technical report no. 20
national carbon
accounting system
Change in Soil Carbon Following
Afforestation or Reforestation
Philip J. Polglase, Keryn I. Paul,
Partap K. Khanna, J. Gwinyai Nyakuengama,
Anthony M. O'Connell, Tim S. Grove
and Michael Battaglia
The lead Commonwealth
agency on greenhouse
matters
The National Carbon Accounting System:
• Supports Australia's position in the international development of
policy and guidelines on sinks activity and greenhouse gas emissions
mitigation from land based systems.
• Reduces the scientific uncertainties that surround estimates of land
based greenhouse gas emissions and sequestration in the
Australian context.
• Provides monitoring capabilities for existing land based emissions
and sinks, and scenario development and modelling capabilities that
support greenhouse gas mitigation and the sinks development agenda
through to 2012 and beyond.
• Provides the scientific and technical basis for international
negotiations and promotes Australia's national interests in
international fora.
http://www.greenhouse.gov.au/ncas
For additional copies of this report phone 1300 130 606
CHANGE IN SOIL CARBON FOLLOWING
AFFORESTATION OR REFORESTATION
Review of Experimental Evidence and Development of a Conceptual Framework
Philip J. Polglase, Keryn I. Paul, Partap K. Khanna,
J. Gwinyai Nyakuengama, Anthony M. O'Connell, Tim S. Grove
and Michael Battaglia
CSIRO Forestry and Forest Products
National Carbon Accounting System
Technical Report No. 20
October 2000
The Australian Greenhouse Office is the lead Commonwealth agency on greenhouse matters.
Printed in Australia for the Australian Greenhouse Office.
© Commonwealth of Australia 2000
This work is copyright. It may be reproduced in whole or part for study or training
purposes subject to the inclusion of an acknowledgement of the source and no
commercial usage or sale results. Reproduction for purposes other than those listed
above requires the written permission of the Communications Team, Australian
Greenhouse Office. Requests and inquires concerning reproduction and rights should
be addressed to the Communications Team, Australian Greenhouse Office,
GPO Box 621, CANBERRA ACT 2601.
For additional copies of this document please contact National Mailing and Marketing.
Telephone: 1300 130 606. Facsimile: (02) 6299 6040.
Email: [email protected]
For further information please contact the National Carbon Accounting System at
http://www.greenhouse.gov.au/ncas/
Neither the Commonwealth nor the Consultants responsible for undertaking this
project accepts liability for the accuracy of or inferences from the material contained in
this publication, or for any action as a result of any person’s or group’s interpretations,
deductions, conclusions or actions in reliance on this material.
October 2000
Environment Australia Cataloguing-in-Publication
Polglase, Philip J.
Change in Soil Carbon following Afforestation or Reforestation: Review
of Experimental Evidence and Development of a Conceptual Framework
/ Philip J. Polglase …[et al.]
p. cm.
(National Carbon Accounting System technical report; no. 20)
Bibliography:
ISSN: 14426838
1. Soils-Effect of afforestation on. 2. Forest soils-Carbon content. I. Polglase, P.J.
II. Australian Greenhouse Office. III. CSIRO. Forestry and Forest Products. IV. Series.
631.417-dc21
ii
Australian Greenhouse Office
ACKNOWLEDGEMENTS
We thank Alan Brown and Kris Jacobsen from CSIRO Forestry and Forest Products for expert
technical editing.
National Carbon Accounting System Technical Report
iii
TABLE OF CONTENTS
Page No.
1.
Executive Summary
1
2.
Recommendations
5
3.
Background
6
4.
Terms of Reference
7
5.
Basic Approaches and the Scope of this Report
8
6.
Abbreviations and Calculations
8
7.
Main Afforestation / Reforestation Regions in Australia
9
8.
Summary of Data Currently Available
10
8.1
Depth of soil sampling
10
8.2
Age of the plantation
13
9.
Methodological Issues of Change in Soil C following Afforestation
17
9.1
Study design
18
9.2
Soil sampling
20
9.3
Soil C fractions and chemical analysis
21
9.4
Soil bulk density
27
10. Conceptual Framework for Understanding Change in Soil C following Afforestation
28
10.1 Carbon balance
28
10.2 Amounts and patterns of net primary production
29
10.3 Allocation of NPP to fine roots
31
10.4 Root longevity
34
10.5 Root decomposition rates
35
11. Factors Affecting Soil C
37
11.1 Site preparation
37
11.2 Previous land use
40
11.3 Climate
46
11.4 Soil texture
51
11.5 Site management
53
11.6 Plantation harvesting and management of harvesting residues
58
12. Australian Case Studies
67
12.1 Mediterranean regions of south-west Western Australia
67
12.2 Subtropical moist regions of Queensland and the north coast of New South Wales
68
12.3 Temperate regions in the Australian Capital Territory and southern New South Wales
71
13. Synthesis
76
14. References
78
15. Appendix 1
93
iv
Australian Greenhouse Office
LIST OF TABLES
Table 7.1.
Area of new plantations established in 1999, and projected for 2000.
Table 8.1.
The initial soil C, change in soil C and the rate of change in soil C observed under
forests/plantations. Data sources are listed in Appendix 1.
13
Mass and C content of various soil fractions (0-30 cm depth) in Woodburn (NSW) soil
(Polglase and Snowdon, unpub.).
22
Table 9.1.
9
Table 9.2.
Amount of C in various components of a 20-year-old Pinus radiata plantation near Canberra,
Australia. Per cent values for various components refer to the respective total amounts in the
above-ground or below-ground fractions. Based on data from Ryan et al. (1996).
24
Table 9.3.
Mean C content in the litter layer of various forest types (from Vogt et al. 1986).
It was assumed that the C content of litter was 50%.
27
Table 10.1. Measured allocation of total NPP to roots for a range of sites (Santantonio 1989).
32
Table 10.2. Modelled allocation of total NPP to roots for a range of sites.
33
Table 10.3. Examples of allocation of NPP to roots in grasses and agricultural systems.
33
Table 10.4. Root longevity assumed for various models.
34
Table 10.5. Decomposition constants for decay of coarse and fine roots.
35
Table 10.6. Relationships for litter decomposition between first-year mass loss, the decomposition constant,
and the time taken to reach 90% mass loss (the stage at which it is assumed that litter becomes
soil humus). Values are derived from equations 1, 2 and 3 above.
37
Table 11.1. Weighted-average change in soil C in the <30 cm layer, after afforestation, during the short-term
(<10 years) and long-term (>10 years) following different former land uses. Agricultural land is
that which could not be easily classified into either pasture or crop. A significant relationship
with plantation/forest age is demonstrated at *P<0.05, **P<0.01, ***P<0.001.
42
Table 11.2. Changes in concentration of soil C (%) in the Waite Agricultural Research Institute Permanent
Rotation Trial (Grace et al. 1995).
43
Table 11.3. Soil OM concentration and the calculated change in soil C in response to various treatments
on ex-agricultural land prior to the establishment of pine or hardwood plantations
(Gilmore and Boggess 1963).
44
Table 11.4. Description and some examples of geographic locations of the four main climatic regions
encompassing the afforestation sites reviewed.
46
Table 11.5. Weighted-average change in soil C in the <30 cm layer, following afforestation, during
short-term (<10 yr) and long-term (>10 yr) studies in different climatic regions. Significant
relationship with plantation/forest age is demonstrated at *P<0.05, **P<0.01, ***P<0.001.
Values in parenthesis represent standard errors.
48
Table 11.6. The change in soil temperature after harvesting forests (no canopy) compared to an uncut
control (closed canopy).
49
National Carbon Accounting System Technical Report
v
LIST OF TABLES
continued
Table 11.7. Weighted-average change in soil C in the <30 cm layer, following afforestation, during the
short-term (<10 years) and long-term (>10 years) in soils with different clay contents.
Significant relationship with plantation/forest age is demonstrated at *P<0.05, **P<0.01,
***P<0.001. Values in parenthesis represent standard errors.
53
Table 11.8. Weighted-average change in soil C in the <30 cm layer, following afforestation, during
short-term (<10 yr) and long-term (>10 yr) studies under different forest species. Significant
relationship with plantation/forest age is demonstrated at *P<0.05, **P<0.01, ***P<0.001.
Values in parenthesis are standard errors.
55
Table 11.9. Weighted-average change in soil C in the <30 cm layer, following afforestation, with
various forest types on land previously used for pasture. Significant relationship with
plantation/forest age is demonstrated at *P<0.05, **P<0.01, ***P<0.001.
Values in parenthesis are standard errors.
56
Table 11.10. Measured root masses for a range of sites.
60
Table 11.11. Modelled root masses for a range of sites.
60
Table 11.12. First-year mass loss from decomposing Pinus radiata needles in control (uncut) and
harvested stands.
61
Table 11.13. Slash inputs to the forest floor after harvesting of Eucalyptus globulus and Pinus radiata
stands in Australia.
63
Table 12.1. Amounts of soil C (g m-2) under Pinus radiata plantations established on either previously
unimproved or improved pasture in southern NSW. Data from Birk (1992).
73
Table 13.1. Summary of processes involved in Figure 13.1.
77
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Australian Greenhouse Office
LIST OF FIGURES
Figure 8.1. The distribution of soil layers included in the sampling depth categories of <10 cm, >10 cm
and <30 cm depth. The width of the bars along the x-axis indicates number of studies.
Data sources are listed in Appendix 1.
10
Figure 8.2. Frequency of observed changes in soil C (g C m-2 yr-1) following afforestation in soil
<10 cm (a), >10 cm soil (b), and <30 cm soil (c). Data sources are listed in Appendix 1.
11
Figure 8.3. Frequency of observed changes in soil C (% yr-1) following afforestation in <10 cm soil (a),
>10 cm soil (b), and <30 cm soil (c). Data sources are listed in Appendix 1.
12
Figure 8.4. Relationship between the percent C change per year in soil sampled from <10 cm depth
and the plantation or forest age. Data sources are listed in Appendix 1.
14
Figure 8.5. Relationship between the percent C change per year in soil sampled from a depth of >10 cm
depth and the plantation or forest age. Data sources are listed in Appendix 1.
This relationship was not significant at P=0.05.
14
Figure 8.6. Relationship between the percent C change per year in soil sampled from <30 cm depth
and the plantation/forest age. Data sources are listed in Appendix 1.
15
Figure 8.7. The weighted-average C change observed in soil sampled from <10 cm depth, >10 cm or
<30 cm under forests of various age categories. Bars indicate standard errors of the means.
Numbers above (or below) the bars indicate the weighted-average percentage change in soil
C (% yr-1). Data sources are listed in Appendix 1.
15
Figure 8.8. (a) SOC4 by depth in cane fields (n=5) and after 10-13 years of afforestation with Eucalyptus
(n=5) in Hawaii; bars indicate the standard error of the mean, (b) SOC3 in cane fields and
after 10-13 years of afforestation with Eucalyptus. (Redrawn from Fig. 2b and c from page 832
of Bashkin and Binkley 1998).
16
Figure 9.1. Proportion of afforested sites reviewed at which C change (to <30 cm depth) was estimated
using paired site, chronosequence or repeated measure studies.
18
Figure 9.2. The weighted-average C change estimated using paired site, chronosequence or repeated
sampling studies of soils sampled <10 cm, >10 cm, or <30 cm under forests. Bars indicate
standard errors of the means, and numbers above (or below) the bars indicate the weighted
average percentage change in soil C (% yr-1). Data sources are listed in Appendix 1.
19
Figure 9.3. Frequency distribution of the number of soil samples taken from the field at sites in which
change in soil C was measured following afforestation (Appendix 1). For studies in which
there was a range in the number of soil samples for various plots, the midpoint of that
range was plotted.
21
Figure 9.4. Proportion of studies at which soil C was measured in sieved (<2 mm, or <5 to <7 mm)
or unsieved soil.
22
Figure 9.5. Proportion of afforested sites reviewed at which soil C was analysed using wet chemical
oxidation (i.e. Walkley-Black method), dry combustion (e.g. Leco or Dumas combustion),
or was calculated using loss-on-ignition.
23
National Carbon Accounting System Technical Report
vii
LIST OF FIGURES
continued
Figure 9.6. Proportion of afforested sites reviewed at which C content of the mineral soil alone was
measured, and where C content of both the litter and the mineral soil was measured.
25
Figure 9.7. The weighted-average C change observed in mineral soil, or mineral soil+litter, sampled
from <10 cm >10 cm or <30 cm under forests. Bars indicate standard errors of the means, and
numbers above (or below) the bars indicate the weighted-average percentage change in soil
C. Data sources are listed in Appendix 1.
26
Figure 9.8. Proportion of afforested sites reviewed at which soil bulk density was measured, or calculated
using the Adams (1973) equation.
28
Figure 10.1. Components of C balance that determine change in soil C following afforestation.
29
Figure 10.2. Patterns of volume gain and annual net primary production (dry matter, DM) in
Eucalyptus globulus for two sites differing in productivity. Output is from the Cabala model
(Battaglia, unpub.).
30
Figure 10.3. Patterns of annual litterfall and root slough (dry matter, DM) in Eucalyptus globulus for two
sites differing in productivity. Output is from the Cabala model (Battaglia, unpub.).
31
Figure 10.4. Comparison of forests and grasslands/crops in allocation of total NPP to roots (after Gower
et al. 1999) The letters A – K refer to various biomes. A-tropical deciduous broad-leaved,
B-tropical evergreen broad-leaved, C-temperate evergreen broad-leaved, D-temperate
deciduous broad-leaved, E-temperate evergreen needle-leaved, F-boreal deciduous
broad-leaved, G-boreal evergreen needle-leaved, H-grassland and tropical savannas,
I-crops, J-arctic tundra, K-desert.
34
Figure 11.1. The weighted-average C change estimated for soils sampled from <10 cm depth,
>10 cm or <30 cm under forests following high-medium or low disturbance during site
preparation. Bars indicate standard errors of the means. Numbers above (or below)
the bars indicate the weighted-average percentage change in soil C (% yr-1).
Data sources are listed in Appendix 1.
38
Figure 11.2. The weighted-average C change estimated for soils sampled from <10 cm, >10 cm or <30 cm
under forests on ex-pasture, ex-cropping and ex-agricultural land. Bars indicate standard
errors of the means. Numbers above (or below) the bars indicate the weighted-average
percentage change in soil C (% yr-1). Agricultural land is that which could not be easily
classified into either pasture or crop. Data sources are listed in Appendix 1.
41
Figure 11.3. The weighted-average C change following afforestation estimated for soils sampled from
<10 cm, >10 cm or <30 cm under forests in tropical, subtropical moist,
temperate/mediterranean and continental moist climatic regions. Bars indicate standard
errors of the means. Numbers above (or below) the bars indicate the weighted-average
percentage change in soil C (% yr -1). Data sources are listed in Appendix 1.
47
Figure 11.4. Soil water content in pasture and adjacent Eucalyptus globulus plantations in WA. Data are
means from 31 paired sites (Grove et al. 2000).
50
viii
Australian Greenhouse Office
LIST OF FIGURES
continued
Figure 11.5. Predicted changes in soil C following afforestation for different assumed microclimates.
‘Ambient’ is the change predicted for temperature and soil conditions that do not change
between pasture and plantation. ‘Drier’ is when soil water content is 10% less under plantation
than pasture; ‘cooler’ is when soil temperature is 2oC less under pasture than plantation, and
‘drier+cooler’ is for the combined effect. The Roth–C model was used, modified for forests
(Polglase et al. 1992).
51
Figure 11.6. The weighted-average C change estimated for soils of low, medium and high clay content
sampled from a depth of <10 cm, >10 cm or <30 cm under forests. Bars indicate standard errors
of the means, and numbers above (or below) the bars indicate the weighted-average percentage
change in soil C (% yr-1). Data sources are listed in Appendix 1.
52
Figure 11.7. The weighted-average C change estimated for soils sampled from <10 cm, >10 cm or <30 cm
under forests of four different types. Bars indicate standard errors of the means, and numbers
above (or below) the bars indicate the weighted-average percentage change in soil C (% yr-1).
Data sources are listed in Appendix 1.
55
Figure 11.8. Frequency distribution diagram summarising change in soil C after forest harvesting
(redrawn from Johnson and Curtis 2000).
59
Figure 11.9. Harvest effects on soil C within the A horizon (redrawn from Johnson and Curtis 2000).
62
Figure 11.10. Decomposition of Eucalyptus globulus residues in WA after harvesting. Fitted models are either
single (wood) or double (leaves) exponential decay functions. k is the rate constant and w the
initial mass (%) for labile (L) and resistant (r) fractions. Data from Shammas (1999).
64
Figure 11.11.Patterns of decomposition of slash residues in two forests. ‘Covington’ is chronosequence data
for mixed hardwood from Covington (1981); 'Polglase' is a model prediction for mountain ash
(Eucalyptus regnans) in Victoria (Polglase unpub.).
66
Figure 12.1. Change in soil C in 0-10 cm layer under 4- to 11-year-old eucalypt plantations on ex-pasture
land in the Mediterranean climatic region of south-west Western Australia.
68
Figure 12.2. Change in soil C in 0-10 cm or 0-50 cm layer under 2- to 50-year-old forest on ex-pasture land
in the subtropical climatic regions of Queensland and the north coast of New South Wales.
69
Figure 12.3. Change in soil C in 0-30 cm layer 2 to 60 years following afforestation of ex-pasture land in the
temperate climatic regions of the Australian Capital Territory and southern New South Wales.
The study of Polglase and Falkiner (unpub.), where irrigation of previously dry land caused a
large initial change in soil C, represents an extreme case
72
Figure 12.4. Change in soil C in 0-30 cm layer, together with litter, 2 to 60 years following afforestation of
ex-pasture land in the temperate climatic regions of the Australian Capital Territory and
southern New South Wales. The study of Polglase and Falkiner (unpub.), where irrigation
of previously dry land caused a large initial change in soil C, represents an extreme case
73
National Carbon Accounting System Technical Report
ix
LIST OF FIGURES
continued
Figure 12.5. Change in soil C in various soil layers to 70 cm depth under irrigated two-year-old
Eucalyptus grandis plantations near Wagga Wagga, New South Wales. Treatments are
different rates of effluent irrigation. Polglase and Falkiner (unpub.).
74
Figure 12.6. Change in soil C in various soil layers to 70 cm depth under irrigated two-year-old
Pinus radiata plantations near Wagga Wagga, New South Wales. Treatments are different
rates of effluent irrigation. Polglase and Falkiner (unpub.).
75
Figure 13.1. Summary of processes controlling change in soil C following afforestation.
See Table 13.1 for an explanation of the numerals.
76
x
Australian Greenhouse Office
1. EXECUTIVE SUMMARY
1.
•
Determination of change in soil carbon (C)
and including this depth), >10 cm (any
after afforestation and reforestation is
relevant to Australia’s National Carbon
soil sampled beyond 10 cm to the
maximum depth sampled), and <30 cm
Accounting System (NCAS) and estimation
(any soil sampled up to and including
of change in soil C stocks over the first
commitment period of the Kyoto Protocol,
this depth, this being the default depth
for sampling by the Intergovernmental
2008-2012. This report reviews the current
Panel for Climate Change, IPCC); and,
‘state-of-knowledge’ of the effects of
•
afforestation on soil C.
2.
increase by about two million ha by 2020
over that present in 1996. Most new
plantations will be on agricultural land
(compliant with terms of the Kyoto
Protocol). The area of new plantations
4.
litter was defined as a discrete entity
and was therefore counted separately
from soil C.
Under the Commonwealth Government
forest industry initiative, Vision 2020, the
area of plantation in Australia is projected to
3.
soil sampling depths were separated
into <10 cm (any soil sampled up to
5.
Data were highly variable, with soil C
exhibiting either large increases or
decreases, particularly for young (<20-yr)
stands. Nonetheless averaged data revealed
many trends:
•
Soil depth: There was little change in
established in 1999 was about 95,000 ha, and
150,000 ha is projected for 2000. The effect of
this plantation development on soil C stocks
soil C in the <30 cm layer during the
first 10 years following afforestation,
and a relatively large and positive
needs to be accounted for under Article 3.3
of the Kyoto Protocol.
increase during the average 19-year
period (263 g m-2, or 0.36% yr-1
Because of the number and complexity of
soil and site processes involved, the effect of
afforestation on soil C stocks is best
predicted through a verified modelling
approach. A first step in developing this
approach is to review the evidence for
change in soil C following afforestation, and
to identify and understand the controlling
processes. This conceptual framework can
then form the basis for model development,
verification and application.
Relevant data on changes in soil C following
afforestation were reviewed. Data were
available from 41 published and
unpublished studies encompassing 197 sites
from around the world where change in soil
C following afforestation was monitored. To
allow comparisons between studies:
National Carbon Accounting System Technical Report
increase). Changes were most
pronounced (significantly) for the <10
cm layer during the first 10 years
following afforestation, the mean
change in soil C being –98 g m-2,
equivalent to a time-weighted rate of
change of –14 g C m-2 yr-1, or
–0.15% yr-1 change in the initial
amount of soil C.
•
Plantation age: For soil in the <10 cm or
< 30 cm layers, there were significant
effects of stand age on C change. Soil C
generally decreased during the first 10
years (particularly the first five years)
of afforestation followed by a slower
rate of recovery and accumulation.
Inputs from tree seedlings to soil are
minimal during the initial stage of
plantation establishment as most of the
net primary production goes to
1
building biomass. It may be three years
•
before residues begin to cast off from
trees, and five to ten years before
6.
Change in soil C in Australian
maximum net primary production is
afforestation sites has largely been
measured on the <2 mm fraction of soil
reached.
analysed using wet chemical oxidation
procedure. Litter C was generally not
measured. Sieving (<2 mm) is
The various methodologies used in the
collection and interpretation of data on soil
C are discussed in terms of their limitations
problematic in that there is potential
for some live pasture roots to be
included in analyses, fine tree roots
and usefulness in interpreting change in soil
C after afforestation. Accurate measurement
of change in soil C following afforestation is
being more easily removed from soil.
This inconsistency between agricultural
and plantation samples may lead to
fraught with difficulties. The value of data
was often diminished because change in soil
C was not the focus in most of the studies
inaccurate identification of change in
soil C and potentially confound
calibration and verification of models.
Furthermore, there are inconsistencies
reviewed. A number of methodological
issues are identified for reference in future
work and for the development of protocols:
•
in accounting for litter C. Considering
soil only, there was an average
Study techniques and experimental design.
Most field studies are retrospective and
decrease in C across all ages and site
conditions. This was reversed when
litter was included, an increase in C
can be classified into paired site
studies, chronosequence studies (soil
under stands of different age sampled
being recorded. Litter C needs to be
accounted for, but measured separately
to soil C.
at the same time), and repeatedsampling (the one site sampled
repeatedly over time). Of these,
chronosequence studies are the least
reliable for evaluating change in soil C,
yet they accounted for 25% of the
studies reviewed. These studies may
have entailed inappropriate ‘matching’
of sites in terms of site topography, soil
type, history and climate.
•
2
Soil C fractions and chemical analysis.
Soil sampling depth, intensity (replication)
and design. To maintain consistent
comparisons, soil sampling should be
based on mass and generic soil
horizons rather than on volume and
depth. Sampling should also be well
replicated (i.e. >25 samples) and
designed. Stratified random sampling
may be required in sites which are
mounded or ripped.
•
Bulk density change. Litter
decomposition and consequent
humification can decrease soil bulk
density. If unaccounted, this may lead
to an overestimation of soil C.
Conversely, deep roots of swaying
trees may compact soil. A ‘mass’ (cf.
‘volume’) approach is therefore the
preferred strategy for sampling.
7.
A conceptual framework was developed for
understanding change in soil C following
afforestation. In Australia, further work may
be required to improve our understanding,
and thus modelling capability, of change in
soil C following afforestation in terms of:
•
Temporal patterns of the net amount of C
captured by plantations (NPP). The
amount and temporal patterns of C
Australian Greenhouse Office
•
allocation in plantations are critical
decomposition. However, there is no
determinants of change in soil C
through their effects on residue inputs.
clear evidence of any effects of the
level (intensity) of site disturbance on
change in soil C. This may partly be
Allocation of NPP to fine roots. The
amount of C input below-ground in
explained by methodological
problems, soil often being sampled
from the inter-row of plantations,
plantations may be less compared to
agriculture as about half of the C
allocated below-ground goes to long-
away from disturbed areas (e.g. rip or
plough lines).
lived, structural roots.
•
•
Root longevity.
•
Root decomposition. Residues such as
a significant affect on change in soil C
sampled from a depth of less than 30
cm. Considering the first 10 years,
-2
dead roots (typically 200-400 g C m )
from the pre-existing crop decompose,
adding to soil C. Fine (<3 mm) and
change in soil C on ex-pasture was
–9.75 g m-2 yr-1, and on ex-crop
(arable) land was +142.3 g m-2 yr-1
perhaps medium (3-10 mm) tree roots
will decompose rapidly, but
decomposition of large woody roots
(>10 mm diameter) will be slower. Tree
(see Table 11.1). If land was cropped,
further decrease in soil C may be
limited because the soil C will largely
consist of stable humus resistant to
roots may also add C deeper in the soil
profile than does pasture.
•
further significant breakdown; if
formerly improved pasture, soil may
have a relatively high C content that is
Litterfall and litter decomposition. Weeds
and grasses are shaded out under
productive plantations and, after
canopy closure, above-ground litterfall
becomes a significant process. It may
take about three years from the time of
commencement of litterfall until the
transfer of litter C to soil begins. As the
susceptible to loss after plantation
development;
•
plantation develops, soil C can
accumulate as a consequence of
decomposition of lignified tree
residues.
8.
discussed. This analysis is used to identify
the most important factors for model
development and verification. These
include:
Site preparation (disturbance): It is
generally thought that soil disturbance
such as ripping and mounding can
increase aeration and alter the
microclimate, accelerating
National Carbon Accounting System Technical Report
Climate and microclimate: Climate
significantly affects change in soil C
following afforestation, decreases
being recorded in temperate zones,
and accumulation in the other three
zones (tropical, sub-tropical moist and
continental moist). The microclimate
may change under plantation
development, affecting decomposition
rates. Soil temperatures decrease as the
tree canopy develops, and soil is
Factors affecting change in soil C are
•
Previous land use: Previous land use has
possibly drier under plantations than
pasture.
•
Soil texture: Soil texture has a
significant effect on change in soil C,
particularly in the longer-term (>10
years). High-clay soils have a relatively
large potential for soil C accumulation.
3
•
Site management: Species selection,
eucalypt plantations on ex-pasture land in
stocking, weed control, thinning,
fertilisation, planting an N2-fixing
the Mediterranean regions of Western
Australia. In subtropical moist regions, soil
C seems to decline for about 15 years after
understorey, and fire management are
all options that affect soil C storage.
plantation establishment before levelling
For example, establishment of radiata
pine decreased soil C, and this was
significant compared to the generally
positive change after establishment of
eucalypts, other hardwood species, and
other softwood species. This difference
was maintained even when all
plantations were on ex-pasture. The
decrease in soil C under radiata pine
may be related to differences in the
quality of litter, much of the residue
from radiata pine remaining
undecomposed and contributing little
to soil C stocks. Weeds and grass, if left
between rows, provide most initial
inputs to the soil system and may be
the major buffer against initial soil
C loss.
•
Harvesting and management of residues:
On average, there is about a 5%
increase in surface soil C following
harvesting. This is attributable to
inputs of C from slash and roots.
Although soil temperature may
increase, it is generally thought that
decomposition may be slower
following harvesting due to drier soil
conditions. The magnitude of change
in soil C in response to harvesting
operations is dependent on the
harvesting technique used, tree species,
time since harvesting, and rotation
length.
9.
4
A number of Australian case studies were
examined in detail to exemplify changes in
soil C following afforestation, and to
illustrate some of the issues involved. There
appears to be no significant relationship
between change in soil C and the age of
out. Similar results were observed in
temperate regions.
10.
In summary, change in soil C will depend
upon the balance between the amount of C
input, and that lost through decomposition.
For model development and verification key
issues identified are:
Amount of C inputs, as affected by factors
including:
•
comparative net primary production
(NPP) of pasture and plantation
phases;
•
temporal dynamics of NPP in
plantations for a range of site
conditions;
•
allocation of C to stand components,
particularly fine roots;
•
temporal patterns of inputs of litter
and root residues; and
•
temporal patterns of weed/grass
persistence (productivity) in plantation
inter-rows.
Amount of C outputs through decomposition,
as affected by factors including:
•
substrate quality of residues (species
composition and the change in this
composition over time);
•
the proportion of input that
decomposes and the time taken for
residue to become humus;
•
differences in decomposition rates of
above-ground and below-ground
residues;
Australian Greenhouse Office
•
differences in decomposition rates of
2.
afforestation for a range of climatic regions,
land-use histories, and soil types. Ideally
coarse and fine roots;
•
•
disturbance, particularly mechanical
site preparation and other management
practices;
this would involve long-term monitoring of
valid paired plantation-agricultural sites.
The initial assessment of these sites would
the initial condition of soil C,
permit a retrospective evaluation of the
determined by previous land use
effects of afforestation, while continued
monitoring (over say 10 to 20 years) would
(intensively cropped versus improved
pasture);
•
Quality data on change in soil C following
climatic variables - soil moisture and
temperature regimes that may differ
reliably identify longer-term patterns of
temporal change.
3.
A standardised procedure for soil sampling.
between pasture and plantation;
This involves developing protocols for:
•
soil texture;
•
•
site management; and
soil sampling (e.g. soil sampling depth,
intensity and design);
•
harvesting and management of harvest
•
processing of soil for chemical analysis
(e.g. sieving, separation of roots,
residues.
treatment of above-ground litter);
2. RECOMMENDATIONS
•
stratification, particularly where soil
has been ripped or mounded; and
Over large areas the integrated effect of afforestation
on soil C is best estimated through a verified
•
accounting for changes in bulk density
of soil.
modelling approach. A number of process-based
models of soil C dynamics have been developed but
none have been verified widely for forests and tree
plantations. For Australia to develop a strong
capability to predict change in soil C after
afforestation, the following is needed:
1.
4.
Data to support interpretation and
prediction of changes in soil C for any given
set of site conditions, by providing an
understanding of effects of:
•
A detailed inventory of the location of
current and future afforestation regions,
including:
differences in microclimate under
agricultural and plantation systems;
•
varying patterns of allocation of C to
roots;
•
species;
•
•
age of plantations;
•
productivity;
litter and root decomposition, for the
development and testing of
decomposition models;
•
site establishment techniques (e.g.
burning, weed control, mounding,
ripping); and
•
deep roots;
•
disturbance (mechanical site
preparation);
•
previous land use;
•
climate;
•
management regimes (e.g. species
selection, rotation length, thinning,
fertiliser application).
National Carbon Accounting System Technical Report
5
•
soil texture;
•
management; and,
•
harvesting and silvicultural
management under Australian
conditions.
3. BACKGROUND
forest soils hold about 40% of all below-ground
(soils, litter, and roots) terrestrial C (Dixon et al. 1994;
Huntington 1995). Therefore, even relatively small
changes that affect forest soil C pools will have a
significant effect on the global C cycle.
In this report, we use the term soil C to include all
non-living, below-ground C, including roots and
charcoal. This pool of soil C is in constant flux, with
Under Article 3.3 of the Kyoto Protocol, countries
inputs in litterfall, slash and root material and
outputs of CO2 evolved during microbial
are required to count the net changes in greenhouse
gas emissions by sources and removals by sinks.
decomposition. The rate of residue generation
depends on plant productivity, and is influenced by
Changes in greenhouse gas emission (measured as
site management factors such as fertiliser
change in C stock) may result from direct humaninduced land-use change and forestry activities
application, weed control and slash management.
The rate of decomposition of residues largely
limited to afforestation, reforestation and
depends upon the quality of the decomposing
deforestation since 1990. Following the
Government’s commitments at the Kyoto
convention, Australia is expected to meet 108% of
substrate, and is faster in warmer, wetter
environments with coarse-textured soils, and is
promoted by soil disturbance.
the 1990 levels of the net greenhouse gas emissions
by the year 2008. The Protocol provides a basic
framework for the inclusion of a limited number of
Following the conversion of agricultural land to
plantations, changes inevitably occur in the quality,
carbon sink activities.
Substantial proportions of Australia’s greenhouse
quantity, timing, and spatial distribution of soil C
inputs. These changes, together with the changes in
the soil microenvironment, affect decomposition
gas emissions occur in the land-use change and
forestry sector (Thompson 2000). Enhancing
greenhouse sinks through afforestation therefore
provides an effective and practical contribution
towards meeting Australia’s international
commitments to address climate change.
rates. For example, decomposition rates may
decrease as a result of afforestation due to the cooler
Several studies have estimated the contribution of
afforestation to the global C cycle at both regional
(Sharpe and Johnson 1981; Maclaren and Wakelin
1991; Turner et al. 1995; Brown 1996; Shvidenko et al.
1997) and global scales (Nilsson and Schopfhauser
1995; Brunnert 1996). Most of the available
information on global budgets gives projections on
C accumulation by vegetation following
afforestation; little information is included on
associated changes in soil C (Scott et al. 1999).
Although changes in soil C following afforestation
About 75% of total terrestrial C is stored in the
world’s soils (Henderson 1995). It is estimated that
6
soil surface under the canopy and litter layer.
Decomposition of soil C added via tree roots may be
decreased by the lower soil temperatures and
reduced microbial activity at depth.
are not well documented, it is generally assumed
that over decades the C content increases following
afforestation (e.g. Grigal and Berguson 1998). This is
because of the observed reductions in the C content
of forest soils after clearing and cultivation (Nilsson
and Schopfhauser 1995; Mosier 1998), and because
of the observed accumulation of soil C under forests
in young volcanic soils (Wilde 1964; Vitousek et al.
1983; Schlesinger 1990), following mine site
rehabilitation (Smith et al. 1997; Costa et al. 1998),
and following mudflows (Dickson and Crocker
1953). Over short time periods (<5 years) there is a
Australian Greenhouse Office
widely-held expectation that soil C will decrease
(ii)
following afforestation.
effects of prior land-use history (e.g.
pasture quality, addition of fertiliser
etc);
The objective of this report is to synthesise available
world-wide information on change in soil C after
afforestation. It is to be used as a ‘state-of-the-
(iii) effects of weedicide, cultivation,
mounding and other site preparation
knowledge’ review, the first step in developing an
techniques on soil C;
enhanced modelling capability to predicting the
effects of plantation development on change in
(iv) interaction of the above with soil type
(texture, fertility), and climate; and
soil C.
(v)
4. TERMS OF REFERENCE
interdependence of initial soil C
content, productivity and management
of preceding agricultural system (land-
This report has been prepared as part of a
use history), and productivity of the
consultancy for the Australian Greenhouse Office.
The consultancy has three components: a ‘state-of-
subsequent tree crop.
knowledge’ assessment, a modelling framework,
and ‘first-cut’ model outputs. Activities within the
consultancy are scheduled to run concurrently but
have been split into two milestones — a draft
report of the literature review, and all other
activities and final report. The report presented
here is the first of two parts constituting the state-ofknowledge review.
PART 2 - MODELLING
1.
Review models currently available for
simulating the effects of afforestation on soil
C, and assess their suitability for use.
Particular emphasis will be given to the
Roth-C model in view of its current use in a
project to assess effects of land clearing on
soil C, and sponsored by the Australian
Greenhouse Office.
PART 1 - REVIEW
1.
Review at the regional level the extent of
plantations established since 1990 on
agricultural land — location, area, current
age, and probable end use. Define the likely
land base for plantings post-2000. This
information will be developed only to the
extent that it can help decide where
experimental and modelling studies should
be concentrated.
2.
Work in this and subsequent stages will
integrate the Roth–C model with the 3-PG
model of plantation growth, the Gendec
model of litter decomposition, and the
CAMFor model of C transfers in managed
forests and wood products. The integrated
model (GRC3) will provide a consistent
basis for this and subsequent work.
2.
Predict change in soil C for select scenarios
of plantation establishment and
management — land-use history, plantation
productivity, soil type, climate and
harvesting.
3.
Undertake limited analysis of sensitivity to
changing parameters and assumptions. A
Review effects of plantation establishment
on soil C. Consider national and
international literature on relevant factors
including:
(i)
demonstrated change in soil C when
plantations are established on
agricultural land, including change
subsequent to harvesting;
National Carbon Accounting System Technical Report
full analysis is to be conducted in a
subsequent, nationally-coordinated
experimental and modelling program.
7
5. BASIC APPROACHES AND THE
SCOPE OF THIS REPORT
4.
change in soil C following afforestation.
These include:
In this report we synthesise information to develop
an account of the current ‘state-of-knowledge’ for
the effects of afforestation on soil C. This synthesis
is based on the relevant data from literature and
unpublished data, discussion of some of the
difficulties associated with measuring change in soil
C to enable sensible interpretation, and a conceptual
framework that develops a basis for predicting
change in soil C following afforestation.
The specific approach was:
1.
5.
data (Section 9). Issues examined include:
•
study design (chronosequence, paired
site and repeat sampling);
•
soil sampling method; and,
•
soil C fractions and chemical analysis
(sieving and inclusion of roots, type of
chemical analysis, inclusion of litter).
3.
8
Development of a conceptual framework
(Section 10) for predicting change in soil C
following afforestation. This section outlines
the changes in C in relation to productivity
and allocation. Issues covered include:
•
C balance;
•
amount and pattern of NPP;
•
allocation of NPP to fine roots;
•
root longevity;
•
root decomposition rates; and,
•
litterfall and litter decomposition.
Disturbance / site preparation;
•
previous land use;
•
productivity and allocation of C;
•
climate and microclimate;
•
soil texture; and
•
site management, including harvesting.
Australian case studies, taken from the review
soil C (Section 12). Results and impacting
processes are discussed in the light of
information presented in previous sections
C had been measured following
afforestation (Section 8).
Discussion of methodologies and how they
affect measured change in soil C to provide
a consistent basis for the interpretation of
•
of data and used as examples of change in
Review of available data from studies
throughout the world where change in soil
2.
Section 11 discusses the factors which effect
(methodological issues, conceptual
framework).
6.
Synthesis (Section 13), that brings together in
a qualitative way the various data and
conceptual issues to describe change in soil
C following afforestation, including a listing
of processes requiring particular
consideration during model development
and testing.
6. ABBREVIATIONS AND CALCULATIONS
Soil organic matter (SOM) is the sum of all organic
matter within the soil and typically constitutes about
half of the soil C. Total soil C is the sum of the
organic and inorganic (carbonates and charcoal)
fractions of soil C. Organic C (OC) is the partially
decomposed and non-living fractions of organic
matter contained within the mineral soil. For all
practical purposes, however, total organic soil C
(living + non-living) in the fine soil fraction (<2 mm
or <5 mm) is considered. In this report and unless
otherwise stated, the term soil C is used to refer to
organic components only. Unless specified, surface
litter is not included in the calculation of soil C.
Australian Greenhouse Office
7. MAIN AFFORESTATION / REFORESTATION
REGIONS IN AUSTRALIA
The average change in soil C over time was
calculated as a mean value weighted for time.
This became necessary because there were a large
number of studies which observed decreases in soil
The area of Australia’s plantation estate and its rate
C over a short period following afforestation.
Therefore, unless the average change in soil C was
of expansion is presented to provide a context for
potential change in soil C. As of September 1999
weighted by the age of the plantation, these short-
Australia had about 389,000 ha of hardwood
term changes may have biased the long-term values
of calculated change in soil C.
plantations (eucalypts) and about 948,00 ha of
softwoods (mostly Pinus radiata). Much of the
softwood estate was established on land cleared of
The weighted-average change in soil C, and the
percentage change in soil C compared to the initial
native forest for that purpose. In recent years there
has been a steady increase in plantations established
soil C content, were calculated as:
on already-cleared agricultural land.
-2
-1
Weighted-average C change (g C m yr ) =
∑(Change in soil C, g m-2) / ∑(Age)
In the five years between 1995 and 1999 nearly
300,000 ha of new plantations were established,
-1
three-quarters of it hardwood. In 1999, about
95,000 ha of new plantations were established, and
about 155,000 ha are anticipated for 2000 (Table 7.1).
Weighted-average percentage C change (% yr ) =
[∑(Change in soil C, g m-2)/∑(age)] /
∑(Initial soil C, g m-2) x 100
Table 7.1. Area of new plantations established in 1999, and projected for 2000*
Area (ha)
Year
State
Hardwood
Softwood
Total
1999
NSW
4,375
2,682
7,057
ACT
0
0
0
VIC
25,326
841
26,167
SA
8003
477
8,480
TAS
16,467
2,374
18,841
Qld
2,513
106
2,619
NT
448
0
448
WA
27,500
3,700
31,200
Total
84,632
10,180
94,812
NSW
5,480
6,966
12,446
ACT
0
0
0
VIC
28,800
1,983
30,783
SA
18,006
999
19,005
TAS
21,344
2,451
23,795
Qld
4,320
4,000
8,320
NT
620
0
620
WA
50,000
10,000
60,000
Total
128,570
26,399
154,969
2000
*‘National Plantation Inventory’. Bureau of Rural Resources, March 2000.
National Carbon Accounting System Technical Report
9
8. SUMMARY OF DATA
CURRENTLY AVAILABLE
The <10 and >10 cm sampling depth soil categories
were used because the 0-10 cm soil layer was
frequently sampled (Fig. 8.1). Also, as most decrease
There are few Australian studies on change in soil C
in soil C concentration is expected in the surface 0-10
following afforestation, most data being from other
countries. Data sets were available (literature and
cm depth, it was appropriate to separate that
category. This is likely to be particularly evident on
unpublished reports) from a total of 41 studies (197
ex-pasture land. The <30 cm sampling depth was
sites) which demonstrated change in soil C
following afforestation (Appendix 1). Data were
used since 30 cm is the IPCC default sampling depth.
summarised to determine the most frequently
For the 126 sites in which C change was measured in
<10 cm soil, the weighted-average change in soil C
was –2.9 g C m-2 yr-1, or –0.09% yr-1 (Table 8.1).
observed effect of afforestation on soil C.
8.1 DEPTH OF SOIL SAMPLING
There was a wide range of sampling depths within
which changes in soil C were observed in these 41
studies. To allow comparison between results, soils
were grouped into three categories. These categories
included soil sampled to a depth of (1) <10 cm; (2)
>10 cm; and (3) <30 cm (Fig. 8.1).
In contrast, across the 66 sites in which soil C was
sampled from a depth >10 cm, there was a weightedaverage increase in soil C of 2.0 g C m-2yr-1, or
0.03% yr-1. For the 197 sites in which C change was
measured in soil <30 cm, the weighted-average
change in soil C was 13.8 g C m-2 yr-1, or 0.36% yr-1.
Sampling depth category
<10 cm
>10 cm
<30 cm
0
10
Soil depth (cm)
20
30
40
50
60
70
80
90
100
Figure 8.1. The distribution of soil layers included in the sampling depth categories of <10 cm, >10 cm and
<30 cm depth. The width of the bars along the x-axis indicates number of studies. Data sources are listed
in Appendix 1.
10
Australian Greenhouse Office
A frequency distribution of the observed change in soil C in absolute and percentage terms is shown in
Figures 8.2 and 8.3, respectively. For all sampling depth categories, there was a large variation in the changes
in soil C. However, a majority of studies reported changes in soil C of +/- 150 g C m-2 yr-1 (Fig. 8.2), or +/2.5% yr-1 (Fig. 8.3).
a
30
20
10
No. of observations
0
20
b
10
0
40
c
30
20
10
0
-300
-240
-180
-120
-60
0
60
-2
120
180
240
300
-1
Change in soil C (g C m yr )
Figure 8.2. Frequency of observed changes in soil C (g C m-2 yr-1) following afforestation in soil <10 cm (a),
>10 cm soil (b), and <30 cm soil (c). Data sources are listed in Appendix 1.
National Carbon Accounting System Technical Report
11
a
30
20
10
0
No. of observations
b
30
20
10
0
50
c
40
30
20
10
0
-15
-10
-5
0
5
10
-1
Change in soil C (% yr )
Figure 8.3. Frequency of observed changes in soil C (% yr-1) following afforestation in <10 cm soil (a), >10
cm soil (b), and <30 cm soil (c). Data sources are listed in Appendix 1.
12
Australian Greenhouse Office
8.2 AGE OF THE PLANTATION
Change in soil C following afforestation depends
also on age of the stand. Table 8.1 shows that within
the first 10 years of afforestation soil C decreased, or
changed little, in the surface soil (<10 cm or <30 cm
depth), but a net increase was observed in soil C in
the lower soil layer (>10 cm depth). In contrast, in
afforested sites more than 10 years old, soil C
increase in the surface soil layer was similar to or
greater than that observed in the lower soil layer.
Table 8.1. The initial soil C, change in soil C and the rate of change in soil C observed under
forests/plantations. Data sources are listed in Appendix 1.
Sampling
depth
Age class
Ave. age
No. of
studies
soil C
Soil C
change
bSoil C
change
(g m-2)
(g m-2yr-1)
(%)
(% yr-1)
Initial
soil C
Change in
soil C
(g m-2)
aChange
in
(cm)
(yr)
(yr)
<10
<10
7
69
2,801
-98
-14.3
-3.50
-0.51
>10
27
57
3,859
17
0.64
0.45
0.02
All
16
126
3,280
-47
-2.93
-1.42
-0.09
<10
5
26
5,975
80
15.3
1.33
0.26
>10
31
40
6,475
19
0.62
0.30
0.01
All
21
66
6,278
43
2.02
0.68
0.03
<10
7
99
3,334
13
1.97
0.38
0.06
>10
31
98
4,414
508
16.2
11.5
0.37
All
19
197
3,871
263
13.8
6.80
0.36
>10
<30
a
Weighted-average calculated as ∑(Change in soil C, g m-2) / ∑(Age)
Weighted-average calculated as ∑(Change in soil C, g m-2 yr-1) / ∑( Initial soil C, g m-2) x 100
b
For soil sampled from a depth below 10 cm, there
was no significant effect of forest age on C change
following afforestation (Fig. 8.5). However, in soils
<10 or <30 cm depth, there was a significant
relationship between C change observed following
afforestation and the age of the forest (Figs 8.4 and
8.6). In these soils, although C may initially decline
following afforestation, there is a rapid recovery of
soil C before attaining an equilibrium level which is
generally slightly above that of the preceding
agricultural soil. Figure 8.7 shows that in soil
samples from <10 cm (or <30 cm), the weightedaverage change in soil C increased from –72.3 (or
–17.3) g C m-2 yr-1 in forests of less than five years of
age, to +10.1 (or +33.1) g C m-2 yr-1 in forests which
were older than 31 years.
The collated results shown are consistent with those
observed for surface soils on sites repeatedly
measured over time (Harrison et al. 1995; Jug et al.
1999; Richter et al. 1999), or from chronosequence
series (Aweto 1981; Ramakrishnan and Toky 1981;
Zak et al. 1990; Trouve et al. 1994; Turner and
Lambert 2000). These studies observed an initial
decline in soil C after afforestation followed by a
gradual increase. The initial decline in C has been
observed to last for 3-35 years following agricultural
abandonment (Aweto 1981; Zak et al. 1990; Richter
et al. 1999). In long-term studies, soil C generally is
found to accumulate following afforestation. The
Broadbalk and Geescroft Wilderness sites of the
Rothamsted long-term experiments demonstrated a
34-55 g m-2 yr-1 accumulation of C over the 100-year
period (Jenkinson 1971).
National Carbon Accounting System Technical Report
13
Age of plantation (yr)
0
10
20
30
40
50
60
70
80
90
100
-1
Change in soil C (% yr )
10
5
0
-5
y = 1.70Ln(x) - 4.68
R2 = 0.22, P<0.01
-10
-15
Figure 8.4. Relationship between the percent C change per year in soil sampled from <10 cm depth and the
plantation or forest age. Data sources are listed in Appendix 1.
Age of plantation (yr)
0
20
40
60
80
100
-1
Change in soil C (% yr )
10
5
0
-5
-10
-15
Figure 8.5. Relationship between the percent C change per year in soil sampled from a depth of >10 cm
depth and the plantation or forest age. Data sources are listed in Appendix 1. This relationship was not
significant at P=0.05.
14
Australian Greenhouse Office
Age of plantation (yr)
0
10
20
30
40
50
60
70
80
90
100
-1
Change in soil C (% yr )
10
5
0
-5
y = 1.07Ln(x) - 2.78
R2 = 0.12, P<0.01
-10
-15
Figure 8.6. Relationship between the percent C change per year in soil sampled from <30 cm depth and the
plantation or forest age. Data sources are listed in Appendix 1.
0.63
80
0.85
-2
-1
Change in soil C (g C m yr )
120
40
0.10
0.30 0.30
0.19
0
-0.23
-0.24
-40
-0.23
-0.31
-0.61
-80
<10 cm, ***
>10 cm, ns
<30 cm, **
-2.64
-120
<5
6-10
11-30
>31
Plantation age (yr)
Figure 8.7. The weighted-average C change observed in soil sampled from <10 cm, >10 cm or <30 cm under
forests of various age categories. Bars indicate standard errors of the means. Numbers above (or below)
the bars indicate the weighted-average percentage change in soil C (% yr-1).
**, significant at P<0.01. ***, significant at P<0.001. ns, not significant. Data sources are listed in Appendix 1.
National Carbon Accounting System Technical Report
15
Change in soil C content over any interval of time
A new equilibrium (or near equilibrium) is reached
reflects the net difference between inputs and
outputs. Inputs of organic matter to a soil come from
between residue inputs and decomposition with the
development of a new plantation. The time taken for
plant litter, either above-ground or from roots.
the equilibrium state was calculated to be 10 years
Output of soil C is primarily associated with soil
respiration as part of organic matter turnover.
following natural forest succession in Nigeria
(0-10 cm, Aweto 1981), 30 years under eucalypt and
During the early stages of stand development little
pine plantations in Congo (0-5 cm, Trouve et al.
detrital matter is produced due to the small biomass
and low rate of litterfall return (Wilde 1964).
1996), 40-60 years under pine-oak stands in
Massachusetts (0-15 cm, Compton et al. 1998), 45-60
Therefore, directly following agricultural
years under conifer forests in Wisconsin (0-15 cm,
abandonment, the decline in C is attributable to the
greater loss of C through decomposition than gain
Wilde 1964), and more than 60 years following
natural forest succession in Minnesota (0-10 cm, Zak
through litter production. The subsequent
et al. 1990).
accumulation of C indicates that annual inputs of C
through primary production exceeded the amount
The change in vegetation type from a C4 crop or
lost by C decomposition.
pasture to a C3 plantation enables quantification of C
changes in soils, using stable C isotope techniques.
-2
-2
Soil carbon (g m )
0
200
400
600
Soil carbon (g m )
800
Soil depth (cm)
a
-5
-10
-10
-15
-15
-20
-20
-25
-25
-30
-30
-35
-35
-40
-45
-50
500
1000
1500
2000
0
0
-5
0
1000
SOC4 in Euc .
SOC4 in Cane
-40
-45
b
SOC 3 in Euc .
SOC 3 in Cane
-50
Figure 8.8. (a) SOC4 by depth in cane fields (n=5) and after 10-13 years of afforestation with Eucalyptus
(n=5) in Hawaii; bars indicate the standard error of the mean, (b) SOC3 in cane fields and after 10-13 years
of afforestation with Eucalyptus. (Redrawn from Fig. 2b and c from page 832 of Bashkin and Binkley 1998).
16
Australian Greenhouse Office
Studies in Hawaii (Binkley and Resh 1999) and the
In contrast to the majority of the afforestation
Ecuadorian Andes (Rhoades et al. 2000) have
generally found that tree-derived soil C accumulated
studies reviewed, some workers have found that soil
C initially increases (Gill and Abrol 1990), or does
while the C4-C sequestered during cropping or
not change over time (Hamburg and Stone 1984).
pasture was lost after afforestation. Bashkin and
Binkley (1998) found that in 0-55 cm soil 10-15 years
Others (Polglase unpub.) have found that there is no
consistent relationship between soil depth and
after afforestation, loss of sugarcane C4-C averaged
change in soil C following afforestation. These
-2
-1
142 g C m yr , and the gain of the eucalypt C3-C
averaged 155 g C m-2 yr-1 (Fig. 8.8). Based on changes
discrepancies, and the large variation in change in
soil C observed among the studies reviewed (Figs
in soil monosaccharides, Trouve et al. (1996) also
inferred the process of substitution between C
8.2 and 8.3), may result from a number of factors.
inherited from the initial savanna and that derived
from eucalypt and pine plantation. They found that
the fraction of C of tree origin was linearly related to
time, prior to reaching equilibrium.
Differences in net accumulation of C in the soil
profile will be influenced by the depthwise inputs of
These include differences among studies such as the
methodologies used, site preparation, previous landuse, climate, soil type, and site management.
Methodologies for determining change in soil C are
discussed in the following Section. Factors affecting
change in soil C are discussed in Section 11.
C to soils following afforestation. In the surface 10 to
30 cm of soil during the first three years of
afforestation, there will be relatively little input from
above-ground litter, yet C from agricultural residues
will continue to decompose. Soil C in surface soil
may decrease as a result. However during this time
at soil depths below 10 cm, inputs of C derived from
deep tree roots may increase (Schiffman and Johnson
1988; Alriksson and Olsson 1995; Quideau and
Bockheim 1996; Jug et al. 1999; Richter et al. 1999).
Whether added C stabilises or declines in the deeper
soil layers will depend on the rate of fine root
turnover. The mass of the fine roots may turnover
about annually, and like leaves, fine roots may reach
their maximum biomass relatively early in stand
development (Grigal and Berguson 1998). Root
turnover may substantially contribute to change in
soil C at depths as great as 100 cm (Brown and Lugo
1990). Van Lear et al. (1995) found that under a 55year-old loblolly pine forest planted on abandoned
agricultural land, nearly 76% of below-ground C was
in the soil (including forest floor and old root
channels), and about 24% was in the root system.
Roots are also major contributors to soil C following
conventional harvest.
9. METHODOLOGICAL ISSUES OF CHANGE
IN SOIL C FOLLOWING AFFORESTATION
In order to assess the changes in soil C after
afforestation and reforestation, temporal
measurements of soil C are needed. Discrepancies
exist in study techniques used to estimate the effect
of land use on change in soil C. In most cases, soil is
sampled only once, and in some cases longer-term
trends are observed in chronosequence studies. Few
workers measured change in soil C by repeated
measures of one site over a prolonged period. There
were also substantial differences in the number of
soils collected to cover temporal, vertical and
horizontal dimensions among the studies reviewed.
In addition, there were differences in the
components of total soil C which were measured,
the chemical analysis procedures used, and whether
soil bulk density was accounted for in the
calculation of soil C content.
National Carbon Accounting System Technical Report
17
9.1 STUDY DESIGN
The most reliable method for measuring C change
involves collecting base-line soil samples prior to
afforestation and subsequent sampling during stand
development. Long-term observations are required
to assess the full impact of land-use change or
management on the dynamics of soil C. In the short
term these effects cannot easily be followed because
of high variability in soil C.
Due to the length of time involved in repeatedsampling studies, indirect methods are commonly
used to measure change in soil C under land-use
change. These include paired-site and
chronosequence studies.
•
Retrospective paired-site studies use the
effects of treatments imposed in the past
either deliberately (by design) or
fortuitously (Powers 1989). A basic
assumption of such studies is that the sites
were initially comparable and the observed
effects are primarily due to the treatment.
Whether sites are comparable or not should
be properly tested to avoid
misinterpretation of the data.
•
Chronosequence studies normally compare
soil data from stands of different ages (Cole
and Van Miegroet 1989). The different plots
represent stages in the sequential
development of soil properties under a
certain land use. It has also been described
as ‘false time’ series because it assumes a
similar initial (‘time-zero’) condition, and
similar site conditions and events. In most
cases the original site conditions are not
documented. Therefore one is not certain
whether a difference between plots has been
caused by a gradual change of properties, or
reflects original differences (Hase and
Fölster 1983; Bruijnzeel 1990).
As highlighted in Section 8, there may be significant
changes in soil C as plantations age, particularly
within the surface 30 cm of soil. However, only 21%
of the sites reviewed had used repeated-sampling
(Fig. 9.1). Paired-site studies with single sampling of
soils were used for most (54%) of the studies
reviewed. Chronosequence studies were used in 25%
of the cases. Furthermore, where paired site or
chronosequence studies were used, the matching of
Repeated measures
21%
Paired sites
54%
Chronosequence
25%
Figure 9.1. Proportion of afforested sites reviewed at which C change (to <30 cm depth) was estimated
using paired site, chronosequence or repeated measure studies.
18
Australian Greenhouse Office
afforested plots to initial soil C conditions was
plot or chronosequence designs, changes were
particularly questionable at 23% of these sites. This
was because comparisons of soil C content between
relatively small compared to those observed at sites
using repeated sampling.
land use, or between stands of varying ages, were
It is possible that studies involving paired sites may
made on a regional scale (Lugo et al 1986; Brown
and Lugo 1990; Alriksson and Olsson 1995;
overestimate C losses when afforested and
cultivated areas are compared. This is because
cultivated lands would be more fertile and the soils
Huntington 1995), or because there were stated
differences between plots in terms of slope or soil
characteristics, or land-use history (Bradstock 1981;
less erodable than those previously abandoned for
Turner and Lambert 2000).
afforestation (Giddens 1957). Using this approach it
is likely that both calculated C losses and potential
Figure 9.2 shows that the three types of studies
gains resulting from changes in land use are most
resulted in different results for change in soil C after
extreme on marginal agricultural land (Huntington
1995). New plantations are often established on
afforestation. There was no significant effect of study
type on C change for soil sampled from >10 cm or
for <30 cm depth. In contrast, there was a significant
infertile soil, either inherently so or as a result of
previous agricultural activities. For example, in
Queensland, Webb et al. (1997) observed that in
effect of study type on the calculated C change
within the <10 cm soil. It appears that at sites where
five ex-agricultural soils there were major
nutritional constraints to the establishment and
surface change in soil C was estimated using paired-
survival of red cedar.
120
80
-2
-1
Change in soil C (g C m yr )
0.30
1.28
40
-0.11
0.06
0.21
0.21
0.44
0
-40
-80
-0.26
<10 cm, ***
>10 cm, ns
<30 cm, ns
-1.99
-120
Paired plots
Chronosequence
Repeated sampling
Type of study
Figure 9.2. The weighted-average C change estimated using paired site, chronosequence or repeated
sampling studies of soils sampled <10 cm, >10 cm, or <30 cm under forests. Bars indicate standard errors
of the means, and numbers above (or below) the bars indicate the weighted-average percentage change in
soil C (% yr-1). Differences in soil C change between studies were:
ns, not significant; and ***, significant at P<0.001. Data sources are listed in Appendix 1.
National Carbon Accounting System Technical Report
19
9.2 SOIL SAMPLING
Three main factors should be considered when
developing soil sampling protocols to monitor
change in soil C. These are depth, intensity per unit
area of site sampled, and the sampling design.
9.2.1 Sampling depth
Measuring changes in soil C to a given depth
become difficult when soil bulk density changes as a
result of plantation establishment (See Section 9.4).
This is likely to be a problem for afforested sites
which have had substantial soil disturbance during
site preparation (e.g. mounding). One way to
overcome the problem of accurately measuring soil
C in the same layer over time is to sample generic
soil horizons, rather than attempt to sample to a
fixed soil depth. For example, Davidson and
Ackerman (1993) noted that sampling by fixed
depths, rather than by generic horizon,
underestimated soil C losses due to cultivation.
Of all the afforestation studies reviewed, only two
(Quideau and Bockheim 1996; Zech et al. 1997)
measured change in soil C in generic soil horizons.
At the remainder of the sites, soil C was measured to
a fixed sampling depth.
Sampling to generic soil horizons would not be
appropriate if soil was disturbed below the depth of
the upper generic soil horizon, or if the upper
generic horizon is relatively deep (i.e. >15 cm). In
such instances, perhaps the best way to monitor
changes in soil C may be to sample soil by a given
mass rather than by a given depth, or volume.
Soil sampling techniques are likely to have a
significant impact on the calculated change in soil C.
Therefore further work is required to investigate the
best possible procedure to accurately measure
changes following afforestation.
20
9.2.2 Sampling intensity
There is considerable heterogeneity in soil properties
at the spatial scale of a few metres or less, and this is
particularly so for soil parameters like SOM content
which are driven by litter inputs. A preliminary soil
survey, and appropriate sampling and planning to
accommodate spatial variation at a plot or
compartment level, are important considerations
when attempting to measure change in surface
soil C.
The sampling intensity varied greatly among the
studies reviewed (Fig. 9.3). For 73% of the studies,
soil C was measured on soil bulked from less than
20 soil samples. This is of concern, particularly when
changes were estimated within the most
heterogeneous surface 10 cm of soil. In a study of
dispersion due to spatial heterogeneity, Trouve et al.
(1996) showed that 25 soil samples collected at 1-m
intervals in each stand gave acceptable precision for
C content.
9.2.3 Sampling design
There are four options for sampling design:
complete enumeration, simple random sampling,
systematic sampling and stratified random
sampling. For C inventory, stratified random
sampling generally yields more precise estimates for
a fixed cost than the other options (MacDicken
1997). Stratified random sampling involves dividing
the population into stratum (or sub-populations)
which can be defined by vegetation, soil type, or
topography. Raison and Khanna (1995) found that in
a native forest site, by stratifying soil samples into
unburnt, burnt and ashbed components, significant
effects of slash management on soil C were
observed. In afforested sites which have been
mounded or ripped, stratified random sampling
may be appropriate. Soil should be sampled from
both disturbed and undisturbed strata.
Australian Greenhouse Office
Number of observations
100
80
60
40
20
0
5
10
15
20
25
30
35
40
45
50
55
Number of soil samples taken in the field
Figure 9.3. Frequency distribution of the number of soil samples taken from the field at sites in which
change in soil C was measured following afforestation (Appendix 1). For studies in which there was a
range in the number of soil samples for various plots, the midpoint of that range was plotted.
9.3
SOIL C FRACTIONS AND CHEMICAL
ANALYSIS
Conceptually, C in a soil sample can be divided into
three components: (1) organic matter; (2) non-living
root C, and (3) charcoal and inorganic C. In practice
however it is sometimes difficult to separate these
components. It is particularly difficult to separate
live roots from fine mineral soil. The surface litter
layer is an additional pool of detrital C. From an
inventory or modelling perspective, the litter layer
may be defined as another component of soil C.
Differences in soil preparation prior to analysis, and
the type of chemical analysis procedure used, can
lead to discrepancies in the components of soil C
measured.
9.3.1 Sieving
In a majority (57%) of the afforestation sites
reviewed, soil C was measured in the <2 mm
fraction only (Fig. 9.4). Few studies (2%) analysed C
in <5 or <7 mm sieved fractions. In 41% of the
studies reviewed, soil was unsieved. If there was no
record of soil sieving procedures provided, it was
assumed that the soil sample was unsieved.
National Carbon Accounting System Technical Report
21
Not sieved
41%
<2 mm
57%
<5 to <7 mm
2%
Figure 9.4. Proportion of studies at which soil C was measured in sieved (<2 mm, or <5 to <7 mm) or
unsieved soil.
After sieving, the soil fraction greater than 2 mm (or 5 mm) is commonly discarded. The weight of the
discarded material may constitute only a small fraction of the total mass. However, the soil C that this
discarded material contains can be a significant fraction of the total soil C. For example, in soil from pine
forest at Woodburn, NSW, it was observed that the weight of the >2 mm and charcoal fraction was 0.82% of
the total weight but it contained 23.2% of the total soil C (Table 9.1).
Table 9.1. Mass and C content of various soil fractions (0-30 cm depth) in Woodburn (NSW) soil
(Polglase and Snowdon, unpub.).
Fraction
Mass
Contribution to total mass
Carbon
Contribution
to total Carbon
(g m-2)
(%)
(g C m-2)
(%)
<2 mm
3,503
99.18
3,640
76.9
>2 mm
22
0.62
780
16.4
Charcoal
7
0.20
320
6.8
3,532
100.00
4,740
100.0
Total
22
Australian Greenhouse Office
The analysis of C in sieved soil will have substantial
implications for calculated change in soil C
following afforestation. Sieving will remove
fragments of litter, dead roots and fungal hyphae
that should be included when estimating soil C
following afforestation. There is likely to be more
coarse organic material under plantations compared
to pasture (Carlyle, unpub.), although contributions
by roots may differ. In the north coast of NSW,
Turner and Lambert (2000) observed that root
material under pastures was about 40% of that
under pines to both 30 cm and 100 cm depth.
Similarly, within 0-100 cm soil, Rhoades et al. (2000)
found that fine roots were 163-753 g m-2 (<1 mm)
and 1-71 g m-2 (1-3 mm) under various pastures and
sugar cane. Under adjacent afforested sites, <1 mm
roots were generally lower (averaging 134 g m-2),
while 1-3 mm roots were generally higher
(averaging 154 g m-2) than observed in agricultural
soils.
9.3.2 Chemical analysis
In 50% of the studies reviewed, soil C was
determined using wet chemical oxidation procedure,
(i.e. Walkley-Black method, Fig. 9.5), 47% of studies
used a dry combustion procedure (e.g. LECO or
Dumas combustion). Only 3% of the studies
reviewed determined soil C from loss-on-ignition.
The dry combustion methods measure total soil C,
and includes inorganic forms such as charcoal or
carbonates. The LECO dry combustion method is
currently widely used in Australia. In the original
Walkley-Black method, the chemical reaction may
not be driven to completion due to insufficient heat.
Wet oxidation methods may also underestimate soil
C content in soils containing high concentrations of
charcoal. By analysing historical data from a wide
range of Australian soils, Skjemstad et al. (2000)
calculated correction factors ranging from 1.12 to
1.34 to convert Walkley-Black data values to values
equivalent to combustion methods.
Loss on ignition 3%
Wet chemical oxidation
50%
Dry combustion
47%
Figure 9.5. Proportion of afforested sites reviewed at which soil C was analysed using wet chemical
oxidation (i.e. Walkley-Black method), dry combustion (e.g. Leco or Dumas combustion), or was calculated
using loss-on-ignition.
National Carbon Accounting System Technical Report
23
In surface soil the history of site management
(frequency and intensity of burning residues) will be
an important determinant of C content. Skjemstad
et al. (1996) observed that 30% of C in four surface
soils occurred as charcoal. The quantity of charcoal
deeper in the soil is expected to be much lower. In
the Woodburn forest where slash was burnt at the
time of plantation establishment, coarse charcoal
was 6.8% of total soil C (Table 9.1) and one can
assume that there was a significant proportion of
9.3.3 Inclusion of litter as soil C
There may be large amounts of C within the litter
layer of forest sites (Table 9.2). Litter is generally not
defined as soil C and was thus not measured in the
majority of studies (Fig. 9.6). There were only 34
sites at which C changes following afforestation
were measured in both mineral soil and the litter
layer. This represented only 19% of those sites where
soil was sampled to a depth of less than 30 cm
(Fig. 9.6).
fine charcoal which remained undetected (Polglase
and Snowdon, unpub.).
Table 9.2. Amount of C in various components of a 20-year-old Pinus radiata plantation near Canberra,
Australia. Per cent values for various components refer to the respective total amounts in the aboveground or below-ground fractions. Based on data from Ryan et al. (1996).
(g C m-2)
(%)
930
7.7
Branches
1,890
15.7
Stem wood+bark
9,200
76.5
680
11.2
2,540
41.9
260
4.3
2,590
42.7
Component
Above-ground
Leaves and twigs
Understorey
Below-ground
Litter layer
Soil 0-60 cm
Fine roots <5 mm
Coarse roots
24
Australian Greenhouse Office
Soil+Litter
19%
Soil
81%
Figure 9.6. Proportion of afforested sites reviewed at which C content of the mineral soil alone was
measured, and where C content of both the litter and the mineral soil was measured.
The inclusion of the litter layer often has a significant effect on the calculated change in soil C density
following afforestation (Fig. 9.7). In mineral soil there was a weighted-average decrease in C at all sampling
depths, but inclusion of litter resulted in a net increase in soil C at all depths.
These results are consistent with a number of studies which have demonstrated a decrease in soil C in the
mineral soil, but a net increase or insignificant change in soil C when the litter layer is included in the
calculation (Hamburg 1984; Sparling et al. 1994; Richter et al. 1995; Giddens et al. 1997; Parfitt et al. 1997; Ross
et al. 1999; Scott et al. 1999; Gifford 2000). For example, under loblolly pine (Pinus taeda L.) established on
previously cultivated soil, Richter et al. (1999) found that approximately 96% of the accumulated C was in the
forest floor.
National Carbon Accounting System Technical Report
25
80
-2
-1
Change in soil C (g C m yr )
120
<10 cm, ns
>10 cm, ***
<30 cm, *
1.03
0.87
0.42
40
0
-0.34
-40
-0.16
-0.95
-80
-120
Mineral soil
Mineral soil + litter
Inclusion in soil C
Figure 9.7. The weighted-average C change observed in mineral soil, or mineral soil+litter, sampled from <10
cm, >10 cm or <30 cm under forests. Bars indicate standard errors of the means, and numbers above (or
below) the bars indicate the weighted-average percentage change in soil C.
ns, not significant. *, significant at P<0.05. ***, significant at P<0.001. Data sources are listed in Appendix 1.
Due to the limited number of sites at which litter C content was measured, in this review C change within
the mineral soil alone was reported. However, estimates of C storage in litter layers of various forest types
are given in Table 9.3. In Australia, the litter C storage had been shown to be between 600 and 1,610 g C m-2
under radiata pine plantations (Forrest and Ovington 1970; Florence and Lamb 1974; Baker and Attiwill 1985;
Turner and Kelly 1985; Birk 1992), and between 380 and 2,200 g C m-2 under various eucalypt plantations
(assuming soil C content of the litter dry mass is 50%, Turner and Lambert 1996). For example, nine years
after afforestation with eucalypt plantations in south-west Western Australia, Sparling et al. (1994) observed
that C addition from litter was 407 g m-2.
26
Australian Greenhouse Office
Table 9.3. Mean C content in the litter layer of various forest types (from Vogt et al. 1986). It was assumed
that the C content of litter was 50%.
Forest type
Carbon content
(g C m-2)
Tropical broadleaf evergreen
1,130
Tropical broadleaf deciduous
440
Tropical broadleaf semi-deciduous
110
Subtropical broadleaf evergreen
1,110
Subtropical broadleaf deciduous
410
Mediterranean broadleaf evergreen
570
Warm temperate broadleaf evergreen
960
Warm temperate broadleaf deciduous
570
Warm-temperate needle-leaf evergreen
1,000
Cool temperate broadleaf deciduous
1,610
Cold temperate needle-leaf evergreen
2,230
Cold temperate needle-leaf deciduous
700
Boreal needle-leaf evergreen
2,230
9.4 SOIL BULK DENSITY
The bulk density of forest soils is generally closely
and inversely related to the organic fraction of the
soil (Fedora et al. 1993). Although there may be no
significant change in bulk density following
afforestation (Lugo et al. 1986; Giddens et al. 1997),
a number of workers have observed that bulk
density decreases (Birk 1992; Jenkinson et al. 1992).
The potential change in bulk density with land use
and time needs to be considered in estimating
change in soil C. Measurement of bulk density at
each sampling time could overcome this limitation,
but with the uncertainty surrounding bulk density
measurements, the limitation still exists.
Bulk density was not measured in 23% of the
afforestation sites reviewed (Fig. 9.8). At these sites,
bulk density (BD) was estimated using the
following equation:
BD= 100/[(%OM/BDOM) + ((100-%OM)/BDmin soil)]
where
%OM is percent soil organic matter,
BDOM is the bulk density of the organic matter
(assumed to be 0.244), and
BDmin soil is the mineral soil bulk density (assumed
to be 1.64) (Adams (1973).
Using the calculated soil BD and concentration of
soil C reported, soil C density (g m-3) could be
calculated.
There are also limitations in using soil cores to
estimate soil rock and gravel content. Hamburg and
Stone (1984) suggested that soil pit sampling was
advantageous in that soil rock volume could be
measured directly.
National Carbon Accounting System Technical Report
27
Calculated
23%
Measured
77%
Figure 9.8. Proportion of afforested sites reviewed at which soil bulk density was measured, or calculated
using the Adams (1973) equation.
10. CONCEPTUAL FRAMEWORK FOR
UNDERSTANDING CHANGE IN SOIL C
FOLLOWING AFFORESTATION
The establishment of plantations on agricultural
land markedly changes cycling of C between plant
and soil. Many processes are affected and these may
modify either inputs of fresh C to soil (amount and
quality) or outputs from decomposition. Controlling
factors may be abiotic or biotic in nature.
This section develops a conceptual framework for
understanding change in soil C after afforestation.
This is to be used for identifying key controlling
processes and where further research may be needed
to develop an enhanced modelling capability.
28
10.1 CARBON BALANCE
The important components of C allocation and
balance in an aggrading forest are shown in Figure
10.1. The primary driver is the amount and temporal
pattern of net primary production (NPP) — the net
amount of C captured by the plantation and which
then is distributed to various tree components.
Patterns of allocation, particularly to roots and the
rate at which these live roots turnover (or sloughed
off) and then decay, become secondary determinants
of change in soil C. Finally, the time taken for
litterfall to establish and rates of litterfall
decomposition (transfer to humus) also affect
temporal dynamics of soil C following afforestation.
Australian Greenhouse Office
1
residues can be relatively quick to establish
something of an equilibrium rate of return, it takes
many more decades for soil C to come into
equilibrium with these inputs.
The above simple framework makes it clear that is
impossible to sensibly interpret change in soil C
without reference to C dynamics in living biomass,
and also to the C cycle in the pre-existing
agricultural phase. The analysis below is therefore
centred on amounts and allocation of C in a newlyplanted forest and transfers from residues to soil.
2
5
3
4
Figure 10.1. Components of C balance that
determine change in soil C following afforestation.
1 Amounts and patterns of net primary
production (NPP)
2 Allocation of NPP to components, particularly
fine roots
3 Root longevity
4 Root decomposition rates
5 Accession of C in litterfall and
decomposition rates.
The change in soil C is dictated by the balance
between inputs and outputs which, if in equilibrium
in the previous agricultural soil, can be greatly
disturbed by plantation establishment. The C
balance in a growing plantation remains in
disequilibrium for a long time. This applies
particularly to soil, where C has a relatively long
mean residence time. Thus, whilst inputs of C in
10.2 AMOUNTS AND PATTERNS OF NET
PRIMARY PRODUCTION
Following afforestation, the time taken for NPP to
reach its maximum level, and the quantity of that
maximum, are important considerations of changes
in soil C. Growth rates of tree biomass are well
described over the short term by sigmoidal
relationships, but patterns of NPP and thus of
inputs in roots and litterfall may follow different
temporal patterns.
Temporal patterns and amounts of NPP depend on
climate, site conditions, species, and management
impacts such as weed control and fertiliser addition.
Few studies have measured maximum NPP (aboveand below-ground components) in Australian
forests, let alone monitored how NPP changes with
time. We thus look to validated models to indicate
the range in patterns and amounts of NPP that can
be expected. One such model is CABALA, a
successor to the PROMOD model that has been
calibrated and extensively applied to blue gum
plantations in Western Australia. The model
specifically predicts allocation of C to plant
components according to site conditions and their
effect on tree physiology. It also includes turnover of
leaves, branches, bark, and coarse and fine roots. Its
main application in forestry is to predict temporal
gains in stem volume, against which it has been
extensively validated (Battaglia and Sands 2000).
National Carbon Accounting System Technical Report
29
Figures 10.2 and 10.3 show predicted output for
significant implications in terms of change in soil
CABALA for Eucalyptus globulus on two sites of
contrasting productivity in WA. Figure 10.2 shows
C following afforestation.
the predicted temporal patterns of stem volume and
annual rates of NPP. The Esperance site was more
productive than the Darkan site. Root slough was
For purposes of modelling, an important
consideration in predicting change in soil C is
comparative NPP between the agricultural and
plantation phases. Whilst it may be assumed that at
predicted to be about 30% of litterfall at Esperance
long-term agricultural sites, crops or pastures may
be at or approaching an equilibrium NPP, Figure
and about 50% of litterfall at Darkan, absolute
values of root slough being comparable at the two
10.2 clearly shows that plantation NPP, and hence
sites (Fig. 10.3). Thus at the more productive
inputs, varies with stand age. Further work is
required to determine the change in NPP over time
Esperance site a greater proportion of NPP goes to
above-ground biomass, including foliage which is
under plantations of varying productivity.
cast off as litter. Such site differences will have
4000
200
3000
150
2000
100
1000
50
NPP (g DM m-2 yr-1)
3
-1
Volume (m ha )
250
Esperance
0
0
Darkan
3 -1
Volume (m ha )
Volume
NPP
150
2000
100
1000
50
0
NPP (g DM m-2 yr-1)
3000
200
0
1
2
3
4
5
6
7
8
9
10
Age (yr)
Figure 10.2. Patterns of volume gain and annual net primary production (dry matter, DM) in Eucalyptus
globulus for two sites differing in productivity. Output is from the CABALA model (Battaglia, unpub.).
30
Australian Greenhouse Office
analogous to leaves and are central to replenishing
soil C particularly given that sloughed roots are
added directly to the soil humus pool.
The allocation of NPP to fine roots can be
determined by a number of methods (Publicover
and Vogt 1993; Fahey et al. 1998). However, inherent
in all of these methods are problems in
distinguishing dead from live roots, and accounting
1200
Esperance
1000
800
600
400
200
0
1000
litterfall
Darkan
-2
-1
litterfall or root slough (g DM m yr )
litterfall or root slough (g DM m-2 yr-1)
10.3 ALLOCATION OF NPP TO FINE ROOTS
Tree roots can be categorised into structural (coarse),
medium and fine roots. Structural roots, being
analogous to stems, have no role in short-term soil C
dynamics. Medium roots (>10 mm diameter for
example) can be considered analogous to twigs and
branches and can be important in short to medium
term soil C dynamics. Fine roots (< 3 mm) are
root slough
800
litterfall+root slough
600
400
200
0
1
2
3
4
5
6
7
8
9
10
Age (yr)
Figure 10.3. Patterns of annual litterfall and root slough (dry matter, DM) in Eucalyptus globulus for two
sites differing in productivity. Output is from the CABALA model (Battaglia, unpub.).
National Carbon Accounting System Technical Report
31
for decay of sloughed roots. For these reasons,
(range 22% - 38%). Gower et al. (1999) reviewed data
modelling exercises that calculate C allocation to
roots are useful because they ensure that ecosystem
on C allocation, giving the ratio of below-ground
C balances are internally consistent. The greatest
difficulty in this approach is in partitioning C
allocated below-ground between coarse (structural),
(total root) allocation to total NPP (Fig. 10.4).
For tropical and temperate forests, allocation to roots
is generally less than 20%, whereas for grasses
medium and fine roots.
allocation is closer to 60% (Figure 10.4). Given that
the values for trees include coarse roots, allocation to
Tables 10.1 and 10.2 list measured and modelled
fine roots will be less (perhaps half) of the 20%
allocation of C to fine roots of trees for a variety of
shown here. These results to some extent are
contrary to those in Tables 10.1 and 10.3.
sites. Table 10.3 gives select examples for C
allocation to fine roots of grasses and crops. As
Nonetheless, it is apparent that, compared to
expected, there is great variation in allocation of C to
grasses, trees may allocate less C to fine roots.
fine tree roots, data ranging from 5% - 68% of total
NPP (Table 10.1). The mean allocation of C to fine
For a particular tree species, climate and soil type
tree roots was only 27% (Table 10.1). Modelled
values for E. globulus growing in WA averaged 14%
allocation. For the crops and grasses listed in Table
10.3 mean C allocation to fine roots was 30%
will influence C allocation to fine roots. It is likely
that C allocation to fine roots will be greatest at
afforested sites which have a high rainfall, are
relatively fertile, and have well-textured soils.
Table 10.1. Measured allocation of total NPP to roots for a range of sites (Santantonio 1989).
Species
Location
Age
Allocation to fine roots
(yr)
(%)
Abies amabilis
Washington, USA
23
46
A. amabilis
Washington, USA
180
68
Picea sitchensis
Scotland, UK
17
15
Pinus contorta
British Colombia, Canada
NA
50
P. contorta
British Colombia, Canada
NA
62
P. contorta
British Colombia, Canada
NA
31
P. contorta
British Colombia, Canada
NA
39
P. elliottii
Florida, USA
8
5
P. elliottii
Florida, USA
26
14
P. radiata
New Zealand
12
5
P. radiata
New Zealand
12
6
P. sylvestris
Sweden
20
51
P. sylvestris
Sweden
20
26
P. sylvestris
Sweden
120
36
Pseudotsuga menziesii
Oregon/Washington, USA
40
36
P. menziesii
Oregon/Washington, USA
40
8
P. menziesii
Oregon/Washington, USA
70
33
P. menziesii
Oregon/Washington, USA
170
46
P. menziesii
Oregon/Washington, USA
120
27
32
Australian Greenhouse Office
Table 10.2. Modelled allocation of total NPP to roots for a range of sites.
Species
Location
Age
Allocation to
total roots
Allocation to
fine roots
(yr)
(%)
(%)
Reference
Eucalyptus globulus
Western Australia
10
27
14
Battaglia (unpub.)
E. globulus
Western Australia
10
29
9
Battaglia (unpub.)
E. globulus
Western Australia
10
26
13
Battaglia (unpub.)
E. globulus
Western Australia
10
20
8
Battaglia (unpub.)
E. globulus
Western Australia
10
47
24
Battaglia (unpub.)
E. globulus
Western Australia
10
23
6
Battaglia (unpub.)
E. globulus
Western Australia
10
23
8
Battaglia (unpub.)
E. globulus
Western Australia
10
28
12
Battaglia (unpub.)
Pinus sylvestris
Finland
NA
23
NA
Makela and Hari (1996)
Pseudotsuga menziesii
NA
40
50
22
Bartelink (1998)
P. menziesii
NA
40
53
40
Bartelink (1998)
Fagus sylvatica
NA
40
42
27
Bartelink (1998)
F. sylvatica
NA
40
58
48
Bartelink (1998)
Table 10.3. Examples of allocation of NPP to roots in grasses and agricultural systems.
Species
Location
Fertility
Medicago truncataula
South Australia
NA
32
Crawford et al. (1997)
Hordeum leporinum
South Australia
NA
33
Crawford et al. (1997)
Vicia faba
South Australia
NA
22
Crawford et al. (1997)
Bromus erectus
Switzerland
Nutrient poor
44
Schlapfer and Ryser (1996)
Arrhenatherum elatius
Switzerland
Nutrient poor
38
Schlapfer and Ryser (1996)
Dactylis glomerata
Switzerland
Nutrient poor
28
Schlapfer and Ryser (1996)
D. glomerata
Switzerland
Intermediate
30
Schlapfer and Ryser (1996)
D. glomerata
Switzerland
Intermediate
30
Schlapfer and Ryser (1996)
D. glomerata
Switzerland
Intermediate
23
Schlapfer and Ryser (1996)
D. glomerata
Switzerland
Rich
30
Schlapfer and Ryser (1996)
D. glomerata
Switzerland
Rich
28
Schlapfer and Ryser (1996)
D. glomerata
Switzerland
Rich
22
Schlapfer and Ryser (1996)
National Carbon Accounting System Technical Report
Allocation to roots (%)
Reference
33
Allocation of NPP to roots
0.8
0.6
0.4
0.2
0.0
A
B
C
D
E
F
G
H
Forests
I
J
K
Grassland/crops
Figure 10.4. Comparison of forests and grasslands/crops in allocation of total NPP to roots (after Gower
et al. 1999) The letters A – K refer to various biomes. A-tropical deciduous broad-leaved, B-tropical
evergreen broad-leaved, C-temperate evergreen broad-leaved, D-temperate deciduous broad-leaved, Etemperate evergreen needle-leaved, F-boreal deciduous broad-leaved, G-boreal evergreen needle-leaved,
H-grassland and tropical savannas, I-crops, J-arctic tundra, K-desert.
10.4 ROOT LONGEVITY
Few data are available to demonstrate the longevity of tree roots. If fine roots were directly analogous to
foliage, it could be assumed that roots live for between one year (productive sites) and three years (less
productive sites). Most estimates of root longevity, used in modelling studies, are assumed values. Some
examples are provided in Table 10.4.
Table 10.4. Root longevity assumed for various models.
Species
Location
Root life-time
Type of roots
(yr)
(fine or total)
Reference
Pinus sylvestris
Sweden
3-5
Fine
Nakane (1984)
P. densiflora
Japan
3-5
Fine
Nakane (1984)
P. elliottii
Florida
3-5
Fine
Nakane (1984)
P. radiata
Canberra
3-5
Fine
Nakane (1984)
Picea spp.
UK
1
Fine
Dewar and Cannell (1992)
Salix spp
UK
1
Fine
Dewar and Cannell (1992)
Populus spp.
UK
1
Fine
Dewar and Cannell (1992)
Nothofagus spp.
UK
1
Fine
Dewar and Cannell (1992)
Pinus spp.
UK
1
Fine
Dewar and Cannell (1992)
Quercus spp.
UK
1
Fine
Dewar and Cannell (1992)
P. sylvestris
Sweden
1.3
Fine
Makela (1986)
P. sylvestris
Sweden
10
Total
Makela and Hari (1986)
Eucalyptus globulus
WA, Australia
1
Fine
M. Battaglia (unpub.)
34
Australian Greenhouse Office
10.5 ROOT DECOMPOSITION RATES
There is some evidence that decomposition of roots
is slower than that of leaves for a wide range of
agricultural sites (Amato et al. 1987; Scheu and
Schauermann 1994). However, compared to aboveground decay little is known of root decomposition
rates in forests, particularly in Australia. This is
primarily due to the practical difficulties, and
consequent errors they introduce, in measurement
of root decay.
Data from litterbag experiments have shown the
decay of some large roots to be extremely slow
(Table 10.5; Yavitt and Fahey 1982; Fahey et al. 1985),
whereas other (Scheu and Schauermann 1994) have
observed no difference in decomposition rate
between fine and coarse roots.
It is possible slow rates of decomposition observed
in litterbag studies were an artefact of that
methodology (Fahey and Arthur 1994). Minirhizotron studies have indicated that decomposition
Some rates of root decay are summarised in Table
of roots may be considerably faster than previously
10.5. Rates vary, but appear to be related to broad
climatic zones. Decomposition of fine roots appears
thought (Hendrick and Pregitzer, 1993; Fahey and
Hughes, 1994).
to be fastest in sub-tropical zones and slowest in
cool temperate zones.
Clearly, the decomposition rate of roots needs
further investigation for tree species across a range
Differences in decomposition rates between fine (<3
of sites.
mm) and large woody (>10 mm) roots are not clear.
Table 10.5. Decomposition constants (k) for decay of coarse and fine roots.
Species
Location
Coarse roots
(>10 mm)
Fine roots
(<3 mm)
k (yr-1)
k (yr-1)
Reference
Pinus, Quercus, Rhododendron sp.
Subtropical India
NA
0.67
Arunachalam et al. (1996)
Pinus, Quercus, Rhododendron sp.
Subtropical India
NA
0.69
Arunachalam et al. (1996)
Pinus, Quercus, Rhododendron sp.
Subtropical India
NA
0.69
Arunachalam et al. (1996)
Alnus glutinosa
South Quebec, Ca
NA
0.43
Camiré et al. (1991)
Populus sp.
South Quebec, Ca
NA
0.40
Camiré et al. (1991)
Mixed hardwoods
Maine, USA
NA
0.43
Lytle and Cronan (1998)
Mixed hardwoods
New Hampshire, USA
NA
0.21
Fahey et al. (1998)
Subtropical rainforest
Puerto Rico
NA
0.54
Silver and Vogt (1993)
Mixed hardwoods
New Hampshire, USA
0.07
0.24
Fahey et al. (1988)
Mixed hardwoods
New Hampshire, USA
0.15
Fahey and Arthur (1994)
Mixed hardwoods
New Hampshire, USA
0.02
Yavitt and Fahey (1982)
Fraxinus excelsior
Germany
0.27
0.13
Scheu & Schauermann (1994)
F. excelsior
Germany
0.27
0.27
Scheu & Schauermann (1994)
National Carbon Accounting System Technical Report
35
10.1.6 Litterfall and litter decomposition
Generally it can be expected that it will take three to
six years for rates of litterfall in plantations to reach
their maximum value. In mature stands, however,
rates of litterfall vary with productivity and species.
For mature native forests in temperate regions of
Australia, the fall of dead leaves is well correlated
to total litterfall and reaches a maximum of about
140 g C m-2 yr-1 (Attiwill et al. 1996). For closedcanopy eucalypt plantations, litterfall is dominated
by leaf-fall, and is generally in the range 100 to
400 g C m-2 yr-1. The difference between native and
plantation forests generally reflects the higher
productivity of managed plantations compared to
older and unmanaged native forest.
Much has been written on factors affecting litter
decomposition (Melillo et al. 1989; Berg et al. 1993;
1.0 yr-1. For eucalypts, decomposition rates for the
total pool of litter (leaves, twigs and branches, other
components) varies between 0.13 and 0.35 yr-1
(n=20) with a mean value of 0.25 yr-1 (Attiwill et al.
1996). Total litter pools have decomposition rates of
between 0.30 to 0.65 yr-1 under northern hemisphere
pines, and between 0.08 and 0.47 in northern
hardwoods (O’Connell and Sankaran 1997).
Temporal patterns of leaf and needle decomposition
generally conform to a double exponential model,
confirming the existence of labile and resistant
pools. Rates of decomposition are commonly
expressed as instantaneous rate constants, first-year
mass loss, or in shorter-term studies graphed as
percentage of initial mass remaining, from which
first-year mass can be calculated (Table 10.6). For
convenience we assume a single-exponential rate of
Couteaux et al. 1993); this literature will not be
reviewed in detail here. In practical terms, C can be
considered to remain as part of the litter pool (forest
decay.
floor) until such time as litter biomass becomes so
fragmented as to be indistinguishable from soil. The
process of litter transformation is given a collective
mL = 100. (1- e-kt)
term of humification. Models of litter decay assume
that about 0.04 to 0.5 of C in litter becomes humus
(the humification coefficient- Dewar and Cannell
1992; Goudriaan 1992; Nakane 1994).
Decomposition of litter is faster under eucalypts
than conifer plantations. Needle litter tends to
remain as semi-decomposed residues on the soil
surface (Nakane 1994). Attiwill et al. (1996)
summarised data for native forests in south-eastern
Australia and found that the mean leaf
decomposition constant (k) for a wide range of sites
and climates was 1.7 yr-1 (range 0.67-3.7 yr-1, n=17).
However, these values were determined as the ratio
of litterfall:mass of the standing crop of litter. In this
situation fragmented leaves were classified into an
indeterminate ‘miscellaneous’ category, thus leading
to slight over-estimation of decomposition rates.
More typical rates come from litterbag studies such
as those of O’Connell (1995) where decomposition
constants for eucalypt leaves varied between 0.4 and
36
The basic equations are:
(1)
where
mL is 1st-yr mass loss (% of initial),
k is the instantaneous decomposition constant (yr-1),
and
t is time (yr).
Thus, the decomposition constant can be calculated
from 1st-year mass loss (t = 1 yr), by
k = -ln.(1- mL/100)
(2)
and the time taken (yr) to reach any stage of
decomposition can be calculated as
t = -ln. (1 – mL / 100)/ k
(3)
Example calculations are summarised in Table 10.6.
Depending on the climate and substrate quality of
litter, it may take one to six years before litter can be
considered to be intimately mixed with soil. This
logistical separation needs to be borne in mind when
constructing decomposition models.
Australian Greenhouse Office
Table 10.6. Relationships for litter decomposition between first-year mass loss, the decomposition
constant, and the time taken to reach 90% mass loss (the stage at which it is assumed that litter becomes
soil humus). Values are derived from equations 1, 2 and 3 above.
First-year mass loss
k
Time to reach 90% mass loss
-1
(% of initial)
(yr )
(yr)
10
0.11
21.85
20
0.22
10.32
30
0.36
6.46
40
0.51
4.51
50
0.69
3.32
60
0.92
2.51
70
1.20
1.91
80
1.61
1.43
90
2.30
1.00
95
3.00
0.77
97
3.91
0.59
99
4.61
0.50
11. FACTORS AFFECTING SOIL C
In the following section we assess the various factors
which will affect change in soil C under plantations
on ex-agricultural land. Issues considered are:
•
disturbance or site preparation;
•
previous land use;
•
productivity and allocation of C;
•
climate and microclimate;
•
soil texture;
•
site management; and,
•
harvesting.
11.1 SITE PREPARATION
Site preparation is practiced for several reasons to:
reduce competition with weedy plants, reduce soil
strength to allow better root penetration, modify
effective soil depth, and improve water infiltration,
drainage and nutrient availability.
Soil C is commonly decreased following site
preparation (Alegre and Cassel 1986; Johnson 1992;
Smethurst and Nambiar 1995; Trouve et al. 1996;
Grigal and Berguson 1998; Brand et al. 2000; Turner
and Lambert 2000), probably due to: soil disturbance
during mechanical treatments (i.e. ploughing,
ripping and mounding), lack of plant growth, and
burning.
This analysis is used to identify those factors that
will be most important for model development and
testing. The framework also helps to interpret some
of the changes in soil C identified from the review of
available data.
National Carbon Accounting System Technical Report
37
11.1.1 Mechanical site treatment
Mechanical site treatment on ex-agricultural sites
may involve pitting (manual digging of a planting
hole), scalping, ripping of soil to varying depths,
broadcast ploughing, disc cultivation, ridging or
mounding of soils, or various combinations of these
operations. The type of mechanical treatment which
may be required varies according to ground cover,
slope and soil conditions (for review, see Florence
1996). For example, mounding is a standard site
preparation practice in many coastal and wet areas
to improve drainage, the root environment for better
nutrition, aeration, temperature and moisture, and
to reduce competition from weedy species.
nutrient-rich surface soil near the tree and
Mechanical disturbance of the soil is thought to
accelerate decomposition. Also, cultivation and
along the planting row. For all sampling depths
reviewed, Figure 11.1 shows that there is no
particularly mounding may lead to soil C loss via
erosion. The practice of mounding also concentrates
significant difference between these defined
accelerates mineralisation of nutrients (Grove et al.
2000). It may also result in the movement or loss of
fine soil particles during erosion of mounds by wind
or water.
The afforestation sites reviewed in Section 8 were
categorised into two levels of mechanical
disturbance following site preparation
(high/medium and low). We define a high/medium
level of mechanical disturbance of soil during site
preparation as mounding, ripping, broadcast
cultivation or disc cultivation. Low-level mechanical
disturbance is defined as no preparation, pitting, or
no more than one pass with a tyned implement
disturbance levels on the resultant change in soil C.
120
80
Change in soil C (g C m -2 yr -1)
0.11
0.39
40
0.44
0.13
0.12
0
-0.16
-40
<10 cm, ns
>10 cm, ns
-80
<30 cm, ns
-120
High/Medium
Low
Disturbance level
Figure 11.1. The weighted-average C change estimated for soils sampled from <10 cm depth,
>10 cm or <30 cm under forests following high-medium or low disturbance during site preparation.
Bars indicate standard errors of the means. Numbers above (or below) the bars indicate the weightedaverage percentage change in soil C (% yr-1). ns, not significant. Data sources are listed in Appendix 1.
38
Australian Greenhouse Office
Soil disturbance during site preparation is expected
•
to change soil C. Therefore the effect of disturbance
level was separately investigated in the studies that
causes loss of soil C, but hard evidence for
this is lacking. Mounding and line ripping
causes localised soil disturbance. In the
were less than ten years of age. However, even in
these relatively short-term studies there remained no
significant effect of disturbance level on change in
majority of studies soil samples are taken
from an inter-row away from disturbed
areas;
soil C (data not shown). As is evident from Figure
11.1, this lack of significance may be related to high
variability in the data on changes in soil C.
•
Although there is not a universal effect of
disturbance level on change in soil C, it is possible
•
typically for conversion of tropical forest to
cultivated land which have been intensively
and repeatedly cropped. This is very
review of over 600 soil profiles worldwide under
both forest and prairie systems, Mann (1985, 1986)
found that cultivation resulted in a substantial net
different to single cultivation of agricultural
land for afforestation, suggesting that the
magnitude of the effect may not be the
loss (at least 20%, mostly in the plough layer) in soils
that were initially relatively high in C, but a slight
net gain in soils that were initially low in C (Johnson
same;
•
1992).
agricultural land that has been previously
intensively cropped and cultivated will
The effect of mechanical disturbance on soil C may
contain C that is more resistant to significant
further loss after cultivation (see Section
also depend on the time period considered. As
discussed in Section 11.2.2, there is much evidence
11.2);
that cultivation accelerates decomposition and thus
leads to a rapid initial decrease in soil C. Carbon
losses have been observed to occur within minutes
of plough tillage forcefully fracturing the soil,
releasing CO2 stored in soil pores and water
•
(Reicosky et al. 1997). However, Aslam et al. (2000)
demonstrated that although freshly cultivated land
may have enhanced CO2 emissions as compared
We make the following comments on evidence for
disturbance effects on soil C:
the strong evidence for loss of soil C under
prolonged cultivation (Mann 1985, 1986) is
C loss, by soil disturbance may be dependent on soil
type and particularly the initial soil C content. In a
tilled and untilled soils. In an afforested pine-oak
stand in central Massachusetts, Compton et al. (1998)
noted that although ploughing had important shortterm effects on soil C storage, long-term (>40-60
years) impacts were not observed.
mechanical site preparation will invariably
decrease soil bulk density and increase
variability in measuring change in soil C;
that the stimulation microbial activity, and thus soil
with untilled soil, once the cultivated seedbed was
re-compacted, CO2 emissions were similar between
it is often assumed that site preparation
for modelling changes in soil C due to site
disturbance it may be possible to stratify the
area according to different disturbance
classes ranging from undisturbed to highly
disturbed. No information on disturbance
classes is presently available to include in
modelling exercises.
11.1.2 Burning of biomass residues
Burning of vegetation residues in native forest or
plantations may cause a slow but long-term increase
in charcoal (Section 11.5.7). In contrast to native
forest or previous plantation land, it is unlikely that
burning of vegetation residues during site
preparation for afforestation will have a significant
impact on charcoal production in Australia,
primarily because residues on ex-agricultural land
produce little charcoal due to the lack of woody
components (Schiffman and Johnson 1988).
National Carbon Accounting System Technical Report
39
11.1.3 Weed control and lack of plant growth
Herbicide is commonly applied prior to plantation
establishment to control agricultural weeds. Where
some of the more persistent grasses are present, the
site may be sprayed first with glyphosate and a preemergent herbicide, and after a fallow period,
cultivated. Follow-up applications of herbicides may
also be required after cultivation (Florence 1996).
Lack of plant growth, and subsequent litter return,
associated with site preparation may result in
decreased inputs of soil C. Furthermore, in the
In many Australian soils, continuous cereal
cropping, especially with traditional soil and crop
management practices, has resulted in losses of
organic matter and associated declines in soil
structure (Dalal and Mayer 1987; Haines and Uren
1990). Blair et al. (1995) analysed paired sites
(cropped and undisturbed/uncropped) from three
locations in northern and central NSW,
demonstrating that soil C declined with cropping.
A similar conclusion was reached by Conteh et al.
(1997).
absence of plants, decomposition rates are initially
accelerated due to the combination of warmer
A fallow phase in crop rotations may accelerate the
temperature, greater water availability and more
above-ground litter (Collins et al. 1992). A reduced
fallow period may not always result in an increase
organic substrate (Henderson 1995).
11.2 PREVIOUS LAND USE
In afforested sites, previous land use will largely
determine initial soil C content, its distribution
through the soil profile, and its decomposition
pattern (substrate quality). These factors affect
observed change in soil C following afforestation,
the main factors being: crop rotation and plant
species previously grown, cultivation, plant residue
retention, fertiliser application, and liming.
11.2.1 Crop rotations and plant species
previously grown
Storage of C in soils prior to afforestation will
depend upon the amount of biomass produced
(productivity), its above- to below-ground allocation
and depth of the rooting system, and the nature of
the organic matter produced. Microbial activity
decreases with soil depth, so deeper allocation of C
through roots is more likely to increase soil-C levels.
Large amounts of recalcitrant secondary organic
compounds in vegetation residues may result in
increased soil C (Grigal and Berguson 1998).
Studying a range of sites in Puerto Rico, Weaver
et al. (1987) concluded that the past land use
appeared to influence C content more than climate,
at least over a recovery period of <40 years after
abandonment of agriculture.
40
loss of soil C due to decreased inputs from roots and
in soil C levels, but it may maintain the existing
levels due to a reduced rate of decline.
It has been shown that there was more soil C under
pasture than under continuous cropping systems in
New South Wales (Ridley et al. 1990; Conteh et al.
1997; Whitbread et al. 1998), and South Australia
(Russell 1960; Grace et al. 1995). In a long-term field
experiment, Grace et al. (1995) observed an increase
in soil C levels (at 0-10 cm and 10-22.5 cm) with an
increase in the frequency of pasture in the crop
rotation.
Crops generally have relatively low root-to-shoot
ratios, and have been genetically selected to
maximise the reproductive storage portions of the
plant at the expense of the root system. As a result,
compared to pasture grasses, particularly perennial
pasture, below-ground additions of C via row-crops
may be relatively small (Koerner et al. 1997; Grigal
and Berguson 1998). Richter et al. (1990) found that a
decline in soil C following cropping was mostly
attributable to low root biomass associated with a
transition from pasture to annual herbaceous
vegetation.
In addition to the quantity of C, plant species grown
during previous land use may also influence the
quality of plant residues and thus soil C levels.
Cereal crop residues generally have higher C:N
Australian Greenhouse Office
ratios than pasture species, particularly leguminous
or for which the only reported previous land-use
pasture species, resulting in lower rates of
decomposition for the cereal. It has been noted that
history was cropping. Ex-agricultural sites were
those where there was a rotation between pasture
and cropping phases, or sites for which the reported
CO2 emissions are higher under pasture than under
cereals (Aslam et al. 2000) and are lowest under
fallow (Schimel 1986). An inter-crop pasture phase is
traditionally regarded as an essential component of
cropping systems to maintain soil C content and the
physical properties of Australian soils (Greenland
1971).
land use was as agriculture.
Figure 11.2 indicates that the effect of former land
use on change in soil C was significant in soil
sampled to <30 cm depth. After afforestation, soil C
tends to decrease on ex-pasture sites and increase on
ex-cropping sites. This is consistent with studies
To investigate the influence of previous land use on
change in soil C following afforestation, previous
which have compared changes in soil C following
afforestation on both ex-cropping and ex-pasture
land use was categorised into three groups: pasture,
land (e.g. Lugo et al. 1986; Harrison et al. 1995;
crops, and agriculture. Pasture included annual
(improved and unimproved) and perennial pastures.
Koerner et al. 1997), where it was demonstrated that
soil C tends to increase on soils with ‘depleted’ C
Ex-cropping sites included land which was either
under continuous cropping for a prolonged period
content as a result of cropping yet decrease on expasture land.
120
1.56
80
Change in soil C (g C m -2 yr -1)
1.34
0.58
40
0.49
0.60
0.20
0
-0.18
-40
-0.13 -0.27
<10 cm, ns
>10 cm, ns
-80
<30 cm, ***
-120
Pasture
Crops
Agric.
Previous land use
Figure 11.2. The weighted-average C change estimated for soils sampled from <10 cm, >10 cm or <30 cm
under forests on ex-pasture, ex-cropping and ex-agricultural land. Bars indicate standard errors of the
means. Numbers above (or below) the bars indicate the weighted-average percentage change in soil C
(% yr-1). Agricultural land is that which could not be easily classified into either pasture or crop.
ns, not significant. ***, significant at P<0.001. Data sources are listed in Appendix 1.
National Carbon Accounting System Technical Report
41
On ex-crop land, the increase in soil C tends to be
depth), Bashkin and Binkley (1998) found that 10-13
lowest in samples from >10 cm depth (Fig. 11.2).
This is consistent with observations that the change
years after eucalypt establishment, soil C increased
by 1,150 g C m-2 in the top 10 cm of soil but
in the vertical distribution of soil C is greatest on
decreased by 1,010 g C m-2 in the 10-55 cm layer.
sites which had been frequently tilled. For these sites
at plantation establishment, there was only a weak
Thus, in the 0-55 cm layer there was no net change
in soil C content.
gradient of C in the surface 20-30 cm of soil as a
Table 11.1 shows that the effect of former land use
result of frequent homogenisation (Post and Kwon
2000). As tree growth commences on ex-cropped
on change in soil C following afforestation is
generally greater during the initial ten-year period
land, C starts to accumulate in the surface soil,
than in the subsequent years (>10 years). This was
partly due to non-mixing of litter in the soil. In
contrast, soil C in lower layers may decrease
substantially as a result of enhanced decomposition
of the residues. For example, in an ex-sugarcane
field which had been frequently tilled (to 40 cm
particularly the case for ex-agricultural sites where
soil C declined within the first ten years of
afforestation, but then increased over the
longer term.
Table 11.1. Weighted-average change in soil C in <30 cm layer, after afforestation, during the short-term
(<10 years) and long-term (>10 years) following different former land uses. Agricultural land is that which
could not be easily classified into either pasture or crop. A significant relationship with plantation/forest
age is demonstrated at *P<0.05, **P<0.01, ***P<0.001. Values in parentheses represent the standard error of
the of mean.
<10-yr
>10-yr
<10-yr
>10-yr
change in soil C
change in soil C
change in soil C
change in soil C
(g m-2 yr-1)
(g m-2 yr-1)
(% yr-1)
(% yr-1)
Pasture
-9.75 (9.52)
-11.0 (5.46)
-0.37
-0.24
Crops
142.3 (45.3)
53.5 (10.0)
3.30
1.96
Agriculture**
-49.3 (18.8)
30.2 (13.9)
-1.92
1.03
Category
of former land use
Under well-managed legume leys, many workers
have observed substantial (20% to 100%) increases in
soil C (see review by Johnson 1992). For example, in
a permanent rotation trial in South Australia, Grace
et al. (1995) noted that the inclusion of a legume
(pasture or grain) in a cereal cropping phase
increased soil C (Table 11.2). The reasons for the
greater C accumulation under N-fixers are not
explicitly known, but it is hypothesised that
increased soil N inputs may cause greater SOM
stabilisation.
The incorporation of legumes in a rotation will have
a significant impact on change in soil C following
subsequent afforestation. For example, Birk (1992)
compared soil C content (0-8 cm) in radiata pine
42
plantations on former improved (containing
subterranean clover) and unimproved (native grass)
pasture in the Tumut region of southern NSW. She
found that C levels were initially higher under the
previously improved pasture soils than in the exunimproved pasture soils. This was reflected in the
higher fertility and growth rates of the associated
pine stands. As a result of the higher initial soil C,
the decrease of soil C during the first 15 years of
afforestation was greater on former improved than
on former unimproved pasture sites. Between the
ages of 2 and 15 years, soil C (0-8 cm) decreased by
109.5 g C m-2 yr-1 under radiata pine on previous
improved pasture. In contrast, the decrease was only
25.9 g C m-2 yr-1 under radiata pine on former
unimproved pasture.
Australian Greenhouse Office
Table 11.2. Changes in concentration of soil C (%) in the Waite Agricultural Research Institute Permanent
Rotation Trial (Grace et al. 1995).
Soil depth
Rotation or phase
0-10 cm
10-22.5 cm
Legume v. non-legume
+0.04
+0.02
Pasture v. peas
+0.05
+0.02
Pasture 2 years v. 1 year
+0.18
+0.06
Pasture 4 years v. 2 years
+0.14
+0.05
residue inputs, over an extended period there may
be greater accumulation of soil C under perennial
Second, tillage may decrease surface soil C content
due to its redistribution by soil inversion (Mead and
Chan 1988; Chan et al. 1992). Third, tillage may
than under annual cropping systems. Compared to
increase soil C loss due to incorporation of stubble
annual crops, perennials also increase shading on the
ground for several months of the year and provide
increased mulch. This tends to decrease soil
into the upper subsoil resulting in better contact and
Due to less soil disturbance, and probably increased
temperatures and therefore decrease decomposition
(Grigal and Berguson 1998).
In summary, soil C under plantations is likely to
increase when established on ex-cropping sites but
decrease on ex-pasture sites, particularly wellmanaged legume pastures or perennial pastures. The
influence of previous land use on change in soil C
will be most evident when plantation rotations are
short, with limited time for C accumulation and
frequent soil disturbance (Brand et al. 2000).
11.2.2 Cultivation
Changes in soil C after afforestation will depend
upon the amount and nature of the C in the preplantation phase. Many Australian soils used for
cropping are fragile and highly degraded. Therefore
in Australia the decline of soil C with cultivation is
often marked (Chan et al. 1992; Whitbread et al.
1998). Declines in soil C with tillage are thought to
be attributable to four main factors. First, annual
tillage accelerates mineralisation rates of soil C by
mixing the soil, disrupting aggregates and increasing
soil aeration and moisture (Prince et al. 1938; Rovira
and Greacen 1957; Dalal and Mayer 1986b; Mann
1986; Chan et al.1992; Moody 1994; Tiessen et al. 1994;
Alriksson and Olsson 1995; Post and Kwon 2000).
moisture conditions and more favourable conditions
for decomposition. Fourth, soil C may be lost by
wind and water erosion once the soil is tilled.
In various reviews (Post and Mann 1990; Johnson
1992; Davidson and Ackerman 1993), it has been
reported that the loss of soil C (20% - 40%) occurs
within the first few years following initial
cultivation. The fractional loss of soil C following
cultivation is positively correlated to the amount of
C initially present (Post and Mann 1990), but this
relationship does not appear to hold when changes
in soil bulk density are taken into account (Davidson
and Ackerman 1993).
Reduced tillage systems and direct drilling practices
have been reported to maintain or increase C
compared to conventional cultivation (Doran and
Smith 1987; Campbell et al. 1989; Prove et al. 1990;
Carter and Mele 1992). Additionally, stubble
incorporation with conventional cultivation results
in a more uniform distribution of soil C throughout
the surface 15 cm layer than direct drilling and
minimum tillage treatments (Chan et al. 1992; Gupta
et al. 1994). Therefore, cropped land that has been
continually tilled is expected to have low amounts
and poor quality of soil C, whereas sites with notillage can have high amount of initial soil C,
particularly within the surface 5 cm of soil.
National Carbon Accounting System Technical Report
43
11.2.3 Plant residue retention
Traditionally, relatively large areas of crop stubble
were burnt to get rid of unwanted crop residues,
decrease the carry-over of disease and assist in
cultivation for the next crop. However, in the longterm, burning of crop residues results in a significant
decline in soil C (0-20 cm) (Collins et al. 1992).
In Australia, long-term experiments (8-10 years)
demonstrated that retention of stubble resulted in
increases in soil C (Dalal and Mayer 1986; Saffigna
et al. 1989; Chan et al. 1992; Gupta et al. 1993; Conteh
et al. 1997). Retaining plant residues increases soil C
decomposition by increasing the numbers of
microorganisms and thereby the rate of oxidation of
organic matter (Stevenson 1986; Oades et al. 1988;
Capriel et al. 1992). However, this is negated by
increased C inputs with plant residue retention.
The net increase in soil C content with stubble
amount, and only weakly related to the type, of crop
residue applied (Larson et al. 1972; Rasmussen and
Collins 1991; Rasmussen and Parton 1994; Conteh
et al. 1997). However, the resistance to
decomposition displayed by material with low N
content means that it can remain as part of the soil C
pool for relatively longer periods compared with
material of high N content.
Studying soils in southern NSW, Chan et al. (1992)
observed that stubble burning had just as much
effect as tillage in reducing the total amount of C in
the top 20 cm of soil. They found a 31% difference in
C in the surface 10 cm (2.42% v 1.68%) between the
extreme management practices of stubble
retention/direct-drilled and stubble
burnt/conventional cultivation. Similar results were
observed on a red earth soil in southern Queensland
(Dalal and Mayer 1986a).
retention has been shown to be closely related to the
Table 11.3. Soil OM concentration and the calculated change in soil C in response to various treatments
on ex-agricultural land prior to the establishment of pine or hardwood plantations (Gilmore and
Boggess 1963).
Tree type
Pines
Hardwoods
44
Treatment
OM in 1955
OM in 1960
Change in soil C
(%)
(%)
(g C m-2 yr-1)
No treatment
0.88
1.25
81
Manure
0.95
1.31
78
Manure+Lime
1.77
1.81
8
Manure+Lime+P
1.87
1.97
20
Plant residues
0.99
0.98
-2
Plant residue+Lime
1.43
1.54
23
Plant residue+Lime+P
1.70
1.68
-4
No treatment
1.26
1.55
61
Manure
1.77
1.81
8
Manure+Lime
1.97
1.97
0
Manure+Lime+P
1.91
1.97
12
Plant residues
1.63
1.44
-40
Plant residue+Lime
1.57
1.54
-6
Plant residue+Lime+P
1.84
1.63
-43
Australian Greenhouse Office
In five-year-old pine and hardwood plantations
Bogges (1963) found that past application of P
established on ex-agricultural land, Gilmore and
Boggess (1963) measured the changes in organic
(+lime) together with incorporation of plant residues
matter (from 1955 to 1960) under the plantations in
response to the previous application of manure, crop
residues, limestone and rock phosphate. All of these
treatments had resulted in higher initial soil C
content at plantation establishment relative to the
untreated soils. However, the previous manure and
plant residue additions had the greatest impact on
calculated changes in soil C following afforestation
(Table 11.3).
11.2.4 Fertiliser application and N-fixation
Generally the higher the supply of nutrients in soil,
the higher is the productivity and hence the C input
to soil (Nilsson and Schopfhauser 1995). However,
higher soil nutrient levels will produce higher litter
quality in the vegetation (which may mean lower
phenolic compounds and lower lignin content) and
therefore higher decomposition. There may also be
fertiliser-induced accelerated microbial activity, and
thus soil C decomposition (Conteh et al. 1997).
resulted in a decrease in soil C associated with
afforestation (Table 11.3).
Mycorrhiza are an integral part of the forest
ecosystem, with recognised functions in forest-tree
nutrition. Since the establishment and growth of
mycorrhiza are influenced by the physical, chemical
and microbiological properties of soils, the history of
land management may also influence mycorrhizal
infection of planted trees (Skinner and Attiwill 1981).
11.2.5 Liming
Soil factors such as acidity influence the amount of
organic matter stored in the soil by retarding
decomposition processes (Jordan 1985) by:
exceeded that of seedlings on adjacent ex-native
forest soils. Regular dressing of superphosphate on
improved pastures had led to high soil P and N. Jug
et al. (1999) found past long-term application of
organic fertiliser increased soil C in afforested sites.
Similarly, in a P-deficient radiata pine plantation in
NSW, Turner and Lambert (1986) noted that there
was up to a 22% increase in soil C 30 years after a
single superphosphate fertilisation. In contrast, some
reducing microbial and faunal activity;
•
producing sclerophyllous leaves containing
small amounts of proteinaceous substances
(N, P and S) and large amounts of structural
material. The C/N (and also C/P) ratios of
such materials are relatively high; and
The net response to fertiliser application will depend
on the soil type and site conditions. Most workers
have observed that soil C increases due to fertiliser
application (Johnson 1992). For example, in the
Gippsland regions of Victoria, Skinner and Attiwill
(1981) noted that the growth of Pinus radiata
seedlings on improved pasture soil (i.e. sites with
mixtures of introduced grasses and legumes)
•
•
forming relatively stable Al-organic matter
complexes.
Liming increases the activity of soil fauna, and thus
facilitates precipitation of Ca that is effective in
stabilising humic substances, affecting the potential
for C storage. Jenkinson (1970; 1991) reported the
results of the Rothamsted studies of change in soil C
since the early 1880s at two sites (Broadbalk and
Geescroft). One site (Broadbalk) was on calcareous
soils that had been limed sometime during the 18th
or early 19th century. The other site (Geescroft)
received N and P fertilisers but no lime and
consequently experienced significant acidification.
The increase in soil C was greater at Broadbalk than
at Geescroft and was considered to be due to liming
(Johnson 1992).
long-term field trials have also demonstrated that N
fertiliser application significantly decreases (Collins
et al. 1992), or has no effect (Ennick et al. 1980;
Hassink 1994) on soil C. For example, Gilmore and
National Carbon Accounting System Technical Report
45
11.3 CLIMATE
Climatic factors play an important role in long-term
development of soil C, or in setting the boundaries
for maximum C sequestration for a particular
management practice in a given area (Jug et al. 1999).
To ascertain the influence of climate on change in
soil C in the afforested sites reviewed, sites were
grouped according to four main climatic regions
(Table 11.4).
Figure 11.3 shows that climate had a significant
effect on change in soil C within the surface soil (010 cm or 0- 30 cm) following afforestation. There
was a relatively large increase in the C content of the
surface soil under tropical and subtropical climatic
regions. In contrast, there was a relatively large
decrease in the surface soil C content under
temperate/mediterranean climatic regions. Post and
Kwon (2000) collated reports similarly
demonstrating rates of change in soil C during forest
or woody vegetation establishment after some
period of agricultural use. They noted that there was
a tendency for rates of soil C accumulation to
increase from temperate regions to subtropical
regions. They inferred that the major factor
determining C accumulation is the amount of
organic matter input, which increases with annual
temperature and water availability. However, forests
in cooler climates have nearly twice as much soil C
as warm temperate forests (Post et al. 1982;
Schiffman and Johnson 1988; Huntington 1995);
there may be a greater capacity for long-term soil C
recovery following afforestation of cooler sites
compared to warmer temperate sites.
Table 11.4. Description and some examples of geographic locations of the four main climatic regions
encompassing the afforestation sites reviewed.
Climatic region
Description*
Afforested sites location
Tropical or savanna
Continuously hot. Heavy precipitation in all
seasons (tropical) or confined to summer (savanna)
Central Africa, NW Ecuador and parts of Hawaii
and Puerto Rico
Subtropical moist
Warm summers, cool winters. Moderate precipitation
in all seasons with summer maximum
SE USA, Virgin Islands, Argentina and parts of
Queensland and the North Coast of NSW, Australia
Temperate or
mediterranean
Hot-warm summers, mild-cool winters.
Moderate to light precipitation with winter maximum
Germany, England, New Zealand, parts of Puerto Rico,
and parts of NSW, ACT and SW WA in Australia
Continental moist
Warm summers, cold winters. Moderate precipitation
all seasons with summer maximum
Sweden and NE USA
*Encyclopedia Britannica World Atlas
46
Australian Greenhouse Office
120
80
0.18 0.61
40
0.23
2.61 0.61
1.73
-2
-1
Change in soil C (g C m yr )
1.67
0.07
0
-0.11
-0.13
-0.42
-40
-0.47
<10 cm, *
>10 cm, ns
-80
<30 cm, ***
-120
Tropical
Sub-tropical moist
Temperate
Continental moist
Climatic category
Figure 11.3. The weighted-average C change following afforestation estimated for soils sampled from
<10 cm, >10 cm or <30 cm under forests in tropical, subtropical moist, temperate/mediterranean and
continental moist climatic regions. Bars indicate standard errors of the means. Numbers above (or below)
the bars indicate the weighted-average percentage change in soil C (% yr-1).
ns, not significant. *, significant at P<0.05. ***, significant at P<0.001. Data sources are listed in Appendix 1.
In temperate/mediterranean climatic regions, soil C varied significantly with the age of the forest (Table
11.5). The rate of soil C decrease was rapid during the first ten years after afforestation, and slow in older
forests.
National Carbon Accounting System Technical Report
47
Table 11.5. Weighted-average change in soil C in the <30 cm layer, following afforestation, during shortterm (<10 yr) and long-term (>10 yr) studies in different climatic regions. Significant relationship with
plantation/forest age is demonstrated at *P<0.05, **P<0.01, ***P<0.001. Values in parenthesis represent
standard errors.
Change in soil C
Climatic region
<10 yr
-2
>10 yr
-1
-2
<10 yr
(g m yr )
(% yr )
(% yr-1)
Tropical
85.0 (32.3)
34.6 (10.4)
3.77
2.33
Sub-tropical moist
84.05 (55.0)
30.4 (7.29)
3.37
1.04
Temperate/Mediterranean **
-17.7 (12.6)
-0.89 (8.04)
-0.53
-0.02
Continental moist
-6.51 (14.7)
23.6 (14.2)
-0.33
0.77
Studying sixteen hardwoods within four distinct
climatic regions, Simmons et al. (1996) reported that
litter production was controlled, in part at least, by
precipitation but not by temperature. Therefore,
where rainfall is seasonal, moisture becomes an
important regulator of litterfall and decomposition.
During periods of water stress, the rate of litterfall
may be high, and decomposition slow.
48
-1
>10 yr
(g m yr )
11.3.1 Mean annual rainfall
It is commonly observed that soil C increases with
increasing mean annual precipitation (Jenny 1980;
Cooper 1983; Lugo et al. 1986; Spain 1990; Sparling
1992; Homann et al. 1995; Nilsson and Schopfhauser
1995). In drier climates, the inputs of C to soils are
low and the turnover of organic matter is slow
(Brown and Lugo 1990).
-1
11.3.2 Mean annual temperature
The amount of soil C generally increases with
increasing mean annual temperature (Cooper 1983;
Lugo et al. 1986; Spain 1990; Sparling 1992; Homann
et al. 1995; Nilsson and Schopfhauser 1995). In some
regions, however, soil C decreases with increasing
mean annual temperature (Jenny 1980). These
discrepancies may be related to initial soil C levels,
and thus soil C loss due to accelerated
decomposition at higher temperatures.
In soils where moisture is available, decomposition
is directly related to the average annual temperature,
and thus at higher temperatures larger inputs of
plant residues required to maintain the same level of
soil C. Studying sixteen hardwoods within four
distinct climatic regions, Simmons et al. (1996) noted
that decomposition rates were lower at sites with
lower annual temperatures. Indeed, C loss through
soil respiration was more sensitive to temperature
than C inputs from litter.
Australian Greenhouse Office
On a global scale, average amounts of detrital C in
forest soils increased from the tropics through
temperate to the boreal forests (Schlesinger 1977).
Low values in the tropical soils are attributed to
rapid decomposition, which compensates for large
litter production (O’Connell and Sankaran 1997). On
average, about 1% of the C in the soil profile is
stored in litter of tropical forest soils compared to
13% in boreal forests.
The amount of soil C increases with elevation, as
low temperature slows the decomposition of
biomass faster than its production. According to
Zinke et al. (1984, in Jordan 1985), the increase can
amount to about 4000 g m-2 per 1000 m, reflecting a
corresponding fall of 6ºC in mean annual
temperature.
11.3.3 Microclimate
Change in soil microclimate following afforestation
is potentially one of the most important factors
determining decomposition rates and thus the
magnitude of change in soil C. There are few direct
comparisons of microclimate between forest and
adjoining agricultural land. Table 11.6 compares soil
temperature under intact forest and adjacent
harvested forest (bare soil covered with harvest
residues and litter). Although not a direct
comparison between forest and agriculture, it serves
to illustrate potential change in the microclimate
following afforestation.
Invariably soil temperature is substantially greater in
the open (harvested) areas than under the intact
forest canopy. The difference is substantial, for a
temperate climate representing about a 2ºC increase.
This has significant implications for modelling
change in soil C.
Table 11.6. The change in soil temperature after harvesting forests (no canopy) compared to an uncut
control (closed canopy).
Species
Location
Temperature change
Mixed hardwoods
West Virginia, USA
+6%
Mattson and Smith (1993)
Populus tremuloides
Ontario, Canada
+16%
Webber (1990)
Mixed hardwood
Texas, USA
+12%
Londo et al. (1999)
Pinus radiata
South Australia
+15%
Smethurst and Nambiar (1990a)
National Carbon Accounting System Technical Report
Reference
49
30
Pasture
Plantation
25
Soil water content (%)
20
15
10
5
0
0-10
10-20
Depth (cm)
Figure 11.4. Soil water content in pasture and adjacent Eucalyptus globulus plantations in WA. Data are
means from 31 paired sites (Grove et al. 2000).
Figure 11.4 shows average soil water contents for pasture and Eucalyptus globulus plantations in the 31
paired-site comparisons of Grove et al. (2000). Soil under plantation is drier than under pasture and this can
be explained by greater interception of rainfall, and higher rates of transpiration. Comparison of water use in
adjacent irrigated E. grandis and pasture at Wagga Wagga, New South Wales, showed that the ratio of water
use to pan evaporation was about 0.8 for plantation and 0.6 for pasture (Myers et al. 1996).
The individual and combined effects of these changes in soil microclimate are demonstrated through Roth-C
modelling analysis (Fig. 11.5). Scenarios are for plantations of moderate productivity established on pasture
of the same NPP (600 g C m-2 yr-1). When soil temperature and moisture is assumed not to change following
afforestation, soil C is predicted to decrease by 180 g C m-2 after 10 years. This decrease is moderated slightly
by drier soil under the plantation, but soil that is 2ºC cooler under plantation reduces substantially the
amount of soil C loss. Soil that is drier and cooler leads to no change in soil C. This analysis has important
implications for development of a modelling framework. Changes in soil microclimate following
afforestation need to be verified for a range of conditions including soil type, climate, and plantation
production (leaf area).
50
Australian Greenhouse Office
6,400
Soil C (g m -2 )
6,300
6,200
Ambient
Cooler
Drier
Drier + Cooler
6,100
0
2
4
6
8
10
Age (yr)
Figure 11.5. Predicted changes in soil C following afforestation for different assumed microclimates.
‘Ambient’ is the change predicted for temperature and soil conditions that do not change between pasture
and plantation. ‘Drier’ is when soil water content is 10% less under plantation than pasture; ‘cooler’ is
when soil temperature is 2°C less under pasture than plantation, and ‘drier+cooler’ is for the combined
effect. The Roth–C model was used, modified for forests (Polglase et al. 1992).
11.4 SOIL TEXTURE
Soil properties that strongly influence C dynamics
are the redox status, cation competition and
concentration (i.e. Ca, Fe and Al) and the particlesize distribution (texture). Poorly-drained soils with
high water content, and resulting low oxygen levels,
have higher C than well-drained soils. This is
because of restricted microbial activity, and thus
decomposition, in poorly drained soils. High levels
of cations, particularly Al, stabilise soil C and protect
it from oxidation. The high surface area of the fine
silt and clay fractions enhances formation of organomineral complexes that protect C from microbial
oxidation (Grigal and Berguson 1998). Thus, clay
minerals bond and protect the organic matter, and
residues typically decompose more rapidly in sandy
soils than in clay soils (Sorensen 1981; Ladd et al.
1985; Jenkinson 1988).
In the studies reviewed, soil redox status (or water
status) and cation content were often not reported,
whereas soil textural class was commonly given.
Therefore, studies were grouped into soil textural
classes based on clay content. Soils low in clay
included sands and sandy loams. Soils with medium
clay content included silty loams or silty clay loams.
High clay soils included clays and clay loams.
National Carbon Accounting System Technical Report
51
The effect of soil texture on the weighted-average change in soil C was highly significant in samples from
<10 cm depth (Fig. 11.6). There was little net change in soil C in soils with low-medium clay content, and a
1.1% y-1 decrease in soils with high clay content. In contrast, >10 cm depth, high clay soils tended to increase
in C content after afforestation, whereas low-medium clay soils showed a decrease.
There are discrepancies between studies which have compared change in soil C following afforestation in
soils of different texture. Some workers (Giddens et al. 1997; Tate et al. 1997; Scott et al. 1999) have found that
the change in soil C was least pronounced in clay soils while others (Lugo et al. 1986) have found that soil C
accumulation was directly related to soil clay content, the relationship between C accumulation and soil
texture being strongest at higher soil C contents. The effect of texture on change in soil C is likely to be
largely dependent on the time period involved.
120
<10 cm, ***
1.12
>10 cm, *
<30 cm, ns
0.75
-1
Change in soil C (g C m yr )
80
-2
40
0.09
0.23
0.01
0
-0.38
-0.09
-40
-0.75
-1.12
-80
-120
Low
Medium
High
Soil clay content
Figure 11.6. The weighted-average C change estimated for soils of low, medium and high clay content
sampled from a depth of <10 cm, >10 cm or <30 cm under forests. Bars indicate standard errors of the
means, and numbers above (or below) the bars indicate the weighted-average percentage change in soil C
(% yr-1). ns, not significant. *, significant at P<0.05. ***, significant at P<0.001. Data sources are listed in
Appendix 1.
52
Australian Greenhouse Office
Table 11.7 indicates that the decrease in C content in
high clay soils was generally restricted to the first 10
grey-clay, and red-earth soils in north-western NSW.
They noted that, after 15 years of cropping, the loss
years after plantation establishment. This, together
of C from the red earth (0-4 cm soil depth) was
with the observation that decreases in soil C of
clayey soils were mainly confined to surface soil (Fig.
greater than the loss of C from soil containing more
clay.
11.6), suggests that large quantities of C, previously
In the longer term (>10 years), clayey soils have the
potential to accumulate large quantities of C (Table
protected in organo-mineral complexes, may be
released during soil disturbance at site preparation.
11.7). Soil fertility may be related to soil clay
Low clay soils also demonstrated a significant
content. Therefore, greater long-term accumulation
of soil C in the high clay soils (cf. the low clay soils)
decline in soil C within the first 10 years of
afforestation (Table 11.7). Due to little protection of
may be related to the greater input of C from litter.
C, decomposition rates will be relatively high,
With the exception of some soils of basaltic origin
particularly in the short-term (<10 years) following
site disturbance. It has often been observed that
(Spain 1990), organic matter status has been related
to clay content over a wide range of Australian soils
microbial turnover of C is faster in coarse- than in
(Spain et al. 1983; Bird 2000).
fine-textured soils (Van Veen et al. 1984; Merckx et al.
1985; Ladd et al. 1992, Hassink 1994). Whitbread et al.
(1988) conducted a survey of cropping in black-earth,
Table 11.7. Weighted-average change in soil C in the <30 cm layer, following afforestation, during the shortterm (<10 years) and long-term (>10 years) in soils with different clay contents. Significant relationship with
plantation/forest age is demonstrated at *P<0.05, **P<0.01, ***P<0.001. Values in parenthesis represent
standard errors.
Change in soil C
Category
<10 yr
-2
>10 yr
-1
-2
<10 yr
-1
>10 yr
(g m yr )
(g m yr )
(% yr )
(% yr-1)
Low clay content*
-11.9 (8.61)
11.6 (6.7)
-0.43
0.50
Medium clay content
47.8 (16.5)
-1.29 0.9)
2.04
-0.02
High clay content**
-19.6 (40.3)
56.0 (11.2)
-0.62
1.01
11.5 SITE MANAGEMENT
Site management will affect C input into the soil (i.e.
via plant productivity), rates of litter decomposition
(i.e. via microclimatic conditions, and the quantity
and quality of residues inputs), and thus soil C. A
number of management practices that will affect
both inputs and decomposition processes are
outlined in the following sections.
-1
11.5.1 Tree species
Tree species clearly differ in productivity, rates of
litterfall and the litter substrate quality (Broadfoot
1951; Challinor 1968; France 1989; Cuevas et al.
1991). Tree species also differ in their allocation of C
to below- and above-ground components, fine root
mortality, and in the depth of C inputs. Furthermore,
the shoot-to-root ratio of some species may be more
responsive to soil type than that of others (Hosner
and Graney 1970).
National Carbon Accounting System Technical Report
53
There are discrepancies within the literature as to
particularly conifers, often decays slowly compared
the effect of tree species on soil C. Jug et al. (1999)
examined the influence of afforestation (by balsam
with that from deciduous hardwoods. In eucalypts,
poplar, aspen and willow) on soil C in three regions
suitable for short-rotation plantations in Germany.
They found no consistent effects of tree
species/clones on soil C. Others (Trouve et al. 1994;
Abbasi and Vinithan 1999) have also found no
significant differences between plantation types in
soil C stocks. In a review, Johnson (1992) reported
that changing forest species can have either no effect
or large effects on soil C, depending primarily upon
rooting patterns.
Eucalypts and radiata pine are the most commonly
planted tree species in Australia. Therefore, we
assessed the effect of these species, together with
other hardwoods (poplar, mahogany etc.) and other
softwoods (mixed pines, spruce etc.), on change in
soil C for the studies reviewed.
Figure 11.7 indicates that there was a significant
effect of species on C change for soils from the <10
cm or <30 cm depths. Soil C tended to change little
under eucalypts, increased under other hardwoods
and softwoods, and decreased under radiata pine.
The smaller increase in soil C under eucalypts or
softwoods than under hardwoods may be related to
lower rates of litter decomposition. Slower rates of
litter decomposition will result in less transfer of
fresh C to the soil. Litter from eucalypts, and
54
low nutrient content, sclerophyllous leaves,
abundant crude fibres and lignin, and the presence
of polyphenols and alleopathic chemicals in leaves
may all contribute to slow decomposition
(O’Connell and Sankaran 1997). The litter of conifers
is generally even more recalcitrant than that of
eucalypts.
Consistent with the collated results shown in Figure
11.7, many workers (Bernhard-Reversat 1987, 1991,
1993; Singh et al. 1989; Wang et al. 1991; Balagopalan
et al. 1992) have found that compared to other
hardwoods (i.e. poplar, acacia, teak and bombax),
eucalypts may be less suitable for building soil C,
especially in sandy soils. For example, studying
coastal sandy soils in India, Gill and Abrol (1990)
assessed the influence of Casuarina equisetifolia and
Eucalyptus tereticornis on soil OC following four, six,
eight and ten years of afforestation. They observed
an increase of soil C under both species. However,
soil C increased at a faster rate and to a greater
depth under C. equisetifolia than under E. tereticornis.
Radiata pine was the only tree type which
demonstrated a significant influence of plantation
age on change in soil C (Table 11.8). There was a
rapid initial decrease in soil C under radiata pine
during the first 10 years of afforestation, followed by
more gradual rate of decline.
Australian Greenhouse Office
120
80
Change in soil C (g C m-2 yr -1)
0.12
1.25
0.86
40
0.03
0.20
0.63
0.33
2.04
0
-0.09
-0.52
-40
-0.47
-0.53
<10 cm, *
>10 cm, ns
-80
<30 cm, ***
-120
Eucalypts
Radiata pine
Other hardwoods
Other softwoods
Tree species category
Figure 11.7. The weighted-average C change estimated for soils sampled from <10 cm, >10 cm or <30 cm
under forests of four different types. Bars indicate standard errors of the means, and numbers above (or
below) the bars indicate the weighted-average percentage change in soil C (% yr-1).
ns, not significant. *, significant at P<0.05. ***, significant at P<0.001. Data sources are listed in Appendix 1.
Table 11.8. Weighted-average change in soil C in the <30 cm layer, following afforestation, during shortterm (<10 yr) and long-term (>10 yr) studies under different forest species. Significant relationship with
plantation/forest age is demonstrated at *P<0.05, **P<0.01, ***P<0.001. Values in parenthesis are standard
errors.
Change in soil C
Forest species
<10 yr
-2
>10 yr
-1
-2
<10 yr
-1
>10 yr
(g m yr )
(g m yr )
(% yr )
(% yr-1)
Eucalypts
2.34 (11.7)
23.9 (12.6)
0.08
2.02
Radiata pine**
-75.4 (36.7)
-25.0 (7.69)
-2.39
-0.44
Other hardwoods
-5.9 (16.9)
48.1 (8.91)
-0.23
1.47
Other softwoods
71.7 (29.6)
5.38 (4.17)
4.67
0.27
National Carbon Accounting System Technical Report
-1
55
Nearly all the sites afforested with radiata pine were on land previously used for pasture, which may have
exaggerated the observed decrease in soil C (Fig. 11.7 and Table 11.8) compared to other forest types. To
remove this confounding factor, Table 11.9 shows change in soil C under the various forest types following
pasture. There was only a slight change in soil C (0.20% yr-1 to –0.04% yr-1 annually) under all forest types
except radiata pine, where soil C decreased by 29 g C m-2 yr-1, or –0.55% yr-1.
Table 11.9. Weighted-average change in soil C in the <30 cm layer, following afforestation, with various
forest types on land previously used for pasture. Significant relationship with plantation/forest age is
demonstrated at *P<0.05, **P<0.01, ***P<0.001. Values in parenthesis are standard errors.
Forest species
Change in soil C
Change in soil C
-2
(g m yr )
(% yr-1)
Eucalypts
-1.11 (9.27)
-0.04
Radiata pine**
-29.0 (10.7)
-0.55
Other hardwoods
1.47 (12.2)
0.05
Other softwoods
3.35 (6.02)
0.20
-1
Thus far, litter has been excluded from the calculated
change in soil C under the various forest types.
However, it is likely that the amount of litter may
contribute substantially to the overall budget of soil
C. For example, 20 years following afforestation on a
ex-grassland sandy-loam soil in Belgium, Muys et al.
(1992) observed significant differences in earthworm
biomass and community structure, and in the
thickness and quality of the litter layer, under five
different species. These effects were explained by the
quality and quantity of the litter.
11.5.2 Stocking
In the short term, tree spacing influences
temperature, moisture and amount of litter, and also
determines the time required to achieve canopy
closure. These factors are strong determinants of
decomposition rates. In the long term, initial spacing
typically has little influence on the rate of forest
growth; at close spacing, trees may sometimes
stagnate, reducing inputs to soil. Binkley and Resh
(1999) found that change in soil C was not related to
spacing.
56
11.5.3 Weed control
Although weeds compete with young trees for both
water (Nambiar and Zed 1980) and nutrients
(Eissenstat and Mitchell 1983; Ellis et al. 1985;
Smethurst and Nambiar 1986b; McLaughlin et al.
1987; Woods et al. 1992), they are also a source of C
input to soils, especially during the initial phases of
stand development. The density of tree planting will
determine the amount and productivity of weeds,
and the persistence of weeds following afforestation.
Depending on these factors, together with the
method of weed control (herbicide application or
slashing) there is likely to be a short-term pulse of
soil C input. Under 2- or 3-year-old radiata pine
plantations in South Australia, Woods et al. (1992)
found that the input of detrital matter from weeds
resulted in a net increase of 390 g m-2 of soil C (0-15
cm). In addition to above-ground input from slashed
or sprayed residues, weeds also contribute to soil C
content via root input. Under radiata pine in South
Australia, weeds had a higher rooting density (32-44
cm cm-3) than pines (0.06-0.18 cm cm-3) in the surface
15 cm of soil (Nambiar 1989; Woods et al. 1992).
Australian Greenhouse Office
Weed control will also result in increased soil
ground. Other workers have found that fertiliser
temperature (due to decreased shading) and a
reduction in water use (Henderson 1995). In climatic
application to forested sites resulted in no change in
regions where soil temperature or moisture limits
biological activity, these conditions are conductive to
increased loss of soil C via decomposition, and an
increase of soil C input via accelerated tree growth.
Additionally, at some sites, weed control may lead to
soil C loss via increased erosion (Henderson 1995).
In summary, the net effect of weeds on soil C will
depend on the type of weeds (i.e. aboveground and
below-ground productivity and decomposability),
area covered and the zone of weed control, soil
fertility and susceptibility to erosion, and the site
climatic conditions.
soil C (Johnson and Curtis 2000). Some studies
(Bauhus and Khanna 1994) have found fertiliser to
increase soil respiration, others (Maheswaran and
Attiwill 1989; Bauhus and Khanna 1994; Aggangan
et al. 1998) have observed no effect. Change in soil C
in response to fertiliser application will depend not
only on tree species, but also site conditions,
plantation age and stand density.
Trees on poor sites may not respond to fertiliser
application because of limitations imposed by soil
water, drainage or other nutrient deficiencies
(Schroeder 1991). It is likely that differences among
observed microbial responses to fertiliser application
also reflects variation in site quality. Therefore,
11.5.4 Thinning
Slash is an important source of nutrients and
maintains long-term productivity (i.e. soil fertility) at
some (Hopmans et al. 1993; Carlyle 1995) but not all
sites (Dyck et al. 1989; Smethurst and Nambiar 1990).
Thinning increases the return of C to the soil
through tree residues and root decomposition.
However, removing a portion of the canopy exposes
the soil to increased insolation and higher
temperature, and consequently speeds
decomposition of organic matter. Therefore, unless
compaction occurs, or the removal of slash from the
site depletes nutrients significantly, changes in soil C
due to thinning will depend upon the intensity of
thinning and may not be significant in the long term
(Henderson 1995).
fertilisation would not necessarily alter soil C where
nutrients were not limiting growth.
Further work is required to identify the interaction
between the thinning intensity and the climate, soil
type and forest type on change in soil C.
By increasing growth, and therefore competition for
space, fertilisation may increase mortality in
unthinned stands. Fertilising thinned stands can
increase growth without the increase in mortality.
Although thinning does not increase total C storage,
fertilising stands that have already been thinned, or
are going to be thinned, is likely to result in gains in
soil C (Schroeder 1991). However it should be noted
that if forests reach a harvest state more quickly in
response to fertiliser application, the net effect of
fertilisation on soil C balance may be minimal.
11.5.5 Fertilisation
In Australia, application of fertiliser is a common
practice at plantation establishment, or after
thinning in order to hasten growth recovery. Many
workers (Schroeder 1991; Johnson 1992; O’Connell
and Grove 1993; O’Connell 1994) have found that
fertilisation increases soil C storage by increasing
growth and litter production both above- and below-
On ex-agricultural land, plantation age is likely to
have a significant effect on change in soil C
following fertiliser application. In afforested sites in
south-west Western Australia, Grove et al. (2000)
reported that high growth rates of plantations are
dependent in part on utilisation by trees of the
stored nutrients. Similarly, Birk (1992) reported a
significant decline in N availability on soils with
increasing age of radiata pine established on an eximproved pasture sites in eastern Australia.
Therefore, fertiliser application may eventually be
required to maintain the rate of net soil C
accumulation.
National Carbon Accounting System Technical Report
57
11.5.6 N2 fixation
Growing lupins under pines (Beets and Madgwick
1998), and acacias with eucalypts (Khanna 1997), has
been shown to increase the productivity of target
species (Brand et al. 2000). Therefore inputs to soil
may be greater with an N-fixing species understorey.
However, litter from many, although not all, Nfixing species decomposes rapidly (O’Connell and
Sankaran 1997). Resh (1999) found that N-fixing
plantations sequestered more soil C than eucalypt
plantations. This was attributed to both the greater
retention of old soil C and to the greater
accumulation of new soil C from litter inputs.
Consequently, there may be potential to accelerate
the total rate of soil C sequestration by the use of Nfixing species, either as plantations or the
understorey of young non-N-fixing plantations.
11.6 PLANTATION HARVESTING AND
MANAGEMENT OF HARVESTING
RESIDUES
Changes in soil C after harvesting are reviewed in
the context that many ‘Kyoto consistent’ forests in
Australia will be harvested during the first and
subsequent commitment periods. After harvesting,
soil C content depends mainly upon:
1.
inputs above-ground from slash residues,
and below-ground from excised roots unless
a coppicing regime is used;
2.
the management of slash and the rate of
decomposition of remaining residues and
consequent inputs to soil;
3.
changes in the soil and litter microclimate
and consequent effects on decomposition
of residues; and
11.5.7 Fire management
In plantations, Queensland is the only State where
controlled burning is still used as a regular practice.
Elsewhere, however, hazardous materials such as
pruning or thinning slash may be removed from the
edges of plantation stands and burnt at roadsides or
in firebreaks.
A number of workers (McKee 1982; Johnson 1992;
Johnson and Curtis 2000) have summarised the
effect of fire on soil C. They reported that the effects
of burning upon both forest floor and soil C were
very dependent upon fire intensity and the time
since the preceding fire.
Hotter fires can cause increases in forest soil C in
sub-surface horizons because of the transport of
hydrophobic organic matter from the surface
horizons and subsequent stabilisation with cations.
Low-temperature fires (e.g. prescribed burning)
generally resulted in either no change or an increase
in C in the top 5 to 10 cm of soil. The cause of the
increase in soil C following prescribed burning may
include incorporation of charcoal and partially
burned organic matter into the mineral soil.
However, because burning decreases C in the forest
floor, there was generally a small loss of C.
58
4.
frequency of harvesting (rotation length).
There are few data in Australia on long-term
changes in soil C after harvesting, particularly for
plantations established on ex-agricultural land. We
therefore look to (mostly) overseas studies of change
in soil C after harvesting of natural forests, and to
modelling analyses. However, some data are
available for inputs of residues after harvesting and
their rates of decay.
11.6.1 Soil C inputs from slash and roots
In a recent extensive review, Johnson and Curtis
(2000) summarised the effects of harvesting on
change in soil C. Results pertain to management of
natural forests and not to harvesting of plantations
on ex-agricultural land. Measured data comes from
a variety of sources (e.g. Mattson and Smith 1993;
Olsson et al. 1996; Knoepp and Swank 1997; Piatek
and Allen 1999), complemented by numerous
modelling studies (Nakane et al. 1987; Dewar 1991;
Dewar and Cannell 1992; Bengtsson and Wikström
1993; Nakane and Lee 1995; and Polglase, unpub.).
With all studies considered, Johnson and Curtis
(2000) found that after harvesting (time not
specified) there was about a 5% increase in A-
Australian Greenhouse Office
horizon soil C (Fig. 11.8). The average net increase in
organic matter after harvesting. At equilibrium the
soil C following harvesting operations is
predominantly due to increased input from slash
mass of fine roots is probably comparable to the
mass of leaves.
and roots.
Root masses in forests have been reviewed recently
Coppicing affects inputs of root residues to soil, but
is not practiced widely for a variety of reasons, e.g.
by Snowdon et al. (2000) although the relative
preference for planting seedlings of genetically
proportions of fine roots (of particular importance in
short-term soil dynamics) were not specifically
improved stock. However, if undertaken, roots
highlighted. Here we therefore give some examples
of fine root masses to indicate the ranges that can be
expected (Tables 11.10 and 11.11). The mean mass of
remain alive under a coppicing regime and as such
reduce the potential size of the source of residue C.
Counterbalancing this is more rapid regrowth of
fine roots across all ages is 400-500 g C m ,
biomass C under a coppicing regime such that
ecosystem C balance may be similar between
indicating the amount that is converted to dead
coppice and conventional management systems.
-2
20
Whole soil
15
Number of observations
A horizon
10
5
0
-100
-75
-45
-15
15
45
75
Percent change after harvest
Figure 11.8. Frequency distribution diagram summarising change in soil C after forest harvesting (redrawn
from Johnson and Curtis 2000).
National Carbon Accounting System Technical Report
59
Table 11.10. Measured root masses for a range of sites.
Species
Location
Age
Coarse roots
-2
Fine roots
Reference
-2
(yr)
(g C m )
(g C m )
Eucalyptus pilularis
Fraser Island, Australia
14
NA
7.7
Applegate (1982)
E. pilularis
Fraser Island, Australia
45
NA
8.6
Applegate (1982)
E. pilularis
Fraser Island, Australia
500
NA
5.8
Applegate (1982)
E. nitens
Tasmania, Australia
3
7.5
1.8
Misra et al. (1998)
E. grandis
Victoria, Australia
6
2.9
1.8
Baldwin and Stewart (1982)
Pinus taeda
South Carolina, USA
55
13.4
3.8
Van Lear et al. (1994)
Picea rubens
Quebec, Canada
40
NA
3.7
Lytle and Cronan (1998)
Mixed hardwoods
New Hampshire, USA
70
NA
1.9
Fahey and Hughes (1994)
Mixed hardwoods
Michigan, USA
NA
NA
2.9
Fahey and Hughes (1994)
Table 11.11. Modelled root masses for a range of sites.
Species
Location
Age
Coarse roots
-2
Fine roots
Reference
-2
(yr)
(g C m )
(g C m )
Pinus densiflora
Hiroshima, Japan
80
16.9
5.8
Nakane et al. (1986)
Eucalyptus regnans
Victoria, Australia
10
4.4
3.8
Polglase (unpub.)
E. regnans
Victoria, Australia
30
9.2
4.5
Polglase (unpub.)
E. globulus
Western Australia
10
9.5
0.7
Battaglia (unpub.)
E. globulus
Western Australia
10
13.1
1.0
Battaglia (unpub.)
E. globulus
Western Australia
10
6.5
0.5
Battaglia (unpub.)
E. globulus
Western Australia
10
7.0
0.3
Battaglia (unpub.)
E. globulus
Western Australia
10
9.8
0.8
Battaglia (unpub.)
E. globulus
Western Australia
10
9.4
0.4
Battaglia (unpub.)
E. globulus
Western Australia
10
12.2
0.7
Battaglia (unpub.)
E. globulus
Western Australia
10
14.9
0.6
Battaglia (unpub.)
60
Australian Greenhouse Office
11.6.2 Microclimate and decomposition
Harvesting may result in marked changes in the
physical environment of a forest site, with
consequent implications for decomposition.
Harvesting increases soil temperature, increasing
rates of decomposition, but drier soil and litter
would decomposition. For the litter and slash layer,
which tends to dry out more quickly and extensively
than soil, moisture availability may be the overriding control on decomposition rates.
Table 11.12 compares first-year mass loss of P. radiata
needles decomposing in control (uncut) and
harvested stands. In two of the three examples
given, decomposition was greater in control stands.
There was only a small difference in rates in the
third example.
As is the case for change in soil microclimate
following afforestation, changes due to harvesting
need to be verified for inclusion into a modelling
framework.
For studies listed in Table 11.12 gravimetric soil
vegetation to take up water. However, this was more
than offset by pan evaporation in the open being
11.6.3 Harvesting technique
The effects of harvesting technique on change in soil
C following afforestation have been reviewed
(Johnson and Curtis 2000). There was an apparent
difference between A horizon and the whole soil
profile in that the effects were most evident in the
A horizon.
three-fold greater than under the canopy. The ratio
of evaporation to throughfall was thus 1.6 in the
harvested area compared with 0.8 in the uncut
Figure 11.9 shows the effect of harvesting method
on change in soil C. Whole-tree harvesting (most
biomass removed from the site) caused an overall
forest.
loss of soil C (-6%). In contrast, harvesting of
sawlogs led to a substantial increase in soil C
(+18%), equivalent to a mean rate of 54 g C m-2 yr-1
moisture was 12% to 30% drier in harvested
compared to uncut forest. Water balance studies by
Smethurst and Nambiar (1990a) showed that
harvested areas received greater rainfall (less
interception by canopy) and had little or no
The management of harvest residues will also affect
soil water content. If residues are removed, the
harvested area can be prone to increased desiccation
by wind. If residues are retained, they might be
expected to have a mulching effect and thereby
reduce evaporative loss from soil, but interception
of rainfall will be greater.
over 10 years if we assume that 0-10 cm soil
contains about 3,000 g C m-2. Differences between
harvesting techniques are explained by sawlog
harvesting leaving residues on site where they
decompose and add to the soil C pool.
Table 11.12. First-year mass loss from decomposing Pinus radiata needles in control (uncut) and harvested
stands.
Location
Control
Harvested
Catalonia, Spain
42%
25%
Cortina and Vallejo (1994)
Rotorua, New Zealand
58%
69%
Gadgil and Gadgil (1978)
Rotorua, New Zealand
35%
16%
Will et al. (1983)
National Carbon Accounting System Technical Report
Reference
61
30
Conifer
25
Change in soil C (%)
20
Sawlog
15
10
Overall
5
0
Mixed
-5
Whole tree
Hardwood
-10
-15
Effect
Figure 11.9. Harvest effects on soil C within the A horizon (redrawn from Johnson and Curtis 2000).
11.6.4 Tree species
Data summarised by Johnson and Curtis (2000) also
demonstrated the effects of tree species on change in
soil C following harvesting. Interestingly, change in
soil C in coniferous forests (+26%) was greater than
change in hardwood forest (-8%) (Fig. 11.9). Reasons
for this difference were not given.
11.6.5 Short-term temporal effects
Johnson and Curtis (2000) noted that temporal
effects of harvesting on soil C were evident but did
not provide any detail. Modelling studies often
predict a slight increase in soil C after harvesting
due to addition of slash and excision of roots,
followed by a decrease before rise to a new
maximum (Nakane and Lee 1995; Polglase unpub.).
However such a pattern usually occurs over many
62
decades. Short-term (<20-yr) changes in soil C may
remain relatively small.
Immediately after harvesting (and thinning) inputs
of C below-ground, but particularly above-ground,
can be substantial. Table 11.13 shows some examples
of slash inputs in eucalypt and pine forests in
Australia. For clear-felled stands inputs in slash
residues range up to 2,600 g C m-2. For the P. radiata
stand (Smethurst and Nambiar 1990a) there was
already a significant amount of C in litter on the
forest floor (1,600 g C m-2). For the E. globulus
stands about 40% of the slash input was as green
leaves.
Australian Greenhouse Office
Table 11.13. Slash inputs to the forest floor after harvesting of Eucalyptus globulus and Pinus radiata
stands in Australia.
Species
Component
Slash input
Reference
-2
(g C m )
E. globulus
Leaves
1,080
Grove et al. (unpub.)a
E. globulus
Other
1,480
Grove et al. (unpub.)a
E. globulus
Total
2,560
Grove et al. (unpub.)a
E. globulus
Leaves
650
Grove et al. (unpub.)b
E. globulus
Other
920
Grove et al. (unpub.)b
E. globulus
Total
1,570
Grove et al. (unpub.)b
P. radiata
Slash
2,600
Smethurst and Nambiar (1990)
P. radiata
Litter
1,600
Smethurst and Nambiar (1990)
P. radiata
Total
4,200
Smethurst and Nambiar (1990)
P. radiata
Needles
450
Carlyle (1995)c
P. radiata
Branches
60
Carlyle (1995)c
P. radiata
Tops
420
Carlyle (1995)c
P. radiata
Total
930
Carlyle (1995)c
Red earth; bgrey sand; cthinned to 54% of basal area
a
Green leaf residues decompose very rapidly, about 80% of initial mass being lost in the first year. This is
equivalent to a mean decomposition constant of 1.55% yr-1, although the temporal pattern of decomposition
is best described by a double-exponential equation (Fig. 11.10). For this example the labile and resistant pools
in green leaves are about 30% and 70% respectively, with turnover rates of 9 and 0.9% yr-1. It is of note that
these rate constants are of the same order as those ascribed to DPM and RPM pools in the Roth-C model.
The relative proportions of labile and resistant masses give some indication of the initial size of the DPM and
RPM pools, and so it is possible that decomposition studies of this kind may be of some value for calibrating
the Roth-C model for decomposition of above-ground litter.
Decomposition of wood residues is, of course, slow (Fig. 11.10) but should not be ignored as a source of soil
C over time-frames of a few years.
National Carbon Accounting System Technical Report
63
Mass remaining (% of initial)
120
k L = 8.9 yr -1
w L = 30%
100
kr = 0.89 yr-1
wr = 70%
80
60
40
leaves
20
0
0
0.5
1
1.5
Mass remaining (% of initial)
100
wood
80
60
40
k = 0.21 yr -1
20
0
0
0.5
1
1.5
Time (yr)
Figure 11.10. Decomposition of Eucalyptus globulus residues in WA after harvesting. Fitted models are
either single (wood) or double (leaves) exponential decay functions. k is the rate constant and w the initial
mass (%) for labile (L) and resistant (r) fractions. Data from Shammas (1999).
64
Australian Greenhouse Office
Whereas Figure 11.10 gives the decomposition
point. The patterns of decay are similar, although
having different inflection points at different stages
11.6.7 Frequency of harvesting
(rotation length)
In plantations grown on short rotations for
pulpwood or energy biomass, trees are planted at
relatively high densities (>1000 stems ha-1) and
harvested after 10-15 years with no intermediate
thinning. In plantations grown on longer rotations
(20-50 years) for solid wood or veneer, the planting
density is lower (500-1000 stems ha-1) and
intermediate non-commercial (i.e. to waste) and
commercial thinning are undertaken to arrive at a
final stocking of 200-400 stems ha-1 (Smith 1986).
of plantation development. For both studies,
Rotation length has a significant impact on soil C
however, by about 15 years the amount of slash has
reached its minimum, and increases as inputs of
via its influence on the frequency of soil disturbance
pattern of a pulse input of residue, Figure 11.11
shows the temporal changes in total litter mass for
two studies. The first is from the chronosequence
study of Covington (1981) in harvested forests in
New Hampshire, USA. The second is from a
modelling study by Polglase (unpublished) of
harvested natural stands of E. regnans in Victoria.
For comparison, results from both studies have been
normalised so that they have the same starting
the rate at which residues are decomposed.
during harvesting. Fast growing, short-rotation
plantations, especially where there is no major
modification to overall nutritional status, will lead
In the context of C accounting, and given that for
these examples we are dealing with initial residue
amounts >2,000 g C m-2, it is important that
to maximised soil C loss (Turner and Lambert 2000).
Shortening forest rotation length is thought to
result in long-term declines in soil C store (Harrison
temporal patterns of change in stocks be adequately
et al. 1995).
above-ground residues (litterfall + mortality) exceed
measured or predicted. In the study of Polglase, for
example, C in the forest floor decreases from 2,500 to
1,500 g C m-2 during the first ten years, a mean rate
of change of –100 g C m-2 yr-1. Carbon then increases
by +70 g C m-2 yr-1 between 11 and 20 years.
National Carbon Accounting System Technical Report
65
Change in soil C (% of initial)
120
100
80
60
40
Covington
20
Polglase
0
0
10
20
30
40
50
Age (yr)
Figure 11.11. Patterns of decomposition of slash residues in two forests. ‘Covington’ is chronosequence
data for mixed hardwood from Covington (1981); ‘Polglase’ is a model prediction for mountain ash
(Eucalyptus regnans) in Victoria (Polglase unpub.).
66
Australian Greenhouse Office
12. AUSTRALIAN CASE STUDIES
concentrations were reported and soil bulk densities
were not measured, the Adams (1972) equation was
There are relatively few data available for change in
used to calculate soil C content of 0-10 and 10-20 cm
soil C from the predominant afforestation regions of
Australia. Where available, data from Australian
afforestation sites are grouped according to climatic
soil. The results showed that only four years after
afforestation, soil C increased by 112 and 80 g m-2 yr-1
in the 0-10 and 10-20 cm soil layers, respectively.
region, and the results discussed in terms of patterns
of change in soil C for the range of conditions.
This represented an increase in soil C of 2.07% in the
surface 10 cm of soil, and 2.57% at 10-20 cm depth.
12.1 MEDITERRANEAN REGIONS OF
SOUTH-WEST WESTERN AUSTRALIA
Eucalypt plantations are being established in southwest Western Australia across a range of soil types
and rainfall gradients (700 to 1500 mm) to supply
the increasing demand for pulpwood (Aggangan
et al. 1998), and to mitigate dry-land salinity
(Sparling et al. 1994). Plantations are commonly
being established on prior agricultural land. Soils are
generally infertile, sandy and of medium to low pH,
and the climate is Mediterranean with hot dry
summers and cool wet winters.
Grove et al. (2000) measured soil C (<2 mm fraction)
There are three paired-site studies (Sparling et al.
1994; Aggangan et al. 1998; Grove et al. 2000) in
which soil C was measured under pasture and
adjacent ex-pasture eucalypt plantations in southwest Western Australia.
At a site near Tammin in the central wheatbelt,
Sparling et al. (1994) measured soil C (<6 mm) under
plots revegetated with a mixture of nine-year-old E.
camaldulensis, E. occidentalis, E. platypus, E. torquata
and other eucalypts. Nine years after afforestation,
soil C to 10 cm depth decreased by 34.7 g m-2 yr-1 (or
–3.41% yr-1 ). However, litter C content increased by
45 g m-2 yr-1, resulting in a net increase in detrital C
of 10.5 g m-2 yr-1 (or 1.04% yr-1).
Aggangan et al. (1998) compared soil C (<5 mm)
under a four-year-old E. globulus plantation, and
pasture, near Augusta. The plantation soils were
ripped and mounds constructed along planting lines
prior to establishment of seedlings. Pasture soils
received an annual dressing of 18 kg P ha-1 as
superphosphate together with 1000 kg ha-1 of lime
under 31 E. globulus plantation and adjacent pasture
sites throughout the higher-rainfall areas. Site
preparation prior to plantation establishment
generally entailed only deep-ripping along the
planting rows. There was only one site where soil
was mounded along the planting row, and in this
case soil sampling was confined to the undisturbed
inter-row area. They found that there was no
significant difference between 0-10 cm soil C content
under pasture and adjacent eucalypt plantations. Six
to eleven years after afforestation, the change in 0-10
cm soil C ranged from –136 g m-2 yr-1 (or -2.86% yr-1)
to 163 g m-2 yr-1 (or 4.72 % yr-1). The average change
in soil C was –2.33 g m-2 yr-1 (s.e 10.8 g m-2 yr-1).
The main constraints to the data of Grove et al.
(2000) are that it is only for the <2 mm fraction in
the 0-10 cm layer of soil. Nonetheless it serves to
illustrate the general range of change in soil C that
can be expected. Grove et al. (2000) concluded that
in order to detect change in soil C following
afforestation at the sites reviewed, a more
comprehensive analysis that includes the full soil
profile is necessary. They also noted that large
differences in total C among 31 sites (range 1.9%9.9% of 0-10 cm soil, <2 mm fraction) could be
explained by variation in soil texture and climate.
A summary of results obtained from the three southwest Western Australian studies is shown in Figure
12.1. All changes in soil C are for the 0-10 cm soil
layer. There appears to be no significant general
relationship between change in soil C and the age of
the eucalypt plantations in this region.
one year prior to sampling. As only soil C
National Carbon Accounting System Technical Report
67
Age of plantation (yr)
0
2
4
6
8
10
12
Change in soil C (% yr -1 )
6
4
2
0
Sparling et al. (1994)
-2
Aggangan et al. (1998)
Grove et al. (2000)
-4
Figure 12.1. Change in soil C in 0-10 cm layer under 4- to 11-year-old eucalypt plantations on ex-pasture
land in the Mediterranean climatic region of south-west Western Australia.
12.2 SUBTROPICAL MOIST REGIONS OF
QUEENSLAND AND THE NORTH COAST
OF NEW SOUTH WALES
Re-establishment of rainforest on pasture land in
some areas of Queensland is being undertaken for
soil restoration, catchment protection, provision of
wildlife habitat and timber production (Maggs and
Hewett 1993). On the north coast of NSW, the area of
land under plantation is also increasing. The
environment is subtropical, with mean annual
rainfall of 1,700 mm, predominantly in summer.
A chronosequence established on E. grandis sites on
In a paired site study in the Atherton Tableland,
Maggs and Hewett (1993) measured soil C (finely
ground) under pasture and adjacent 50-year-old
rainforest which regenerated on pastoral land. As
only soil C concentrations were reported and soil
bulk densities were not measured, the Adams (1972)
equation was used to calculate soil C content of 0-10
cm soil. In four different soil types, it was found that
the C content to 10 cm depth increased by between
14 and 25 g m-2 yr-1, or between 0.19% and 0.42% yr-1.
height, 780 stems ha-1, 34.4 m2 ha-1 basal area). Soil
68
the north coast of NSW was studied by Turner and
Lambert (2000). The previous vegetation was mixed
pasture and woodland on soils derived from shale.
Establishment of the plantations involved spraying
with herbicide to kill grasses, ploughing, planting,
and treating each tree with 200 g of a mixed N and
P fertiliser. At the time of the study, no thinning had
been undertaken. The plantations ranged from two
years of age (and 3.2 m height, 996 stems ha-1,
4.9 m2 ha-1 basal area) to 35 years of age (and 39.2 m
C contents (<2 mm) were reported as 10,545 g C m-2
to a depth of 10 cm, and 42,182 g m-2 to a depth of
50 cm. Due to the uncertainty of the validity of
absolute changes (see comments below), only the
percent changes in soil C are given here. This study
was excluded from the analysis of weighted-average
changes in soil C observed in the group of
afforestation studies reviewed in Sections 9 and 10.
Australian Greenhouse Office
Changes in soil C observed in studies of Maggs and Hewett (1993) and Turner and Lambert (2000) are shown
in Figure 12.2. There was little difference in the percent change in soil C between the 0-10 and 0-50 cm soil
layers sampled by Turner and Lambert (2000). There is a decline in C in the surface 10 or 50 cm for about 15
years after plantation establishment and then a general levelling out. The initial decline in soil C was 10%12% yr-1 during the first two years after afforestation. Twenty-five years after afforestation, change in soil C
was only –1.13 to –1.18 % yr-1.
Age of plantation (yr)
0
10
20
30
40
50
60
Change in soil C (% yr -1)
2
0
-2
-4
-6
-8
Maggs and Hewett (1993), 0-10 cm
-10
Turner and Lambert (2000), 0-10 cm
-12
Turner and Lambert (2000), 0-50 cm
-14
Figure 12.2. Change in soil C in 0-10 cm or 0-50 cm layer under 2- to 50-year-old forest on ex-pasture land
in the subtropical climatic regions of Queensland and the north coast of New South Wales.
The paper by Turner and Lambert (2000) used a
chronosequence approach to estimate change in soil
C following afforestation. The calculated decrease
(0-50 cm) during the first two years was about
3,900 g m-2 (1,900 g m-2 yr-1) for P. radiata plantations
and 8,400 g m-2 (4,200 g m-2 yr-1) for the E. grandis
chronosequence. Turner and Lambert (2000) further
state that it may take 10-20 years before losses from
soil C are offset by accumulation in biomass. These
results should be treated with caution until trends
are confirmed with further data. The concerns are:
1.
These calculated losses in soil C were by far
the largest recorded in any of the studies
reviewed. In contrast to the loss of
National Carbon Accounting System Technical Report
4,200 g C m-2 yr-1 for the first two years
under E. grandis, the next greatest loss
among all studies was 2,000 g m-2 yr-1
(0-40 cm) recorded by Ramakrishnan and
Toky (1981, also a chronosequence study),
then losses of 830 g C m-2 yr-1 (0-100 cm,
Hansen (1993)) and 620 g C m-2 yr-1
(0-25 cm, Grigal and Berguson (1998)), both
paired-site studies. Among all studies
where loss of soil C was recorded, the mean
value was 83 g C m-2 yr-1, excluding the
data of Turner and Lambert (2000).
69
2.
This is an unreplicated chronosequence
5.
study. It is an essential requirement that the
starting point (soil C content) at each site be
constant depth (volume) and were not
the same. This would need to be
demonstrated for the E. grandis
chronosequence where:
•
sites were geographically isolated;
•
sites were on various parent material,
adjusted for mass.
6.
preparation is used it needs to be made
clear how this disturbed area was sampled.
Similarly, if soil was mounded but soil
collected from the inter-row, it must be
plantations had been established on
demonstrated that scarified areas were not
sampled: that is, samples taken from an area
sites that were either pasture or
woodland;
•
•
there was notable variation between
the chronosequence plots with respect
to slope (Bradstock 1981);
from which soil was removed to create the
mound, thus sampling subsoil with lower C
concentration.
7.
site preparation and establishment
methods varied between the plots. This
highly resistant to decomposition.
Otherwise the amount of input required for
soil C to attain the reported equilibrium
progressively modified after the oldest
of these stands was planted in 1962. In
particular, complete cultivation of the
70
•
the oldest stand had been established
in a former rainforest gully which had
been burnt by a wildfire in 1951 and
was thus not an afforested site; and
•
the management history and
productivity of the pasture phase is
unknown.
3.
The <2 mm fraction only was considered,
and as shown previously this may exclude a
significant proportion of soil C.
4.
The concentrations and amounts of soil C in
these soils are exceedingly large. The
Walkley-Black method was used for analysis
and it is not clear how these values were
converted to total soil C.
The effects of site disturbance aside, there is
no plausible explanation for such large
initial loss. Soils can contain large initial
amounts of C only if the organic matter is
was because the methods of
establishment on old farm sites were
site before planting was adopted in
order to combat excess competition
from grasses.
The large initial change in soil C is ascribed
to site disturbance but this needs to be
substantiated. Where mechanical site
either Lower Permian sediments or
Upper Permian Granodiorite.
•
It is probable that soil bulk density differed
among sites, yet results are presented for
values is impossibly high.
8.
Because soil C values presented are so large,
the conclusion that the results ‘… have
significant implications for fast-growing,
short-rotation plantations for pulpwood or
biofuels and soil C decline can be expected
to continue over subsequent rotations’
cannot be substantiated. Pasture sites
typically contain about 3,000 g m-2 of soil C
(Table 8.1) in comparison to the 40,000 g m-2
reported by Turner and Lambert (2000).
Losses of soil C under short-rotation E.
globulus recorded by Grove et al. (2000) for
example were nowhere near as large as in
the Turner and Lambert (2000) analysis; in
fact soil C may sometimes increase after
afforestation.
Australian Greenhouse Office
12.3 TEMPERATE REGIONS IN THE
AUSTRALIAN CAPITAL TERRITORY AND
SOUTHERN NEW SOUTH WALES
Over the last 30 years in south-eastern Australia,
radiata pine and eucalypts have increasingly been
planted on ex-pastoral land. There are two pairedsite studies (Gifford and Barrett 1999; Gifford 2000),
and one repeated-sampling study (Polglase and
Falkiner unpub.) in which soil C was estimated or
measured following afforestation in the ACT and
southern NSW.
In the Snowy Mountains, high-tension power line
easements traverse areas planted to radiata pine.
Only some of these pastures had been improved by
introductions of desirable grass and legume species,
and probably P fertiliser. These easements were used
by Gifford and Barrett (1999) to compare total soil C
content (including charcoal) under pasture and
soils for between 12 and 60 years. They found that
8 to 18 years following afforestation, the change in
total soil C to 30 cm depth ranged from -42 to
8.82 g C m-2 yr-1, and averaged–16.8 g C m-2 yr-1
(s.e 8.82). This was equivalent to a change in the
percentage of total soil C of between –0.97% and
0.22% yr-1.
Soil C (<2 mm) was measured initially, and again at
age two, four and eight years under effluentirrigated P. radiata and E. grandis plantations
established on ex-pasture near Wagga Wagga, NSW
(Polglase and Falkiner unpub.). Two to eight years
after afforestation, the change in soil C to 30 cm
depth ranged from –437 to 178 g C m-2 yr-1, and
averaged –134 g m-2 yr-1 (s.e. 42.1). This was
equivalent to a change in the percentage of total soil
C of between –11.7 and 6.22 % yr-1.
adjacent to pine which had been established on expasture land. They found that 8 to 18 years after
Figure 12.3 summaries the changes in soil C
observed in the three afforestation studies reviewed
afforestation, the change in total soil C to 30 cm
depth ranged from –97 to 38 g C m-2 yr-1, and
within the temperate region of south-eastern
Australia. Results available indicate that although
there is an initial decline in soil C following
averaged –42.0 g C m-2 yr-1 (s.e. 17.4). This was
equivalent to a change in the percentage of total soil
-1
C of between –1.70 to 0.80% yr .
Gifford (2000) measured total soil C under pasture
and adjacent 12- to 60-year-old P. radiata plantations
in the Brindabella region of the ACT. At both 0-30
cm and 0-100 cm, there was no significant difference
in total soil C content under pasture and plantation
which had been growing on ex-perennial pasture
afforestation, the soil C contents recover after ten
years. We note, however, the study of Polglase and
Falkiner (unpub.) represents an extreme case.
Plantations were established on previously dryland
pasture and then irrigated. This induced a marked
‘composting’ effect that accounted for the high
initial decrease in soil C. Under non-irrigated
conditions the decrease after plantation
establishment is not expected to be so great.
National Carbon Accounting System Technical Report
71
Age of plantation (yr)
0
10
20
30
40
50
60
70
Change in soil C (% yr -1)
6
4
2
0
-2
-4
-6
-8
-10
Gifford and Barrett (1999)
Gifford (2000)
Polglase and Falkiner (unpub.)
-12
-14
Figure 12.3. Change in soil C in 0-30 cm layer 2 to 60 years following afforestation of ex-pasture land in the
temperate climatic regions of the Australian Capital Territory and southern New South Wales. The study of
Polglase and Falkiner (unpub.), where irrigation of previously dry land caused a large initial change in soil
C, represents an extreme case.
Birk (1992) also measured soil C content under an ex-pasture soil in southern NSW. She compared soil C
within the surface 8 cm under 2-, 4-, 6-, 9- and 15-year-old radiata pine plantations on former improved and
unimproved pasture. These results could not be included in Figure 12.3 because no initial soil C
measurements were made. Being a chronosequence study it comes with the same qualifications as those
discussed in relation to the Turner and Lambert (2000) report. However, consistent with results shown in
Figure 12.3, Birk (1992) observed that soil C either changed little (i.e. following unimproved pasture) or
decreased (i.e. following improved pasture) after afforestation of ex-pasture sites in southern NSW
(Table 12.1).
72
Australian Greenhouse Office
Table 12.1. Amounts of soil C (g m-2) under Pinus radiata plantations established on either previously
unimproved or improved pasture in southern NSW. Data from Birk (1992).
Stand age (yr)
2
4
6
9
15
Unimproved
2854
2718
3081
2643
2517
Improved
3773
2832
3379
2980
2349
Both Gifford (2000) and Polglase and Falkiner (unpub.) measured litter C content. Using these results, the C
from radiata pine litter was found to linearly increase from 0 g C m-2 at two years of age (Polglase and
Falkiner, unpub.) to 1530 g C m-2 at 25 years of age (Gifford 2000). After two to eight years of effluent
irrigation, the C content in eucalypt litter was 97 to 184 g C m-2 (Polglase and Falkiner unpub.). When litter C
was included in the calculation of soil C, the change in soil C following afforestation generally increased
(Fig 12.4).
Age of plantation (yr)
0
10
20
30
40
50
60
70
Change in soil C (% yr-1)
8
6
4
2
0
-2
-4
-6
-8
-10
-12
Gifford (2000)
Polglase and Falkiner (unpub.)
-14
Figure 12.4. Change in soil C in 0-30 cm layer, together with litter, 2 to 60 years following afforestation of
ex-pasture land in the temperate climatic regions of the Australian Capital Territory and southern New
South Wales. The study of Polglase and Falkiner (unpub.), where irrigation of previously dry land caused a
large initial change in soil C, represents an extreme case.
National Carbon Accounting System Technical Report
73
In the effluent-irrigated study, weeds were
there tended to be a decrease in soil C content
repeatedly slashed within the first two years. For
each treatment, the C added from weed residues
within the surface 20 cm, and an increase in soil C
was calculated as 518-548 g C m under E. grandis
content at soil depths below 20 cm (Figs 12.5 and
12.6). This was particularly evident in the high-
and 834 g C m-2 under P. radiata. Despite the
effluent treatments. In plots irrigated with fresh
relatively high additions there was no relationship
between addition of C from weeds and the observed
water, change in soil C was more uniform with
-2
depth. Effluent added high concentrations of
nutrients to the surface of the soil which may have
change in soil C following afforestation.
stimulated decomposition and thus loss of soil C in
Polglase and Falkiner (unpub.) also investigated the
change in soil C to 70 cm. Under both forest types
upper soil layers.
Change in soil C (% yr-1)
-15
-10
-5
0
5
10
15
20
25
30
0
2.5
Soil depth (cm)
7.5
15
25
35
45
60
High
Medium
Low
Water
70
Figure 12.5. Change in soil C in various soil layers to 70 cm depth under irrigated two-year-old Eucalyptus
grandis plantations near Wagga Wagga, New South Wales. Treatments are different rates of effluent
irrigation. Polglase and Falkiner (unpub.).
74
Australian Greenhouse Office
Change in soil C (% yr-1)
-15
-10
-5
0
5
10
15
20
25
30
0
2.5
Soil depth (cm)
7.5
15
25
35
45
60
High
Medium
Low
Water
70
Figure 12.6. Change in soil C in various soil layers to 70 cm depth under irrigated two-year-old Pinus
radiata plantations near Wagga Wagga, New South Wales. Treatments are different rates of effluent
irrigation. Polglase and Falkiner (unpub.).
National Carbon Accounting System Technical Report
75
13. Synthesis
Section 10 developed a conceptual framework for
assessing the potential for change in soil C following
afforestation. Figure 13.1 and Table 13.1 synthesise
this information in an analysis of the more
important processes affecting C dynamics.
Figure 13.1. Summary of processes controlling change in soil C following afforestation. See Table 13.1 for
an explanation of the numerals.
76
Australian Greenhouse Office
Table 13.1. Summary of processes involved in Figure 13.1.
Stage
Process
Effect on soil C
(+ve or –ve)
Agriculture
1. The soil may have been under agriculture for some time. If cropped,
soil C may consist of mostly stable humus resistant to further significant
breakdown. If improved pasture, the soil may have a relatively high C
content that is susceptible to loss after plantation development.
Plantation established
2. Soil disturbance such as ripping and mounding is thought to increase
aeration and alter the microclimate, accelerating decomposition.
-ve
3. Residues such as dead roots from the pre-existing crop decompose,
adding to soil C.
+ve
4. Weeds and grass, if left between rows, provide most inputs to the soil
system and may be the major buffer against soil C loss.
+ve
5. Inputs from tree seedlings to soil are minimal at this stage as most of
the net primary production goes to building biomass. It may be three years
before residues begin to cast off from trees, and five to ten years before
maximum net primary production is reached.
-ve
Plantation aggrading
+ve or -ve
6. a. The amount of C input below-ground may be less compared to agriculture
-ve
as about half of the C allocated below-ground goes to long-lived, structural roots.
b. Fine (<3 mm) and perhaps medium (3-10 mm) tree roots will decompose
rapidly, but decomposition of large woody roots (>10 mm diameter) is
likely to be slower.
-ve
7. Weeds and grasses are shaded out under productive plantations and, after
canopy closure, above-ground litterfall becomes a significant process.
As with roots, it may take about three years from the time of commencement
of litterfall until transfer to soil humus is effected.
-ve
8. As time progresses, soil C can accumulate as a consequence of decomposition
of lignified tree residues.
+ve
9. Soil temperatures decrease as the tree canopy develops. Soil is possibly drier
compared to pasture. Decomposition is slowed leading to C accumulation.
+ve
10. Tree roots add C deep in the soil profile.
+ve
This analysis is used to highlight those processes most critical for model development and testing. These are:
Land use
•
Initial soil C quality in relation to type of agricultural land use (intensively cropped
versus improved pasture).
Inputs
•
•
•
•
Comparative NPP of pasture and plantation phases;
Temporal dynamics of NPP in plantations for a range of site conditions;
Allocation of C to stand components, particularly fine roots; and
Temporal patterns of inputs in litter and root residues.
Residue decomposition
•
•
•
•
•
Substrate quality control on decomposition rates;
Climatic control on decomposition rates;
Decomposition rates of residues and time taken to become soil humus;
Comparison of decomposition rates between above-ground litter and roots; and
Comparison of decomposition rates between fine and coarse roots
Weeds/ grass
•
Temporal patterns of weed/grass persistence (productivity) in plantation inter-rows.
Microclimate
•
Comparison of soil moisture and temperature regimes between pasture and plantation.
Disturbance
•
Effects of disturbance, particularly mechanical site preparation, on the soil environment
and decomposition rates.
Roots
•
Consistent treatment of live roots in soil sampled from agricultural and plantation land.
National Carbon Accounting System Technical Report
77
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Australian Greenhouse Office
APPENDIX 1
Sources of data and numerical codes used to describe site and sampling conditions for studies that measured
change in soil C after afforestation.
Climate: 1=Subtropical wet/savanna, 2=Subtropical moist, 3=Mediterranean/marine temperate,
4=Continental moist
Ex-land use: 1=Ex-pasture, 2=Ex-crops, 3=Ex-agriculture
Soil type: 1=Sand/sand loam, 2=Silty clay/silty loam, 3=Clay/clay loam
Spp: 1=Eucalypt, 2=Radiata pine, 3=Hardwoods (poplar, mahogany, etc.), 4=Softwoods (mixed pines,
spruce), 5=Other
Disturbance: 1=High, 2=Medium, 3=Low
Type of study: 1=Adjacent plots of different land use (Paired plot), 2=Adjacent plots of different ages
(Chronosequence), 3=Same plot over time (Retrospective), 4=Reference subsoil layer
Reference
Location
Layer
Age (yr)
Climate
Ex-land
use
Soil
type
Spp.
Disturbance
Type of
study
Aggangan et al. (1998)
Augusta, WA
0-10 cm
4
3
1
1
1
1
1
Aggangan et al. (1998)
Augusta, WA
0-20 cm
4
3
1
1
1
1
1
Aggangan et al. (1998)
Augusta, WA
10-20 cm
4
3
1
1
1
1
1
Alriksson & Olsson (1995)
Sweden
0-15 cm
20
4
3
1
4
3
4
Alriksson & Olsson (1995)
Sweden
0-15 cm
40
4
3
1
4
3
4
Alriksson & Olsson (1995)
Sweden
0-15 cm
55
4
3
1
4
3
4
Aweto (1981)
Nigeria
0-10 cm
3
1
2
NA
5
3
2
Aweto (1981)
Nigeria
0-30 cm
3
1
2
NA
5
3
2
Aweto (1981)
Nigeria
10-30 cm
3
1
2
NA
5
3
2
Aweto (1981)
Nigeria
0-10 cm
7
1
2
NA
5
3
2
Aweto (1981)
Nigeria
0-30 cm
7
1
2
NA
5
3
2
Aweto (1981)
Nigeria
10-30 cm
7
1
2
NA
5
3
2
Aweto (1981)
Nigeria
0-10 cm
10
1
2
NA
5
3
2
Aweto (1981)
Nigeria
0-30 cm
10
1
2
NA
5
3
2
Aweto (1981)
Nigeria
10-30 cm
10
1
2
NA
5
3
2
Bashkin and Binkley (1998)
Hawaii
0-10 cm
11.5
1
2
2
1
NA
1
Bashkin and Binkley (1998)
Hawaii
0-55 cm
11.5
1
2
2
1
NA
1
Bashkin and Binkley (1998)
Hawaii
10-55 cm
11.5
1
2
2
1
NA
1
Binkley and Resh (1999)
Hawaii (Hilo)
0-15 cm
3
1
2
NA
1
2
3
Binkley and Resh (1999)
Hawaii (Hilo)
0-30 cm
3
1
2
NA
1
2
3
National Carbon Accounting System Technical Report
93
Reference
Location
Layer
Age (yr)
Climate
Ex-land
use
Soil
type
Spp.
Disturbance
Type of
study
Binkley and Resh (1999)
Hawaii (Hilo)
15-30 cm
3
1
2
NA
1
2
3
Brown & Lugo (1990)
Puerto Rico
0-25 cm
10
1
2
3
4
NA
1
Brown & Lugo (1990)
Puerto Rico
0-50 cm
10
1
2
3
4
NA
1
Brown & Lugo (1990)
Puerto Rico
25-50 cm
10
1
2
3
4
NA
1
Brown & Lugo (1990)
Puerto Rico
0-25 cm
22.5
1
2
3
3
NA
1
Brown & Lugo (1990)
Puerto Rico
0-50 cm
22.5
1
2
3
3
NA
1
Brown & Lugo (1990)
Puerto Rico
25-50 cm
22.5
1
2
3
3
NA
1
Brown & Lugo (1990)
Virgin Islands
0-25 cm
26
2
2
3
3
NA
1
Brown & Lugo (1990)
Virgin Islands
0-50 cm
26
2
2
3
3
NA
1
Brown & Lugo (1990)
Virgin Islands
25-50 cm
26
2
2
3
3
NA
1
Brown & Lugo (1990)
Virgin Islands
0-25 cm
40
2
2
3
3
NA
1
Brown & Lugo (1990)
Virgin Islands
0-50 cm
40
2
2
3
3
NA
1
Brown & Lugo (1990)
Virgin Islands
25-50 cm
40
2
2
3
3
NA
1
Brown & Lugo (1990)
Puerto Rico
0-25 cm
35
3
2
3
3
NA
1
Brown & Lugo (1990)
Puerto Rico
0-25 cm
51
1
2
3
3
NA
1
Brown & Lugo (1990)
Puerto Rico
0-50 cm
51
1
2
3
3
NA
1
Brown & Lugo (1990)
Puerto Rico
25-50 cm
51
1
2
3
3
NA
1
Brown & Lugo (1990)
Puerto Rico
0-25 cm
42.5
1
2
3
3
NA
1
Brown & Lugo (1990)
Puerto Rico
0-50 cm
42.5
1
2
3
3
NA
1
Brown & Lugo (1990)
Puerto Rico
25-50 cm
42.5
1
2
3
3
NA
1
Brown & Lugo (1990)
Virgin Islands
0-25 cm
55
2
2
3
3
NA
1
Brown & Lugo (1990)
Virgin Islands
0-50 cm
55
2
2
3
3
NA
1
Brown & Lugo (1990)
Virgin Islands
25-50 cm
55
2
2
3
3
NA
1
Brown & Lugo (1990)
Virgin Islands
0-25 cm
100
2
2
3
3
NA
1
Brown & Lugo (1990)
Virgin Islands
0-50 cm
100
2
2
3
3
NA
1
Brown & Lugo (1990)
Virgin Islands
25-50 cm
100
2
2
3
3
NA
1
Brown & Lugo (1990)
Puerto Rico
0-25 cm
50
3
2
3
3
NA
1
Giddens et al. (1997)
New Zealand
0-10 cm
17
3
1
1
2
NA
1
Giddens et al. (1997)
New Zealand
0-10 cm
13
3
1
1
2
NA
1
Giddens et al. (1997)
New Zealand
0-10 cm
19
3
1
1
2
NA
1
Giddens et al. (1997)
New Zealand
0-10 cm
20
3
1
1
2
NA
1
Giddens et al. (1997)
New Zealand
0-10 cm
20
3
1
2
2
NA
1
Giddens et al. (1997)
New Zealand
0-10 cm
16
3
1
2
2
NA
1
Giddens et al. (1997)
New Zealand
0-10 cm
18
3
1
2
2
NA
1
Giddens et al. (1997)
New Zealand
0-10 cm
19
3
1
2
2
NA
1
Giddens et al. (1997)
New Zealand
0-10 cm
24
3
1
1
2
NA
1
94
Australian Greenhouse Office
Reference
Location
Layer
Age (yr)
Climate
Ex-land
use
Soil
type
Spp.
Disturbance
Type of
study
Giddens et al. (1997)
New Zealand
0-10 cm
30
3
1
2
2
NA
1
Gifford (2000)
ACT, site 53
0-30 cm
15
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 53
0-100 cm
15
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 53
30-100 cm
15
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 56
0-30 cm
17
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 56
0-100 cm
17
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 56
30-100 cm
17
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 57
0-30 cm
12
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 57
0-100 cm
12
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 57
30-100 cm
12
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 52
0-30 cm
25
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 52
0-100 cm
25
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 52
30-100 cm
25
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 55
0-30 cm
28
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 55
0-100 cm
28
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 55
30-100 cm
28
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 51
0-30 cm
60
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 51
0-100 cm
60
3
1
NA
2
NA
1
Gifford (2000)
ACT, site 51
30-100 cm
60
3
1
NA
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 21
0-30 cm
8
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 21
0-100 cm
8
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 21
30-100 cm
8
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 20
0-30 cm
8
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 20
0-100 cm
8
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 20
30-100 cm
8
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 22
0-30 cm
16
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 22
0-100 cm
16
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 22
30-100 cm
16
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 27
0-30 cm
18
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 27
0-100 cm
18
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 27
30-100 cm
18
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 23
0-30 cm
18
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 23
0-100 cm
18
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 23
30-100 cm
18
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 24
0-30 cm
18
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 24
0-100 cm
18
3
1
2
2
NA
1
National Carbon Accounting System Technical Report
95
Reference
Location
Layer
Ex-land
use
Soil
type
Spp.
Disturbance
Type of
study
Gifford and Barrett (1999)
Tumut/Tum, site 24
30-100 cm
18
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 26
0-30 cm
16
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 26
0-100 cm
16
3
1
2
2
NA
1
Gifford and Barrett (1999)
Tumut/Tum, site 26
30-100 cm
16
3
1
2
2
NA
1
Gilmore & Boggess (1963)
Illinois, USA, O
0-15 cm
4
4
1
2
3
3
3
Gilmore & Boggess (1963)
Illinois, USA, M
0-15 cm
4
4
1
2
3
3
3
Gilmore & Boggess (1963)
Illinois, USA, ML
0-15 cm
4
4
1
2
3
3
3
Gilmore & Boggess (1963)
Illinois, USA, MLP
0-15 cm
4
4
1
2
3
3
3
Gilmore & Boggess (1963)
Illinois, USA, R
0-15 cm
4
4
1
2
3
3
3
Gilmore & Boggess (1963)
Illinois, USA, RL
0-15 cm
4
4
1
2
3
3
3
Gilmore & Boggess (1963)
Illinois, USA, RLP
0-15 cm
4
4
1
2
3
3
3
Gilmore & Boggess (1963)
Illinois, USA, O
0-15 cm
5
4
1
2
4
3
3
Gilmore & Boggess (1963)
Illinois, USA, M
0-15 cm
5
4
1
2
4
3
3
Gilmore & Boggess (1963)
Illinois, USA, ML
0-15 cm
5
4
1
2
4
3
3
Gilmore & Boggess (1963)
Illinois, USA, MLP
0-15 cm
5
4
1
2
4
3
3
Gilmore & Boggess (1963)
Illinois, USA, R
0-15 cm
5
4
1
2
4
3
3
Gilmore & Boggess (1963)
Illinois, USA, RL
0-15 cm
5
4
1
2
4
3
3
Gilmore & Boggess (1963)
Illinois, USA, RLP
0-15 cm
5
4
1
2
4
3
3
Grigal & Berguson (1998)
Minnesota, USA
0-25 cm
6
4
1
1
3
NA
1
Grigal & Berguson (1998)
Minnesota, USA
0-25 cm
7
4
2
3
3
NA
1
Grigal & Berguson (1998)
Minnesota, USA
0-25 cm
15
4
1
3
3
NA
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al.. (2000)
SW WA
0-10 cm
7
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
10
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
10
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
9
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al.. (2000)
SW WA
0-10 cm
7
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
7
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
6
3
1
1
1
3
1
Grove et al.. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
9
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
9
3
1
1
1
3
1
96
Age (yr) Climate
Australian Greenhouse Office
Reference
Location
Layer
Age (yr) Climate
Ex-land
use
Soil
type
Spp.
Disturbance
Type of
study
Grove et al. (2000)
SW WA
0-10 cm
11
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
9
3
1
1
1
3
1
Grove et al.(2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
10
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
7
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
8
3
1
1
1
3
1
Grove et al. (2000)
SW WA
0-10 cm
9
3
1
1
1
3
1
Grove et al.(2000)
SW WA
0-10 cm
10
3
1
1
1
3
1
Guggenberger et al. (1994)
Germany
0-75 cm
87
4
2
2
4
NA
1
Hansen (1993)
Great Plains, USA
0-100 cm
4
4
2
NA
3
NA
1
Hansen (1993)
Great Plains, USA
0-100 cm
6
4
2
NA
3
NA
1
Hansen (1993)
Great Plains, USA
0-100 cm
13
4
2
NA
3
NA
1
Hansen (1993)
Great Plains, USA
0-100 cm
15
4
2
NA
3
NA
1
Hansen (1993)
Great Plains, USA
0-100 cm
16
4
2
NA
3
NA
1
Hansen (1993)
Great Plains, USA
0-100 cm
16
4
2
NA
3
NA
1
Hansen (1993)
Great Plains, USA
0-100 cm
18
4
2
NA
3
NA
1
Hansen (1993)
Great Plains, USA
0-100 cm
30
4
2
NA
3
NA
1
Huntington (1995)
Georgia
0-25 cm
70
2
3
1
5
NA
4
Huntington (1995)
Georgia
0-100 cm
70
2
3
1
5
NA
4
Jenkinson et al. (1992)
Broadbalk at Rothamsted
0-23 cm
100
3
2
2
3
3
3
Jenkinson et al. (1992)
Geescroft at Rothamsted
0-23 cm
100
3
2
2
3
3
3
Johnston et al. (1996)
Minnesota, USA
0-25 cm
39
4
3
1
5
3
3
Jug et al. (1999)
Germany (Wildeshausen)
0-10 cm
7
3
3
1
3
NA
3
Jug et al. (1999)
Germany (Wildeshausen)
0-30 cm
7
3
3
1
3
NA
3
Jug et al. (1999)
Germany (Wildeshausen)
10-30 cm
7
3
3
1
3
NA
3
Jug et al. (1999)
Germany (Canstein)
0-10 cm
10
3
3
1
3
NA
3
Jug et al.. (1999)
Germany (Canstein)
0-30 cm
10
3
3
1
3
NA
3
Jug et al. (1999)
Germany (Canstein)
10-30 cm
10
3
3
1
3
NA
3
National Carbon Accounting System Technical Report
97
Reference
Location
Layer
Ex-land
use
Soil
type
Spp.
Disturbance
Type of
study
Jug et al.. (1999)
Germany (Abbachhof)
0-10 cm
10
3
3
2
3
NA
3
Jug et al. (1999)
Germany (Abbachhof)
0-30 cm
10
3
3
2
3
NA
3
Jug et al. (1999)
Germany (Abbachhof)
10-30 cm
10
3
3
2
3
NA
3
Lugo et al (1986)
Puerto Rico
0-50 cm
10
1
1
3
5
3
1
Lugo et al (1986)
Puerto Rico
0-25 cm
10
3
3
3
5
3
1
Lugo et al (1986)
Puerto Rico
0-50 cm
20
1
1
3
5
3
1
Lugo et al (1986)
Puerto Rico
0-50 cm
23
1
1
3
5
3
1
Lugo et al (1986)
Puerto Rico
0-50 cm
40
1
1
3
5
3
1
Lugo et al (1986)
Puerto Rico
0-25 cm
35
3
3
3
5
3
1
Lugo et al (1986)
Puerto Rico
0-50 cm
45
1
1
3
5
3
1
Lugo et al (1986)
Puerto Rico
0-50 cm
52
1
1
3
5
3
1
Lugo et al (1986)
Puerto Rico
0-25 cm
50
3
3
3
5
3
1
Lugo et al (1986)
Virgin Islands
0-50 cm
25
2
2
3
5
NA
1
Lugo et al (1986)
Virgin Islands
0-50 cm
40
2
2
3
5
NA
1
Lugo et al (1986)
Virgin Islands
0-50 cm
52
2
2
3
5
NA
1
Maggs and Hewett (1993)
Atherton, Qld
0-10 cm
50
2
1
1
5
3
1
Maggs and Hewett (1993)
Atherton, Qld
0-10 cm
50
2
1
1
5
3
1
Maggs and Hewett (1993)
Atherton, Qld
0-10 cm
50
2
1
2
5
3
1
Maggs and Hewett (1993)
Atherton, Qld
0-10 cm
50
2
1
2
5
3
1
Morris and Grey (1984)
Swaziland
0-20 cm
13
1
1
NA
4
NA
1
Morris and Grey (1984)
Swaziland
0-100 cm
13
1
1
NA
4
NA
1
Morris and Grey (1984)
Swaziland
20-100 cm
13
1
1
NA
4
NA
1
Morris and Grey (1984)
Swaziland
0-20 cm
26
1
1
NA
4
NA
1
Morris and Grey (1984)
Swaziland
0-100 cm
26
1
1
NA
4
NA
1
Morris and Grey (1984)
Swaziland
20-100 cm
26
1
1
NA
4
NA
1
Parfitt et al. (1997)
New Zealand (Ngaumu)
0-10 cm
20
3
1
2
2
3
1
Parfitt et al. (1997)
New Zealand (Ngaumu)
0-20 cm
20
3
1
2
2
3
1
Parfitt et al. (1997)
New Zealand (Ngaumu)
10-20 cm
20
3
1
2
2
3
1
Polglase and Falkiner (unpub.)
Wagga EW, NSW
0-10 cm
2
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EW, NSW
0-70 cm
2
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EW, NSW
10-70 cm
2
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EL, NSW
0-10 cm
2
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EL, NSW
0-70 cm
2
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EL, NSW
10-70 cm
2
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EM, NSW
0-10 cm
2
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EM, NSW
0-70 cm
2
3
1
3
1
3
3
98
Age (yr) Climate
Australian Greenhouse Office
Reference
Location
Layer
Age (yr)
Climate
Ex-land
use
Soil
type
Spp.
Disturbance
Type of
study
Polglase and Falkiner (unpub.)
Wagga EM, NSW
10-70 cm
2
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EM, NSW
0-10 cm
4
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EM, NSW
0-70 cm
4
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EM, NSW
10-70 cm
4
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EM, NSW
0-10 cm
8
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EM, NSW
0-70 cm
8
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EM, NSW
10-70 cm
8
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EH, NSW
0-10 cm
2
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EH, NSW
0-70 cm
2
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga EH, NSW
10-70 cm
2
3
1
3
1
3
3
Polglase and Falkiner (unpub.)
Wagga PW, NSW
0-10 cm
2
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PW, NSW
0-70 cm
2
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PW, NSW
10-70 cm
2
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PL, NSW
0-10 cm
2
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PL, NSW
0-70 cm
2
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PL, NSW
10-70 cm
2
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PM, NSW
0-10 cm
2
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PM, NSW
0-70 cm
2
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PM, NSW
10-70 cm
2
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PM, NSW
0-10 cm
4
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PM, NSW
0-70 cm
4
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PM, NSW
10-70 cm
4
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PM, NSW
0-10 cm
8
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PM, NSW
0-70 cm
8
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PM, NSW
10-70 cm
8
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PH, NSW
0-10 cm
2
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PH, NSW
0-70 cm
2
3
1
3
2
3
3
Polglase and Falkiner (unpub.)
Wagga PH, NSW
10-70 cm
2
3
1
3
2
3
3
Quideau & Bockheim (1996)
Madison, USA
0-15 cm
32
4
1
1
4
NA
1
Quideau & Bockheim (1996)
Madison, USA
0-30 cm
32
4
1
1
4
NA
1
Quideau & Bockheim (1996)
Madison, USA
15-30 cm
32
4
1
1
4
NA
1
Quideau & Bockheim (1996)
Madison, USA
0-15 cm
42
4
1
1
4
NA
1
Quideau & Bockheim (1996)
Madison, USA
0-30 cm
42
4
1
1
4
NA
1
Quideau & Bockheim (1996)
Madison, USA
15-30 cm
42
4
1
1
4
NA
1
Ramakrishnan & Toky (1981)
NE India
0-40 cm
5
1
2
1
5
3
2
Ramakrishnan & Toky (1981)
NE India
0-40 cm
10
1
2
1
5
3
2
National Carbon Accounting System Technical Report
99
Reference
Location
Layer
Age (yr)
Climate
Ex-land
use
Soil
type
Spp.
Disturbance
Type of
study
Ramakrishnan & Toky (1981)
NE India
0-40 cm
15
1
2
1
5
3
2
Ramakrishnan & Toky (1981)
NE India
0-40 cm
50
1
2
1
5
3
2
Resh (1999)
Puerto Rico (Toa Baja)
0-40 cm
7
1
1
NA
1
1
3
Resh (1999)
Puerto Rico (Toa Baja)
0-40 cm
7
1
1
NA
5
1
3
Resh (1999)
Puerto Rico (Toa Baja)
0-40 cm
7
1
1
NA
5
1
3
Resh (1999)
Puerto Rico (Lajas)
0-40 cm
16
1
1
NA
1
2
3
Resh (1999)
Hawaii (upper Kamae)
0-40 cm
15
1
2
NA
1
2
3
Resh (1999)
Hawaii (Chinchuck)
0-40 cm
16
1
2
NA
1
2
3
Resh (1999)
Puerto Rico (Lajas)
0-40 cm
16
1
1
NA
5
2
3
Resh (1999)
Puerto Rico (Lajas)
0-40 cm
16
1
1
NA
5
2
3
Resh (1999)
Hawaii (upper Kamae)
0-40 cm
15
1
2
NA
5
2
3
Resh (1999)
Hawaii (Chinchuck)
0-40 cm
16
1
2
NA
5
2
3
Richter et al. (1999)
South Carolina (Calhoun)
0-15 cm
11
2
2
1
4
NA
3
Richter et al. (1999)
South Carolina (Calhoun)
0-60 cm
11
2
2
1
4
NA
3
Richter et al. (1999)
South Carolina (Calhoun)
15-60 cm
11
2
2
1
4
NA
3
Richter et al. (1999)
South Carolina (Calhoun)
0-15 cm
20
2
2
1
4
NA
3
Richter et al. (1999)
South Carolina (Calhoun)
0-60 cm
20
2
2
1
4
NA
3
Richter et al. (1999)
South Carolina (Calhoun)
15-60 cm
20
2
2
1
4
NA
3
Richter et al. (1999)
South Carolina (Calhoun)
0-15 cm
25
2
2
1
4
NA
3
Richter et al. (1999)
South Carolina (Calhoun)
0-60 cm
25
2
2
1
4
NA
3
Richter et al. . (1999)
South Carolina (Calhoun)
15-60 cm
25
2
2
1
4
NA
3
Richter et al. (1999)
South Carolina (Calhoun)
0-15 cm
33
2
2
1
4
NA
3
Richter et al. (1999)
South Carolina (Calhoun)
0-60 cm
33
2
2
1
4
NA
3
Richter et al. (1999)
South Carolina (Calhoun)
15-60 cm
33
2
2
1
4
NA
3
Richter et al. (1999)
South Carolina (Calhoun)
0-15 cm
40
2
2
1
4
NA
3
Richter et al. . (1999)
South Carolina (Calhoun)
0-60 cm
40
2
2
1
4
NA
3
Richter et al. (1999)
South Carolina (Calhoun)
15-60 cm
40
2
2
1
4
NA
3
Ross et al. (1999)
New Zealand
0-10 cm
19
3
1
1
2
3
1
Ross et al. (1999)
New Zealand
0-20 cm
19
3
1
1
2
3
1
Ross et al. (1999)
New Zealand
10-20 cm
19
3
1
1
2
3
1
Schiffman & Johnson (1988)
Virginia
0-10 cm
50
2
3
3
4
1
1
Schiffman & Johnson (1988)
Virginia
0-33 cm
50
2
3
3
4
1
1
Schiffman & Johnson (1988)
Virginia
10-33 cm
50
2
3
3
4
1
1
Scott et al. (1999)
New Zealand (Tikitere)
0-10 cm
23
3
1
2
2
NA
1
Scott et al. (1999)
New Zealand (Tikitere)
0-50 cm
23
3
1
2
2
NA
1
Scott et al. (1999)
New Zealand (Tikitere)
10-50 cm
23
3
1
2
2
NA
1
100
Australian Greenhouse Office
Reference
Location
Layer
Age (yr)
Climate
Ex-land
use
Soil
type
Spp.
Disturbance
Type of
study
Scott et al. (1999)
New Zealand (Puruki)
0-10 cm
23
3
1
2
2
NA
1
Scott et al. (1999)
New Zealand (Puruki)
0-50 cm
23
3
1
2
2
NA
1
Scott et al. (1999)
New Zealand (Puruki)
10-50 cm
23
3
1
2
2
NA
1
Scott et al. (1999)
New Zealand (Kaingaroa)
0-10 cm
54
3
1
2
2
NA
1
Scott et al. (1999)
New Zealand (Kaingaroa)
0-50 cm
54
3
1
2
2
NA
1
Scott et al. (1999)
New Zealand (Kaingaroa)
10-50 cm
54
3
1
2
2
NA
1
Scott et al. (1999)
New Zealand (Ngaumu)
0-10 cm
52
3
1
3
2
NA
1
Scott et al. (1999)
New Zealand (Ngaumu)
0-30 cm
52
3
1
3
2
NA
1
Scott et al. (1999)
New Zealand (Ngaumu)
10-30 cm
52
3
1
3
2
NA
1
Sparling et al. (1994)
Tammin, WA
0-10 cm
9
3
2
1
1
NA
1
Tolbert et al. (2000)
Mississippi, USA
0-15 cm
3
2
2
2
3
NA
3
Tolbert et al. (2000)
Tennessee, USA
0-30 cm
3
2
2
2
3
NA
3
Tolbert et al. (2000)
Alabama, USA
0-60 cm
4
2
2
2
3
NA
3
Tolbert et al. (2000)
Alabama, USA (+cover)
0-60 cm
4
2
2
2
3
NA
3
Trouve et al. (1994, 1996)
Congo
0-5 cm
2
1
1
1
1
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
3
1
1
1
1
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
5
1
1
1
1
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
6
1
1
1
1
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
8
1
1
1
1
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
10
1
1
1
1
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
3
1
1
1
4
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
9
1
1
1
4
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
13
1
1
1
1
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
14
1
1
1
1
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
15
1
1
1
1
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
16
1
1
1
1
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
19
1
1
1
1
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
11
1
1
1
4
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
13
1
1
1
4
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
15
1
1
1
4
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
17
1
1
1
4
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
18
1
1
1
4
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
21
1
1
1
4
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
23
1
1
1
4
NA
2
Trouve et al. (1994, 1996)
Congo
0-5 cm
28
1
1
1
4
NA
2
Whiteley (1991)
Leeds, UK
0-30 cm
40
3
2
3
3
NA
1
National Carbon Accounting System Technical Report
101
Reference
Location
Layer
Age (yr)
Climate
Ex-land
use
Soil
type
Spp.
Disturbance
Type of
study
Whiteley (1991)
Leeds, UK
0-86 cm
40
3
2
3
3
NA
1
Whiteley (1991)
Leeds, UK
30-86 cm
40
3
2
3
3
NA
1
Yeates et al. (1997)
New Zealand
0-10 cm
9
3
1
1
2
NA
1
Yeates et al. (1997)
New Zealand
0-10 cm
17
3
1
1
2
NA
1
Yeates et al. (1997)
New Zealand
0-10 cm
13
3
1
1
2
NA
1
Yeates et al. (1997)
New Zealand
0-10 cm
19
3
1
1
2
NA
1
Yeates et al. (1997)
New Zealand
0-10 cm
20
3
1
1
2
NA
1
Yeates et al. (1997)
New Zealand
0-10 cm
20
3
1
2
2
NA
1
Yeates et al. (1997)
New Zealand
0-10 cm
16
3
1
2
2
NA
1
Yeates et al. (1997)
New Zealand
0-10 cm
18
3
1
2
2
NA
1
Yeates et al. (1997)
New Zealand
0-10 cm
19
3
1
2
2
NA
1
Yeates et al. (1997)
New Zealand
0-10 cm
24
3
1
1
2
NA
1
Yeates et al. (1997)
New Zealand
0-10 cm
30
3
1
2
2
NA
1
Zak et al. (1990)
Minnesota, USA
0-10 cm
3
4
3
1
3
1
2
Zak et al. (1990)
Minnesota, USA
0-10 cm
5
4
3
1
3
1
2
Zak et al. (1990)
Minnesota, USA
0-10 cm
6
4
3
1
3
1
2
Zak et al. (1990)
Minnesota, USA
0-10 cm
7
4
3
1
3
1
2
Zak et al. (1990)
Minnesota, USA
0-10 cm
8
4
3
1
3
1
2
Zak et al. (1990)
Minnesota, USA
0-10 cm
9
4
3
1
3
1
2
Zak et al. (1990)
Minnesota, USA
0-10 cm
10
4
3
1
3
1
2
Zak et al. (1990)
Minnesota, USA
0-10 cm
19
4
3
1
3
1
2
Zak et al. (1990)
Minnesota, USA
0-10 cm
30
4
3
1
3
1
2
Zak et al. (1990)
Minnesota, USA
0-10 cm
35
4
3
1
3
1
2
Zak et al. (1990)
Minnesota, USA
0-10 cm
46
4
3
1
3
1
2
Zak et al. (1990)
Minnesota, USA
0-10 cm
53
4
3
1
3
1
2
Zak et al. (1990)
Minnesota, USA
0-10 cm
60
4
3
1
3
1
2
Zech et al. (1997)
Argentina
0-10 cm
50
2
2
1
2
NA
1
Zech et al. (1997)
Argentina
0-60 cm
50
2
2
1
2
NA
1
Zech et al. (1997)
Argentina
10-60 cm
50
2
2
1
2
NA
1
Zhang et al. (1999)
Nebraska, USA
0-10 cm
80
4
1
2
3
NA
1
Zou and Bashkin (1998)
Hawaii
0-25 cm
10
1
2
2
1
NA
2
102
Australian Greenhouse Office
National Carbon Accounting System Technical Report
103
Series 1 Publications
1.
Setting the Frame
2.
Estimation of Changes in Soil Carbon Due to Changes in Land Use
3.
Woody Biomass: Methods for Estimating Change
4.
Land Clearing 1970-1990: A Social History
5a. Review of Allometric Relationships for Estimating Woody Biomass for Queensland, the Northern
Territory and Western Australia
5b. Review of Allometric Relationships for Estimating Woody Biomass for New South Wales, the
Australian Capital Territory, Victoria, Tasmania and South Australia
6.
The Decay of Coarse Woody Debris
7.
Carbon Content of Woody Roots: Revised Analysis and a Comparison with Woody Shoot
Components (Revision 1)
8.
Usage and Lifecycle of Wood Products
9.
Land Cover Change: Specification for Remote Sensing Analysis
10. National Carbon Accounting System: Phase 1 Implementation Plan for the 1990 Baseline
11. International Review of the Implementation Plan for the 1990 Baseline (13-15 December 1999)
Series 2 Publications
12. Estimation of Pre-Clearing Soil Carbon Conditions
13. Agricultural Land Use and Management Information
14. Sampling, Measurement and Analytical Protocols for Carbon Estimation in Soil, Litter and Coarse
Woody Debris
15. Carbon Conversion Factors for Historical Soil Carbon Data
16. Remote Sensing Analysis Of Land Cover Change - Pilot Testing of Techniques
17. Synthesis of Allometrics, Review of Root Biomass and Design of Future Woody Biomass Sampling
Strategies
18. Wood Density Phase 1 - State of Knowledge
19. Wood Density Phase 2 - Additional Sampling
20. Change in Soil Carbon Following Afforestation or Reforestation
21. System Design
22. Carbon Contents of Above-Ground Tissues of Forest and Woodland Trees
23. Plant Productivity - Spatial Estimation of Plant Productivity and Classification by Vegetation Type
24. Analysis of Wood Product Accounting Options for the National Carbon Accounting System
25. Review of Unpublished Biomass-Related Information: Western Australia, South Australia, New
South Wales and Queensland
26. CAMFor User Manual
accounting and forecasting capability for human-induced sources and
sinks of greenhouse gas emissions from Australian land based
systems. It will provide a basis for assessing Australia’s progress
towards meeting its international emissions commitments.
technical report no. 20
The National Carbon Accounting System provides a complete
Change in Soil Carbon Following Afforestation or Reforestation
http://www.greenhouse.gov.au