
methods to determine heartwood characteristics in sandalwood is untested, but if successful they
would provide useful tools to improve plantation evaluation and management.
This section presents results from destructive harvesting and non-destructive sampling of sandalwood
between 8 and 15 years of age. Destructive harvests aimed to describe wood volume and pattern of
heartwood production within trees aged 8 and 15 years, whilst core sampling was used to examine the
occurrence of heartwood and oil within 11-year-old sandalwood grown with different host species. In
addition to measurements of the usual heartwood, fungal rots in these trees were often associated with
an encapsulation that has been shown to contain heartwood (Barbour et al. 2010), but did not appear
to be part of the normal heartwood formation process. A preliminary investigation of two nondestructive wood-evaluation methods, electrical impedance and acoustic time-of-flight, was also
undertaken.
4.4.1 The destructive harvest of 8-year-old sandalwood, Trial 8
Method
Trial establishment
Trial 8 was originally established in 2000 to assess the growth response of S. album in a multi-species
plantation environment. Primary, short-lived host species included Sesbania formosa, Acacia
auriculaformis and A. crassicarpa, with secondary, long-term hosts being Cathormion umbellatum,
Castenospernum australe, Dalbergia latifolia and Dalbergia retusa. A primary host-to-sandalwood
ratio of 2:1 was planted with sandalwood in every second row with a primary host either side. Rows
were 3.6 m apart with 3 m spacing between sandalwood and secondary host trees within rows. During
2002 an inappropriate application of herbicide overspray resulted in widespread deaths of both host
and sandalwood. The remaining trees were retained and received little management except for bole
pruning and regular irrigation during the dry season.
55
Plate 4.3 Typical 8-year-old tree from this trial
Destructive harvest
At 8 years of age, 30 trees with clear boles were selected for harvesting and were pulled out by their
roots (see Plates 4.3 and 4.4). The trees were laid on the ground and measured for height, basal
diameter, breast height diameter, crown break diameter and bole length. Trees were then sectioned
into roots, bole and crown and each section weighed. Discs were then cut from the bole section at the
base, lower third, upper third and top, and green weight recorded. After air-drying for 8 weeks a dry
weight was obtained. Image analysis of disc photographs with Image J (NIH, USA) was used to
determine under-bark disc area, heartwood area, and area of wood rot for manually outlined areas on
each disc. Whilst wood rot data is presented here, a more comprehensive analysis of rot, including
fungal isolation and identification, was undertaken within a separate RIRDC project (Barbour et al.
2010).
Plate 4.4 A sample of the 8-year-old wood assessed after the destructive harvest
Simple and multiple linear regressions were used to determine relationships between measured
variables (XLStat, 2006). For multiple regression, model selection was determined by comparing the
56
coefficient of determination (R2) and Akaike information criteria (AIC). The normal distribution of
residuals was checked using the Kolmogorov-Smirnov test.
Results
A typical tree from this 8-year-old trial was 4.9 m tall with a bole 1.8 m long with a basal diameter of
14.7 cm, which gradually tapered to 10.2 cm at breast height diameter and to 9.9 cm just prior to
crown break (Table 4.18). These 8-year-old trees on average weighed 60.9 kg which was made up of
15.1 kg of stump, 17.5 kg of bole with the remainder being the branches (Table 4.18). The
commercially valuable portion of the tree, roots and bole, typically made up 54 per cent of total mean
tree weight.
The mean water content of the 120 discs as indicated by weight loss after air drying was 33.1 ± 6.7
per cent, and was lowest in the basal discs with 29.5 ± 10.1 per cent, and highest in the upper third
disc with 34.8 ± 4.7 per cent. For individual trees, mean weight loss ranged from 15.4 ± 3.0 to 38.7 ±
5.1 per cent.
Table 4.18 Growth parameters for 30 trees destructively harvested after 8 years from Trial 8
(mean ± s.d., minimum and maximum)
Parameter
Mean
Minimum
Maximum
Tree height (m)
4.9 ± 0.6
3.64
6.50
Bole length (m)
1.8 ± 0.16
1.01
2.54
Basal diameter (cm)
14.7 ± 1.1
11.90
17.00
DBH (cm)
10.2 ± 1.5
8.30
15.10
Crown break diameter (cm)
9.9 ± 1.7
7.00
15.10
Weight of tree bole (kg)
17.5 ± 3.1
11.26
24.70
Weight of tree crown (kg)
28.2 ± 13.4
8.00
70.00
Above ground tree weight (kg)
45.7 ± 14.7
18.30
85.33
Root weight (kg)
15.1 ± 4.0
5.58
22.80
Total tree weight (kg)
60.9 ± 16.0
33.54
106.11
The production of heartwood within the tree bole was highly variable as highlighted by standard
deviations that were larger than sample means of the aromatic wood within the discs (Table 4.19).
Among the 120 discs, 59 did not have any heartwood and three trees had no heartwood. Heartwood
was clearly most prevalent in the basal disc of the bole, however within eight trees there was no
heartwood in the basal disc.
The highest mean aromatic wood area from the four discs within an individual tree was 23.9 cm2 ±
16.5, some 18.6 ± 20.1 per cent of the bole wood. The single highest area and percentage of
heartwood within a single disc was 67.0 cm2, 45.2 per cent of the disc area. The area of heartwood in
basal discs did not display a linear relationship with disc area (P = 0.313, R2 = 0.048), that is discs
with larger cross-sectional area did not have a larger area of heartwood.
57
Table 4.19 Total disc area and the area and percentage of heartwood and rot with discs located
along the bole of 30 sample trees in Trial 8 (mean ± s.d.)
Disc position
Top bole
Disc area
(cm2)
Heartwood area
(cm2)
Rot/damage
area (cm2)
Heartwood
(%)
Rot/damage
(%)
53.9 ± 20.7
3.1 ± 6.2
1.9 ± 4.0
4.2 ± 7.8
3.1 ± 6.7
Upper 3rd bole
57.5 ± 15.0
1.6 ± 3.3
1.8 ± 3.6
3.0 ± 6.7
3.5 ± 7.2
Lower 3rd bole
77.6 ± 19.5
2.71 ± 4.5
3.1 ± 5.8
3.2 ± 4.5
3.6 ± 6.5
1245.0 ± 22.8
14.5 ± 17.3
4.0 ± 8.03
11.2 ± 3.0
3.0 ± 5.8
Base
There was a taper of the bole from base to crown break (Figure 4.14a), where the disc area declined
from 100 per cent at the base to 62 per cent in the lower third, 46 per cent in the upper third and 43
per cent at the top of the bole. The taper of heartwood within the bole was more rapid. At the base, the
heartwood accounted for 11.2 per cent of the disc; this heartwood declined rapidly to 3.2 per cent in
the lower third (approximately 60 cm up the bole) and did not change from this level up the bole of
the tree.
No significant linear relationship was found between the percentage of heartwood in basal discs and
that of lower third discs (P = 0.118, R2 = 0.124). Heartwood shape was often irregular due to its
association with heartwood rot (Figure 4.14b) and variability in longitudinal development of
heartwood along the bole in 8-year-old trees.
The occurrence of rot within the bole was highly variable between trees (Table 4.18). Among the 120
discs, 73 had no rot and seven trees were free of rot. The proportion of heartwood rot within a disc
was as high as 20.4 ± 12.1 per cent of the disc area. Within the 47 discs with rot damage, 14 had no
aromatic heartwood and only one of these was from the base of the bole.
Analysing the discs with both rot and heartwood indicated a weak but significant (P = 0.008, R2 =
0.209) linear relationship between rot and heartwood (Figure 4.15a). As the presence of rot increased,
the amount of heartwood increased.
The discs were clearly separated into two groups; those with the heartwood rot originating from the
centre of the tree and those with rot originating in another area of the disc (Figure 4.15b). These
separate relationships were both highly significant (P<0.001) and accounted for a high proportion of
the variation in the data. Discs with rot in the centre of the bole included a large number of basal discs
(nine of 20 samples) compared to discs with non-centre damage which included only one basal disc in
13 samples.
58
a
total area
heartwood
area
Rot/dam.
area
b
Figure 4.14 Stylistic representation of mean heartwood and rot areas within discs along the
bole (a), and an example of non-uniform heartwood production with rot in the centre
(b) from Trial 8
a
50
40
50
40
35
30
25
20
15
35
30
25
15
10
5
5
0
10
20
30
y = 1.81 + 0.26x
R2 = 0.764
P <0.001
20
10
0
y = 7.18 + 1.47x
R2 = 0.758
P <0.001
45
Disc heartwood %
Disc heartwood %
b
y = 7.43 + 0.61x
R2 = 0.209
P = 0.008
45
0
40
0
Disc Rot/Damage %
10
20
30
40
Disc Rot/Damage %
Figure 4.15 Relationships between the percentage of rot and aromatic wood within (a) all discs
and (b) a comparison of discs with rot originating in the centre and other sites in
boles from Trial 8
Discussion
This trial did not follow typical silvicultural practices for a tropical sandalwood plantation in
Kununurra. Selecting the dominant trees ensured that each of these trees had sufficient hosts for
optimum growth, and final stocking after the chemical damage meant that there was minimal spatial
competition. Sun-scorch may have been a compounding issue as this can damage the bark allowing
disease entry and restricting growth.
There were two sites for fungal disease entry into the bole of trees. The first entry site appeared to be
through the centre of the tree via the juvenile wood and this resulted in cavity formation. This entry
site positively stimulated heartwood production (Figure 4.15b). The second type of infection entered
via entry sites other than the centre of the tree. Whilst this infection also increased heartwood in
59
relation to area damaged, there was only a relatively small increase in heartwood. For example, for a
25 per cent loss of heartwood area due to infection in the centre of the tree (juvenile wood) was on
average associated with a response that produced heartwood in 45 per cent of the disc area, whereas
when the fungus entered via at a site other than the centre (via the sapwood), the tree responded with
production of heartwood in only 7 per cent of the disc area (Figure 4.15b). A more comprehensive
appraisal of rot and identification of candidate fungal species in sandalwood have been undertaken, in
which fungal species from at least 11 genera were isolated from rot sections and implicated as
potential causal agents (Barbour et al. 2010).
Under silviculture conditions described here, 8-year-old sandalwood trees had an average total fresh
weight of 60 kg of which around 33 kg, or approximately 22 kg of air dry wood, was from the root and
bole wood. Heartwood was observed at the bole base of three-quarters (73 per cent) of 8-year-old
trees and this could provide a commercial opportunity for thinning programs. The mid and upper
sections of the tree contained sapwood, but the root stump and lower-third section of the bole
contained up to 11 per cent heartwood and could have value as wood for the incense/agarbhartti
industries. The cost associated with processing (de-sapping) trees at 8 years of age, which contain
only small amounts of heartwood, may restrict profitability of these value-added products (principally
oil from extraction).
4.4.2 The destructive harvest of 15-year-old sandalwood, Trial 4
Method
Trial establishment
Trial 4 was planted in 1994 originally to determine the suitability of three long-term hosts, Cassia
siamea, Acacia mangium and Peltophorum sp., each planted in separate blocks with sandalwood. The
original planting had 926 sandalwood per hectare planted in two out of three rows with 232 long-term
hosts per hectare planted in the remaining row. Sandalwood rows were 3.6 m apart with the host row
in the middle equidistant from the sandalwood trees. Poor sandalwood and host survival was observed
at 8 years of age and so regular irrigation ceased in 2002. Generally only edge trees, close to water
channels, survived.
Destructive harvest
Whilst random sampling is the preferred option, because of the low-maintenance regime and poor host
survival, the largest 40 trees in the trial were selected for harvesting to provide a sample more
representative of growth from a maintained plantation. Analysis indicated that the selected sample
followed a normal distribution based on basal diameter and DBH (Figure 4.16). Among those
selected, 19 were within 20 m from the end irrigation channel, 14 between 20 and 40 m, and 7
between 60 and 40 m from the channel.
Trees were cut at the bole base before tree height and diameter of up to three large branches dividing
from crown break were measured. The tree was then divided into bole and canopy sections. The
whole canopy was weighed followed by a sub-sample of canopy branches with a diameter greater than
4 cm. When heartwood was visible where a branch had been cut from the bole, the large end diameter
(LED) and branch length was measured and then cut at approximately 15 cm intervals from the small
end diameter (SED) until heartwood was visible. Heartwood was clearly distinguishable from
sapwood as a dark yellow to brown colouration of wood. End discs were then labelled and
photographed with a scale. The length and weight of the heartwood branch section was then
measured, and discs taken from the LED and SED ends of the branch.
The bole was weighed and measured for total length and basal, breast height and crown break
diameters. Boles were then cut into thirds, and 5 cm width discs were cut from the bole base, lower
60
third, mid third and at crown break. All discs were then labelled and photographed from above with a
ruler scale at the disc surface. The disc parameters: total disc area over-bark, area under-bark,
heartwood and rot area, were measured sing Image J software (NIH, USA). Disc parameters were
interpreted, their outline manually traced and the cross-sectional areas were calculated by the image
analysis package.
The root mass was divided into two sections, termed butt and roots, for volume estimation. The butt
referred to the continuation of the bole from ground level to where the lateral roots emerged, and the
root section was the lower mass which included the region where lateral roots emerged. A sub-sample
of 20 root masses were cut vertically through the centre of the butt to where the lateral roots emerged,
then horizontally through to this vertical cut. A photograph was taken of the vertical and horizontal
face of each root section. Image analysis was then used to determine butt length and heartwood taper
from top to bottom of butt, half-disc area and half-disc aromatic wood area.
Volume estimation
Bole volume under-bark was modelled for each tree using Smalian’s formula, using either total bole
length (Equation 7) or the sum of sectional third volumes (Equation 8):
Bole vol (cm3) = (((3.142 x LER2) + (3.142 x SER2))/2) x bole length
Equation 7
Bole vol (cm3) = ∑ ((((3.142 x LER12) + (3.142 x SER12))/2) x section length1) + ((((3.142 x
LER22) + (3.142 x SER22))/2) x section length2) + ((((3.142 x LER32) + (3.142 x SER32))/2) x
Equation 8
section length3)
where LER and SER are the large end radius and small end radius respectively, of the three bole
sections.
Canopy stem volume (CSV) was modelled as a cone using either the end area of the crown break, or
the end areas of up to the three largest branches dividing from crown break as in Equation 9:
CSV (cm3) = (((3.142 x LER2) x (tree height – bole height))/3
Equation 9
where LER is the diameter at crown.
Above-ground stem volume (under-bark) was modelled as the sum of bole volume and canopy stem
volume.
Heartwood volume within the bole of each tree was modelled as the sum of the third sectional
volumes calculated using cross-sectional areas from discs with each third having a large end area
(LEA) and small end area (SEA), as per Equation 10:
Heartwood vol (cm3) = ∑ (((LEA1 + SEA1)/2 x section length1) + ((LEA2 + SEA2)/2 x section
Equation 10
length2) + ((LEA3 + SEA3)/2 x section length3))
Where heartwood was not present at the small end diameter of a section a conical volume was used,
with the LEA of the heartwood and section length substituted into the formula of Equation 9.
Heartwood within the branches was calculated as per Equation 7, with bole length substituted by the
length of heartwood within the branch.
Oil analysis
The 20 trees selected for root sampling were also used for oil analysis. Wood samples were taken
from the root stump at 15 cm below stump top, from the basal disc, and then each bole third disc that
contained heartwood. Heartwood shavings were collected from three holes made vertically through
the disc with a 10 mm drill bit, one in the centre of the heartwood, and the other two at two-thirds
61
distance to the heartwood edge. Where the heartwood was too small for three holes, either one or two
were made, making sure that only heartwood was sampled. Samples were placed in labelled envelopes
and sent to Australian Botanical Products (Horsham, VIC) for oil extraction and gas chromatography
analysis. Methods used by Australian Botanical Products are described in Brand et al. (2007).
Results
Growth and heartwood
14
Frequency
12
10
8
6
4
2
0
0-10.7
10.812.9
13.015.1
15.217.417.3
19.5
Diameter class
19.621.7
21.8 +
Figure 4.16 Basal diameter class distribution of the 40 trees sampled in Trial 4
Measured growth parameters for the 40 trees indicated that on average bole weight accounted for
around 37 per cent of total above-ground fresh weight, with branches greater than 4 cm diameter
accounting for 31 per cent of the crown weight and 19.5 per cent of total above-ground fresh weight
(Table 4.20). There was substantial variation within each parameter, bole fresh weight varied from 10
to 63 kg and root mass from 10 to 57 kg. Total crown weight varied from 10 to 153 kg with the
subsample of branches greater than 4 cm diameter ranging between 3 and 61 kg.
Field measurements for the basal diameter and crown break diameter were 1.61 cm and 0.95 cm larger
than those measured during photographic analysis respectively (Table 4.21). Disc photographic
analysis showed average bark thickness varied between 7.8 and 8.4 mm along the bole, with an overall
mean bole bark thickness of 8.0 ± 1.60 mm. The proportion of heartwood within disc cross sections
decreased along the stem and at the base the mean area was 44.99 ± 25.80 cm2 compared to 5.83 ±
8.21 cm2 at crown break. The variability of heartwood also increased along the bole as indicated by
the larger proportional standard deviations of the means. Heartwood was observed in all basal discs,
declining to 36 discs at the first third, 29 at the second third, 28 at bole break and it was only present
in the branches of 21 trees. The basal discs had a considerably lower proportion of rot compared to
other bole locations, but there was no trend for rot occurrence further along the bole.
Total above-ground wood volume, and sapwood and heartwood volumes were estimated (Table 4.22).
Heartwood was estimated to account for 19.9 per cent of the bole volume and 14.3 per cent of total
stem volume. Heartwood proportion declined along the stem, and the lower-third bole accounted for
58 per cent of above ground heartwood compared to less than 6 per cent in the canopy stem. Stem
volume varied according to the measurements used. Here the under-bark photographic analysis
measurements were used to calculate the sum of sectional bole volumes. This method was considered
more accurate as it accounted for changed taper along the stem. The method more likely to be used in
large-scale measurements would be a full-length bole volume with canopy branch volume estimated
using crown-break diameter, adjusted for under-bark measurements using mean bark thickness. This
method gave a mean stem volume of 45963.7 ± 23640.2 cm3, which was 127 per cent the volume
estimated using the method applied here.
62
The estimated root stump volume of the 20 tree subsample was 4972.1 ± 2797.3 cm3, with an
estimated 1566.8 ± 969.5 cm3 of aromatic wood, or 31.5 per cent of total estimated volume. The mean
whole-stem tree under-bark stem volume was 39579 ± 30444 cm3, with total heartwood of 6959 ±
5171 cm3 or 17.6 per cent of volume.
Table 4.20 Field-determined parameters for the 40 trees sampled from Trial 4
Parameter
Mean ± s.d.
Basal diameter (cm)
15.7 ± 2.8
Breast height diameter (cm)
11.9 ± 2.2
Crown break diameter (cm)
10.4 ± 3.0
Branch diameter (cm)
10.8 ± 2.7
Bole length (cm)
279.8 ± 80.2
Tree height (cm)
637.0 ± 115.2
Total crown (kg)
53.7 ± 30.9
Branch >4 cm (kg)
16.8 ± 12.9
Bole (kg)
31.6 ± 12.5
Total above ground (kg)
85.3 ± 39.1
Root stump (kg)
22.2 ± 10.4
Whole tree (kg)
107.5 ± 48.6
All weights (kg) are fresh weight.
Table 4.21 Parameters calculated from photographic analysis of the four discs along the boles
from trees in Trial 4 (mean ± s.d.)
Over-bark
diameter (cm)
Under-bark
diameter (cm)
Bark thickness
(cm)
Heartwood area
(%)
Rot area
(%)
Base
14.1 ± 2.6
13.2 ± 2.5
0.837 ± 0.150
30.6 ± 12.4
1.5 ± 2.4
Lower 3rd
11.2 ± 2.0
10.4 ± 1.9
0.778 ± 0.144
17.5 ± 12.6
6.1 ± 11.3
Upper 3rd
9.8 ± 1.7
9.0 ± 1.6
0.806 ± 0.160
12.0 ± 11.3
5.2 ± 11.2
Crown break
9.5 ± 4.6
8.7 ± 2.1
0.777 ± 0.176
7.2 ± 8.4
5.5 ± 13.3
Disc position
Table 4.22 Mean estimated under-bark volume and heartwood volume and the percentage
heartwood (± s.d.) for bole sections, canopy stem and total above-ground volume
Tree section
Under-bark volume
(cm3)
Sapwood volume
(cm3)
Heartwood volume
(cm3)
Heartwood
(%)
Upper third
5959.1 ± 2415.0
5305.1 ± 2079.2
654.0 ± 722.6
11.0
Middle third
7302.9 ± 3151.5
6102.5 ± 2012.9
1200.4 ± 995.4
16.4
Lower third
11138.8 ± 5251.1
8122.5 ± 3973.3
3012.3 ± 1935.8
27.0
Total bole
24400.8 ± 13015.3
19534.1 ± 8408.6
4866.7 ± 3296.4
19.9
Canopy stem
11635.7 ± 9715.4
11343.1 ± 9413.5
292.7 ± 451.5
2.6
Total stem
36036.6 ± 17556.7
30877.2 ± 14929.9
5159.4 ± 3568.2
14.3
The whole-tree mean weight of the 20 tree subsample was 109.47 ± 54.31 kg, of which 49.8 per cent
was contributed by the root stump and bole with mean weights of 22.95 ± 12.00 kg and 31.53 ± 14.38
63
kg respectively. These parameters were similar to those of the broader 40 tree sample, which indicated
that the results of the root sampling were indicative of all sampled trees.
Oil analysis
The average oil yield of the 79 samples of pure heartwood from the five sample locations was 55.4 ±
23.7 g per kg, or 5.5 per cent. The highest average oil yield across sample locations was 68.6 ± 18.5 g
per kg in the root stump, and the average yield declined at each section along the stem to the lowest
mean yield of 34.3 ± 11.7 g per kg at the top of the bole (Table 4.23). Oil yield within individual trees
did not strictly follow the pattern of decline along the stem, for example the maximum single sample
yield of 122.6 g per kg occurred at the second-third disc location (Table 4.23). Across the nine trees
that had heartwood at all five sample locations, the average oil yield per tree ranged from 36.0 ± 11.8
to 64.8 ± 17.8 g per kg.
The average yield of alpha and beta-santalol within the oil followed the same distribution pattern as
total oil (Table 4.23), and there were only slight changes in their contributions to the composition of
the oil at the five sample locations (Table 4.24). The 79 samples of oil on average contained 70.3 ±
6.0 per cent of combined alpha and beta-santalol, with individual contributions of 48.9 ± 3.8 per cent
for alpha-santalol and 21.5 ± 2.5 per cent for beta-santalol.
Table 4.23 Total oil yield (g/kg) and santalol composition of the five sample locations in 20 trees
subsampled from Trial 4 (mean ± s.d.)
Yield (g/kg)
Sample
location
n
Total oil
Alphasantalol
Betasantalol
Total
santalol
Minimum
total oil
Maximum
total oil
Root
20
68.6 ± 18.5
33.2 ± 7.0
14.6 ± 3.2
47.7 ± 10.2
41.1
99.8
Bole base
20
63.9 ± 22.1
31.3 ± 10.3
14.2 ± 5.0
45.4 ± 15.3
32.2
108.7
Bole 1st
third
17
50.6 ± 16.4
24.6 ± 8.4
10.9 ± 4.0
35.5 ± 12.4
20.4
89.7
Bole 2nd
third
13
43.3 ± 30.6
20.8 ± 15.1
9.2 ± 7.1
30.0 ± 22.2
9.6
122.6
Bole top
9
34.3 ± 11.7
16.6 ± 5.6
6.8 ± 2.6
23.4 ± 8.2
23.7
53.5
Table 4.24 Proportion of alpha and beta-santalol in oil from the five sample locations in 20 trees
subsampled from Trial 4 (mean ± s.d.)
Composition (%)
Sample
location
n
Alpha
santalol
Beta
santalol
Total
santalol
Minimum total
santalol
Maximum total
santalol
Root
20
49.3 ± 5.0
21.7 ± 2.4
71.0 ± 7.3
52.8
78.4
Bole base
20
49.3 ± 2.8
22.3 ± 2.2
71.7 ± 4.7
59.7
78.9
Bole 1st third
17
48.7 ± 3.6
21.5 ± 2.6
70.2 ± 6.0
56.5
77.8
Bole 2nd
third
13
48.2 ± 4.0
20.9 ± 2.8
69.1 ± 6.5
52.4
77.0
Bole top
9
48.4 ± 3.1
19.7 ± 1.7
68.1 ± 4.6
57.2
73.7
64
The pattern of declining oil yield along the tree was examined further using linear regression.
Heartwood within the root stump was sampled at a fixed height of –0.15 m, basal discs fixed at zero
metres, and the bole third sampling heights were calculated by the division of total length (m) by
three. There was a moderately weak (R2 = 0.261) but significant (P<0.001) relationship such that for
every 1 m along the tree the oil yield declined by 12.9 g per kg (Figure 4.17a). There was no trend
apparent between sample location height and total alpha and beta-santalol composition (Figure 4.17b).
There was also no trend between sample oil yield and the stem or heartwood cross-sectional area of
the corresponding disc (Figure 4.18a). Similarly, the proportion of heartwood cross-sectional area did
not appear to influence oil yield (Figure 4.18b). That is, the stem size, the amount and percentage of
cross-sectional heartwood, was not an indicator of the of oil yield at a given location.
Estimates of oil yield per tree were calculated by converting the geometric volumes to kilograms using
a heartwood density of 0.9 (Rao et al. 1998), then multiplying the root stump and bole sections by the
average oil yield (g per kg) of the samples taken from either end of the section. For root stumps only
the single sample was used to determine yield. The mean estimated total oil yield per tree was 307.3 ±
215.9 g, with individual trees ranging from 18 to 778 g (Figure 4.19). On average, the lower third of
the bole accounted for the highest proportion of oil yield at 50.7 per cent per tree, followed by 28.4
per cent in the root stump, 15.5 per cent in the middle third of the bole and 5.4 per cent in the upper
third.
a 140
120
100
75
80
60
40
70
65
60
55
50
20
0
-0.25
85
80
% composition
Total oil yield (g/kg)
b
y = 64.56 -12.931x
R2 = 0.261
P<0.001
45
0.25
0.75 1.25 1.75 2.25
Sample height (m)
2.75
40
-0.25
3.25
0.25
0.75 1.25 1.75 2.25
Sample height (m)
2.75
3.25
Figure 4.17 Relationship between the height of the sampled disc within the tree (m) and (a) the
total oil yield, and (b) the percentage composition of total santalol within the oil in
20 trees subsampled from Trial 4
65
120
120
Total oil yield (g/kg)
b 140
Total oil yield (g/kg)
a 140
100
80
60
40
100
20
80
60
40
20
0
0
0
Disc
100
HW
200
300
400
0
20
40
% of heartw ood in disc
Cross sectional area (cm2)
60
Figure 4.18 Relationship between total oil yield (g/kg) of individual samples and (a) the cross2
sectional disc and heartwood area (cm ), and (b) the percentage of heartwood in 20
trees subsampled from Trial 4
Est. oil yield per tree (g)
800
700
600
500
400
300
200
100
0
1
roots
low er
2
3
mid
4
upper
8
9
14
16
17
21
23
25
26
27
30
32
35
36
37
40
Tree identity
Figure 4.19 Estimated oil yield (g) for each of 20 subsampled trees in Trial 4, indicating the
contribution of the root stump, lower third, middle third and upper third of the bole
Discussion
All 40 of the 15-year-old sandalwood trees harvested produced at least some heartwood, evaluated as
a yellow to brown colouration of wood within cross-sectional discs. On average these trees were 6.37
m tall, had a bole length of 2.78 m with a basal diameter of 15.7 cm and crown break diameter of 10.4
cm. Heartwood was estimated as 31.5 per cent of the stump volume and 21.5 per cent of the bole
volume, with inconsistent and low amounts of heartwood extending up into the canopy stem and
branches.
This harvest only considered one planting, grown in what could be considered adverse conditions,
where the number of hosts and water availability may have been limiting since age 10. The results
may not necessarily reflect those that would occur in intensively managed plantation-grown
sandalwood, where sandalwood may be larger than those sampled here at 15 years of age. For
example, earlier in this report the (Section 4.2.2, Trial 6) sandalwood grown with long-term host
66
Cathormion umbellatum, at 9 years of age had a mean basal diameter of 13.7 cm when stocked at 617
stems per hectare, or 16.2 cm when stocked at 231 stems per hectare, compared to 15.7 cm measured
for these 15-year-old trees. In plantations it is assumed that long-term host stocking, spacing and water
availability will remain largely constant throughout the rotation and should provide an advantage to
growth given a suitable host species is used and stocking rates do not promote excessive competition.
A general pattern of decline in oil yield was observed from the roots to crown break across the 20 tree
subsample. Heartwood from the crown break had on average only half of the yield found in root
stumps. This trend occurs in sandalwood trees grown in forests in India (Rai 1990) and more
specifically in studies on 10-year-old and 14-year-old plantation trees grown at Kununurra (McComb
2009; Jones et al. 2007). Oil composition, particularly in regard to santalols, did not vary greatly along
the stem suggesting that oil quality was relatively stable within trees. The level of alpha and betasantalol were within the range specified by the ISO standard (ISO 3518:300E) of 41–55 per cent
alpha-santalol and 16–24 per cent beta-santalol, and thus confirm that high-quality oil was produced
in 15-year-old trees.
The oil yields here of 6.9 per cent at the stem base were higher than earlier reports from plantation
trees grown at Kununurra (McComb 2009; Brand et al. 2006; Brand et al. 2007) which had an average
oil yield ranging between 2.3 to 3 per cent at the base of trees aged 14 to 15 years. Brand et al. (2006,
2007) undertook analyses on samples containing both heartwood and sapwood from cross-sectional
core sampling and thus oil yield from pure heartwood would be expected to be higher. Interestingly,
oil yields were within the range expected of older trees in natural stands in India, as broadly suggested
by Rai (1990) and more explicitly in a study by Jayappa et al. (1995) where root oil yield is 6.5–8.5
per cent declining to 2.5–5.5 per cent further up the tree. The oil yields here could be influenced by
point sampling compared with whole-disc heartwood sampling. Alternatively, yields may be
influenced by the somewhat adverse environmental conditions, such as increased exposure to sunlight
and lower water availability, compared to trees in a forest or under better plantation management.
Such environmental stresses have been proposed as potential factors affecting the initiation and
development of heartwood (Rai 1990). However, the most likely cause of lower yields is the younger
age of trees.
The estimates of whole-tree oil yields indicated that an average of 330 g of oil could be solvent
extracted from 15-year-old trees grown under similar environmental and silvicultural conditions.
However, because the methodology used here is based on a relative small sample of 20 trees using
geometric-modelled heartwood volume and point oil analysis, as opposed to whole-heartwood
extraction, the results should be viewed as an approximation of actual yields from these trees. This
study, however, clearly indicates that a large variation in tree size and heartwood oil yield can be
expected in plantation-grown sandalwood at 15 years of age.
4.4.3 Characterisation of heartwood and oil development in 11-year-old
sandalwood with three host species, Trial 7
Method
Trial establishment and design
Trial 7 establishment and design has been previously reported in detail by Barbour (2008). Three
species, Cathormion umbellatum, Dalbergia latifolia and Millettia pinnata which promote better
sandalwood growth and survival at 9 years of age, were used as long-term hosts for sandalwood which
were selected for core sampling (see Plate 4.5). For each host-species treatment, sampled sandalwood
trees were selected to reflect a normal distribution of the basal diameters measured in 2008. Fifteen
sandalwood trees were selected for each host treatment, with three chosen from each of the five
replicates to equally represent the environment across the site.
67
Plate 4.5 The plot combining sandalwood with the long-term host Dalbergia
Measurement and core sampling
Prior to coring, basal diameter, diameter at breast height, diameter at crown break and bole length of
the sandalwood were measured. Sandalwood were cored at 30 cm above ground level using a 0.5 cm
diameter hand-increment corer. Cores were extracted in an east to west orientation (along row)
through the centre of the tree and a polymer sealant was used to cap the core hole. Cores were gently
sanded on one side to allow for a clear distinction between sapwood and heartwood, which was
defined as a yellow to brown discolouration possessing a typical sandalwood aroma. Total core and
heartwood length (diameters) were measured and the hypothetical cross-sectional areas and heartwood
percentage were calculated.
Whole-increment cores were air dried, ground with a coffee grinder and then weighed to four decimal
places. Oil was extracted from samples into ethanol for 7–14 days with isobutyl benzene as an internal
standard (12 mM). A standard curve was constructed using oil from S. album (Sigma Aldrich) to
estimate total oil content in each sample. The chemical composition was determined by gas
chromatography with flame ionization detection (GC-FID) using a Shimadzu GC-17 A instrument
equipped with a DB-WAX column (Alltech, 30 m, 0.25 mm inside diameter, 0.25 µm film thickness)
and a flame ionisation detector. Injection volume was 1.0 µL, the injection port temperature was
200°C and detector temperature was 250°C. Helium (2.4 ml per min) was the carrier gas and a split
ratio of 10:1 was used. Oven temperature was held at 40°C for 5 min before ramping to 230°C at 10°C
per min and held for 20 min (total run time was 45 min). Peak identification was facilitated by
calculating retention indices and previous MS data. Integration was performed using Shimadzu GCSolutions software. Areas were recorded for all detectable peaks and per cent composition was
calculated by taking the area of the peak divided by total chromatogram area x 100. Samples which
contained small amounts of total oil tended to overestimate the proportion of the major components.
Statistical analysis
Differences in sandalwood heartwood and oil parameters between host treatments were tested using
ANOVA. Linear regression was used to test for relationships between total core, disc parameters and
aromatic wood parameters, and proportional data was angular transformed to satisfy the normality
assumption. Trends between heartwood traits and the interaction indices host count index (HCI) and
host size-distance index (HSDI) (see Section 4.3.1, Trial 7) were examined with scatter plots at search
68
horizons of 6, 9, 12 and 15 m from the target sandalwood. Those displaying visible trends were
further examined using linear regression. In this scenario it was thought that the interaction indices
could be representative of environmental conditions, such as light and host root availability, and that
these resources could influence heartwood development.
Results
Over-bark sandalwood parameters for the host treatments did not vary substantially (Table 4.25).
Sandalwood growing with either Dalbergia or Millettia were of a similar size, based on bole volume,
whilst on average sandalwood in the Cathormion treatment had around 69 per cent of the bole volume
of sandalwood grown with Millettia.
Table 4.25 Over-bark measurements for sandalwood trees growing with the three host
treatments in Trial 7 (mean ± s.d.)
Host treatment
Cathormion
Base diameter
(cm)
DBH
(cm)
CBD
(cm)
Bole Length
(cm)
Bole volume
(cm3)
15.9 ± 3.7
10.1 ± 3.6
10.7 ± 4.4
174.0 ± 55.5
26390.8 ± 14446.9
Dalbergia
17.1 ± 3.8
11.8 ± 2.6
11.5 ± 2.9
204.8 ± 49.5
35898.3 ± 18288.2
Millettia
16.7 ± 2.8)
12.0 ± 2.2
10.8 ± 2.5
238.9 ± 76.4
38361.1 ± 17570.3
Heartwood was present in 35 of the 45 sandalwood sampled. There was only one sandalwood tree
grown with Dalbergia without aromatic heartwood, compared to four and five sandalwood without
aromatic heartwood with Cathormion and Millettia hosts respectively. Core and heartwood properties
of sandalwood with the three host species did not vary greatly (Table 4.26). Sandalwood sampled with
Dalbergia hosts had the longest mean cores, core aromatic heartwood length and percentage, and the
largest cross-section disc heartwood percentage, although none of these variables were statistically
significant (P<0.05). The largest aromatic heartwood diameter for Cathormion, Dalbergia and
Millettia was 8.7, 7.3 and 10.1 cm respectively, and the highest proportion of aromatic heartwood
calculated on the basis of hypothetical discs was 33.6, 41.7 and 43.0 per cent respectively. Whilst
Dalbergia and Millettia had very similar mean aromatic heartwood area and percentage area,
sandalwood hosted with Dalbergia displayed more consistent heartwood production across the
sampled trees than Millettia.
Table 4.26 Core and cross-sectional parameters for sandalwood grown with the three host
treatments in Trial 7 (mean ± s.d.)
Core length
(cm)
Heartwood
length
(cm)
Total crosssectional area
(cm2)
Heartwood
area
(cm2)
Cross-sectional
heartwood area
(%)
Cathormion
11.4 ± 3.1
3.0 ± 2.5
109.2 ± 55.4
12.2 ± 15.6
9.0 ± 9.1
Dalbergia
13.0 ± 2.9
4.0 ± 1.9
138.2 ± 57.9
15.5 ± 12.7
11.5 ± 9.8
Millettia
12.5 ± 2.2
3.2 ± 3.2
126.4 ± 45.3
16.3 ± 23.3
11.2 ± 14.2
Host
treatment
There was a positive linear relationship between cross-sectional disc area and cross-sectional
heartwood area (P = 0.001, R2 = 0.225), and a very weak but significant relationship between disc area
and heartwood percentage (P = 0.049, R2 = 0.087). Examination of scatter plots revealed that for each
host treatment there was one outlier. With the outliers removed significant relationships between disc
area and heartwood were found for sandalwood with Cathormion (P>0.001, R2 = 0.658), Millettia (P
= 0.003, R2 = 0.527) and Dalbergia (P = 0.015, R2 = 0.403) host treatments. Cathormion was the only
treatment where sandalwood displayed a significant relationship between disc area and heartwood
69
A 90
y Cath= -14.401 +0.272x
R2 = 0.658
P >0.001
Heartwood area (cm2)
80
70
y Dal =-3.456 + 0.122x
R2 = 0.403
P = 0.015
y Mil = -43.901 + 0.510x
R2 = 0.527
P = 0.003
60
50
40
30
20
10
0
0
Cath
50
Dal
Mil
100
150
Disc area (cm2)
200
B
0.8
Heartwood % (transformed units)
percentage (Figure 4.20B). The nature of the relationships between disc and heartwood area, as
indicated by the regression coefficients (slope), suggested that the response of heartwood area in
relation to disc area occured most rapidly in Millettia, followed by Cathormion and then Dalbergia.
For example, a cross-section area increase of 100 cm2 at the stem base for sandalwood when hosted
with Millettia would be expected to have an increase of around 52 cm2 in heartwood area, compared
to 12 cm2 when Dalbergia is the host.
0.7
0.6
y Cath =-0.064 + 0.0032x
R2 = 0.702
P>0.001
0.5
0.4
0.3
0.2
0.1
0.0
250
0
Cath
50
Dal Mil
100
150
Disc area (cm2)
200
250
2
Figure 4.20 Relationships between sandalwood cross-sectional disc area (cm ) and (A) crosssectional heartwood area, and (B) cross-sectional heartwood proportion (%) in trees
from Trial 7 (note, a single outlier was removed for each host treatment, and heartwood %
was in angular transformed units to normalise residuals)
Trends between heartwood traits and the host size-distance index (HSDI) were more visually
identifiable compared to host count indices (HCI). Despite identifying potential trends there was only
one significant linear relationship, which was found between heartwood percentage and HSDI for the
Cathormion treatment at the 15 m horizon (P = 0.042, R2 = 0.302; Figure 4.21A). Whilst definitive
relationships suitable for heartwood prediction were not found, the nature of the trends visible
between interaction indices and heartwood traits generally varied between host treatments (Figure
4.21B). The Cathormion treatment displayed a negative trend where heartwood traits declined as the
number (HCI) and relative size of hosts (HSDI) increased, as opposed to the positive trends indicated
for Dalbergia. The strength of relationships with regard to the search horizon also had an opposing
trend. In the Cathormion treatment the strength of the relationship with heartwood parameters
increased as the search horizon broadened from 6 m (R2 = 0.019), to 9 m (R2 = 0.123), to 15 m (R2 =
0.302); this contrasted with the Dalbergia treatment where relationships weakened as the search
horizons increased from 6 m (R2 = 0.186), to 9 m (R2 = 0.173), to 15 m (R2 = 0.004). Trends were not
observed between heartwood and competition indices for sandalwood within the Millettia treatment.
Multiple linear regressions examined the relationships between heartwood parameters, area and
proportion, with two explanatory variables, disc cross-sectional area and HSDI. Only the HSDI
horizon that displayed the strongest relationship with heartwood area and proportion, as a single
regressive variable for each host treatment, was used. Heartwood area displayed significant
relationships for all treatments, and Cathormion had the strongest relationship (P <0.001, R2 = 0.708),
followed by Millettia (P = 0.015, R2 = 0.534) and Dalbergia (P = 0.048, R2 = 0.423). Cathormion was
however the only treatment to improve the predictive strength (based on adjusted R2 values) compared
to the explanatory variable in single regressions. Heartwood proportion was only significant for the
Cathormion treatment (P <0.001, R2 = 0.792), which provided a stronger predictive model compared
to the explanatory variables in single regressions.
70
A 0.8
B 45
y Cath 0.623 + -0.0003x
R2 = 0.302
P = 0.042
Heartwood % (transformed)
0.7
35
Heartwood %
0.6
40
0.5
0.4
0.3
30
25
20
15
0.2
10
0.1
5
0
0.0
0
Cath 15m
500
1000
1500
Size dependent index (HSDI)
Dal 9ml
5
2000
Cath 15 m
Mil 15m
10
15
20
25
30
Host count index (HCI)
Dal 15m
35
40
Mil 15m
Figure 4.21 Relationships between heartwood % and (A) host size-distance index (HSDI) and,
(B) host count index (HCI) in trees from Trial 7. (A) displays significant linear regression
for Cathormion and (B) displays general trend lines. Note that (A) displays heartwood % in
angular transformed units to normalise residuals of linear regression.
The percentage oil yields from ground sandalwood cores taken from 30 cm above ground were similar
between host treatments (P = 0.219), with means ranging from 1 per cent for Cathormion to 1.7 per
cent for Dalbergia (Table 4.27). The maximum oil yield from single trees for host treatments was 2.6
per cent, 3.1 per cent and 4.3 per cent for Cathormion, Dalbergia and Millettia respectively. The ten
core samples that did not appear to contain heartwood had a mean oil yield of 0.08 ± 0.04 per cent,
compared to those containing heartwood which had an average of 1.7 ± 1.0 per cent. The proportion
of santalols within the oil was not different between host treatments for alpha-santalol (P = 0.5), but
beta-santalol varied (P = 0.019) and sandalwood in the Dalbergia treatments had a greater proportion
than those from the Cathormion treatment. Santalol proportions across all samples ranged from 42 to
60 per cent for alpha-santalol and 19 to 30 per cent for beta-santalol.
There were no differences between the amount (g per kg) of oil extracted from host treatments (P =
0.220), nor for the amount of alpha-santalol (P = 0.246) and beta-santalol (P = 0.190) (Table 4.27).
The maximum alpha and beta-santalol yield for individual samples within host treatments was 13.5 g
per kg and 6.4 g per kg respectively for sandalwood with Cathormion, 16.5 g per kg and 8.0 g per kg
for Dalbergia, and 22.6 g per kg and 11.1 g per kg for Millettia. The mean oil yields when samples
without heartwood were excluded were 12.8 ± 8.2 g per kg for Cathormion treatment, 17.8 ± 8.9 g per
kg for Dalbergia, and 19.0 ± 12.5 g per kg for Millettia.
There was a moderately strong and significant relationship (R2 = 0.60, P <0.001) between oil yield
and the proportion of heartwood within core samples. Because core samples contained sapwood and
heartwood in uneven proportions, oil yields (g per kg) were adjusted by multiplying original gas
chromatograph yield by a dilution factor equal to the ratio of sapwood to heartwood within core
samples. The mean sandalwood oil yield after applying the dilution factor was 37.9 ± 27.9 g per kg
(3.8 per cent), and these oil yields varied between host treatments (P = 0.045). The Dalbergia
treatment had a mean of 51.8 ± 26.3 g per kg (5.2 per cent), which was higher than 27.5 ± 21.8 g per
kg (2.2 per cent) for the Cathormion treatment, but not different from 34.4 ± 27.9 g per kg (3.4 per
cent) for the Millettia treatment.
71
Table 4.27 Proportion and yield (g/kg) of alpha-santalol, beta-santalol and total oil from cores
sampled at 30 cm from sandalwood with Cathormion, Dalbergia and Millettia hosts
(mean ± s.d.)
Host
Cathormion
Dalbergia
Millettia
Total
No.
samples
15
15
15
45
Percentage composition
alphabetasantalol
santalol
51.9 ± 2.7
25.1 ± 2.1
50.9 ± 2.8
25.8 ± 2.0
50.6 ± 4.5
23.6 ± 2.6
51.1 ± 3.5
24.8 ± 2.4
Yield (g/kg)
alphabetasantalol
santalol
5.0 ± 4.6
2.4 ± 2.2
8.4 ± 4.9
4.3 ± 2.5
6.5 ± 6.9
3.2 ± 3.5
6.6 ± 5.6
3.3 ± 2.8
Oil yield
(%)
0.97 ± 0.88
1.67 ± 0.96
1.30 ± 1.30
1.31 ± 1.09
Discussion
The rate of heartwood development in relation to overall wood production and heartwood proportion
was similar between sandalwood planted with the three host species. This contrasts to the findings of
McComb (2009) where the proportion of heartwood at the stem base of 14-year-old clonal
sandalwood ranged from 17.5 to 34.9 per cent between host species. The difference in the crosssectional heartwood area, whilst still not statistically significant, was noticeably larger between host
species compared to heartwood proportion. The cross-sectional heartwood area of sandalwood grown
with Cathormion was on average only 78per cent and 74 per cent of those grown with Dalbergia and
Millettia respectively. If it is assumed that longitudinal heartwood development was constant across
host species, then sandalwood grown with Cathormion could have around 250 kg less heartwood per
harvested tonne compared to those grown with Dalbergia or Millettia. If for example heartwood yield
at 15 years of age was an arbitrary 10 kg per sandalwood tree when grown with Millettia, the total
yield per hectare could be reduced by as much as 1.2 tonnes per hectare when using Cathormion hosts
at a stocking rate of 462 sandalwood stems per hectare.
The variability of heartwood production displayed for Cathormion and Millettia may also negatively
impact the number of commercially valuable trees within a plantation. If the samples here were indeed
representative of the broader plantation population, the number of trees containing heartwood would
be considerably higher for sandalwood grown with Dalbergia which had 93 per cent of samples with
heartwood compared to 67–74 per cent of sandalwood planted with Cathormion and Millettia. At a
stocking rate of 462 stems per hectare, as used in this trial, the number of sandalwood with heartwood
at 11 years of age could range from 429 when grown with Dalbergia, compared to between 310 and
342 when grown with Cathormion and Millettia respectively. In the destructive harvest of 8-year-old
sandalwood earlier in this section, 26 per cent of the sample did not have heartwood at the base of the
stem, and similar proportions of trees without heartwood at 30 cm have been reported at the age of 10
years (Jones et al. 2007) and 14 years (Brand et al. 2006). These studies have provided increasing
evidence that a considerable proportion of up to 20 per cent of sandalwood will not develop
substantial amounts of heartwood within the 15-year rotation envisaged by the plantation industry. If
the selection of host species can reduce the proportion of low-value trees and maintain competitive
external growth rates and heartwood proportion, as displayed by Dalbergia here, it would be very
valuable to the industry.
The relationships between disc area and heartwood traits indicated that it was the amount and not
proportion of heartwood that was more consistently and strongly related to sandalwood diameter. The
results confirm that the amount of heartwood in cross section at the stem base diameter was only
moderately accounted for by the external diameter of trees aged 11 years. There also appeared to be
differences in the strength and nature of these linear relationships when sandalwood was grown with
the different host species, which suggests that applying a universal predictive equation for heartwood
across host species may not achieve a large degree of accuracy.
72
The examination of a possible relationship between tree-tree interaction indices and heartwood traits
was an attempt to account for a proportion of the environmental component of heartwood formation
and development. The indices used here indicated the number (HCI) and relative size (HSDI) of hosts
within specified neighbourhoods of target sandalwood, and this helped to explain differences in the
competition environments within and between host species. In this trial there was visual
differentiation in the response of heartwood formation to interaction indices to the three host species.
Broadly speaking, as the number and size of hosts increased within a 15 m radius of sandalwood,
heartwood traits (amount and proportion) declined for the Cathormion treatment, increased for
Dalbergia, and displayed no discernable impact on sandalwood with Millettia. The analysis did not
however offer direct insight into reasons for these differences. The indices provided an indication of
the physical size and density of trees in the environment, but it was more likely that differences were
more strongly defined by physiological changes in the relationships that occur between host and
sandalwood as a result of competition.
The oil extracted from sandalwood cores taken at 30 cm above the ground all met the minimum level
specified within the ISO standard for Santalum album oil (ISO 3518:300E) for alpha-santalol (41–55
per cent) and beta-santalol (16–24 per cent). This indicates a quality oil product is possible from 11year-old plantation-grown sandalwood. The oil yield was however relatively low at around 1.3 per
cent, a range of less than 0.5 per cent to just over 4 per cent for individual samples. This is relatively
similar to the findings of Jones et al. (2007) where core samples from 10-year-old sandalwood
growing at Kununurra displayed oil yield ranging from less than 0.5 per cent to just less than 5 per
cent. As the core samples included both sapwood and heartwood, the results will be lower than for
pure heartwood samples, and after yield was adjusted using a dilution factor of the sapwood-toheartwood ratio, the average heartwood oil yield was calculated to be around 4 per cent. It is
important to note that such calculated values should only be seen as approximations and the preferred
method would be to extract and analyse pure heartwood samples. The method used here was because
the amount of heartwood within core samples was rarely over 1 g, with many samples having less than
0.5 g of heartwood, which made them difficult to work with.
The differences displayed in mean oil yield between the three host treatments was low when
examining the raw gas chromatogram results. However, considering the unequal heartwood
proportions in the samples and the moderately strong linear relationship that existed between
heartwood proportion and oil yield, it is possible that the oil yields tended to reflect the differences in
heartwood development between host species, and not necessarily differences in the rate of oil
production per unit of heartwood. The dilution-adjusted average oil yield of the three host species did
display more variation, and sandalwood with Dalbergia had an average yield 3 per cent higher than
the Cathormion treatment. This difference may be a function of the more consistent sandalwood
heartwood production as well as improved growth, and an associated positive relationship with
heartwood development (Figure 4.20), when hosted with Dalbergia compared to Cathormion. Other
potential causes for the differences, such as variability in compounds extracted from hosts
(Radomiljac et al. 1998c), would require further research to confirm that there are specific host effects
on oil production beyond those attributed to influences of host species on sandalwood size.
The observed variation in heartwood occurrence and development of the sandalwood suggested large
differences in heartwood yield at the plantation level could occur as a result of host choice.
Furthermore, the differentiation of relationships between heartwood traits and the diameter and treetree interaction indices could indicate fundamental differences in the response of heartwood
production in sandalwood grown with different host species. The differences in oil yield between host
species would likely be secondary to overall oil productivity compared to the host affect on heartwood
production. That is, a host species that is able to produce bigger sandalwood is likely to produce more
heartwood and thus a greater ability to produce oil. Currently there is limited knowledge to explain
why differences in heartwood and oil can occur between host species, and considerable scope exists
for investigations into the physical parameters and physiology of host-sandalwood interactions to
identify how and why these differences occur.
73
4.4.4 Preliminary evaluation of non-invasive methods for aromatic wood
determination in Santalum album, Trials 4 and 8
Methods
Electrical impedance tomography
The electrical impedance of three standing sandalwood trees, one aged 8 years (Trial 8) and two aged
15 years (Trial 4), was measured using a PiCUS Treetronic (Argus, Rostock) instrument. Within each
tree, measurements were recorded at 100, 300, 500, 750 and 1000 mm along the bole. At each site 24
electrodes (nails) were hammered into the tree at points equidistant around the diameter. An electrical
current was applied through two electrodes to produce an electrical field measured by the electrodes
through the cross section of the tree. The shape of the electrical field was determined by the resistivity
of the wood through the cross section, indicated by differences in voltage between pairwise electrodes
(Rust et al. 2007). The data was then interpreted by experienced technicians using the instrument
software (PiCUS Q72) to produce tomograms of each test site along the bole.
After data acquisition, the trees were felled and discs approximately 4 cm in width were taken from
sites along the bole. A photograph of each disc was taken and each electrode was labelled so that the
photograph could be aligned with the corresponding tomogram.
The tomograms were then visually compared with the disc photographs to identify if the physical
traits recognised as heartwood or rot on the discs were interpreted by electrical impedance.
Acoustic time-of-flight
An IML Hammer (Instrumenta Mechanic Labor GmbH, Germany) was used to measure the stress
wave velocity of four cross sections at different heights along the bole of eight standing sandalwood
trees, four aged 9 years (Trial 8) and four aged 15 years (Trial 4). The IML hammer applied an
acoustic stress wave and recorded the time taken for the signal to pass through two transducers located
on opposite sides of the tree. The velocity was calculated by dividing the distance the signal traveled
by the time recorded to pass through both transducers and as such the method is often referred to as a
‘time-of-flight’ measurement (Searles and Moore 2009).
The four 9-year-old trees were tested at approximately 130, 450, 830 and 1120 mm and the four 15year-old trees were tested at 160, 500, 940 and 1325 mm. At each height, measurements were taken
along two axes, one along the row (R IML) and the other across the row at 90 degrees to this (A IML).
After the acoustic measurements were recorded, the trees were felled and discs approximately 4 cm
wide were taken from each of the sampled heights along the stem. The discs were then photographed
with a scale set at the discs’ face in preparation for image analysis. The program Image J (NIH, USA)
was used to manually trace the physical traits of the discs from photographs to calculate values for
over-bark disc area, under-bark disc area, heartwood area, disc rot area, as well as the diameter of the
disc and heartwood through the disc centre.
The relationships between the IML readings (R IML and A IML) and the heartwood area, diameter
and percentage traits of the discs were then examined using simple linear regression (Xlstat).
Results
Electrical impedance tomography
The tomograms produced (Figure 4.22) did not correspond to a large degree of accuracy with the
visual features identified as heartwood on the extracted discs. For example, in Tree 1 (Figure 4.22) the
tomogram at 1000 mm along the bole appeared to display the small area of heartwood, albeit in an
74
exaggerated state, as an area of high impedance (red), however at the base (100 mm) of the bole the
similar colouration on the tomogram was not verified as heartwood on the disc. On Tree 2 (Figure
4.22), heartwood was clearly defined and consistent throughout the bole length, yet the 3-D tomogram
does not appear to provide a clear distinction between sap wood and heartwood and thus the ability of
the technique to determine heartwood content or proportion was compromised.
Overall there was a large degree of ambiguity in the tomograms which could not be easily interpreted
without completing a destructive harvest. This method may be useful in identifying trees that deviate
from the norm. It would be hoped that a typical tree was represented by Tree 2 (Figure 4.22), with
constant aromatic wood along the bole. Deviations from the corresponding typical tomogram,
particularly inconsistent colouration, would be used to indicate trees that lack heartwood and/or the
presence of wood rot or other damage. However, considerably more testing would be required ensure
typical trees display consistent tomograms.
Figure 4.22 The electrical impedance tomograms for the 8-year-old tree (Tree 1, left), and the
extrapolated 3-D tomogram and extracted discs for the 8-year-old (centre) and 15year-old tree (Tree 2, right) respectively (note, area of blue indicates low impedance
(higher moisture content) and area of red indicates high impedance (lower moisture
content))
Acoustic time-of-flight
The linear relationships between IML reading and heartwood parameters measured had weak
coefficients of determination (R2) when the 16 discs sampled from 9-year-old trees were used (Figure
4.23). The strongest relationship was between the A axis IML and heartwood diameter, and this had
75
an R2 of 0.362 (P = 0.014) (Figure 4.23c). Removing the discs without heartwood produced stronger
relationships between measured heartwood parameters and IML readings along the R axis. For
example, the R2 of the relationship with heartwood diameter within the discs increased to 0.768 (P =
0.004) compared to 0.207 (P = 0.076).
The discs from 15-year-old trees had generally stronger linear relationships between IML readings
and heartwood parameters than in 9-year-old trees. Similar to the 9-year-old samples, the
measurements along the A axis produced stronger relationships compared to the R axis. The strength
of these relationships along the A axis ranged from moderately weak, with R2 of 0.335 (P = 0.019)
and R2 = 0.385 (P = 0.0.01) for heartwood and percentage respectively, to a moderate R2 value of
0.501 (P = 0.002) for heartwood diameter. The strength of the relationships may have been negatively
influenced by the small sample size, where potentially a large variation in underlying wood properties
between trees could be skewed compared to a larger sample. Indeed the relationships between
heartwood diameter and A IML within individual trees were considerable stronger when using all
data, with three of the four trees sampled having an R2 greater than 0.740.
The weaker relationships between IML reading heartwood parameters in the 9-year-old compared to
15-year-old trees may be a result of the lack of consistent heartwood production within the younger
trees. In the younger trees it is likely the low amount of heartwood prevented it from registering a
consistent acoustic signature, and instead it responded to other wood properties independent of
heartwood.
76
a
b
1700
1400
1600
1300
1500
1200
1400
IML reading
IML reading
1500
1100
1000
900
1300
1200
1100
800
1000
700
900
600
0
c
2
4
6
Heartw ood area w ithin disc (cm2)
800
8
0
d
1600
1300
1500
1200
1400
1100
1000
900
200
250
Cont’d
1200
1100
1000
700
900
600
800
0
2
4
Heartw ood diameter (cm)
6
0
f
1500
1200
1400
IML reading
1600
1300
1100
1000
900
1200
1100
1000
700
900
600
10
15
30
1300
800
5
20
1700
1400
0
10
Heartw ood diameter (cm)
1500
IML reading
150
1300
800
800
20
20
Heartw ood % w ithin disc
R IML
100
1700
1400
IML reading
IML reading
1500
e
50
Heartw ood area w ithin disc (cm2)
30
40
50
60
Heartw ood % w ithin disc
A IML
Figure 4.23 Relationships between IML readings and (a) heartwood area with discs for 9-yearold trees from Trial 8 and (b) 15-year-old trees from Trial 4, heartwood diameter
within discs for (c) 9-year-old and (d) 15-year-old trees, and percentage heartwood
within discs for (e) 9-year-old and (f) 15-year-old trees
77
Discussion
Neither method was able to accurately determine heartwood yield within discrete cross sections along
the length of the bole in the limited sample tested. Because of the very limited sample size and scope
of the testing, however, it could not be concluded that these methods are not able to determine
aromatic wood within standing trees.
In the case of electrical impedance, it may be that further manipulation of the recorded data using the
product software was required to provide an image output that reflected the specific chemical
structure of heartwood. Indeed the operators were encouraged by initial results and expressed an
interest in continuing further analysis. This more intensive testing and calibration was beyond the
scope of the project, however, industry may decide that it is worthwhile pursuing this method.
The acoustic time-of-flight testing did not provide definitive results, but trends in the data were
encouraging enough to suggest the possibility for it to be used in estimating heartwood or closely
related parameters. In particular, the stronger positive relationships with heartwood of the 15-year-old
compared to the 9-year-old trees, which had considerably less heartwood, suggested that acoustics
could be detecting mechanical wood parameters related to heartwood. Also, the stronger positive
relationships along the four bole sample sites within individual trees indicated that with a reduction in
noise created by the differing wood properties between trees, heartwood appeared to register stronger
relationships with the acoustic tool.
Of the two methods the acoustic time-of-flight is likely to be the easier to deploy in the field, and
provide faster data interpretation. It appeared as though the data interpretation of electrical impedance
required not only considerable experience with the product software, but also a familiarity with
common patterns of electrical impedance within trees. Whilst time-of-flight instruments, such as the
IML hammer, required expertise to use, they have been designed with in-field use by foresters in
mind. Once a validated calibration has been made for a trait within a species and environment, the
established equation could then be used to determine result.
The presence of heartwood was indicative of the presence of oil; however, the proportion of oil within
the wood was indeterminable by visual inspection. Core sampling has been a desirable method in the
past because it allows for a direct measure of oil yield and heartwood yield within a chosen cross
section. If the methods used here can indeed be calibrated to provide estimates of heartwood, even
further estimation would be required to determine an approximate oil yield. If further sampling is
undertaken to verify these methods, the addition of oil yield is recommended because the extra
information may provide clarity to the analysis.
78
5
High-value timber trials
Early sandalwood silvicultural research in the late 1980s tested several timber species in conjunction
with sandalwood including: Azaderachta indica, Cassia siamea, Dalbergia sissoo, Khaya
senegalensis, Pterocarpus indicus, Terminalia pilularis and T. platophylla (McKinnell 1990). With an
aim to discover suitable hosts for sandalwood it was hoped that some species could provide an
additional commercial product. Under this scenario sandalwood growth was not always favourable;
however, the encouraging growth rates of some host species stimulated the planting of trial plots for
timber species monoculture. This chapter summarises the growth performance of species planted with
the aim of provide valuable wood or forest products, such as oil seeds, when planted in monocultures
or with sandalwood.
5.1 A summary of Khaya senegalensis growth within trials of
different age and silviculture, Trials 5, 7, 11, 12 and 15
African mahogany, Khaya senegalensis, belongs to the family Meliaceae, and is in one of two genera,
the other being the true mahoganies Swietenia, in the subfamily Swietenioideae. Khaya senegalensis
is native to tropical Africa in a band extending east to west between latitudes of 8oN and 15oN (Arnold
et al. 2004). It is a deciduous tree that when fully grown reaches 15 to 20 m tall with a diameter up to
1.5 m and a clean bole length typically of between 8 to 16 m (Jøker and Gaméné 2003). Across its
natural range it is used for medicinal purposes, fuel wood, fodder and as amenity or shade tree
(Arnold 2004). Beyond traditional uses it has also gained commercial value because of its richly
coloured wood that resembles that of the true mahogany, Swietenia macrophylla, and it has been
utilised as a replacement for this species in high-quality furniture, cabinetry, joinery and flooring.
With the increasing scarcity of true mahogany and social and ecological pressures to reduce its use,
replacement timbers such as African mahogany are becoming more widely accepted and used (Arnold
2004). This inevitably places pressure on the natural resource and there is an increasing requirement
for plantations meet demand.
African mahogany was introduced into northern Australia as a street tree in the 1950s, with species
evaluation trials first being established in the 1960s and 1970s in the Northern Territory and
Queensland (Arnold et al. 2004; Nikles et al. 2004). Its initial introduction to Kununurra at the Frank
Wise Institute occurred within trial plots, testing its suitability as a host for sandalwood plantations
during the early 1990s. However, it did not prove to be a suitable host because of its rapid growth,
which enabled it to occupy the site, dominate the canopy and ultimately suppress sandalwood growth
(Barbour 2008; Done et al. 2004). It is this vigour, as well as the aforementioned timber qualities, that
has given rise to its recognition as a prime candidate for a plantation species in Kununurra and the
broader northern-Australia region and resulted in the commencement of research programs and
commercial plantations (Nikles et al. 2004; Armstrong et al. 2007). A summary of the growth of the
African mahogany in FPC trial plots at Kununurra is presented.
Methods
Trial establishment
Five trials containing African mahogany were measured during the course of this project. The age and
planting configurations varied between trial plots (Table 5.1). Trial plots 5, 11 and 15 were planted as
demonstration plots with no treatment comparisons intended and thus no experimental design was
employed, whereas Trial plots 7 and 12 were planted as treatments within a broader experimental
design. All trial plots were established on the Cununurra cracking clay soils at the Frank Wise
Institute, where the land was laser levelled and mounded for flood irrigation. All plots received
79
minimal silviculture with limited stem pruning, no thinning and no fertiliser application. Flood
irrigation was applied approximately once a month during the dry season since establishment.
Measurement
The specific measurements taken for each trial plot were as follows:
•
Trial 5: all African mahogany within the trial were assessed, with basal diameter, DBH, bole
length and tree height measured
•
Trial 7: basal diameter, diameter at breast height, and tree height were measured for all trees
within the five replicated block plots
•
Trial 11: a subplot of four rows by 120 m was selected from the larger block of eight rows by 200
metres, and the diameter at breast height and bole length measured
•
Trial 12: basal diameter, diameter at breast height, bole length and tree height were measured for
the four internal rows of each of the five block plots replicated within the experimental design
•
Trial 15: an internal subplot of four rows by seven trees was selected from the larger block
planting of six rows by 10 trees; the DBH, bole length, and tree height were measured.
Survival percentage, basal area (using DBH) and diameter increment were calculated for each trial
and where applicable bole and stem volume was estimated using Smalian’s and conical volume
formula respectively. Growth at the hectare level was then calculated by multiplying mean data by the
number of surviving stems per hectare.
Table 5.1 Summary description of trial plots in which Khaya senegalensis was planted
Trial
Year
Age
when
measured
5
1997
11
2.7 m x 3 m
1235
154
Multi-species plot with sandalwood,
Sweitenia, Cassia & Cathormion,
established host:sandal ratio 2:1
7
1999
9
3.6 m x 3 m
926
463
Block plantings with sandalwood,
established host:sandal ratio 1:1
11
1996
12
3.6 m x 4 m
1389
694
Alternating line planting at 1:1 ratio
with Enterolobium sp.
12
1996
12
2.7 m x 3 m
1235
1235
Single species block planting
15
1999
9
3.6 m x 3 m
926
926
Single species block planting
Trial spacing
(between x
within row)
Total
SPH
Khaya
SPH
Design note
Results
African mahogany had good survival under Kununurra conditions. More than 90 per cent of trees
survived within all trial plots assessed (Table 5.2).
The growth rates (DBH MAI) across trials was relatively constant at between 2.4 and 2.8 cm per year
(Table 5.2), with the exception of Trial 12 which had a markedly lower growth rate. However, in Trial
12 although African mahogany had the best growth performance, most of the 10 species planted had
lower tree health and condition compared to other plantings at the Frank Wise Institute. Climatic
factors and watering regimes were consistent across all trials and so localised soil conditions may
80
have been a contributing factor to the low growth rate; however, detailed site evaluations would be
required to confirm this suggestion. No accurate records of seed source were held across trials, so it is
possible that an inferior genetic resource was used to establish this particular trial.
Table 5.2 Khaya senegalensis growth measurements across Trials 5, 7, 11, 12 and 15. Results at
the hectare level were calculated using surviving number of Khaya stems per
hectare
Basal
diameter
(cm)
DBH
(cm)
146
35.4 ±
5.6
97
449
11
90
12
15
Trial
Survival
(%)
Survival
(SPH)
5
95
7
DBH
MAI
Basal
area
Bole
length
(m)
Height
(m)
ESV
(m3)
ESV
(m3 ha-1)
0.312 ±
0.175
45.6
-
-
-
-
(cm yr-1)
(m2 ha-1)
26.4 ±
5.6
2.4
8.0
2.7 ±
1.3
13.6 ±
2.5
33.6 ±
7.2
24.3 ±
5.7
2.7
20.8
1.7 ±
0.7
-
624
-
33.6 ±
6.6
2.8
55.3
3.4 ±
1.9
-
92
1136
26.8 ±
9.4
22.3 ±
8.3
1.9
44.4
3.5 ±
1.6
11.2 ±
2.4
0.173 ±
0.141
196.5
90
833
-
24.7 ±
5.0
2.7
39.9
4.7 ±
1.7
12.8 ±
1.3
0.202 ±
0.093
144.1
Discussion
Despite often occurring as solitary trees in its native range, African mahogany coped well with the
competitive plantation environment. This supports earlier observations, for example a trial in the
Northern Territory had 91 per cent survival after 34 years with trees planted in an un-thinned stand at
over 4000 stems per hectare (Nikles et al. 2004). Trees coped equally well across trials with a range of
competitors and various stocking regimes. For example, when planted with Enterolobium sp. as a
direct competitor within rows (Trial 11), African mahogany produced the highest MAI (2.8) of the
surveyed trials. Also in comparing the two trials aged 9 years (Trials 7 and 15), the mean DBH was
the same despite different growth environments: in Trial 7 it was grown with sandalwood at half the
stocking rate of Trial 15, which had high inter-specific competition. The ability of African mahogany
to survive and grow well in a range of competitive environments, including presumed parasitism from
sandalwood, should allow for flexible silviculture regimes with various stocking and thinning options
likely to produce desirable growth rates.
Whilst there was no formal measurement/assessment made of stem straightness, it was widely
observed across all trials that a large proportion of trees had crooked stems with very few trees
displaying apical dominance (Figure 5.1), and this is similar to observations in other studies across
northern Australia (Nikles et al. 2004). These problems are likely to be prevalent due to establishment
with unimproved genetic stock and application of less than optimised silviculture. For example,
historical trial notes indicate that African mahogany was susceptible to damage from strong seasonal
winds, because of the early development of a large broad crown. This frequently caused trees to bend
and/or shift within mounds, particularly after heavy rain or irrigation, which reduced stem form
quality across trials (Figure 5.1). Current research programs in the Northern Territory are expected to
yield improvements in genetics and silviculture (Nikles et al. 2004) and similar methods could be
applied to improving the performance of future plantations in the Kununurra region, or by gaining
access to seed produced by such programs. At the simplest level, the establishment of plantations
using seed collected from trees displaying a superior phenotype for bole straightness and apical
81
dominance (Plate 5.1) will provide a better chance of yielding a larger proportion of acceptable stems
across a plantation than deploying indiscriminately collected seed.
Plate 5.1 Examples of wind-swept boles (top left), crooked boles (top right), and a tree
displaying favourable phenotype (bottom left), in a 9-year-old African mahogany
plantation
In an economic evaluation of a potential African mahogany plantation industry in the Northern
Territory, Whitbread (2003) considered a target of 40 to 50 cm DBH achievable over a 20-year
rotation on average sites with thinning to a final stocking rate of 100 to 105 stems per hectare. Based
on these parameters African mahogany gave positive internal rates of return even for 2 ha stands when
some level of value adding (sawing and/or drying) was undertaken. The growth rates seen here were
on par or exceeded trials at the same age in the Northern Territory, upon which Whitebread (2003)
based his growth assumptions. It is thought that with appropriate silviculture African mahogany could
meet the growth targets outlined in the analysis, but the economic viability of plantations under flood
irrigation in the ORIA will be dependent on a different set of commercial sensitivities than those
found in the Northern Territory.
82
5.2. Comparison of the growth of eleven high-value timber
species, Trial 12
Method
Trial establishment
Trial 12 was established in 1996 to test the growth performance of 11 high-value timber species on
flood-irrigated Cununurra cracking clay soil. The species were: Dalbergia melanoxylon, Dalbergia
cochinchinensis, Dalbergia latifolia, Swietenia macrophylla, Khaya senegalensis, Khaya anthotheca,
Cedrela odorata, Toona australis, Intsia bijuga, Castanospermum australe and Swietenia mahogani.
Land was prepared for flood irrigation with rows mounded in pairs 1.8 m apart, with 3.6 m between
row pairs. Seedlings were planted into mounded rows at spacing of 3 m in separate species blocks of
six rows wide by five trees long, the equivalent of 1235 SPH (stems per hectare). Each species was
randomly allocated to plots across the four replicates. Because of low seedlings numbers, Dalbergia
latifolia and Swietenia macrophylla were only planted in two of the replicates.
The trial was kept weed-free through chemical and physical means across the life of the trial. Records
of fertiliser application were not kept and it is unknown if and when it was applied. Form pruning was
reported to have occurred when trees were 4 years old.
In 2001 Dalbergia melanoxylon blocks were removed from the trial as field staff had recognised it as
having potential to become a weed (see Randal 2002). At this time Intsia bijuga had only 6 per cent
survival and no further measurements were recorded.
Measurement
The trial was assessed in 1998 for survival and height, with the addition of DBH to assessments in
1999, 2000 and 2001. In 2008 and internal subplot of four rows of each treatment plot was assessed to
exclude edge effects and inter-specific competition. Survival, basal diameter, DBH and height were
measured. Stem straightness was assessed using a five-point scoring system, with ‘1’ being worst in
the trial and ‘5’ the best in the trial, with the aim for category frequencies to approach a normal
distribution.
Data from 2008 was analysed using a linear mixed model to estimate mean growth parameters where
replicate and species were fixed effects and plot a random effect. Raw data from the early measure in
2001 was not available, and results calculated previously by department researchers were presented
here.
Results
Both species of Khaya had very high survival at 12 years of age and Dalbergia latifolia, Swietenia
macrophylla and Cedrela odorata also had strong survival (Figure 5.1). Intsia bijuga had no surviving
trees after 12 years and poor survival was experienced by Toona australis. All species except Intsia
bijuga and Dalbergia melanoxylon, which was removed from the trial in 2001, had moderate to strong
survival at 5 years of age. Dalbergia cochinchinensis and Toona australis were the only species to
display a marked decline in survival from 5 to 12 years of age.
83
120.0
120.0
100.0
Survival (%)
100.0
80.0
80.0
60.0
60.0
40.0
40.0
20.0
20.0
0.0
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
0.0
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
1
2
3
4
5
6
7
10
11
8
9
Figure 5.1 Tree survival (%) for high-value timber species in Trial 12 from 1998 to 2008
(Dalbergia melanoxylon (1), Dalbergia cochinchinensis (2), Dalbergia latifolia (3),
Swietenia macrophylla (4), Khaya senegalensis (5), Khaya anthotheca (6), Cedrela
odorata (7), Toona australis (8), Intsia bijuga (9), Castanospermum australe (10), and
Swietenia mahogani (11))
The height after 2 years was relatively constant between six species that were around 200 cm tall
(Figure 5.2a). The main exceptions were Khaya senegalensis, which was 126 cm taller than the
nearest species, and Intsia which was 48 cm shorter than the next closest species. Within the first 5
years there was considerable variation in height growth rates and rank height between and within
species, for example Khaya anthotheca was ranked fourth at 1 year old and shifted to first at 5 years
and Toona australis went from eighth after 1 year to fifth at 5 years. However, after 12 years the
rankings for height reflect those at 5 years, with only Swietenia macrophylla and Khaya anthotheca
switching rank from third to first, and first to third respectively.
The ranking for mean DBH over the first 5 years was relatively constant compared to ranks for mean
height (Figure 5.2b). However, the rank in DBH at12 years generally did not reflect those at 5 years as
was the case for height ranks, with the exception of three species, Khaya senegalensis, K. anthotheca
and Swietenia macrophylla.
84
Height (cm)
1500
1500
1250
1250
1000
1000
750
750
500
500
250
250
0
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
DBH (cm)
a
b
1
2
3
4
0
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
6
7
8
9
10
11
5
25
25
20
20
15
15
10
10
5
5
0
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
0
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
1
2
3
4
6
10
5
7
11
8
9
Figure 5.2 Height (a) and DBH (b) for high-value timber species in Trial 12 from 1998 to 2008
(Dalbergia melanoxylon (1), Dalbergia cochinchinensis (2), Dalbergia latifolia (3),
Swietenia macrophylla (4), Khaya senegalensis (5), Khaya anthotheca (6), Cedrela
odorata (7), Toona australis (8), Intsia bijuga (9), Castanospermum australe (10), and
Swietenia mahogani (11))
The estimated stem volume per hectare (Figure 5.3A) combined survival with mean height and DBH,
and therefore was an indicator of total productivity of each species at the trial site. The rank estimated
that volume of each species was relatively consistent across all assessment years, and the performance
at 5 years was strongly reflected in the yield at 12 years. Toona australis was the only species that
declined in productivity between 5 and 12 years of age, because its high mortality over this period
outweighed growth. Swietenia macrophylla and Khaya senegalensis displayed noticeably higher
productivity at 12 years with an estimated stem volume of 166 and 161 m3 per hectare respectively,
which was around 60 m3 per hectare higher than the closest moderately productive species Khaya
anthotheca and Cedrela odorata.
The mean annual increment between age 1 year to age 5 years was greater than that for the period
between 5 years to 12 years for Dalbergia cochinchinensis, Dalbergia latifolia, Swietenia
macrophylla, Castanospermum australe and Swietenia mahogani, indicating that these species had
lower growth rates during the initial establishment phase compared to that experienced once they were
established (Figure 5.3B). The remaining species displayed the reverse of this trend where growth was
more rapid in the first years after establishment than in later years.
85
Est. stem volume ha-1 (m3)
180
180
160
160
140
140
120
120
100
100
80
80
60
60
40
40
20
20
0
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
MAI ESV ha-1 (m3)
A
B
1
2
3
4
0
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
6
5
7
10
8
11
16
16
14
14
12
12
10
10
8
8
6
6
4
4
2
2
0
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
0
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
2
3
4
6
5
7
8
10
11
3
Figure 5.3 (A) Survival-adjusted estimated stem volume per hectare (m ), and (B) mean annual
increment for estimated stem volume of high-value timber species in Trial 12
between 1998 and 2008 (Dalbergia melanoxylon (1), Dalbergia cochinchinensis (2),
Dalbergia latifolia (3), Swietenia macrophylla (4), Khaya senegalensis (5), Khaya
anthotheca (6), Cedrela odorata (7), Toona australis (8), Castanospermum australe (10),
and Swietenia mahogani (11))
Estimated means for growth parameters and stem straightness scores varied with species at age 12
years (Table 5.3). Estimates for all parameters were significantly different (P<0.001) between species.
Khaya senegalensis and Swietenia macrophylla had the largest basal diameter, DBH and height. Bole
height was greatest for Khaya anthotheca followed by K. senegalensis, indicating that these species
may have superior form compared to the other species for sawn timber production. There was no
outstanding mean stem straightness displayed by any of the species and mean scores were low, to at
best, moderate. Dalbergia cochinchinensis and Castanospermum australe had particularly poor mean
scores which reflected the 70 and 77 per cent of individual trees which scored 1 and 2 for these
species respectively. The species with highest proportion of scores above 4 were Cedrela odorata and
Swietenia macrophylla with 35 and 31 per cent respectively. These species would display greater
improvements in stand stem straightness and form if selective thinning was employed compared to the
next best species, Toona australis (19 per cent).
86
Table 5.3 Estimated parameters assessed for the nine high-value timber species surviving after
12 years (2008) in Trial 12 (means ± error of estimate)
Basal diameter
(cm)
DBH
(cm)
Bole height
(m)
Tree height
(m)
Straight score
Dalbergia
cochinchinensis
22.0 ± 1.4
18.0 ± 1.2
1.9 ± 0.4
9.5 ± 0.6
1.9 ± 1.1
Dalbergia latifolia
25.2 ± 3.4
18.5 ± 2.9
1.4 ± 0.8
9.4 ± 1.3
2.14± 1.2
Swietenia macrophylla
27.2 ± 4.0
20.1 ± 3.4
2.1 ± 1.0
14.2 ± 1.5
2.5 ± 1.2
Khaya senegalensis
27.2 ± 3.0
22.0 ± 2.5
3.1 ± 0.7
11.5 ± 1.1
2.3 ± 1.2
Khaya anthotheca
23.5 ± 3.0
17.0 ± 2.6
5.0 ± 0.7
11.2 ± 1.1
2.4 ± 1.2
Cedrela odorata
24.7 ± 3.0
18.5 ± 2.6
2.9 ± 0.7
10.2 ± 1.1
2.7 ± 1.2
Toona australis
21.0 ± 3.6
17.6 ± 3.0
2.1 ± 0.8
7.3 ± 1.3
2.2 ± 1.2
Castanospermum
australe
15.9 ± 3.3
11.4 ± 2.8
2.1 ± 0.8
8.2 ± 1.2
2.0 ± 1.2
Swietenia mahogani
17.4 ± 3.1
13.7 ± 2.7
1.6 ± 0.7
8.1 ± 1.1
2.2 ± 1.1
Species
Discussion
The survival and growth results provide a comparative guide of the potential of these species to
establish and grow in flood-irrigated plantations in the ORIA. The species were grouped, based on
their performance, into poor (Dalbergia cochinchinensis, Intsia bijuga, and Swietenia mahogani),
moderate (Dalbergia latifolia, Khaya anthotheca, Cedrela odorata, Toona australis and
Castanospermum australe), and good (Swietenia macrophylla and Khaya senegalensis) performers.
There were no records of the seed source used for each species and like most other timber plantings at
the Frank Wise Institute it was likely that the seed was sourced from bulk lots of unimproved seed
available commercially at the time. Therefore the growth performance may not necessarily be
representative of the full potential of the species, especially considering the generally widespread
geographical distributions of the species tested and the potential for improvement through selection
and matching of superior genotypes to the site. For example, highly significant differences in mean
diameters and height were found for Swietenia macrophylla in three trials in Costa Rica, where at one
site the smallest family had only achieved approximately 62 per cent of the diameter of the largest
family at 4.5 years (Navarro and Hernández 2004). Further to this Patiño (1997) suggested that the
large differences in the morphology of leaves, fruits and wood properties between provenances of
Swietenia could point to the existence of biotypes that are adapted to a range of habitats. The selection
of specific provenances or biotypes suitable to northern Australia within the tested species would be
likely to improve growth performance.
The tree form of all species was generally poor and characterised by swept and crooked stems, low
bole break and unfavourable branching. Neither of the high performing species, Khaya senegalensis
or Swietenia macrophylla displayed ideal form traits for sawlog production; however, Swietenia did
have superior stem straightness compared to African mahogany, and also had a high enough number
of comparatively straight stems (31 per cent) for selection of superior phenotypes in a thinning
regime. Poor form is not uncommon for African mahogany as observed within trials across northern
Australia (Nikles et al. 2004; Reilly et al. 2005), however, it is not an insurmountable problem with
considerable improvements expected through the implementation of selection and breeding programs
(Nikles et al. 2004). The plantation deployment of genetic material showing favourable form
characteristics should be a priority for these fast-growing species. Among species with moderate
growth, Cedrela odorata and Khaya anthotheca displayed the most potential because of favourable
bole length and straightness, making them more suitable for sawlog production. The lack of
knowledge about application and suitability of form pruning, the use of less than optimal silviculture,
87
as well as potentially poor genetic stock, precludes rejection of any of these species based on form
traits alone.
Khaya senegalensis has gained recognition as a potential plantation species across northern Australia
through the impressive growth rates achieved across multiple trial plantings throughout the region.
The diameter mean annual increment of Khaya in this trial was low compared to other similarly aged
plots at the Frank Wise Institute (Section 5.1), however its favourable growth compared to other
species provides further evidence of its suitability as a plantation species in the ORIA. Swietenia
macrophylla, has not been tested to the same extent across northern Australia, but results of Reilly et
al. (2005) suggest moderate performance up to 5 years of age compared to African mahogany on unirrigated sites in the Northern Territory. The similar growth rates and favourable form compared with
African mahogany within this trial suggest further research may be warranted in the ORIA and
potentially across broader northern Australia, especially where irrigation is available. Swietenia
macrophylla should have good commercial potential as a plantation species, as a continued expansion
of sustainable resources is required to alleviate the decline in the natural population caused by
deforestation and exploitative logging within its natural distribution (Patiño 1997). Swietenia
plantations have largely been concentrated in Oceania (Fiji, Solomon Island) and Asian regions
(Indonesia, Phillipines and Sri Lanka) (Odoom 2001) and this could provide the opportunity to tap
into the ready-made markets established by these neighbouring countries.
Despite its poor form, Dalbergia latifolia remains a species of considerable interest as a result of its
ability to promote excellent sandalwood growth (Barbour 2008). The selection of host species that
have their own commercial value is a desirable outcome for the sandalwood industry, and one that has
not yet been widely achieved in plantations. Dalbergia latifolia is valued due to its very dense golden
brown to dark brown wood, commonly traded as Indian, or East Indian rosewood (Lemmens 2008). It
is suited to furniture and cabinetry and is widely used as a tone wood in high-end acoustic guitars and
it can demand prices similar to teak (Lemmens 2008). Dalbergia is known to have a branching habit
with short boles when grown under wide spacing (Lemmens 2008), as observed here, and the
manipulation of branching and stem straightness through silvicultural practices within sandalwood
plantations may be limited due to the required spatial arrangement of hosts to ensure maximised
sandalwood growth. It would thus be desirable to select and deploy genotypes that display a
favourable form when grown in spatial configurations commonly used in sandalwood plantations. The
commercial return from Dalbergia would be dependent on the amount of heartwood the tree is able to
produce. In this trial Dalbergia displayed moderate growth and projections could see an estimated
average breast height diameter of around 20 cm at the 15-year rotation length for sandalwood. Future
harvesting trials are required to determine whether the properties of Dalbergia wood grown in short
rotations, as part of sandalwood plantations, meet the market expectations for the species.
5.3 Growth assessment of high-value timber demonstration plots,
Trials 10, 11, 13 and 15
Methods
Trial establishment
All trials were established on land prepared for flood irrigation, with mound and tree spacing as
indicated in Table 5.4. Historical watering schedules have not been maintained for these trials;
however, they would have likely followed the regular routine of at least one application every 2
months during the dry season, reducing to an as-required basis as they aged. There was no evidence of
form pruning in Trials 10 and 11, and scarring on stems in Trials 13 and 15 suggest at least one
pruning had occurred prior to current management taking over the site in 2006. No thinning was
undertaken on these trials.
88
Measurement
Assessment of tree height, DBH and bole length in the trials occurred in 2008. In Trials 10, 11 and 15
at least two subplots, representing opposite ends of the trial, were measured except for
Castanospermum where only a single plot was possible. For Swietenia and Dalbergia plots the entire
internal block was measured.
Table 5.4 Description of high-value timber demonstration plots in Trials 10, 11 and 15
Trial
Species
Year
planted
Age
Trial spacing
(between x
within row)
SPH
Design note
10
Gmelina arborea
1993
15
3.6 x 3
926
Single species block
11
Enterolobium
cyclocarpum
1996
12
3.6 x 4
694
Alternating line planting
at 1:1 ratio with Khaya
Swietenia
mahogani
1997
11
2.7 x 3
1235
Dalbergia retusa
1997
11
2.7 x 3
1235
Pterocarpus
indicus
1999
9
3.6 x 3
926
Cedrela odorata
1999
9
3.6 x 4
927
Castanospermum
australe
1999
9
3.6 x 5
928
13
15
Demonstration plots,
single species blocks
Demonstration plots,
single species blocks
Results
Survival varied across species and Swietenia, Pterocarpus and Castanospermum displayed the poorest
survival (Table 5.5).
Enterolobium had a diameter that was 2.5 times larger than Swietenia and Dalbergia, which were just
1 year younger, and 1.7 times larger than Gmelina which was 3 years older (Table 5.5). Pterocarpus
and Castanospermum displayed growth rates that resulted in mean diameters equal to Gmelina six
years earlier. These growth rates may underestimate the potential of these species within a sawlog
regime as the trials were not thinned, and the smaller trees that would be targeted for removal, reduce
the means. For example, if Gmelina was reduced to one-third of the original stocking rate (308 SPH)
by 15 years, the mean DBH of the remaining trees in the subplots after thinning would be 25 ± 3 cm
and the estimated stem volume would be 0.210 m3 per tree.
Form of the trees was evaluated by a combination of the mean bole length (Table 5.5) and the number
of stems at breast height (Figure 5.4). Castanospermum and Gmelina displayed superior form
compared with the other species, with average bole length equal to around one-third of total tree
height, and around 80 per cent of trees had single stems at breast height. Dalbergia had the worst stem
form with a very short bole length and a high proportion of multiple stems at breast height. The other
species had comparatively moderate form with a bole length around 20 per cent of total height.
89
Table 5.5 High-value timber growth measurements in Trials 10, 11, 13 and 15. Results at the
hectare level were calculated using surviving number of stems per hectare.
Basal
area
Bole
length
Tree
height
ESV
Survival
Survival
DBH
78.3
725
18.1
±
7.5
1.3
18.7
3.1
±
0.2
10.1 ±
1.9
0.115
±
0.125
83.4
80
1111
31.2
±
8.6
2.6
85
2.0
±
4.9
-
-
-
48.3
597
12.3
±
6.1
1.1
7.1
1.2
±
0.6
6.5
±
1.9
0.038
±
0.048
22.7
85
1050
12.6
±
4.8
1.1
13.1
0.3
±
0.8
8.2
±
2.3
0.040
±
0.042
42.0
58.8
544
18.2
±
5.1
2.0
14.2
1.7
±
1.2
8.8
±
1.3
0.086
±
0.056
46.8
Cedrela odorata
79
732
14.3
±
4.6
1.6
11.8
1.0
±
0.8
5.5
±
1.1
0.034
±
0.028
24.9
Castanospermum
australe
66.7
618
18.4
±
2.9
2.0
16.4
3.3
±
1.2
11.3 ±
1.0
0.103±
0.032
63.7
Trial
Species
(%)
10
Gmelina arborea
11
Enterolobium
cyclocarpum
Swietenia
mahogani
(SPH)
13
Dalbergia retusa
Pterocarpus
indicus
15
DBH
MAI
(cm)
(cm
y-1)
2
(m
ha-1)
(m)
(m)
ESV
3
(m )
100%
80%
60%
40%
2
Cedrela
Pterocarpus
Dalbergia
Swietenia
3
Castenospernum
1
Gmelina
0%
Enterolobium
20%
Figure 5.4 Frequency (%) of high-value trees in Trials 10, 11 and 12 with one, two and three
stems at breast height
90
(m3
ha-1)
Discussion
Swietenia mahogani, Dalbergia retusa and Cedrela odorata performed poorly and did not appear
suitable to the flood-irrigated Cununurra clay. Enterolobium cyclocarpum, Pterocarpus indicus and
Castanospermum australe performed much better than these species and displayed acceptable growth
in comparison with other high-value timber species trials at the Frank Wise Institute which are shown
elsewhere in this chapter. These species have not been commonly planted for commercial or trial
purposes in Australia but the limited results available indicated growth was at least equivalent to, or
better than, those reported elsewhere. For example, Castanospermum had an average diameter of 5.7
cm and a height of 4.8 m at 6 years old in sub-tropical Queensland (Lamb and Borschmann 1998), and
up to 5.07 cm diameter in a trial series in the Northern Territory (Clark et al. 2009). In the same trial
series Pterocarpus indicus had average diameters of 11.5 to 12.3 cm at different sites when aged 5 to
6 years. These other trials did not have the benefit of irrigation. These positive comparisons indicated
that further testing to more accurately evaluate and compare the performance of fast growing species
would be justified.
Growth rates alone will not be the only consideration for the selection of species suitable for further
investigation. Enterolobium for example, produced the most promising growth rate of these species;
however, it may not be suitable as a sawlog species because of its poor form characterised by
multiple, or basket leaders occurring at crown break. In this trial Enterolobium was planted as a
nitrogen-fixing companion tree with Khaya senegalensis in an attempt to provide a facilitative effect
from increased nitrogen resources. It appeared as though this may have been successful as growth of
Khaya was better in this configuration (Trial 11) than in other trials described earlier in the Khaya
summary section (see Table 5.2).Commercial multi-species plantations have not been widely
established in Australia despite considerable research displaying the benefits of these arrangements
(Nichols et al. 2006), and as such it is not foreseeable that Enterolobium would be widely used in such
a capacity on the high-value land in the ORIA. Elsewhere it has mainly been grown to be utilised as
an amenity tree, for shade in agroforestry or as livestock fodder for which it is well-suited because of
its large spreading crown. However, its timber has also been used for veneers, cabinetry and boat
construction (Hughes and Stewart 1990). The market demand for Enterolobium timber is likely to be
limited compared to the more commercially acceptable species tested here, including Pterocarpus
indicus which is well known in the international timber trade as Narra (Thomson 2006). Low land
availability and its high cost limit further evaluation of timber species in the ORIA and so future trials
should be targeted at species with tangible market value.
The growth and form characteristics of the species assessed here will need to be supplemented by the
evaluation of the physical, mechanical and aesthetic wood properties as the trials approach a
commercial rotation age of between 20 to 25 years. In particular it is important that the aesthetic
characteristics of colour, grain and figure, which largely endow these species with commercial value
for use as craft wood, approach the standards of the wood currently traded from native or more mature
plantations.
5.4. The growth of teak (Tectona grandis) on levee soil, Trial 14
Teak, Tectona grandis L.f., is a large deciduous tree belonging to the Verbenaceae family that
naturally occurs in India, Myanmar, Laos and Thailand. Its heartwood has a fine grain, is golden in
colour and is resistant to damage by weathering termites and fungus. These qualities make it well
suited to the manufacturing of high-value timber products, such as furniture, flooring and boats
(Pandey and Brown 2000). It has been widely established in commercial plantations in areas across its
natural range as well as in tropical Asia, northern Africa, Latin America (Pandey and Brown 2000)
and more recently in northern Australia.
Teak tolerates a variety of conditions but prefers deep well-drained soils in warm moist tropical
climates with a marked dry season (Pandey and Brown 2000). An opportunity existed for the FPC
91
(then Department of Conservation and Land Management) to plant a demonstration teak trial on the
levee soils at the Frank Wise Institute. Levee soils in the Kununurra region are typically brown or red
with a fine sandy to loam texture changing to a fine sandy clay loam at depth, and they have a neutral
pH (Schoknecht and Grose 1996). This soil type was believed to be better suited for teak growth
compared to the Cununurra cracking clays. Trial 14 was established in 1998 to determine the
suitability of the Kununurra climate, and the levee soil for growing teak. The management and growth
performance of the plantation was assessed over a 10-year period.
Methods
Trial establishment
Trial 14 was established in December 1998 from tissue-cultured clones sourced from Thailand. The
pedigree and number of clonal lines were unknown. A total of 0.88 ha was established with rows
deep-ripped at 4 m apart and trees spaced at 4 m within rows, the equivalent of 625 stems per hectare
(SPH). The trial was watered by drip irrigation two to three times a week which delivered
approximately 10 ml per tree per day during the dry season and no irrigation was applied during the
wet season.
At planting an experiment was conducted to determine an effective chemical control for the termite
species Mastotermes darwiniensis. Two pesticides, Dursban containing chloropyryphos and Termidor
containing fipronil, were used and tested against a control (no treatment). Two concentrations were
used for both chemicals with 20 ml and 40 ml of Dursban per tree, and 0.4 ml and 0.8 ml Termidor
per tree. These treatments were not arranged with any experimental design within the plantation.
Since undertaking this trial the control of termites appeared to have occurred on a somewhat ad hoc
basis with the few records maintained showing that chemical application usually occurred in response
to evidence of infestation.
During the first year, an herbicide spraying program was employed to reduce weed competition. An
outbreak of the defoliation insect, Hyblaea puera, occurred approximately 6 weeks after planting and
this was treated with carbaryl. Another outbreak of H. puera occurred in 2000 with no further records
found to indicate an ongoing problem.
The first pruning was done at 4 months to remove side branching that appeared on the lower half of
the stem. Further records of pruning were not recorded up until 2006 when the trees were pruned and
the trial selectively thinned to the current stocking of 326 SPH. Selection for thinning was done to
remove small and malformed trees (see Plate 5.2).
92
Plate 5.2 The teak trial showing the variability in performance
Measurement
The trial was measured for DBH and height in 2001 and 2006. In 2008 commercial bole height and
DBH were recorded for an internal block of 18 rows by 18 positions.
Results
Growth
Survival at 3 years was 78 per cent, decreasing to 72 per cent at 8 years before thinning occurred.
There was no tree deaths post thinning at age 10 years.
The growth performance was measured and estimated for parameters at age 3, 8 and 10 years (Table
5.6). The ESV per hectare for standing trees (per hectare data for final stocking, Table 5.6) at 3 and 8
years old was 8.54 ± 0.22 m3 and 47.98 ± 1.4 m3. Estimated wood volume was compared for trees
selected and unselected for thinning at 8 years old and this indicated an improvement in ESV per
hectare of 2.079 m3 based on a final stocking of 326 SPH. This rather small improvement is testament
to the uniformity of tree growth of the clonal material used in the planting.
The MAI of DBH at the three measurements times indicated that trees were growing fastest at 3 years
of age when mean diameters increased by 3.33 ± 0.056 cm, compared with 2.22 ± 0.029 cm and 1.93
± 0.025 cm at ages 8 and 10 respectively. The mean change in DBH between individual trees at age 8
to 10 was only 0.97 ± 0.057 cm. This represents an annual increment over the 2-year period of 0.485
cm compared to the DBH MAI of 1.93 ± 0.25 cm for 10 years of growth, which suggested tree growth
was in decline.
93
Table 5.6 Growth parameters for teak aged 3, 8 and 10 years at Kununurra in Trial 14 (mean ±
s.e.)
2001
2006
2008
Parameter
3 years old
8 years old
10 years old
DBH (cm)
9.9 ± 0.1
17.8 ± 0.2
19.3 ± 0.3
Height (m)
642.3 ± 7.7
12.5 ± 0.1
-
-
-
4.7 ± 0.4
0.008± 0.0002
0.0258 ± 0.0005
0.0301 ± 0.0008
0.019± 0.0005
0.108 ± (0.003)
-
-
0.140 ± 0.0033
Bole length (cm)
2
Basal area (m )
3
ESV (m )
3
EBV (m )
2
Basal area/ha (m ha )
2.69
8.36
9.83
3
-1
6.214
35.210
-
3
-1
-
-
45.49
2.07
4.40
-
-
-
4.55
ESV/ha (m ha )
EBV/ha (m ha )
3
-1
3
-1
MAI (ESVm ha )
MAI (EBVm ha )
-1
All per hectare results are based on final stocking rate (326 SPH at 10 years).
Termite control
At 10 months of age a total of 10.26 per cent of the trial had evidence of termite infestation. The
chemical experiment (Table 5.7) indicated that Termidor (a.i. Fipronil) appeared to have been more
effective than Dursban (a.i. Chloropyryphos) in preventing termite infestation at the trial site.
However, the lack of experimental design and the potentially biased placement of treatments do not
allow for fair comparisons and definitive conclusions. For example, both of the double-rate treatments
were placed on outside rows possibly closer to the termite source and as a result they included more
infested trees than the single-rate applications of internal rows.
There did not appear to be any consistant trends in mean DBH at 3 years of age amongst the chemical
treatments. This indicated that early termite infestation reduced growth up to this age (Table 5.7).
Runts present within the treatments also influenced results. Indeed a box plot analysis indicated that
24 trees with a DBH of less than 4 cm were outliers (runts), and once removed the difference in mean
DBH between chemical treatments reduced to 0.96 cm from 1.99 cm before outlier removal (Table
5.7). The number of outliers/runts per treatment did not appear to be related to termite infestation at
an early age, for example the double-rate Dursban treatment had the highest level of infestation but
only had one outlier.
94
Table 5.7 Proportion of teak trees infected with termites assessed 10 months after planting in
Trial 14, DBH per pesticide treatment at 3 years of age and DBH with outliers/runts
removed (mean ± s.e.)
Treatment
Rows
treated
Trees infected
with termites
(%)
2001
2001
3 yr old DBH
(cm)
outlier adjusted
DBH (cm)
Number
of
outliers
Control
13 & 14
10.5
9.7 ± 0.3
10.1 ± 0.3
1
Double rate Dursban
25 & 26
25
9.3 ± 0.8
9.7 ± 0.8
1
Double rate Termidor
1&2
9.5
9.9 ± 0.3
9.7 ± 0.3
6
Dursban
15 to 24
11.7
8.4 ± 0.5
10.3 ± 0.2
11
Termidor
3 to 12
5.9
10.4 ± 0.2
10.6 ± 0.1
5
Discussion
Growth results for teak in Trial 14 were probably an indication of not more than moderately good
growth potential for similar sites in the region because of the ad hoc management of the trial,
including pruning, termite control and a late thinning. A more controlled silvicultural regime would
have produced better results. For example, observations of the early occurrence and rapid growth of
lateral branches, which required the first pruning at 4 months, indicated that the planting density used
was less than ideal. Whilst teak has been successfully grown in planting designs ranging from 1.8 m x
1.8 m to 4m x 4m (Kaosa-ard 1998), it was possible the spacing used here promoted early lateral
branching and potentially reduced growth by diverting resources away from the main stem
(Krishnapillay 2000). In addition to this, the lack of early thinning was likely to have negatively
impacted growth rates through increased competition. Teak is commonly planted at a higher density
of around 1111 SPH and is thinned twice within the first 10 to 12 years, firstly when the trees are
between 8 to 9 m tall (3–4 years) and secondly once trees reach 15 to18 m (Kaosa-ard 1998;
Krishnapillay 2000). However, extra establishment and management costs would need to be factored
in if employing such a system.
With no other teak trials or plantations in the Kununurra region, the closest data of comparable age
comes from the Northern Territory where Robertson and Reilly (2005) compared the growth of teak
plantations across different sites and various management regimes. The conditions most similar to
those in Kununnura were at Katherine where the trial was drip irrigated and planted on river levee
soils. At the Katherine site at 2.5 years, trees had a diameter of 4.5 cm and height of 4.7 m increasing
to 9.9 cm and 8.2 m respectively at 4.5 years. These figures are somewhat lower than the growth
experienced in this trial where mean DBH reached 9.9 cm at 3 years. On a broader scale the results
seemed to fall within the expected early growth rates seen in countries such as Malaysia
(Krishnapillay 2000).
Although comprehensive records have not been kept on termites, it did appear that the occurrence and
severity of termite infestation reduced as the trial aged. Robertson and Reilly (2005) also suggest in
the Northern Territory that termites only appear be a problem during the early growth of teak to
around 5 years of age. However, the last appearance of termites within this trial was at age 9, and
therefore chemical treatment was still periodically required. Whilst early growth rates did not appear
to be adversely impacted by termites, the full effect will not be known until harvest where damage to
heartwood can be assessed. Observations during thinning at 8 years suggested it was likely at least a
moderate proportion trees will have some heartwood damage.
95
5.5 Growth, seed yield and oil characteristics of Millettia pinnata,
Trial 16
Methods
Millettia pinnata (syn Pongamia pinnata) is a medium-sized leguminous tree found naturally in India,
across tropical south-east Asia and into the Pacific including northern Australia (Scott et al. 2008). It
was introduced into cultivation at Kununurra as an experimental host for sandalwood, where it
successfully promoted early growth of the parasite (Barbour 2008). In addition, the oil derived from
Millettia seed is well recognised for its potential use in biodiesel production (Scott et al. 2008), and it
may provide an opportunity for a stand-alone plantation industry and a diversified revenue stream for
sandalwood growers. Whist Millettia pinnata seed oil is broadly been recognised as suitable for
biodiesel production, the viability of the undertaking will largely depend upon oil quality and seed
yield of the genetic resources used in a given environment. Within this section Millettia growth, and
seed and oil yield within the FPC plantation collection are assessed to aid in determining the
suitability of the current Millettia pinnata genetic resource and silviculture practices for seed and oil
production.
Trial establishment
Millettia pinnata seedlings were established in 1999 in mounded Cunnurra clay prepared for flood
irrigation. Trees were spaced at approximately 3 m within each row and 5.4 m between rows, a
stocking of 617 stems per hectare across 0.3 ha. Trees were measured in October 2008, where
diameter at breast height was recorded for up to five stems, and total tree height was measured. Where
seed was present it was hand collected and weighed. Bee hives were introduced at the trial site in
January 2009 and seed was collected from a random sample of 20 trees in October 2009.
Plate 5.3 The Millettia pinnata plot at the time the seed harvesting was completed for this report
Measurement and collection
Mature seed pods were hand collected (Plate 5.3) from 109 mature Millettia trees that had set seed
within the FPC Trials 4, 7 and 16 (see Appendix A for trial details) at the Frank Wise Institute in
October 2008. Seeds were extracted from the pods and the physical parameters of length, breadth,
96
thickness, and average weight of 100 seed were measured. Trees in Trial 4 were 14 years at seed
collection, with Millettia established in a mixed-species arboretum planting with low density
sandalwood. At collection trees in Trial 7 were 9 years old and were established with sandalwood at a
host-to-sandalwood ratio of 1:1.
Seeds were dried and ground before oil was extracted in n-hexane using the methods of Kesari et al.
(2008) and results were expressed as the proportion of oil per dry weight of seed. The fatty acid
composition of seeds from a sample of 23 trees selected from across the range of oil content was
analysed using a gas chromatograph fitted with flame ionization detector following a method adapted
from Mukta et al. (2009).
Results
Survival of Millettia was approximately 70 per cent at 9 years in Trial 16. The mean DBH was 22.1 ±
6.7 cm with a range between 5.3 to 39.4 cm. Tree height averaged 9.8 ± 2.3 m and ranged between 3.9
to 15.2 m. The average number of stems at breast height was 2.4 and 12 per cent of trees had a single
stem, 42 per cent had two stems, 36 per cent had three stems and 9 per cent had four or more stems.
Seed was produced by 37 per cent of trees in Trial 16 (44 of 133), 26 per cent in Trial 7 (58 of 220)
and 83 per cent (10 of 12) in Trial 4. The mean weight of seed pods collected in 2008 from Trial 16
(age 9 years) was 1015 ± 1050 g per tree, 812 ± 242 g for Trial 7 (age 9 years) and 8012 ± 3372 g for
Trial 4 (age 14 years). Seed comprised 40 per cent of the total fresh weight of pod and seed, which
equated to a pure weight of approximately 406 g per tree, or 312 seeds (based on weight in Table 5.8)
for Trial 16. In 2009 with the presence of bee hives, the total weight of the 20 tree sample was 248 kg,
an average of 12443 ± 23872 g per tree. This was greater than a 10 fold increase in average yield per
tree, with an approximate pure seed weight of 4977 g per tree. The highest total pod-on weight for an
individual tree was 5 kg in 2008 and 91 kg in 2009, approximately 2 kg and 36 kg of pure seed
respectively.
Physical seed traits from 109 trees were assessed from across the FPC trials (Table 5.8). Oil content of
seed averaged 37.5 ± 2.8 per cent of dry weight, and ranged from 31 to 45 per cent between trees.
There was little variation in the physical traits of seeds across trials, culminating in mean 100 seed
weight of 146 ± 18 g, 129± 27 g and 130 ± 28 g for Trials 4, 7 and 16 respectively. Similarly there
was little variation in oil content of seed between trials with means of 40 ± 2 per cent, 38 ± 3 per cent
and 37 ± 3 per cent for Trials 4, 7 and 16 respectively.
There were significant positive correlations between physical seed variables and the mean weight of
100 seeds (Table 5.9). However, increased seed size was not correlated to an increase in the
proportion of oil content.
Table 5.8 Seed traits of Millettia pinnata (n = 109, mean ± s.d.)
Seed trait
Minimum
Maximum
Mean
Length (mm)
18.2
25.6
22.0 ± 1.6
Breadth (mm)
12.5
18.4
15.1 ± 1.3
Thickness (mm)
4.4
8.2
6.7 ± 0.8
100 seed weight (g)
66.7
184.6
130.5 ± 27.2
Oil content (%)
31.0
45.0
37.5 ± 2.8
97
Table 5.9 Correlations between measured seed variables of Millettia pinnata (n = 109)
Seed
length
Seed
breadth
Seed
thickness
100 seed
weight
Oil
content
Seed length
1
0.343
0.491
0.603
0.125
see breadth
<0.001
1
0.315
0.584
0.158
seed thickness
<0.001
0.001
1
0.744
0.234
100 seed wt
<0.001
<0.001
<0.001
1
0.086
Oil content
0.195
0.101
0.014
0.375
1
Variable
Note: correlations above the diagonal, p value of Pearson correlation at α = 0.05 below the diagonal.
Gas chromatography indicated the presence of nine fatty acids from the seed samples. More than half
(53 per cent) of the fatty acid component was oleic (a C18:1 compound), followed by linoleic (C18:2)
at 16 per cent, palmitic (C16:0) at 10 per cent, stearic (C18:0) at 6 per cent, and very small
proportions of linolenic, arachidic, behenic, lignoceric, and 11-eicosanoic (Table 5.10).
Table 5.10 Composition of fatty acids within oil derived from seed of Millettia pinnata (n = 23,
mean ± s.d.)
Minimum
(%)
Maximum
(%)
Mean
(%)
Palmitic
8.7
11.3
10.1 ± 0.1
Stearic
4.9
8.0
6.3 ± 0.7
Fatty acid
Oleic
50.1
56.7
53.9 ± 1.9
Linoleic
12.3
18.4
15.8 ± 1.6
Linolenic
2.1
4.4
2.7 ± 0.6
Arachidic
1.3
2.1
1.5 ± 0.2
Discussion
Millettia pinnata grew faster in monocultures than as a host for sandalwood. At 9 years of age
Millettia growing in a pure stand at a density of 617 stems per hectare had an average diameter at
breast height of 22 cm. This diameter is greater than the 14.5 cm reported by Barbour (2008) for 9year-old Millettia planted at 462 stems per hectare in a mixed stand with sandalwood (926 SPH total)
(Trial 7). Considering the two trials shared similar environments (separated by 200 m) and were from
the same genetic source, the disparity in growth suggests that sandalwood has some detrimental effect
on the growth of Millettia. The parasitic nature of sandalwood did not greatly influence seed size
characteristics, oil content or seed yield. The pure stand of Millettia had marginally larger seed and
higher yield, but they had slightly lower oil content, than those growing with sandalwood.
Fatty acid composition is important in determining the suitability of oils derived from seed for
biodiesel production, influencing cetane number (ignition quality), viscosity, cloud point and coldfilter plugging point, which are important considerations for storage and use (Knothe 2008). The
composition of oil seed from Kununurra conforms to the ranges of major fatty acids suggested by
Scott et al. (2008) for Millettia; palmitic (5–15 per cent), stearic (5–10 per cent), oleic (40–55 per
cent) and linoleic (15–20 per cent), with smaller amounts of linolenic and arachidic acid (Arpiwi et al.
2011). Some of the large seed had high oil content with more than half the fatty acid as oleic acid.
Hence the FPC genetic resource and the Kununurra growing environment appeared suitable for
producing oil seed with the same qualities that have seen Millettia seed recognised as a candidate for
biodiesel feedstock, and selection of superior lines is possible within the Kununurra collection.
98
Given the suitability of the oil composition and relative consistency of oil yield from seeds between
trees and across trials seen here, the viability of commercial biodiesel production would largely
depend upon seed yield. Seed yield within and between the three trials was highly variable, and the
older 14-year-old trees (Trial 4) had a substantially higher average yield compared to the two 9-yearold trials. There is little information available regarding Millettia seed yield and patterns of
production. In Kununurra, bee hives enhanced average yield in 2009 to around 5 kg of pure seed per
tree, but this was still substantially lower than the agronomic estimates made by Scott et al. (2008)
that equate to annual production of 36 kg per tree. The presence of bee hives improved seed
production, but only a few individual trees produced a substantial amount of seed. Monitoring of
annual seed production patterns in the future would allow for the selection of fecund individuals that
could provide the basis of a deployment population aimed at decreasing variability and improving
yield at the plantation level.
99
6
Implications
6.1
Sandalwood trials
Sandalwood host selection demonstration plots
•
Cassia siamea, Khaya senegalensis, Peltophorum pterocarpum and Swietenia mahogani were not
suitable hosts for sandalwood, producing poor growth and survival rates when planted in multi or
single-host environments. Without knowledge of the physiological limitation of these host
species, the development of large canopy structures appears to be the primary limiting factor of
these species as successful hosts for sandalwood in the planting configurations used here. The
broad and dense canopies that were evident with these hosts in the trials were thought to create an
environment in which the shade tolerance of sandalwood was exceeded, thus suppressing growth
and increasing mortality. Other species such as Bauhinia cunninghamii and Acacia anuera were
not successful hosts but their growth habit is not thought to be limiting.
•
At 17 years and 18 years sandalwood established in trial plantations at an initial stocking of 462
stems per hectare had a mean annual basal diameter increment of between 1.1 and 1.4 at age 17
and 18 when grown with Cathormion umbellatum. Sandalwood survival at this age was between
30 and 56 per cent, equivalent to 140 and 259 stems per hectare respectively.
Sandalwood growth with Cathormion umbellatum
•
Because of it historical use and consistent performance as a host, it is proposed that Cathormion
umbellatum be used as a benchmark species against which sandalwood growth comparisons can
be made. At 15 years old, a plantation with sandalwood and host planted at a 1:1 ratio, 462 stems
of each, could be expected to produce sandalwood with an average basal diameter between 19 and
22 cm and a height of 6 to 6.5 m.
•
Sandalwood size was considerably affected by stocking density when planted with Cathormion
hosts at 9 years old, where there was a trend of increased average sandalwood size with declining
density. For example, those established at 231 stems per hectare had stem volumes that were 1.6
times greater than those established at 617 stems. Plantation yield (stem volume) did however
generally increase with higher density, where higher stocking rates outweighed the benefits of the
larger average individual trees in lower density plantings. The commercial implications of various
stocking rates will be depend not only on final wood yields but also on balancing the costs of
establishment, management, harvesting and post-harvest processing, including de-barking and desapping between a lower number of larger sandalwood compared to a higher number of smaller
sandalwood. The impact of stocking on heartwood development and yield has not been assessed
and monitoring this should be considered in the future.
Investigation of spatial competition analysis
•
This report contains the first documented attempt to utilise spatial competition indices in
sandalwood plantations. Two different methods have be utilised, one in a trial with no formal
design and the other as a supplement to more common analysis of a randomised complete block
design. There are certainly limitations in the interpretation of the results; however, as a
preliminary investigation of competition indices it has provided evidence that considerable scope
exists to improve the understanding of sandalwood-host interactions in plantations. Improvements
to the method are also possible as there is large number of alternative competition indices and
neighbourhood calculations cited in the literature, as well as using different tree parameters as
indicators of competition.
100
•
The use of spatial competition indices has shown there is differentiation in the competitive nature
of host species and their effect on sandalwood growth. The more common approach to trial
analysis generally indicates a hierarchical result of effectiveness, that is, host species are good,
average or poor. Despite some limitation the spatial competition analysis provided some evidence
as to why the host performed in a particular way and in doing so offered insight in potential
improvements in utilising the hosts. For instance, there were general trends of decreasing
sandalwood growth where the relative size of Cathormion and Mellettia hosts increase, but the
same did not occur in relation to the number of hosts. This indicates that retaining host number
but altering host size, for example by canopy pruning, may improve host effectiveness.
Sandalwood heartwood and oil development
•
Destructive harvesting showed that heartwood occurred in 8-year-old sandalwood, however, the
amount and longitudinal development was generally low and variable between trees. At 15 years
heartwood was present at least at the base of all 40 trees sampled and had improved to an average
of 30 per cent of basal area compared to 11 per cent at age 8 years. There was also considerably
more consistent longitudinal development of heartwood along the stem with heartwood still being
observed in several trees at greater than 3.5 m along the stem, where at 8 years heartwood was not
found over 1.8 m. The heartwood volume at 15 years was estimated to be on average around 1.6 L
in the root stump, 4.9 L in the bole and 0.3 L in the canopy stem, or approximately 18 per cent of
total stem volume.
•
The oil yield typically increased with distance along the stem with the highest proportion being an
average of greater than 6 per cent in the root stump and lower bole. Oil quantity further along the
stem was still reasonably good with an average yield of 3.4 per cent recorded for trees with
heartwood at crown break. The average proportion of alpha and beta-santalol within the oil
indicates a high quality product meeting the criteria of the ISO standard for Santalum album oil
(ISO 3518:300E). The oil composition varied only slightly at sample sites along the stem with the
average total santalol levels ranging from 68 to 72 per cent, suggesting that wood products would
not need to be separated before distillation to retain a quality product.
•
Average estimated stem oil yield per tree was 307 grams at 15 years old, but as would be expected
the oil yields were similar to heartwood volume in that they were highly variable between trees,
with a low of 18 grams and a high of around 780 grams. The lower-third portion of the bole
accounted for some 50 per cent of total average estimated oil yield compared to 28 per cent in the
root stump. Given that oil quality is stable across the tree the lower-third of the bole would be of
higher commercial value than the root stump section which would contribute a larger proportion
of total harvesting and processing costs.
•
Heartwood was present in 78 per cent of sandalwood core sampled at 11 years old, where only
one of 15 sandalwood sampled with Dalbergia latifolia did not have heartwood compared to four
and five for Cathormion umbellatum and Millettia pinnata respectively. The amount and
proportion of heartwood was not significantly different between sandalwood with the three host
species. However, if the differences in heartwood occurrence and yield held true at the plantation
scale there would be substantial differences in the number of sandalwood containing heartwood
and the total yield with different host species. Further research is required to confirm these initial
findings and also to investigate the causes, whether environmental or physiological, of the
variation in heartwood formation and yield with different host species.
6.2
•
High-value timber trials
With the high growth rates observed in the ORIA, a small African mahogany plantation industry
has emerged in the region. This current project has confirmed the superior growth rates, but has
also reinforced the poor form characteristics that have been expressed in trials across northern
101
Australia. To aid the development of the industry, additional research is required to identify and
deploy genotypes that exhibit superior form. An immediate response of plantation managers
should be to deploy material, by seed or clonally, from trees displaying a superior phenotype.
•
Indian rosewood, Dalbergia latifolia, is the only species valued for its timber product that has
proved successful as a host for sandalwood. Its current uptake as a host species in plantations is
increasing and thus could provide an option for income diversification. There is a need to
investigate whether the Indian rosewood grown in short rotation is able to produce wood with
physical and appearance qualities that make it desired, particularly as a tone wood for guitars and
other stringed instruments.
•
Because of the limited availability and high cost of land any future timber research trials should
consider only those species with potential to produce high-value products with well-established
markets. Trials of such species should aim to evaluate the growth and form characteristics of
several provenances from ‘best bet’ sources based on matching soils and climate data. The genetic
base of species tested to date has been narrow and used generic seed which has limited the ability
to identify their potential.
•
One of the deficiencies in the timber trials reported on here is the lack of applied silviculture,
management and record keeping. In future, trials should follow a prescribed silviculture regime
throughout the rotation as to better reflect the potential growth and yield that would occur in a
commercially managed plantation. As part of this, records must be kept of actions such as
fertilising, pruning, thinning and irrigation so that there can be a more accurate evaluation of both
system and tree performance.
•
The oil quality and quantity of Millettia pinnata seed at Kununurra is within the range reported to
have identified the species a candidate feedstock for biodiesel production. However, seed
production appears to be a major limiting factor with the highest pure seed yield per tree at only
approximately 36 kg. There was also considerable variation in production between trees, and
whilst the presence of bee hives improved seed production only a few individual trees produced a
substantial amount of seed.
102
7
Recommendations
RIRDC supported this project so that 16 silviculture trials could be measured and reported on that
were grown in the ORIS in the north of Western Australia with flood irrigation.
The first outcome was the discovery of the heartwood rot within Santalum album at the Frank Wise
Institute. The first recommendation to RIRDC was to further investigate the heartwood rot and this
culminated in RIRDC report Heartwood Rot Identification and Impact in Sandalwood (Santalum
album) (Barbour et al. 2010).
This project additionally recommends that:
•
Time-course studies of different planting designs is undertaken to quantify changing spatial
relationships between hosts and sandalwood so that silviculture recommendations over the full 15year rotation can be made.
•
The exploration of new secondary hosts is continued. The concept of a hedge of Millettia pinnata
or the inter-row integration of horticulture and agriculture needs further exploration.
•
Studies are undertaken to understand heartwood formation as this is a key to regulating its
production within the bole of the tree and the amount of final product produced.
•
A selection program (using new technologies that correlate to wood quality) is initiated for the
development of a timber product from African mahogany, teak and Dalbergia. The latter species
also requires a review of current germplasm in relation to its natural distribution and current
nursery techniques.
•
Mechanical systems are developed for the selective harvest of sandalwood, the removal of the
clay, and the separation of heartwood and sapwood.
•
The possibility of products from the remaining biomass at harvest is explored.
•
A method for non-destructive assessment of heartwood and heartwood rot would be extremely
useful in tree selection and thus optimisation of tree value. The first assessment of acoustic timeof-flight measurement and electrical impendance techniques did not give clear answers but there
are many other permutations of these that still need to be explored.
103
Appendix A
A summary of sandalwood and high-value timber trial plantings assessed during the project. (LH = long-term host, IH = intermediate host, HVT = high-value
timber)
Sandalwood plantings
104
No.
Year
Species
Design
Original aim
Notes
1
1990
S. album & LH Cathormion umbellatum & IH
Acacia ampliceps
No statistical design
Demonstration plot
2
1991
S. album & LH Cathormion umbellatum,
Bauhinia cunninghamii, Acacia aneura
Randomised LH species
blocks with 7 replicates
Evaluate S. album
growth with three LH
3
1993
S. album & LH Cassia siamea, Peltophorum sp.
& IH Acacia trachycarpa, Sesbania formosa
No statistical design,
separate LH blocks
Demonstration plot
with HVT host
4
1994
S. album & LH Acacia mangium, Cassia
siamea, Peltophorum sp. & IH various
Blocks of a single LH with
unknown randomised IH
treatments
Comparison of LH
and IH effect on S.
album
5
1997
S. album & LH Cathormion umbellatum,
Cassua siamea, Swietenia mahogani, Khaya
senegalensis
No statistical design.
Mixed host design
Demonstration plot of
sandalwood with
mixed HVT hosts
6
1999
S. album & LH Cathormion umbellatum & IH
Acacia trachycarpa, Sesbania formosa
Six stocking and parasite
host ratios. No
randomisation or
replication
Evaluate S. album
growth in different
host environments
Trial was analysed using a pseudo-replicate
structure.
7
1999
S. album & LH Cathormion umbellatum,
Cedrela odorata, Dalbergia latifolia, Khaya
senegalensis, Melletia pinnata, Pterocarpus
indicus & IH Acacia trachycarpa
Randomised LH species
blocks with 5 replicates
Evaluate S. album
growth with three LH
Trial previously reported in RIRDC publication
No.08/138 (Barbour 2008).
Original design redundant as result of poor
survival. Host infill with Millettia has occurred at
various stages
Original design redundant as result of poor early
survival. Irrigation ceased in 2003. Trial used for
destructive harvest.
8
2000
9
2001
S. album & LH Castenospernum australe,
Cathormion umbellatum, Dalbergia retusa,
Sweitenia humilis, Tectona grandis & IH
Sesbania formosa
Randomised LH species
blocks with 7 replicates
Evaluate S. album
growth with several
LH species
Herbicide use in early development caused many
deaths. Design redundant, trial used for
destructive harvest.
S. album & LH Cathormion umbellatum & IH
Sesbania formosa
6 host-to-parasite ratio
treatments randomised
with 6 replicates
Identify host ratio to
optimise S. album
growth
Overcrowding was identified in 2003 and 3 rows
per block were removed. Three treatments no
exist, all host, all parasite, 1:1 ratio.
High-value timber plantings (HVT)
105
No.
Year
Species
Design
Original aim
Notes
10
1993
Gmelina arborea
No statistical design.
Single species block plot
Demonstration plot
No silvicultural treatments.
11
1994
Khaya senegalensis and Enterolobium
cyclocarpum
No statistical design.
Mixed species plot at 1:1
ratio within rows
Demonstration plot
No silvicultural treatments.
Dalbergia cochinchinensis, Dalbergia latifolia,
Swietenia macrophylla, Khaya senegalensis,
Khaya anthotheca, Cedrela odorata, Toona
australis, Castnospermum australe, Swietenia
mahogani
Single species randomised
block plots with 4
replicates
Comparison of HVT
timber growth in
cracking clay soil
Dalbergia melanolxylon was established but later
removed as it posed a weed threat.
12
1996
Trees pruned at 4 years old.
13
1997
Khaya senegalensis, Swietenia mahogani,
Dalbergia retusa
No statistical design.
Single species block plots
Demonstration plot
for HVT selection
Dalbergia melanolxylon was established but later
removed as it posed weed threat.
14
1998
Tectona grandis
No statistical design.
Single species block plots
Demonstration
planting on levee soil
Pruned at 4 months and again at 8 years before
thinning.
15
1999
Castnospermum australe, Cedrela odorata,
Pterocarpus indicus & K. senegalensis.
No statistical design.
Single species block plots
Demonstration plot
displaying HVT
species growth
No silvicultural treatments.
16
1999
Melletia pinnata (pongamia)
No statistical design.
Single species block plots
Demonstration plot
and seed collection
area
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111
Flood-irrigated Tropical Timber
Trials in the North of Western
Australia
by L. Barbour, J. Plummer and L. Norris
Pub. No. 12/044
This report records a joint project between the Rural
Industries Research and Development Corporation, the Forest
Products Commission of Western Australia, Elders Forestry
and the University of Western Australia to ensure that 16 of
the original plantation trials and plantings of tropical species
established in the Ord River Irrigation Scheme (ORIS) by
the Western Australian Government were assessed and
published.
The main target groups of this research are researchers
and managers, especially within the Western Australian
Government system, non-governmental organisations
and commercial and private companies actively growing
sandalwood in the ORIS. The included information on growth
rates and essential oil production will be of interest to
investors and consultants.
RIRDC is a partnership between government and industry
to invest in R&D for more productive and sustainable rural
industries. We invest in new and emerging rural industries, a
suite of established rural industries and national rural issues.
Most of the information we produce can be downloaded for
free or purchased from our website <www.rirdc.gov.au>.
RIRDC books can also be purchased by phoning
1300 634 313 for a local call fee.
Phone: 02 6271 4100
Fax: 02 6271 4199
Bookshop: 1300 634 313
Email: [email protected]
Postal Address:PO Box 4776,
Kingston ACT 2604
Street Address:Level 2, 15 National Circuit,
Barton ACT 2600
www.rirdc.gov.au
Plate 4.3 Typical 8-year-old tree from this trial
Destructive harvest
At 8 years of age, 30 trees with clear boles were selected for harvesting and were pulled out by their
roots (see Plates 4.3 and 4.4). The trees were laid on the ground and measured for height, basal
diameter, breast height diameter, crown break diameter and bole length. Trees were then sectioned
into roots, bole and crown and each section weighed. Discs were then cut from the bole section at the
base, lower third, upper third and top, and green weight recorded. After air-drying for 8 weeks a dry
weight was obtained. Image analysis of disc photographs with Image J (NIH, USA) was used to
determine under-bark disc area, heartwood area, and area of wood rot for manually outlined areas on
each disc. Whilst wood rot data is presented here, a more comprehensive analysis of rot, including
fungal isolation and identification, was undertaken within a separate RIRDC project (Barbour et al.
2010).
Plate 4.4 A sample of the 8-year-old wood assessed after the destructive harvest
Simple and multiple linear regressions were used to determine relationships between measured
variables (XLStat, 2006). For multiple regression, model selection was determined by comparing the
56
Plate 4.5 The plot combining sandalwood with the long-term host Dalbergia
Measurement and core sampling
Prior to coring, basal diameter, diameter at breast height, diameter at crown break and bole length of
the sandalwood were measured. Sandalwood were cored at 30 cm above ground level using a 0.5 cm
diameter hand-increment corer. Cores were extracted in an east to west orientation (along row)
through the centre of the tree and a polymer sealant was used to cap the core hole. Cores were gently
sanded on one side to allow for a clear distinction between sapwood and heartwood, which was
defined as a yellow to brown discolouration possessing a typical sandalwood aroma. Total core and
heartwood length (diameters) were measured and the hypothetical cross-sectional areas and heartwood
percentage were calculated.
Whole-increment cores were air dried, ground with a coffee grinder and then weighed to four decimal
places. Oil was extracted from samples into ethanol for 7–14 days with isobutyl benzene as an internal
standard (12 mM). A standard curve was constructed using oil from S. album (Sigma Aldrich) to
estimate total oil content in each sample. The chemical composition was determined by gas
chromatography with flame ionization detection (GC-FID) using a Shimadzu GC-17 A instrument
equipped with a DB-WAX column (Alltech, 30 m, 0.25 mm inside diameter, 0.25 µm film thickness)
and a flame ionisation detector. Injection volume was 1.0 µL, the injection port temperature was
200°C and detector temperature was 250°C. Helium (2.4 ml per min) was the carrier gas and a split
ratio of 10:1 was used. Oven temperature was held at 40°C for 5 min before ramping to 230°C at 10°C
per min and held for 20 min (total run time was 45 min). Peak identification was facilitated by
calculating retention indices and previous MS data. Integration was performed using Shimadzu GCSolutions software. Areas were recorded for all detectable peaks and per cent composition was
calculated by taking the area of the peak divided by total chromatogram area x 100. Samples which
contained small amounts of total oil tended to overestimate the proportion of the major components.
Statistical analysis
Differences in sandalwood heartwood and oil parameters between host treatments were tested using
ANOVA. Linear regression was used to test for relationships between total core, disc parameters and
aromatic wood parameters, and proportional data was angular transformed to satisfy the normality
assumption. Trends between heartwood traits and the interaction indices host count index (HCI) and
host size-distance index (HSDI) (see Section 4.3.1, Trial 7) were examined with scatter plots at search
68
Flood-irrigated Tropical Timber
Trials in the North of Western
Australia
by L. Barbour, J. Plummer and L. Norris
Pub. No. 12/044
This report records a joint project between the Rural
Industries Research and Development Corporation, the Forest
Products Commission of Western Australia, Elders Forestry
and the University of Western Australia to ensure that 16 of
the original plantation trials and plantings of tropical species
established in the Ord River Irrigation Scheme (ORIS) by
the Western Australian Government were assessed and
published.
The main target groups of this research are researchers
and managers, especially within the Western Australian
Government system, non-governmental organisations
and commercial and private companies actively growing
sandalwood in the ORIS. The included information on growth
rates and essential oil production will be of interest to
investors and consultants.
RIRDC is a partnership between government and industry
to invest in R&D for more productive and sustainable rural
industries. We invest in new and emerging rural industries, a
suite of established rural industries and national rural issues.
Most of the information we produce can be downloaded for
free or purchased from our website <www.rirdc.gov.au>.
RIRDC books can also be purchased by phoning
1300 634 313 for a local call fee.
Phone:
02 6271 4100
Fax:
02 6271 4199
Bookshop:
1300 634 313
Email:
[email protected]
Postal Address: PO Box 4776,
Kingston ACT 2604
Street Address: Level 2, 15 National Circuit,
Barton ACT 2600
www.rirdc.gov.au