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Forest Ecology and Management 255 (2008) 300–307
www.elsevier.com/locate/foreco
Planting mahogany in canopy gaps created by commercial harvesting
J. do C.A. Lopes a, S.B. Jennings b,*, N.M. Matni c
a
Embrapa Amazônia-Oriental, CP 48, Belém, Pará 66.095-100, Brazil
b
Oxfam GB, Oxfam House, John Smith Drive, Oxford OX4 2JY, UK
c
Nordisk Timber Ltda., CP 1541, Belém, Pará 66.820-000, Brazil
This paper is dedicated to the memory of Tim Whitmore.
Abstract
Attempts at natural forest management of mahogany (Swietenia macrophylla King) have so far met with limited success, whilst many
plantations are beset by the shoot borer Hypsipyla spp. In this paper we present preliminary results of an approach to enrichment planting that aims
to balance economic returns (rapid growth and good silvicultural form) with intervention costs and changes to forest structure. Mahogany seedlings
were planted in gaps created by selective timber harvesting and that ranged in vertical projected area from 91 to 542 m2 (mean = 257 m2).
Seedlings grew within the matrix of gap regrowth, with limited control of competing vegetation. Sixty-one percent of seedlings had survived by 4.4
years (equivalent to an annual mortality rate of 10.5% year1), and had reached a mean height of 4.5 m. Stocking levels of mahogany were similar
to that of naturally regenerated commercial species in unplanted gaps of the same age, but mahogany seedlings were significantly taller. The
incidence of shoot borer attack on mahogany stems was relatively low (54.7%), but, more importantly, most damaged stems (58%) responded by
producing a single replacement leader. The cost of the proposed methodology (US$ 94 per gap over 4.4 years) was low compared to the high value
of mahogany timber relative to other species in the forest. The implications of planting mahogany in gaps for forest management and the potential
benefits to conservation of the species are considered.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Brazilian Amazon; Canopy gaps; Height growth; Hypsipyla; Silviculture; Swietenia macrophylla
1. Introduction
Mahogany (Swietenia macrophylla King) is one of the
world’s most valuable timbers. Yet most mahogany logging in
Brazil and elsewhere has been at best poorly regulated and at
worst illegal (Rodan et al., 1992; Greenpeace, 2002). Such
logging removes most of the commercial-sized trees (Gullison
et al., 1996; Snook, 1996), may deplete the genetic variability
of the species (Newton et al., 1996), and has acted as a catalyst
for deforestation (Verı́ssimo et al., 1995). The unsustainable
nature of this trade resulted in the neotropical populations of
mahogany being included in Appendix II of the Convention on
International Trade in Endangered Species (CITES) in
November 2002. More recently, legislation has been adopted
in Brazil that seeks to ensure long-term management of the
species. The effects of these measures remain to be seen.
* Corresponding author. Tel.: +44 1865 472153.
E-mail address: [email protected] (S.B. Jennings).
0378-1127/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.foreco.2007.09.051
Sustainable management of mahogany in natural forest is
seen as an important means of ameliorating these impacts
(Jennings et al., 2000). However, several studies have argued
that there is little or no regeneration after logging in Bolivia
(Quevedo, 1986; Gullison et al., 1996), Mexico (Snook, 1993;
Dickinson and Whigham, 1999), and Brazil (Verı́ssimo et al.,
1995; Grogan et al., 2003, 2005). It has been suggested that this
is because mahogany regenerates as single-aged stands
following catastrophic disturbance, and that selective logging
causes insufficient disturbance to provide the conditions
necessary for regeneration (Snook, 1996). This view was
challenged in a recent review of the available evidence, which
concluded that not only there was no evidence that mahogany
requires catastrophic disturbance in order to regenerate, but that
regeneration is often dense after logging in areas transitional
between savannah and high forest (Brown et al., 2003).
Unfortunately, attempts to increase the density of natural
regeneration of mahogany through silvicultural interventions
have been attempted only rarely, and have met with mixed
success (reviewed in Mayhew and Newton, 1998).
J.C.A. Lopes et al. / Forest Ecology and Management 255 (2008) 300–307
In contrast to the limited application of natural forest
management of mahogany, the species has been grown in
plantations throughout the tropics. Although it has grown
rapidly in different types of plantation (monospecific and mixed
planting in the open, enrichment planting in lines, etc.) and on
different soils, most plantations have been bedevilled by the all
but ubiquitous shoot borers, Hypsipyla grandella and H.
robusta (Lepidoptera: Pyralidae) (Griffiths, 2001). Shoot borers
rarely kill mahogany trees, but they do kill the terminal shoot,
as a result of which the tree usually produces several
replacement stems. This usually results in trees with low
branches and reduced commercial value. The most successful
approaches to controlling the species are likely to involve a
variety of silvicultural techniques that together: reduce the
chance of Hypsipyla locating mahogany trees; reduce susceptibility to attack; promote vigorous vertical growth after attack;
and encourage natural enemies of the shoot borer (Newton
et al., 1993; Mayhew and Newton, 1998; Hauxwell et al., 2001).
In this paper, we describe a technique of enrichment planting
in which small numbers of mahogany seedlings are planted
within canopy gaps created by timber harvesting. The seedlings
grow within the matrix of gap regeneration vegetation, with
periodic cleaning confined to maintaining overhead light. The
methodology was developed with the full participation of the
site’s forest manager (N. Matni) in order to identify a practical
balance between competing influences on forest management.
These influences include the high economic costs and severe
change to forest structure caused by traditional planting
methods, against the need for high economic return, which can
be achieved by rapid growth and good tree form. The desired
outcome of this method is commensurately limited to having at
least one marketable mahogany stem available during the next
rotation for each tree harvested (of whatever species). The
expectations were that (1) the forest gap environment would
provide sufficient illumination for silviculturally acceptable
growth and survival of mahogany with limited maintenance, (2)
the incidence and/or impact of Hypsipyla would be lower than
in conventional plantations and (3) there would be economic
advantages over leaving the forest to regenerate after logging
without seedling enrichment planting in gaps.
2. Materials and methods
2.1. Study area
Research was conducted at Fazenda Pataua (58420 S,
488560 W), approximately 570 km south of Belém, in Pará
state, Brazil. The forest is approximately 3000 ha in size, and is
surrounded by pasture and eucalypt plantations. Precipitation
was 1600 mm in 1999 and 2100 mm in 2000, with a dry season
of 5 months during which monthly precipitation was <100 mm.
The topography is gently undulating, with ridges usually no
more than 5–10 m above the courses of the numerous small,
seasonal streams that dissect the area. The forest is evergreen
with a 25 m canopy surpassed by emergents, most commonly
Brazilnut (Bertholletia excelsa Humb. & Bonpl.). The area was
logged for mahogany in 1983 and for 21 other species between
301
1992 and 1998. Mahogany is present at very low density: 0.05
trees 20 cm ha1 and 0.033 logged stumps ha1 (Jennings
and Baima, 2005), and natural regeneration is scarce
(0.14 individuals ha1 between 1 and 20 cm diameter).
2.2. Design and measurements
Fifty gaps created by logging operations during the 1998 dry
season (July–October) were selected for the experiment. The
most common tree felled to create these gaps was Cedrelinga
catenaeformis (Ducke) Ducke (Mimosaceae). As the gaps were
all recent, natural regeneration was still poorly developed
(generally <0.5 m tall). The vertical projection of the canopy
gaps was estimated by measuring the diameter of the longest
axis and the diameter perpendicular to that, and gap area
estimated according to the formula for an ellipse (Barton et al.,
1989). Gap size ranged from 91 to 542 m2 (mean 257 m2,
S.E. = 134).
Twenty gaps were randomly allocated as controls and were
not manipulated in any way. These effectively control for the
null hypothesis that growth, density and species value are
higher in the absence of intervention. The other possible type of
control – planting mahogany and then not carrying out
maintenance – was not done because of its negligible practical
value: mahogany stems would have been rapidly overtopped
and suffered low growth and high mortality.
Mahogany seedlings were produced from locally collected
seeds planted in 2 l polythene sacs filled with a mixture of forest
soil, sand and well-rotted manure at a ratio of 3:1:1. They were
raised in a field nursery under light neutral shade for 4 months
until they were 0.22 m in height (S.E. = 0.05).
Mahogany seedlings were planted in the remaining 30 gaps
early in the first wet season after logging (December 1998).
Some of the coarse woody debris remaining in the gaps was cut
to improve accessibility and facilitate planting. Seedlings were
planted at a spacing of 5 m 5 m and were uniquely labelled.
The only criteria for planting were that (1) the planting site
should be clear from coarse woody debris or stumps; and (2) the
seedling should be within the vertical projection of the gap (i.e.,
have direct overhead illumination). The number of seedlings
planted per gap therefore varied according to gap size, from 6 to
16 (total planted = 290; mean per gap = 9.7; S.E. = 3.2).
Natural regeneration within 1 m diameter of the seedling
was manually cut back. Soil samples, homogenised from four
sub-samples collected from 0 to 20 cm and 20–40 cm depth,
were taken from each gap and analysed for chemical
composition by the Soil Laboratory at Embrapa Amazônia
Oriental, Belém, Pará.
The rationale for this planting methodology was that
mahogany seedlings should grow within the matrix of natural
gap regeneration (Oliveira, 2000; Snook and Negreros-Castillo,
2004). Maintenance of the planted gaps was therefore kept to a
minimum, manually cutting back only vegetation growing
directly above each seedling (such as the fast-growing pioneer
species Cecropia spp. and Trema micrantha (L.) Blume), and
vegetation within 1 m diameter of the base of the stem. Cut
material was left in situ. Maintenance was carried out 3 months
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after planting, every 6 months until April 2000, once more in
2001, and then again in May 2003.
Mahogany seedlings were measured at each maintenance.
Height was measured with a rule, or with a telescopic
measuring pole for seedlings >2 m height. The diameter of all
seedlings 2 cm diameter at breast height (dbh) was measured
with a steel diameter tape. The crown illumination index (Clark
and Clark, 1992; Jennings et al., 1999) of each seedling was
estimated before and after maintenance.
A single two-way ANOVA was used to assess the effect of
illumination (calculated as a time-weighted median for each
gap, as the crown illumination index is a semi-ordinal scale)
and soil nutrients on log-transformed mean seedling height
after 4.4 years.
The incidence of shoot borer (H. grandella) on each seedling
was recorded, either present or in the past through the
characteristic damage to the dead leader. Finally, the number of
stems produced by each seedling in response to shoot borer
attack was recorded. One gap was not measured on the last
occasion due to a serious accident to the researcher, and data
from this gap is not reported here.
The annualised mortality rate, m, of planted seedlings, was
calculated following the equation of Sheil et al. (1995):
m¼1
Nt
N0
a discounting rate that is stable over decades—problematic in
a traditionally volatile economy such as Brazil’s, and even
more so as such a rate would cover a time when decreasing oil
supply and global climatic change are likely to cause
substantial but unpredictable changes to the world’s
economies;
prediction of timber volume at least 30–40 years into the
future, based on extrapolation of short-term growth and
mortality rates; and
predictable changes to the relative timber prices of different
species.
We believe that such assumptions are unjustified, and
therefore decided to simply record timber prices and costs of
planting. This is intended as a preliminary indication of the
comparison between planting mahogany and ‘log and leave’
only, and it is expected that a more rigorous economic
comparison will become possible when volume yields at this
site can be more reliably estimated.
3. Results
1=t
(1)
where N0 and Nt are the population counts at the beginning and
end of the measurement interval, t, in years. Mean annualised
absolute height growth rate of seedlings (AGR) was calculated
as
AGR ¼
methods used in forestry rely on assumptions that are difficult
to justify in this study. These include:
H1 H0
t
(2)
where H0 and H1 are seedling heights at the beginning and end
of the measurement interval, t, in years (Hunt, 1978).
Control gaps were measured in May 2003. Stems of all
species that have commercial value as sawn wood and/or
veneer in the internal or export market were identified, counted,
and measured for height, diameter and crown illumination as
described above.
2.3. Economic considerations
The costs of gap planting were recorded by the forest
manager for all phases of the study: seedling production, gap
preparation and planting, and maintenance. These costs include
materials, labour, consumables, and depreciation of equipment.
We have chosen not to make direct economic comparison
between planting mahogany and ‘log and leave’ because most
3.1. Planted gaps
All of the planted gaps still contained at least two surviving
mahogany seedlings after 4.4 years, with a mean number of
seedlings per gap of 6.1 (S.E. = 2.8). Overall seedling survival
was 61.4%, equivalent to an annual mortality rate of 10.5%
year1.
Mahogany seedlings had attained a mean height of 4.6 m
(S.E. = 2.2) after 4.4 years. More than one in three seedlings
(36.3%) reached at least 5 m height, the tallest of which was
12.5 m. The majority of seedlings (74.2%) reached the
minimum measurement diameter (2 cm dbh). On a per-gap
basis, 8 of the 29 gaps (27.6%) had a mean seedling height in
excess of 5 m (Fig. 1). Twenty-one gaps (72.4%) had at least
one seedling 5 m in height, and 27 (93.1%) had one or more
seedlings 2 cm dbh.
A growth function for the mahogany seedlings was derived
by linear regression of seedling height at each measurement
(Fig. 2). The regression equation was
H m ¼ 0:990A þ 0:343
(3)
where Hm is the mean height and A is the age in years. The
regression was highly significant and explained most of the
variation in the data ( p < 0.001, R2 = 99.1%).
Table 1
Mean pH and concentration of exchangeable cations of soil from 29 planted gaps in a Brazilian rain forest (S.E. in parentheses)
Depth (cm)
pH
P (mg/dm3)
K (mg/dm3)
Na (mg/dm3)
Ca (mmol/dm3)
Mg (mmol/dm3)
Al (mmol/dm3)
0–20
20–40
3.9 (0.4)
4.1 (0.6)
2.3 (1.3)
1.5 (1.1)
55.8 (27.4)
50.8 (26.9)
26.1 (24.6)
21.8 (28.7)
6.9 (7.2)
6.4 (5.2)
5.2 (3.4)
5.1 (5.1)
23.5 (8.2)
22.4 (7.8)
J.C.A. Lopes et al. / Forest Ecology and Management 255 (2008) 300–307
303
Fig. 1. Mean height after 4.4 years (shaded, 95% confidence intervals) and height of tallest individual (unshaded) of mahogany planted in 29 canopy gaps.
The majority of individuals (73.2%) had a time-weighted
crown illumination index of 3, indicating overhead illumination
(Clark and Clark, 1992), with the rest scoring either 2.5 (12.8%:
no overhead illumination but significant lateral illumination) or
4 (14%: overhead plus lateral illumination). However, all but
5.6% of seedlings had crown illumination scores <3 at some
time, indicating that maintenance operations were not frequent
enough to maintain continuous overhead illumination (particularly between the 3rd and 5th year). This is supported by
analysis of height increment. Mean absolute height growth rate
remained between 0.9 and 1.3 m year1 over the first 2.5 years,
but then declined to 0.6 m year1 during the final measurement
interval (Fig. 3).
Both crown illumination and pH of soil 0–20 cm depth had
significant positive effects on mean seedling height (two-way
ANOVA, d.f. = 1, F = 12.89, p = 0.002 and d.f. = 1, F = 8.21,
p = 0.010, respectively), whilst the concentration of phosphorus
in soil 0–20 cm depth (d.f. = 1, F = 6.88, p = 0.016) had a
significant negative effect. Other soil nutrients at this depth (K,
Na, Ca, Mg and Al) had no significant effect on height, and no
soil variables from 20 to 40 cm depth had any significant effect
(Table 1).
The incidence of shoot borer attack was relatively low, with
54.7% of seedlings attacked at some stage over the study
period. However, the generally low incidence of shoot borer
attack masked considerable variation among gaps (Fig. 4). This
Fig. 2. Height growth of mahogany seedlings planted in canopy gaps. The bold
line is the linear regression of height against time, and the fine lines indicate the
95% confidence limits around the regression. Points a, b, and c indicate height
calculated from growth functions published by JICA (1982, from Fiji), Llera
and Melandez (1989, Mexico) and Neil (1986, Vanuatu), respectively.
variation could not be explained either by the original number
of seedlings planted (i.e., mahogany density: linear regression,
p = 0.061), nor canopy illumination ( p = 0.847). Of the trees
suffering shoot borer damage, 58% responded by producing a
single replacement leader, whilst the rest produced two or more
stems.
3.2. Control gaps
Seedlings and saplings of 19 commercial species were found
within the control gaps (Table 2), with a mean of 4.2
(S.E. = 2.9) species per gap. None of these gaps contained any
natural regeneration of mahogany (note that one naturally
regenerated mahogany seedling established in a planted gap).
Most commercial species in control gaps were fast-growing
pioneer (sensu Swaine and Whitmore, 1988) or light
demanding climax species.
A comparison of seedling performance in control and
planted gaps is given in Table 3. Unplanted gaps had a mean of
9.1 (S.E. = 6.9) commercial stems, which was not significantly
different from the number of mahogany stems in planted gaps
(Mann–Whitney U-test; n = 29, 20; W = 670; p = 0.066). One
gap had no stems of commercial species present.
The mean height of commercial stems was 3.0 m
(S.E. = 1.4), significantly shorter than mahogany stems (twotailed t-test, N = 29, 20; p = 0.002). A significantly smaller
percentage of naturally regenerated commercial stems had
reached 5 m height than mahogany stems (17.5% vs. 36.3%,
respectively; Chi-squared test, x2 = 21.65, d.f. = 1, p < 0.001).
Similarly, fewer naturally regenerated stems had reached 2 cm
Fig. 3. Mean absolute height growth rate (AGR) over 4.4 years of mahogany
seedlings planted in felling gaps. Bars indicate 95% confidence intervals.
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J.C.A. Lopes et al. / Forest Ecology and Management 255 (2008) 300–307
Table 3
Comparison between planted and control gaps
Mean occupancy (number of stems)
Gaps occupied (%)
Mean height (m)
Stems >5 m height (%)
Stems 2 cm dbh (%)
Planted
Control
6.14 (2.81)
100
4.55 (2.24)**
36.3***
74.2***
9.05 (6.87)
95
2.99 (1.39)
17.5
38.1
Numbers marked with ** ( p < 0.01) or *** ( p < 0.001) are significantly
higher for mahogany in planted gaps than for naturally regenerating commercial
species in controls (see text for details of statistical tests). The mean standard
error about the means is given in parentheses.
Fig. 4. Proportion of mahogany seedlings attacked by Hypsipyla in 29 gaps.
dbh compared to mahogany stems (38.1% vs. 74.2%,
respectively; Chi-squared-test, x2 = 44.8, d.f. = 1, p < 0.001).
expensive of the other commercial species, and the costs of gap
planting represent only a small fraction of this value differential
(8–30%). This suggests that there is considerable potential for
economic gain from planting mahogany in felling gaps.
3.3. Cost of gap planting and timber values
4. Discussion
The cost of producing mahogany seedlings, planting, and
maintenance operations was equivalent to US$ 94 per gap
(Table 4). This is equivalent to US$ 283–378 per ha (assuming
a normal selective felling rate for the Brazilian Amazon of three
to four trees per hectare), or US$ 9 per planted seedling and
US$ 16 per survivor.
Mahogany has a sawnwood price of US$ 700–1400 per m3
FOB (Association of Timber Exporters of Pará, personal
communication, 2006). By comparison, the commercial species
found in control gaps have much lower values than mahogany
(mean US$ 323 per m3, range US$ 225–390; Table 2).
Mahogany – even at the lowest price grade – is therefore at
least US$ 310 per m3 (79%) more valuable than the most
The method reported here was designed to provide a
compromise between tree growth, stem quality, impact on
forest structure, and financial investment rather than to produce
ideal growth conditions for mahogany. It was therefore
encouraging that mean height growth of gap-planted mahogany
(1.04 m year1) was broadly equivalent to that described from
other silvicultural systems. Confidence intervals calculated for
the growth function of gap-planted mahogany allow comparison of seedling height with that predicted after 4.4 years by
published growth functions for mahogany from different
silvicultural systems (Fig. 2). Two of these predicted heights
(from conventional monoculture, Neil, 1986; and shade trees in
Table 2
Abundance, frequency of occupation, and timber value of commercial species found in 20 control gaps
Name
Family
Ecological
groupa
Mean number of
individuals per gap
Gaps
occupied (%)
Value
(US$ per m3)b
Virola sp.
Jacaranda copaia (Aubl.) D. Don
Trattinnickia rhoifolia Willd.
Simarouba amara Aubl.
Apuleia molaris Spruce ex Benth.
Parkia pendula (Willd.) Benth. ex Walp.
Goupia glabra Aubl.
Cedrelinga catenaeformis (Ducke) Ducke
Schefflera morototoni (Aubl.) Maguire, Steyerm. & Frodin
Schizolobium amazonicum Huber ex Ducke
Parkia gigantocarpa Ducke
Symphonia globulifera L.f.
Astronium lecointei Ducke
Ceiba pentandra (L.) Gaertn.
Sterculia speciosa K.Schum.
Trattinnickia burseraefolia (Mart.) Willd.
Hymenaea sp.
Aspidosperma sp.
Parkia multijuga Benth.
Vatairea paraensis Ducke
Myristicaceae
Bignoniaceae
Burseraceae
Simaroubaceae
Caesalpinaceae
Mimosaceae
Celastraceae
Mimosaceae
Araliaceae
Caesalpinaceae
Mimosaceae
Clusiaceae
Anacardiaceae
Bombacaceae
Sterculiaceae
Burseraceae
Caesalpinaceae
Apocynaceae
Mimosaceae
Fabaceae
LDC
P
LDC
LDC
LDC
LDC
P
LDC
P
P
LDC
STC
LDC
LDC
LDC
LDC
LDC
LDC
LDC
LDC
2.05
1.45
0.95
0.85
0.65
0.45
0.40
0.30
0.30
0.30
0.25
0.25
0.20
0.20
0.15
0.15
0.15
0.05
0.05
0.05
70
40
45
30
20
15
20
20
30
10
20
25
10
15
15
10
10
5
5
5
150–330
350y
350y
275
275–360
350y
225
225
No data
350y
350y
No data
320
350y
350y
390
350y
No data
350y
350y
a
Ecological groups are based on the knowledge of local foresters: P, pioneer; LDC, light demanding climax; STC, shade tolerant climax.
Values are for sawn timber FOB except those marked y where prices are for plywood as no export market for sawnwood exists. Species for which no export market
exists are marked ‘no data’. Prices were kindly provided by the Association of Timber Exporters of Pará (AIMEX) and Nordisk Timber Ltda.
b
J.C.A. Lopes et al. / Forest Ecology and Management 255 (2008) 300–307
305
Table 4
Cost of producing mahogany seedlings, planting and maintenance over 4.4 years
Operation
Cost (US$ per gap)
Seedling production
Seed
Materials
Labour
0.49
1.54
0.80
Sub-total
2.83
Planting
Petrol (chainsaw)
Diesel (truck)
Equipment depreciation
Labour
Sub-total
Maintenance
Diesel (truck)
Equipment depreciation
Labour
Sub-total
Total
5.00
8.00
0.19
12.40
Notes
80% seed germination, 10% seedlings discarded
2 l plastic sacs, manure
Equipment: truck, chainsaw, manual digger, machetes
One driver, one chainsaw operator, four field assistants
25.59
8.00
0.12
5.07
13.19
65.97
Truck, chainsaw, manual digger, machetes
One driver, two labourers
Maintenance repeated five times
94.38
cocoa plantations, Llera and Melandez, 1989) were within the
95% confidence intervals of our growth function. The third
(conventional monoculture; JICA, 1982) was above the upper
confidence interval, but as this point has no associated error, it is
not clear whether this represents significantly greater growth.
Indeed, Mayhew and Newton (1998) consider height growth of
1 m year1 to be acceptable for mahogany in plantations. The
mean height growth reported here represents a significant
improvement over that reported from gap and skid-trail planted
mahogany where no maintenance was carried out (mean
height = 3.31 m after 5 years; Oliveira, 2000). Maintaining
rapid growth is critical, because once suppressed, mahogany
quickly loses the capacity to respond to subsequent increased
light levels with rapid growth (Grogan et al., 2005).
Increased height growth could almost certainly be achieved
by more frequent maintenance, as many stems were overtopped
and shaded by pioneer vegetation during the longer intervals
between maintenance. Although it would increase costs, a
twice-yearly maintenance regime for the first 3 years, followed
by annual cleaning as necessary, may well be warranted.
Additional improvements to the methodology could be gained
by reducing costs through direct seeding (Negreros-Castillo
and Hall, 1996), through improved nursery practices (Mexal
et al., 2002), or by using provenances more resistant to the shoot
borer (Newton et al., 1999).
It is worth noting here that preliminary analyses using gap
size as an explanatory variable for seedling responses showed
no significant results, despite the wide range of gap sizes. Plants
respond to a range of abiotic and biotic factors, rather than to
gap size per se, and gap size is a poor surrogate for these
variables (Brown, 1993; Brown and Jennings, 1998). Gap size
also fails to provide any measure of the microclimatic variation
within the gap (Raich, 1989). Therefore, measurements based
on the illumination conditions experienced by individual
seedlings growing within a gap, such as the crown illumination
index used here, are both more ecologically and analytically
meaningful than gap size. Nevertheless, the results presented
here do suggest a straightforward methodology for gap planting
that could readily be understood and implemented by forest
managers and workers, and does not involve any estimation of
gap size, namely: plant seedlings only in those parts of felling
gaps that have direct overhead illumination.
The incidence of shoot borer attack (54.7%) was lower than
that reported from most other silvicultural systems, where 60–
100% of trees between 3 and 5 years old are typically attacked
(Mayhew and Newton, 1998; Newton et al., 1999). In common
with many other reports of variable shoot borer attack, reasons
for the relatively low incidence of attack and variation in
incidence among gaps were not ascertainable from this study,
which focused on silvicultural results rather than biological
mechanisms. Shoot borer attack is determined by a number of
interdependent factors (Mayhew and Newton, 1998; Hauxwell
et al., 2001), but given the low density of mahogany within the
forest and growth of mahogany seedlings within a matrix of
natural gap regeneration, we hypothesise that it may have been
due to a combination of reduced apparency of mahogany stems
within dense gap regeneration, and perhaps a high incidence of
natural enemies of Hypsipyla.
Perhaps more important than the incidence of attack was the
high proportion of attacked stems (58%) that responded with a
single strong leader (‘host recovery’ in the terminology of
Mayhew and Newton, 1998). This response is likely to be the
result of the gap environment in which the seedlings grew,
which, compared to conventional plantations, provided less
total illumination, direct overhead illumination, and limited
(mostly indirect) lateral light.
306
J.C.A. Lopes et al. / Forest Ecology and Management 255 (2008) 300–307
Whilst we recognise that it may be imprudent to draw too
many conclusions on the basis of evidence gathered over a short
time period, we believe that early indications from this study
are encouraging. The method described above has the potential
to secure at least one mahogany stem for each tree harvested;
mahogany growth was equivalent to that found in other
silvicultural systems and superior to that of naturally
regenerating commercial species; and the costs of the
intervention are likely to be outweighed by the high value of
mahogany timber compared to other species in the forest. It
should also be borne in mind that many planted gaps will be
able to support more than one mahogany stem plus stems of
other commercial species because the vertical projection of a
felling gap is much larger than the crown diameter of logged
trees (falling trees typically take down numerous other and
usually smaller stems). This means that the comparisons made
here likely underestimate the benefits of planting and
maintaining mahogany.
Mahogany occurs in a wide range of population densities
and size structures in the Brazilian Amazon (Brown et al.,
2003). In forests such as the site used here, mahogany’s
population density is so low that there is little prospect that
management through natural regeneration will be commercially viable. This leaves forest managers with the options of
either managing the forest for other species present, which are
of lower value and yield lower economic returns, or investing
in conventional enrichment planting (such as line planting),
which is expensive, causes severe modification to forest
structure, and in which mahogany often suffers badly from
Hypsipyla.
The gap-planting technique described here provides a third
option. Planting mahogany in gaps created by logging would,
given typical logging rates in the region, result in three and four
planted gaps per hectare. If each gap yielded an average of one
marketable stem, this would result in a hugely valuable
resource to the forest owner. The indication from results
presented here are that it would also accelerate regeneration,
potentially resulting in trees reaching a larger size within a fixed
rotation period. The technique would also increase the
population density of mahogany: in the forest here, by at least
60 times. As mahogany begins to produce fruit at approximately 30 cm dbh (Gullison et al., 1996; Jennings and Baima,
2005), a size well below legal felling limits, this could provide a
significant (albeit temporary) increase in seed rain and
therefore regeneration. Increasing population density is
particularly important in the management of light demanding
climax species such as mahogany, as they are vulnerable to loss
of genetic diversity through harvesting (Jennings et al., 2001).
As long as locally produced seed, collected from a range of
trees, is used to produce seedlings, the proposed methodology
could also play a role in maintaining population-level genetic
diversity. Providing forest managers, including indigenous
communities, with workable options for managing mahogany
in situ is a potentially important step (Jennings et al., 2000;
Zimmerman et al., 2001) in reversing the depressing trends of
deforestation (INPE, 2005) and degradation (Asner et al., 2005)
in the Brazilian Amazon.
Acknowledgements
This is an output from a research project funded by the
United Kingdom Department for International Development
(DFID) Forestry Research Programme Project No. R6912. The
views expressed here are not necessarily those of DFID.
Fieldwork was supported by Nordisk Timber Ltda. The
assistance of the Oxford Forestry Institute, University of
Oxford, where S. Jennings was based at the time of the research,
is also greatly appreciated. The valuable suggestions made by
anonymous referees are gratefully acknowledged.
References
Asner, G.P., Knapp, D.E., Broadbent, E.N., Oliveira, P.J.C., Keller, M., Silva, J.N.,
2005. Selective logging in the Brazilian Amazon. Science 310, 480–482.
Barton, A.M., Fetcher, N., Redhead, S., 1989. The relationship between tree fall
gap size and light flux in a neotropical rain forest in Costa Rica. J. Trop.
Ecol. 5, 437–439.
Brown, N., 1993. The implications of climate and gap microclimate for seedling
growth conditions in a Bornean lowland rain forest. J. Trop. Ecol. 9, 239–
244.
Brown, N., Jennings, S., 1998. Gap-size niche differentiation by tropical
rainforest trees: a testable hypothesis or a broken-down bandwagon? In:
Newbery, D.M., Prins, H.H.T., Brown, N.D. (Eds.), Dynamics of Tropical
Communities. Blackwell Science Ltd., London, UK.
Brown, N., Jennings, S., Clements, T., 2003. The ecology, silviculture and
biogeography of mahogany (Swietenia macrophylla), a critical review of the
evidence. Per. Plant Ecol. Evol. Syst. 6, 37–49.
Clark, D.A., Clark, D.B., 1992. Life history diversity of canopy and emergent
trees in a neotropical rain forest. Ecol. Monogr. 62, 315–344.
Dickinson, M.B., Whigham, D.F., 1999. Regeneration of mahogany (Swietenia
macrophylla) in the Yucatan. Int. For. Rev. 1, 35–39.
Greenpeace, 2002. Partners in Mahogany Crime. Greenpeace International,
Amsterdam, The Netherlands.
Griffiths, M.W., 2001. The biology and ecology of Hypsipyla shoot borers. In:
Floyd, R.B., Hauxwell, C. (Eds.), Hypsipyla Shoot Borers in Meliaceae:
Proceedings of an International Workshop, Kandy, Sri Lanka, August 20–
23, 1996. Australian Centre for International Agricultural Research, Canberra, Australia, pp. 74–80.
Grogan, J., Galvão, J., Simões, L., Verı́ssimo, A., 2003. Regeneration of big-leaf
mahogany in closed and logged forests of southeastern Pará, Brazil. In:
Lugo, A., Figueroa Colón, J.C., Alayón, M. (Eds.), Big-Leaf Mahogany:
Genetics, Ecology, and Management. Springer-Verlag, New York, NY,
USA, pp. 193–208.
Grogan, J., Landis, R.M., Ashton, M.S., Galvão, J., 2005. Growth response by
big-leaf mahogany (Swietenia macrophylla) advance seedling regeneration
to overhead canopy release in southeast Pará, Brazil. For. Ecol. Manage.
204, 399–412.
Gullison, R.E., Panfil, S.N., Strouse, J.J., Hubbell, S.P., 1996. Ecology and
management of mahogany (Swietenia macrophylla King) in the Chimanes
forest, Beni, Bolivia. Bot. J. Linn. Soc. 122, 9–34.
Hauxwell, C., Mayhew, J., Newton, A.C., 2001. Silvicultural management of
Hypsipyla species. In: Floyd, R.B., Hauxwell, C. (Eds.), Hypsipyla Shoot
Borers in Meliaceae: Proceedings of an International Workshop, Kandy, Sri
Lanka, August 20–23, 1996. Australian Centre for International Agricultural Research, Canberra, Australia, pp. 151–163.
Hunt, R., 1978. Plant Growth Analysis. Studies in Biology, vol. 69. Arnold,
London, UK.
INPE, 2005. PRODES: Assessment of Deforestation in Brazilian Amazonia
(available at www.obt.inpe.br/prodes/index.html).
Jennings, S.B., Baima, A.M.V., 2005. The influence of population and forest
structure on fruit production in mahogany (Swietenia macrophylla King)
and their consequences for sustainable management. Int. For. Rev. 7, 363–
369.
J.C.A. Lopes et al. / Forest Ecology and Management 255 (2008) 300–307
Jennings, S.B., Brown, N.D., Sheil, D., 1999. Assessing forest canopies and
understorey illumination: canopy closure, canopy cover and other measures.
Forestry 72, 59–74.
Jennings, S.B., Brown, N.D., Whitmore, T.C., Silva, J.N.M., Lopes, J. do C.A.,
Baima, A.M.V., 2000. To conserve rainforest, we have to help local people
live sustainably. Nature 405, 507.
Jennings, S.B., Brown, N.D., Boshier, D.H., Whitmore, T.C., Lopes, J. do C.A.,
2001. Ecology provides a pragmatic solution to the maintenance of genetic
diversity in sustainably managed tropical forests. For. Ecol. Manage. 154,
1–10.
JICA, 1982. Report of site assessment on plantations of hard-wood in Viti Levu,
Fiji. Japan International Cooperation Agency report for the Department of
Forestry, Fiji.
Llera, Z.M., Melandez, N.F., 1989. Evaluacı́on de especies forestales tropicales
como alternative para la sustitucı́on del arbol de sombre mote (Erythrina
spp.) en el cultivo de cacao. In: Linares, N.L. (Ed.), Simposio Agroforestale
en Mexico, Tomo I. Faculdade de Ciencias Forestales, Universidad Autonoma de Nuevo León, Monterrey, Mexico.
Mayhew, J.E., Newton, A.C., 1998. The Silviculture of Mahogany. CABI
Publications, Wallingford, UK.
Mexal, J.G., Cuevas Rangel, R.A., Negreros-Castillo, P., Paraguirre Lezama, C.,
2002. Nursery production practises affect survival and growth of tropical
hardwoods in Quintana Roo, Mexico. For. Ecol. Manage. 168, 125–133.
Negreros-Castillo, P., Hall, R.B., 1996. First-year results of partial overstory
removal and direct seeding of mahogany (Swietenia macrophylla) in
Quintana Roo, Mexico. J. Sust. For. 3, 65–76.
Neil, P.E., 1986. Swietenia macrophylla (mahogany) in Vanuatu. Forest
Research Report No. 4/86. Vanuatu Forest Service, Port Villa, Vanuatu.
Newton, A.C., Baker, P., Ramnarine, S., Mesen, J.F., Leakey, R.R.B., 1993. The
mahogany shoot borer: prospects for control. For. Ecol. Manage. 57, 301–
328.
Newton, A.C., Cornelius, J.P., Baker, P., Gillies, A.C.M., Hernández, M.,
Ramnarine, S., Messen, J.F., Watt, A.D., 1996. Mahogany as a genetic
resource. Bot. J. Linn. Soc. 122, 61–73.
307
Newton, A.C., Watt, A.D., Lopez, F., Cornelius, J.P., Mesén, J.F., Corea, E.A.,
1999. Genetic variation in host susceptibility to attack by the mahogany
shoot borer: Hypsipyla grandella (Zeller). Agric. For. Entom. 1, 11–18.
d’Oliveira, M.V.N., 2000. Artificial regeneration in gaps and skidding trails
after mechanised forest exploitation in Acre, Brazil. For. Ecol. Manage. 127,
67–76.
Quevedo, L., 1986. Evaluacion del efecto de la tala selectiva sobre la renovacion
du um bosque humedo Subtropical en Santa Cruz, Bolivia. Msc Thesis,
Universidad de Costa Rica, CATIE, Turrialba, Costa Rica.
Raich, J.W., 1989. Seasonal and spatial variation in the light environment in a
tropical dipterocarp forest and gaps. Biotropica 21, 299–302.
Rodan, B.D., Newton, A.C., Verı́ssimo, A., 1992. Mahogany conservation:
status and policy initiatives. Environ. Conserv. 19, 331–338.
Sheil, D., Burslem, D.F.R.P., Alder, D., 1995. The interpretation and misinterpretation of mortality rate measures. J. Ecol. 83, 331–333.
Snook, L.K., 1993. Stand dynamics of mahogany (Swietenia macrophylla King)
and associated species after fire and hurricane in the tropical forests of the
Yucatan Peninsula, Mexico. PhD Thesis, Yale University, New Haven, CT,
USA.
Snook, L.K., 1996. Catastrophic disturbance, logging and the ecology of
mahogany (Swietenia macrophylla King): grounds for listing a major
tropical timber species in CITES. Bot. J. Linn. Soc. 122, 35–46.
Snook, L.K., Negreros-Castillo, P., 2004. Regenerating mahogany (Swietenia
macrophylla King) on clearings in Mexico’s Maya forest: the effects of
clearing method and cleaning on seedling survival and growth. For. Ecol.
Manage. 189, 143–160.
Swaine, M.D., Whitmore, T.C., 1988. On the definition of ecological species
groups in tropical rain forests. Vegetatio 75, 81–86.
Verı́ssimo, A., Barreto, P., Tarifa, R., Uhl, C., 1995. Extraction of a high-value
natural resource in Amazonia: the case of mahogany. For. Ecol. Manage. 72,
39–60.
Zimmerman, B., Peres, C.A., Malcolm, J.R., Turner, T., 2001. Conservation and
development alliances with the Kayapó of southeastern Amazonia, a
tropical forest indigenous people. Environ. Conserv. 28, 10–22.