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The impacts of large-scale, low-intensity fires on the forests of continental South-East Asia

Authors:
  • Department of National Park, Wildlife and Plant Conservation, Thailand

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South-east Asia's tropical forests harbour high levels of species richness and endemism. In continental South-east Asia strong rainfall seasonality driven by the Asian monsoon lead to ground-fires during the dry season in most years. How these fires influence the region's landscape mosaic of evergreen and deciduous forests and the biodiversity they support is poorly understood. In this paper we report on the impacts of the El Niño–Southern Oscillation-induced 1997–98 fires that burned across much of western Thailand. We compare fire effects in the three common regional forest types – seasonal evergreen (SEG); mixed deciduous (MDF); and deciduous dipterocarp – and use data from a 50-ha study plot to evaluate the impacts of fire on these forests. We found few differences among the forest types. The fires created more large gaps in MDF than the other forest types. The SEG experienced greater fire mortality in the smallest size classes, abundant resprouting, and showed some evidence of lagged mortality among larger trees. The resilience of the SEG to fire and lack of major differences in fire effects among the forest types suggest that infrequent landscape-scale fires may have little effect on biodiversity in the landscape mosaic of seasonal tropical forests of continental South-east Asia.
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International Journal ofWildland Fire 2008, 17, 782–792 www.publish.csiro.au/journals/ijwf
The impacts of large-scale, low-intensity fires on the forests
of continental South-east Asia
Patrick J. Baker
A,D
, Sarayudh Bunyavejchewin
B
and Andrew P. Robinson
C
A
Australian Centre for Biodiversity and School of Biological Sciences, Monash University,
VIC 3800, Australia.
B
Research Office, National Parks, Wildlife and Plant Conservation Department, Chatuchak,
Bangkok 10900, Thailand.
C
Department of Mathematics and Statistics, University of Melbourne, Parkville, VIC 3010, Australia.
D
Corresponding author. Email: patrick.baker@sci.monash.edu.au
Abstract. South-eastAsia’s tropical forests harbour high levelsofspecies richness and endemism. In continental South-
east Asia strong rainfall seasonality driven by the Asian monsoon lead to ground-fires during the dry season in most
years. How these fires influence the region’s landscape mosaic of evergreen and deciduous forests and the biodiversity
they support is poorly understood. In this paper we report on the impacts of the El Niño–Southern Oscillation-induced
1997–98 fires that burned across much of westernThailand. We compare fire effects in the three common regional forest
types – seasonal evergreen (SEG); mixed deciduous (MDF); and deciduous dipterocarp – and use data from a 50-ha study
plot to evaluate the impacts of fire on these forests. We found few differences among the forest types. The fires created
more large gaps in MDFthan the other foresttypes.The SEGexperienced greater fire mortality in thesmallestsize classes,
abundant resprouting, and showed some evidence of lagged mortality among larger trees. The resilience of the SEG to
fire and lack of major differences in fire effects among the forest types suggest that infrequent landscape-scale fires may
have little effect on biodiversity in the landscape mosaic of seasonal tropical forests of continental South-east Asia.
Introduction
In the 14th and 15th centuries, as Europeans were exploring the
far reaches of their known world, map-makers would mark the
end of ‘discovered’landswithspecific phrases to warn sailors of
the uncertainty and dangers that might lie beyond. On one early
representation of the known world, the Lenox Globe, a small
copper sphere made in 1503, the phrase Hic sunt dracones’–
Here be dragons is inscribed over the region that we now know
as South-east Asia. This phrase may have originated from the
legends of elemental dragons, common to many Asian cultures,
that had begun to trickle back toEurope on spice-laden caravans
and merchant ships. In today’s world, there are few places that
remain unexplored; however, ‘Here be dragons’is an apt phrase
to describe the current understanding of largefires in South-east
Asia, for this is in many ways unexplored territory. Much of our
currentunderstanding oftherole offiresin thetropicalforests of
South-east Asia is based on anecdote and conjecture. Few data
are available on the impacts of fire in general in these ecosys-
tems. Even less is known of large, landscape-scale fires in the
region.Indeed,fundamental questionsabout theimpacts offires,
large and small, on the structure, composition, and dynamics of
tropical forests in South-east Asia remain largely unanswered
and unexplored. The lack of empirical data on landscape-scale
fires severely restricts the development of consistent operational
guidelines and strategic policies for managing fire in the region.
The tropical forests of continental and insular South-east
Asia harbor some of the highest levels of species richness and
endemism in the world (Sodhi et al. 2004). Within the two
broadbiogeographicrealmsof theregionwestofWallace’s Line,
the Indo-Burmese and Sundaland regions, there are hundreds
of species of mammals, amphibians, and reptiles, more than a
thousand species of birds, tens of thousands of plant species
and untold numbers of insects. Species-level endemism varies
across the different biogeographic regions of South-east Asia,
but may exceed 50% across a range of phyla in some areas (e.g.
Sodhiet al.2004). Becauseof thisgreatbiologicalrichness,both
known andunknown, potential threatstotropical forests, suchas
unrestricted logging and hunting, fragmentation, andconversion
to agriculture, represent potential threats to thousands of plant
and animal species.
Forest fires are not typically considered a threat to tropical
forests. However, in recent decades a growing number of stud-
ies have documented the occurrence of fires in tropical forests
and their impacts on the resident flora and fauna (Sanford et al.
1985; Leighton andWirawan 1986; Kinnaird and O’Brien 1998;
Cochrane and Schulze 1999; Goldammer 1999; Peres 1999;
Barlow et al. 2003a, 2003b; Cochrane 2003; Haugaasen et al.
2003; Slik and Eichhorn 2003).Although fires have occurred in
continentaland insularSouth-eastAsiathroughout theHolocene
(Haberle et al. 2001; Penny 2001; Maxwell 2004; Hope et al.
2005), their geographical extent was not fully appreciated until
the massive Bornean fires of 1982–83 and 1997–98. In both
cases, an intense El Niño–Southern Oscillation (ENSO) event
generated extremedrought conditions overcontinental and insu-
lar South-east Asia that were accompanied by extensive fires
throughouttheregion.InKalimantanalone,thefiresarebelieved
to have burned at least 5 million hectares each time, although
estimates of the total area burned vary (Malingreau et al. 1985;
© IAWF 2008 10.1071/WF07147 1049-8001/08/060782
Impacts of large fires in continental South-eastAsia Int. J. Wildland Fire 783
Siegert et al. 2001). Such extensive fires, and the impacts they
had on both human populations and biodiversity within the
region, forced tropical forest scientists, policy makers, and the
general public to re-evaluate their understanding of the role of
fire in tropical forests and, in particular, the role of extreme
climatic conditions in generating landscape-scale wildfires that
could burn through even the wettest rainforests.
Although most of the attention during the 1997–98 fires was
on Malaysia and Indonesia, the ENSO-induced drought led to
extensive fires elsewhere in the region. Unlike the aseasonal
forestsofinsularSouth-eastAsia,theseasonaltropicalforestson
the continent experiencefire relatively frequently. Each year, the
Asian monsoon system generates a dry season of 2–6 months in
whichlittle to no rain falls across a regionstretching from south-
ern India to eastern Vietnam. The landscapes of this region are
dominated by a patchwork mosaic of three well-described forest
types seasonaldryevergreen,mixed deciduous, anddeciduous
dipterocarp – that differ markedly in stand structure and species
composition (Champion and Seth 1968).The seasonal evergreen
forestcontainsthemostspecies,hasacanopy>50mtall,andhas
a relatively small proportion of deciduous canopy trees, which
in most years allows the relative humidity in the understorey
to remain high even during the dry season. Mixed deciduous
forests have fewer species, a shorter main canopy (30–40 m tall)
and a majority of canopy trees that are deciduous during some
or all of the dry season. The predominance of deciduous trees
means that during this period considerable sunlight penetrates
through to the understorey and ground layer, lowering relative
humidity at ground level and increasing drying of fine fuels.
Bamboos are relatively common in the mixed deciduous forest
and occasional patches of grass are found throughout the forest.
Many of the bamboo species of continental South-east Asia are
monocarpicand flower gregariously.The synchronousmortality
over large areas provides a large, but infrequent, source of fuels
into the mixed deciduous forest systemsandmay influence local
and regional fire dynamics (Keeley and Bond 1999; Saha and
Howe 2001). The deciduous dipterocarp forest has the fewest
tree species, being dominated by one of 5–6 deciduous diptero-
carpspecies(e.g.Shoreasiamensis,Dipterocarpusobtusifolius),
the shortest main canopy (typically <25m tall), and is almost
completely deciduous for several months during the dry season.
Most importantly, however, the groundstorey of the deciduous
dipterocarp forest is dominated by grasses that dry during the
dry season when the canopy oftheforest isleafless (Troup 1921;
Williams et al. 2008).
Although fire is a relatively common feature of continental
South-east Asia, the nature of the fire regimes in the landscape
mosaic of forest types is poorly understood. Because of dif-
ferences in fuel composition and microclimatic conditions at
the forest floor, it is widely believed that deciduous diptero-
carp forests burn more frequently than mixed deciduous forests,
which in turn burn more frequently than seasonal evergreen
forests. Goldammer (1993) noted that deciduous dipterocarp
forests may burn annually, but that the frequent, low-intensity
ground-fire regime commonly associated with deciduous dipte-
rocarp forests was likely an anthropogenic artefact. Stott et al.
(1990) have suggested that the natural fire regime in these
landscapes has a ‘long-term cycle’ (i.e. infrequent fires). Such
assertions, however, may be misleading. First, there are no
empiricaldata onfire historiesfrom any forestswithin theregion
on which to base such assertions. Second, the limited anecdo-
tal data may not be representative of current or historical fire
regimes, particularly for the seasonal evergreen forests, which
are often more remote and less well known. Third, the complex
interdigitation of the forest types across these landscapes means
that the fire regimes are likely to be highly variable spatially and
temporally (as will be discussed in greater detail below).
The mosaic nature of these forested landscapes is of critical
importance to the conservation of biodiversity in continen-
tal South-east Asia. Among the terrestrial fauna of tropical
Asia, the larger species, especially the ungulates (e.g. elephant
(Elephasmaximus),gaur(Bosgaurus),banteng(Bosjavanicus))
and carnivores (e.g. tiger (Panthera tigris), leopard (Panthera
panthera)),areconcentratedintheselandscapemosaicsofdecid-
uous and evergreen forest. The grasses and bamboo thickets of
the deciduous forests supply the main grazing during the wet
season, whereas the understorey of the evergreen forest pro-
vides browse during the dry season. Importantly, the evergreen
forest provides cover throughout the year. As such, maintaining
an abundant andwidely distributed evergreen component within
the regional forest mosaic is seen as a key element of conserva-
tion plans for theterrestrial fauna of continental South-eastAsia
(Nakhasathien and Stewart-Cox 1990).
The occurrence of fires, therefore, raises grave concerns for
regional biodiversity. Of the three dominant forest types in the
region, the seasonal evergreen forest type is considered to be
the most sensitive to individual fires, with most tree species
believed to lack common adaptations to fire, such as thick bark
or the ability to resprout vigorously (Stott 1988; Rabinowitz
1990). Studies of fire effects in Borneo in the wake of the 1998
fires have shown that fire has dramatic impacts on the commu-
nity structure and composition of evergreen forests (Kinnaird
and O’Brien 1998; Slik and Eichhorn 2003). Because settle-
ment and development of formerly remote sites in continental
South-east Asia have increased substantially, the forest mosaic
hasbecome increasingly fragmentedinrecentdecades,exposing
more forests to more frequent ignition sources. Conservationists
are increasingly concerned that changes in fire regimes in these
landscapes will reduce the area of seasonal evergreen forest and
shift much of the landscape towards less evergreen forest and
more deciduous forest, resulting in a net loss of species diver-
sity as a consequence of ecosystem simplification (e.g. Ashton
1990; Rabinowitz 1990). However, this is largely unexplored
territory.
Because large fires are relatively uncommon, direct obser-
vations of their impacts on forest dynamics and local species
assemblages are rare, particularly for remote tropical forests.
Empirical data are sorely needed to underpintheongoing debate
about fire management in the seasonal tropical forests of con-
tinental South-east Asia. In the present paper, we report on the
impacts of a landscape-scale fire in deciduous and evergreen
foreststhatoccurredinwesternThailandattheHuaiKhaKhaeng
WildlifeSanctuary(HKK)duringthe1997–98ENSOevent.Our
study was an opportunistic one – such fires have only occurred
three times in the past 20 years at HKK – but took advantage of
a well-established research infrastructure within the sanctuary,
which included a long-term forest dynamics plot that had been
established 5 years before the fire. We focussed on two specific
784 Int. J. Wildland Fire P. J. Baker et al.
questions relevant to understanding the impacts of a large fire
on the forest mosaic at HKK. First, do fire effects differ among
the three major forest types found on the landscape? Second,
in the more diverse, and putatively more fire-sensitive, seasonal
evergreen forest, were certain species, functional groups, or size
classes more prone to fire-induced mortality?
Study area
The Huai Kha Khaeng Wildlife Sanctuary is one of Thailand’s
premierwildlife sanctuariesand isof great conservationvalue.It
is the second largest of 17 National Forests and Wildlife Sanctu-
ariesthattogetherconstituteThailand’sWesternForestComplex,
the largest area of contiguous protected forest in continental
South-eastAsia.The forests in theWestern Forest Complex sup-
port a widerangeof threatened andendangered plant andanimal
species including tigers, clouded leopards, elephants, banteng
and gaur (Nakhasathien and Stewart-Cox 1990). In recognition
of their importance for the conservation of the regionalflora and
fauna, HKK and the neighbouringThungYai-Naresuan Wildlife
Sanctuary were awarded UNESCO World Heritage Site status
in 1991.
Fires are a recurrent event at HKK. In the past two decades,
fires have been recorded somewhere within the sanctuary nearly
every year, although sanctuary-wide fires occur much less fre-
quently (1991, 1998, 2004). Increasing population densities and
agricultural activities adjacent to the buffer zone surrounding
HKK have led to a ready ignition source. Although extensive
landscape-scale fires are relatively rare, there is concern that
incursionsoffire intothe species-rich seasonalevergreenforests
are becoming more common and pose a serious threat to its
long-term presenceacrossthe landscape(Rabinowitz1990).The
1998 fires, whichburned through 1500km
2
of forest, were the
largest fires at HKK in at least the past 30 years.
Since 1991, forest scientists from the Royal Forest Depart-
ment ofThailand, the National Parks,Wildlifeand Plant Conser-
vation Department, and the Center for Tropical Forest Science
oftheSmithsonian Institutionhavebeen working together onthe
establishment and maintenance of a large-scale, permanent for-
estdynamicsstudyplot inseasonalevergreenforest atHKK.The
plot, whichcovers 50haandincludesevery tree >1cmdiameter
at breast height (DBH), includes 80000 trees from 291 species
and has been measured three times (in 1994, 1999, and 2004). In
February and March of 1998, the HKK fires burned through the
50-ha plot and adjacent areas of mixeddeciduous and deciduous
dipterocarp forest, providing a unique opportunity to describe
and compare the impacts ofa landscape-scale fire on each of the
major forest typesandtoexamine the potential role oflarge fires
in structuring and maintaining the landscape forest mosaic.
Methods
Fire intensity and fire-induced mortality among forest types
To determine if landscape-scale fires have different impacts on
the different forest types, we conducted an intensive survey of
tree mortality, as well as an extensive survey of fire-induced
gap formation in each of the three forest types. For our inten-
sive survey of fire effects in each forest type, we established two
20×125mtransects<1weekafter fire(March 1998)in areasof
seasonal evergreen, mixed deciduous and deciduousdipterocarp
forest that had been burnt by the fires. Each transect was divided
into 100 5×5m quadrats. To characterise the relative intensity
of the fire within each quadrat, we recorded whether fire had
occurred in each quadrat, the percentage of the quadrat area that
had beenburned, andtheaverage crownscorch height within the
quadrat based on loss or scorching of leaves. Within each tran-
sect, we also used a nested sampling design to characterise tree
abundance and mortality in different size classes. We identified
and measured all trees (>10cm DBH) within 10m of the tran-
sect, all poles (4.5–10 cm DBH) within 5 m of the transect, and
all saplings(1–4.5cm DBH) within1m of thetransect.The total
samplearea foreachtransectwas2500m
2
,1250 m
2
,and 250m
2
for trees, poles, and saplings, respectively. In addition, we tal-
lied, but did not identify, seedlings (<1cm DBH) in 1-m
2
plots
every 5m along the transect.The total sample area for seedlings
in each transect was 25 m
2
. For all trees, poles, and saplings,
the following information was recorded at the time the transect
was established: species, DBH, crown scorch, and whether the
individual was dead or alive. Crown scorch was scored from
1to5(1=80–100%, 2=60–80%, 3 =40–60%, 4=20–40%,
and 5 <20%crown scorch); deciduousspecieswerenoted.Each
transect was revisited at the end of the rainy season (November
1998, 8 months after fire) and the following information was
recorded for each individual: dead or alive, presence or absence
of sprouting, and the presence or absence of basal scarring.
To characterise the stand-scale impacts of the fires, we esti-
mated the number and size of canopy gaps that were created by
fire-killed trees in each forest type. For the seasonal evergreen
forest, a detailed assessment of damage was conducted in the
50-ha plot. Using the 20×20m grid system within the plot, 26
parallel 1000-m transects were established, beginning from the
northern edge of the plot. The size of each canopy gap created
by a fallen tree or group of trees was measured in two perpen-
dicular directions and calculated as the area of an ellipse. The
mode of death for each fallen tree was recorded as burnt-out
above or below 2m height on the stem, or as incidental mor-
tality (knocked over by a falling tree). Large permanent study
plots were not available for the mixed deciduous and decidu-
ous dipterocarp forests types. Instead, within each forest type,
we selected a large area of relatively homogeneous forest where
we established series of parallel transects 30 m apart and of
varying length.All fire-killed trees>10cm DBH that had fallen
within 15m of the transect were identified and measured. Total
areas sampled for the mixed deciduous and deciduous diptero-
carp forests were 12.5 and 12.1ha, respectively. All three forest
types were sampled 4–6 weeks after the fires had occurred. The
total area of canopy gaps created by the fires and the size distri-
bution of the canopy gaps were calculated for each forest type.
We compared gap size distributions among forest types using
non-parametric Kruskal–Wallis ANOVA.
Fire-induced mortality in the seasonal evergreen forest
To assess whether specific elements of the seasonal evergreen
forestcommunityare particularlysusceptibleto fire,weused the
50-ha plot database to compare species-specific mortality and
abundance patterns for seasonal evergreen forest tree species
during 1994–99, the period in which the 1998 fires occurred,
and 1999–2004, when no fires entered the plot.The 1999census
Impacts of large fires in continental South-eastAsia Int. J. Wildland Fire 785
was initiated in May 1998, 2 months after the fires occurred,
and completed 10 months later. We fitted locally weighted
smoothing (Loess) splines and estimated confidence intervals
for mortality as a function of tree size (DBH) for each species
separately and for all species pooled for the fire interval and
the non-fire interval. The Loess smoothing splines are fitted to
a variable probability sample of size 4000 from the measured
trees of each species, selected with probability proportional to
tree size. If there were fewer than 4000 representatives from the
species, then all trees were used. We used a sample size of 4000
to work around memory limits of the available algorithms. The
Loess fitting algorithm used the sampling weights, if sampling
was done. We also examined whether tree species from differ-
ent functional groups (evergreen v. deciduous) or possessing
certain life-history traits (large size: 90th percentile DBH; fast
growth: 90th percentile growth rate) were more or less prone to
fire-induced mortality. To determine whether tree species in the
seasonal evergreen forest were capableof sprouting, we checked
the 50-ha plot database for records of basal sprouts from trees
in the post-fire census period.
Results
Comparison of fire effects across the three forest types revealed
few differences. Nearly every study quadrat in each forest type
was burned. The proportion of each quadrat burned ranged
from 20 to 100%, but did not differ significantly among for-
est types. Mortality patterns were heterogeneous among size
classes and forest types. The greatest difference was between
sapling mortality in seasonal evergreen forest (24%) and mixed
deciduous forest (63%); however, most of the mixed deciduous
forestspeciesresproutedseveralmonthsafterthefire.Basalscar-
ring was greater in the seasonal evergreen forest (55%) than in
the mixed deciduous (32%) and deciduous dipterocarp forests
(30%). Scorch heights ranged from 0m in unburned quadrats
to 4m in a single quadrat in the seasonal dry evergreen forest.
The distribution of scorch heights did not differ significantly
among forest types, although the mixed deciduous forest had
a slightly lower mean scorch height (1.12 ±0.53m) than the
seasonal evergreen (1.46±0.67m) and deciduous dipterocarp
(1.48±0.48m) forests (Fig. 1).
In contrast, the stand-scale assessment of fire impacts on
canopy gap formation revealed substantial differences among
forest types. In the deciduous dipterocarp and seasonal dry ever-
green forest types,there was relatively little canopy disturbance.
In contrast, the mixed deciduous forest suffered substantial
canopy disturbance from the fire. Canopy gaps ranging from 25
to 1000 m
2
were created in the three forest types during the fires
and for 2 months afterward. In the 50-ha plot, the 1998 forest
fires created 85 new gaps, or 1.7 gaps ha
1
and mean gap size
was 95m
2
(Fig. 2). The total area of fire-created gaps in the
seasonal evergreen forest was 1.61% of the total area surveyed.
In the 12.5ha of deciduous dipterocarp forest, only three small
(mean gap size =35m
2
) gaps occurred as a result of the fires.
The few fire-induced canopy gaps andtheirsmall size accounted
for only 0.09% of the deciduous dipterocarpforestcanopy being
disturbed by the 1998 fires at HKK. In the 12.1-ha study area
of mixed deciduous forest 5km to the east of the 50-ha plot, the
fires created 52 gaps (4.3ha
1
) with a mean gap size of 105m
2
.
50
40
30
20
10
0
01234
Percentage of total quadrats sampled
Scorch height (m)
Deciduous dipterocarp forest
Mixed deciduous forest
Seasonal evergreen forest
Fig. 1. Distribution of scorch heights among the three forest types: sea-
sonalevergreenforest (SEG),mixeddeciduousforest(MDF), and deciduous
dipterocarp forest (DDF). In each forest type, scorch height was measured
in 100 contiguous quadrats within each of two transects. Scorch height was
determined based onthe averageheight of leafand crownscorch withineach
quadrat.
Although the mixed deciduous forest gaps were slightly larger
than those in the seasonal dry evergreen forest, the greater fre-
quencyof gapsinthe mixeddeciduous forestmeantthat thetotal
area of fire-created gaps (4.5%) was substantially greater than
in the other two forest types.
Within the species-rich seasonal evergreen forest, detailed
analysis of demographic data from the 50-ha plot revealed sev-
eral striking patterns. First, there were significant differences
in mortality patterns between the first (fire) and second (fire-
free) census intervals (Fig. 3). Overall mortality was higher in
the first interval (6.7%) than the second interval (4.2%). There
were also distinct patterns in size-dependent mortality. Mortal-
ity rates among small trees (<2 cm DBH) were nearly twice
as great in the first census (Fig. 3) owing to their shorter stature
(andconsequentlygreatercrown scorch)andthinnerbark (Baker
and Bunyavejchewin2006).Mortality rates during the fire inter-
val (i.e. intercensus period 1994–99 during which the 1998 fire
occurred) were also higher for trees 20–40-cm DBH, but were
not substantially different for trees >40 cm DBH. Examination
of mortality profiles for several abundant species demonstrated
that the plot-wide patterns masked considerable interspecific
heterogeneity in fire-induced mortality (Fig. 4). In most cases,
the smallest trees experienced higher mortality rates during
the fire interval than the non-fire interval the two dominant
dipterocarps of the forest canopy, Hopea odorata and Dipte-
rocarpus alatus, being the exceptions. An interesting feature of
the species-specificcomparisonsof mortalityrates is that during
the fire-free interval, several species had higher mortality rates
in the largest size classes. Species exhibiting this pattern were
all large canopy species and included Hopea odorata, Diptero-
carpus alatus, Neolitsea obtusifolia, Tetrameles nudiflora, and
Saccopetalum lineatum. Observations in the years following the
fires suggest that among large trees, fire-induced mortality may
be subject to temporallagsasthe fire-scarred bases or weakened
786 Int. J. Wildland Fire P. J. Baker et al.
0 100 200 300 400 500 600 700 800 900 1000
Northing
0
100
200
300
400
500
Westing
Fig. 2. Location of all 85 gap-creating treefalls created by the 1998 El Niño–Southern Oscillation (ENSO)-associated
fires as they burned through the Huai Kha Khaeng 50-ha plot.
0 20 40 60 80 100
0.0
0.2
0.4
0.6
0.8
1.0
Diameter (DBH)
P(Dead)
94–99
99–04
Fig. 3. Loess-smoothed estimates of the probability (P) of mortality rates
for the two intercensus intervals (1994–99 and 1999–2004) as a function of
diameter at breast height (DBH, cm) for all trees on the Huai Kha Khaeng
50-ha plot. The grey lines around each smoothing represent one standard
error in each direction.
buttress roots increase a tree’s susceptibility to being toppled by
wind storms associated with the onset of the annual summer
monsoon. Haugaasen et al. (2003) have reported similar lagged
mortality among largetreessubjectto low-intensitygroundfires
in theAmazon.The only other large canopy tree,Vatica odorata,
showed no difference in large tree mortality during the fire-
and fire-free intervals. In contrast, the mid-storey trees Baccau-
rea ramiflora, Croton roxburghii, and Polyalthia viridis all had
greater mortality in the largesizeclassesduringthe fire interval.
Multiplecensusesforsuchalargenumberoftreesandspecies
at the HKK 50-ha plot also allowed us to determine the effects
of the fire on species loss and species immigration. Our data
show that neither species richness nor abundance was substan-
tially affected by the fire. Most species changed relatively little
in abundance (Fig. 5). Nine species were lost and four species
gained between the 1994 and 2004 censuses. All of the species
that were lost between 1994 and 2004 were rare none had >40
individualsin 1994. However, among individual species, the fire
produced some clear winners and losers. Croton roxburghii, the
most abundant species on the plot, increased in abundance by
250% (11411 stems to 28778 stems). In contrast, Solanum eri-
anthum, an understorey treelet, lost most of its population (1504
stems to 14 stems). The 50-ha plot data also demonstrate that
many of the species in the seasonal evergreen forest do resprout
after fires. During the 1999 recensus, which was conducted in
the months that followed the 1998 fire, we recorded for every
stem whether basal sprouts were present.We recorded sprouting
in 163 species from the50-ha plot.Although sproutingoccurred
intreesranging from 1to 50cmDBH, sprouting was much more
common and prolific in the smallest stems. In some instances,
as manyas 25 sprouts were recorded on a single tree; the median
number of sprouts per tree was two (Fig. 6).
Comparison of functional groups and life-history traits
revealedlittleevidenceofdifferentialmortalityasaconsequence
of the fire. Pre- and post-fire abundances were similar for decid-
uous and evergreen species (Fig. 5). Fire-associated mortality
was correlated with tree stature, measured as the 90th percentile
DBH of each tree species, but not with growth rate, measured
as the 90th percentile DBH growth rate of the species (Fig. 7).
The relationship between mortality and tree stature was strongly
negativebetween1and15cm,afterwhichtherewaslittlechange
in the probability of mortality with increasing stature.
Discussion
Landscape-scale fires in continental and insular South-eastAsia
are widely believed to be detrimental to biodiversity within the
region (e.g. Rabinowitz 1990; Taylor et al. 1999; Sodhi et al.
2004). Short-term studies and anecdotal observations suggest
that wildlife is impacted directly through fire-induced mortality
(e.g. Stott 1986; Kinnaird and O’Brien 1998) or indirectly as
forest trees, which provide habitat and serve as food sources, are
Impacts of large fires in continental South-eastAsia Int. J. Wildland Fire 787
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0.8
1.0
CROTRO diameter (DBH)
P(Dead)
94–99
99–04
0 20406080100
0.0
0.2
0.4
0.6
0.8
1.0
VATIOD diameter (DBH)
P(Dead)
94–99
99–04
0 20406080100
0.0
0.2
0.4
0.6
0.8
1.0
POLYVI diameter (DBH)
P(Dead)
94–99
99–04
0 20406080100
0.0
0.2
0.4
0.6
0.8
1.0
HOPEOD diameter (DBH)
P(Dead)
94–99
99–04
0 20406080100
0.0
0.2
0.4
0.6
0.8
1.0
DIPTAL diameter (DBH)
P(Dead)
94–99
99–04
0 20406080100
0.0
0.2
0.4
0.6
0.8
1.0
NEOLOB diameter (DBH)
P(Dead)
94–99
99–04
0 20406080100
0.0
0.2
0.4
0.6
0.8
1.0
TETRNU diameter (DBH)
P(Dead)
94–99
99–04
0 20406080100
0.0
0.2
0.4
0.6
0.8
1.0
GARCSP diameter (DBH)
P(Dead)
94–99
99–04
0 20406080100
0.0
0.2
0.4
0.6
0.8
1.0
SACCLI diameter (DBH)
P(Dead)
94–99
99–04
0 20406080100
0.0
0.2
0.4
0.6
0.8
1.0
BACCRA diameter (DBH)
P(Dead)
94–99
99–04
Fig.4. Loess-smoothedestimates of the probability (P)ofmortality rates asafunctionof diameter at breast height (DBH,cm)for10
common species on the Huai Kha Khaeng 50-ha plot. Species abbreviations are Baccaurea ramiflora (BACCRA), Croton roxburghii
(CROTRO), Dipterocarpus alatus (DIPTAL), Garcinia speciosa (GARCSP), Hopea odorata (HOPEOD), Neolitsea obtusifolia
(NEOLOB), Polyalthia viridis (POLYVI), Saccopetalum lineatum (SACCLI),Tetrameles nudiflora (TETRNU), and Vatica odorata
(VATIOD). The grey lines around each smoothing represent one standard error in each direction.
788 Int. J. Wildland Fire P. J. Baker et al.
Species presence by sph 1994
Species presence by sph 2004
HYPTST
MELIAZ
MELILU
MURRPA
SOLAER
CASEGE
COLOJA
DALBAS
GLYCPE
MALLBA
MANGCA
POLYSU
CROTRO
0 0.1 1 10 100
0
0.1
1
10
100
Fig. 5. Comparisons of species-specific abundances between the first census interval, during which the 1998 fires
occurred, and the second census interval, which was fire-free. Values are in stems per hectare (sph). Evergreen species
are denoted with an empty circle and deciduous species with a cross. For some species, mostly those of low abundance,
the phenology is not known; these species are represented by a full grey circle. A line depicting a 1: 1 relationship is
drawn as a guide. Species that did not change in abundance between census intervals are located on the line. Species
that increased in abundance are above the line; species that decreased in abundance are below the line. Species that
were lost from the plot after the fire are on y =0; species that appeared in the plot following the fire are on x =0. The
species identified in the graph are those with the greatest difference in population density between intercensus intervals.
Species abbreviations are Caseariagrewiifolia (CASEGE),Croton roxburghii (CROTRO),Colona javanica(COLOJA),
Dalbergia assamica (DALBAS), Glycosmis pentaphylla (GLYCPE), Hyptianthera stricta (HYPTST), Mallotus barba-
tus (MALLBA), Mangifera caloneura (MANGCA), Melia azederach (MELIAZ), Melicope lunaankenda (MELILU),
Murraya paniculata (MURRPA), Polyalthia suberosa (POLYSU), Solanum erianthum (SOLAER).
killed by the fires (e.g. Rabinowitz 1990; Kinnaird and O’Brien
1998). However, empirical evidence of catastrophic impacts by
fire in South-east Asian forests and their associated flora and
fauna is limited. This may be because there are few studies
that have documented the long-term impacts of fire on these
forestsor,alternatively,the fireshaveless impactthanpreviously
believed.
The HKK Wildlife Sanctuary is one of the few sites in
continental South-east Asia where research on the impacts of
landscape-scale fires have been conducted in an area within
which the forests are very well studied. The ENSO of 1997–98
generated extremely dry conditions atHKK that allowed several
small fires on the periphery of the sanctuary in January 1998
to become a much larger landscape-scale fire front that over the
next 3 months burned hundreds of square kilometres of forest.
The status of HKK in Thailand as a national conservation icon
meant that the 1998 fires were heavily covered in the national
media on several occasions appearing on the front page of
every national newspaper simultaneously. Inevitably, the media
reported the fires as ecological catastrophes (e.g. ‘When Nature
Goes on a Fiery Rampage’, Bangkok Post, 18 February 1998).
Our study of fire impacts across the landscape mosaic of for-
est types at HKK suggested that the impacts of these fires on
the abundance and composition of tree species were relatively
limited, even in the putatively fire-sensitive seasonal evergreen
forest. We had anticipated that the substantial differences in for-
eststructureandcomposition amongthe three majorforest types
at HKK would lead to large differences in the amount of damage
Impacts of large fires in continental South-eastAsia Int. J. Wildland Fire 789
0 1020304050
DBH (cm)
5
0
10
15
20
25
No. of stump sprouts
Fig. 6. Relationship between number of basal sprouts on a tree stem and the diameter at breast height (DBH) of the tree. Owing
to the large number of tree stems with sprouts (n=8504) in the 50-ha plot database, individual points have been jittered by 20%
and overlain on a bivariate density plot to illustrate the relative abundance of number of stems as a function of DBH.
0 1020304050
0.0
0.2
0.4
0.6
0.8
1.0
90th percentile of diameter growth (cm per decade)
Mortality rate
0 50 100
150
0.0
0.2
0.4
0.6
0.8
1.0
90th percentile of diameter (cm)
Mortality rate
Fig. 7. Probability of mortality as a function of two life history traits: tree stature (left panel) and tree growth rate (right panel). Each point represents
one species and is based on the 90th percentile diameter at breast height (DBH) (left panel) or 90th percentile DBH growth rate (right panel) calculated
from the 50-ha plot data. A Loess smoothing spline indicates the locally weighted mean values as a function of either tree stature or tree growth rate.
that they incurred in the fires. Instead, we found that among
the forest types, there were relatively few differences in fire
extent,relative fire intensity (estimated from scorch height), and
mortality patterns across a range of size classes.
Despite the wide areal extent of the fires and the extreme
climatic conditions, the fires were predominantly low-intensity
surface fires with flame lengths ranging from 5 to 50 cm. The
fires never entered the canopy in any of the forest types and, in
790 Int. J. Wildland Fire P. J. Baker et al.
general, appeared to affect only trees <2m tall. Other studies
have shown that fires in tropical forests are often low-intensity
surface fires and that the initial impact of the fire is to kill the
aboveground portions of the smallest trees (e.g. Cochrane and
Schulze 1999; Peres 1999). One reason that fire impacts may
vary little among forest types is that fire intensity is consis-
tently low in each forest type. Despite differences in fine fuel
composition on the forest floor, scorch heights were not differ-
ent among the forest types. This is most likely a consequence
of the interaction between flame length and the speed of the
fire front (Agee 1993). In the deciduous dipterocarp forest, the
groundstoreyvegetationisdominatedbygrassesandherbaceous
vegetation. Flame lengths in these areas can be relatively high
(50–150cm),buttheopenunderstoreyallowsthefireto progress
quickly through the stand. In contrast, the seasonal evergreen
forest understorey is dominated by tree seedlings and leaf litter.
Flame lengths are shorter (5–30 cm), but the fire moves much
more slowly through the forest.
Within the seasonal evergreen forest, the 1998 fire led to
widespread aboveground mortality, despite the fire intensity
being relatively low. Low-intensity surface fires are typical in
tropical forests, particularly those in less seasonal environments
or in relatively moist edaphic conditions (e.g. Cochrane and
Schulze 1999; Peres 1999). Although the impacts of these fires
on wildlife may be limited, as many can move out of the way
of the slowly advancing fireline, the fires may influence com-
munity composition. Kinnaird and O’Brien (1998) noted that
species richness and abundance of the bird community in the
wake of the 1998 fires in evergreen forests in Sumatra did not
change. However, they found that the mortality of canopy trees
led to a decrease in frugivores and an increase in insectivores,
such as woodpeckers, which feed on wood-boring beetles that
attack injured or recently killed trees. What the long-term con-
sequences of the 1998 fireswill be on bird communities or other
species assemblages at HKK is unknown. Long-term studies
that document changes in community composition of the flora
and fauna in the wake of landscape-scale fires are sorely needed
across the region.
We found that in the immediate aftermath of the 1998 fire,
most mortality was in the smallest size classes (<5cm DBH).
Not surprisingly, the stature of a species as measured by its 90th
percentile DBH wasstrongly correlatedwithits susceptibility to
fire-induced mortality. This suggests that those small-statured
tree species that lack adaptations to fire, such as resprouting or
a persistent soil seedbank, will be most sensitive to changes
in population size induced by large fires. In contrast, small-
statured species that are well adapted to fire, such as Polyalthia
suberosa, which has particularly thick, corky bark, may benefit
from the fires (Fig. 5). Manystudiesinboth temperate and tropi-
calregionshavedemonstratedthatfire-inducedmortalityisoften
size-dependent for trees because larger trees have thicker bark
and are better able to protect the vascular cambium from catas-
trophic heating (e.g. Gill andAshton 1968; Hengst and Dawson
1994; Pinard and Huffman1997).Slik and Eichhorn (2003) also
found similar patterns of size-dependent mortality among ever-
green rainforest trees in East Kalimantan following the 1998
fires. Mortality was not restricted to the smallest trees, however.
We found evidence of a distinct delay in fire-induced mortal-
ity among large trees of several abundant canopy tree species.
Haugaasen et al. (2003) found a similar pattern of delayed mor-
tality in large trees after low-intensity surface fires in tropical
forest in the Central Amazon.
The size-dependent patterns of aboveground mortality and
dieback are counterbalanced by size-dependent patterns of
resprouting. Smaller trees were more susceptible to fire-induced
mortality, butwerealsomorelikely toresprout, oftenvigorously,
within months of the fire. For the seasonal evergreen forest,
which has long been considered the most sensitive of the main
forest types to fire, the outcome of these opposing dynamics
is a forest little changed by the 1998 ENSO fires. We found
little impact of the fires on community composition and pop-
ulation size structures within the seasonal evergreen forest. A
recent study has shown that there is no relationship between
bark thickness, a common surrogate for heat resistance (and
therefore fire tolerance), and various measures of population
size structures for 10 of the dominant tree species on the 50-ha
plot (Baker and Bunyavejchewin 2006).Our results are in direct
contrast to those from the aseasonal forests of South-east Asia
that experienced significant changes in structure and composi-
tion after the 1998 fires (e.g. Slik and Eichhorn 2003; Cleary
et al. 2006). Although the lack of long-term studies of forest
compositionchangefollowinglarge,landscape-scale fires limits
our ability to generalise our results, which derive from a single
extreme fire event from a single landscape within continental
South-east Asia, they do suggest that the ability to withstand
individual fire events may be a fundamental character that dis-
tinguishes the lowland evergreen dipterocarp forests of seasonal
South-eastAsian environments, located primarily in continental
sites, from their aseasonal analogues across the region (Baker
and Bunyavejchewin, in press).
In continental South-east Asia, there is concern that an
increase in fire frequency would allow the less diverse decid-
uous dipterocarp or mixed deciduous forest types to invade and
gradually replace the more species-rich seasonal evergreen for-
est(Stott 1988;Rabinowitz1990).Previousstudies atHKK have
shown that seedlings of common tree species from the seasonal
evergreen and mixed deciduous forests grow equally well when
planted in gaps in either forest type (Baker 1997). In a follow-
up survey 10 years after the seedlings were planted, we found
that the only species to survive in the fire-prone mixed decidu-
ous forest was Hopea odorata, the dominant canopytree species
in the seasonal evergreen forest, despite having been exposed
to three fires in a decade. More extensive studies of how tree
species from each of the forest types regenerate and how fires
impactthisregeneration areneeded before itispossibletoassess
potential shifts in the relative abundance of the evergreen and
deciduous forest types.
An overarching theme of the present review has been the
lack of data on the impacts of large-scale fires on biodiversity
in South-east Asia. Detailed data on tree species mortality and
abundance from the HKK 50-ha plot and surrounding stands
of mixed deciduous and deciduous dipterocarp forests in the
wake of the 1998 ENSO-associated fires provide much needed
empirical data on the impacts of landscape-scale fires in the
seasonal forests of mainland South-east Asia. Although the
results suggest that landscape-scale fires in the forest mosaic of
continental South-east Asia may not be particularly disastrous
for tree species, there remain many unanswered questions. For
Impacts of large fires in continental South-eastAsia Int. J. Wildland Fire 791
example, can the effects of a single, landscape-scale fire burn-
ing at low intensity have long-term consequences for variability
in demography? Can variability in demography, combined with
widespread heterogeneity in local fire intensity and canopy gap
formation, provide a mechanism for the tree species and forest
types to coexist in mosaic fashion across the landscape? Despite
our concerns for the remarkable diversity associated with the
tropical forests of South-eastAsia, we will not make progress in
understanding how landscape-scale fires influence the structure
and composition of the forest and the distribution and abun-
dance of its inhabitants across a range of spatial and temporal
scales without substantial increases in fire ecology research in
South-east Asia. Hic sunt dracones.
Acknowledgements
We would liketo thank the National ResearchCouncil ofThailand, the Royal
Forest Department and the staff ofthe Huai Kha KhaengWildlife Sanctuary
for enabling us to conduct this research at HKK.We would alsolike to thank
the National ScienceFoundation for support through grant DEB-0075334 to
PeterAshton and Stuart Davies, the USDA Forest Service through a grant to
Chad Oliver, and SigmaXi for a Grant-in-Aid-of-Resaerch to P.J. Baker.We
would also like to thank Dick Williams, Ross Bradstock, and an anonymous
reviewer for insightful comments on the manuscript. This is publication 182
of the Australian Centre for Biodiversity.
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... In seasonal dry tropical forests in Southeast Asia, fire disturbance is a key element in maintaining forest structure and species diversity because it not only leads to death of trees but also provides opportunities for new recruits to establish (Baker & Bunyavejchewin, 2017). Fire events in tropical dry forests are usually low-intensity surface fires with short flame lengths and often occur during the dry season (Stott, 1988;Baker, Bunyavejchewin & Robinson, 2008;Bunyavejchewin, Baker & Davies, 2011). Surface fires usually cause high tree mortality rates for small-sized trees (Slik & Eichhorn, 2003;Baker, Bunyavejchewin & Robinson, 2008), open up space for recolonization, and boost seed germination of some tree species (Fenner, 2000;Knox & Clarke, 2006;Otterstrom, Schwartz & Velázquez-Rocha, 2006). ...
... Fire events in tropical dry forests are usually low-intensity surface fires with short flame lengths and often occur during the dry season (Stott, 1988;Baker, Bunyavejchewin & Robinson, 2008;Bunyavejchewin, Baker & Davies, 2011). Surface fires usually cause high tree mortality rates for small-sized trees (Slik & Eichhorn, 2003;Baker, Bunyavejchewin & Robinson, 2008), open up space for recolonization, and boost seed germination of some tree species (Fenner, 2000;Knox & Clarke, 2006;Otterstrom, Schwartz & Velázquez-Rocha, 2006). In addition, loss of aboveground vegetation due to fire reduces potential neighborhood competition for surviving individuals. ...
... Because of the non-random mortality, temporal turnover in functional composition should be non-random (Swenson, Anglada-Cordero & Barone, 2011;Prado-Junior et al., 2016). When larger trees have higher chance to survive after fire disturbances than smaller trees (Slik & Eichhorn, 2003;Baker, Bunyavejchewin & Robinson, 2008), we would expect the post-fire functional composition should be more similar to the pre-fire composition in large trees than in small trees. Even though there are studies that focused on the effect of fire disturbance on species turnover according to tree size variability in tropical forests (Slik & Eichhorn, 2003;Baker, Bunyavejchewin & Robinson, 2008), there is no study that investigates how functional turnover varies with size classes in relation to fire disturbances. ...
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Background Disturbances are crucial in determining forest biodiversity, dynamics, and ecosystem functions. Surface fire is a significant disturbance in tropical forests, but research on the effect of surface fire on structuring species and functional composition in a community through time remains scarce. Using a 20-year dataset of tree demography in a seasonal evergreen tropical forest in Thailand, we specifically addressed two essential questions: (1) What is the pattern of temporal turnover in species and functional composition in a community with frequent fire disturbance? (2) How did the temporal turnover vary with tree size? Methods We analyzed species compositional and functional temporal turnovers in four different tree size classes among five tree censuses. We quantified species turnover by calculating Bray-Curtis dissimilarity, and investigated its underlying mechanisms by comparing pairwise dissimilarity of functional traits with simulations from null models. If fire disturbances contribute more to a stochastic process, the functional composition would display a random pattern. However, if they contribute more towards a deterministic process, the functional composition should reveal a non-random pattern. Results Over 20 years (1994–2014), we observed changes in species composition, whereas functional composition remained relatively stable. The temporal turnover patterns of species and functional compositions varied with tree sizes. In particular, temporal functional turnover shifted very little for large trees, suggesting that changes in species composition of larger trees are contributed by species with similar functional traits through time. The temporal functional composition turnovers of smaller trees (DBH ≤ 5 cm) were mostly at random. We detected a higher functional turnover than expected by null models in some quadrats throughout the 50-ha study plot, and their observed turnover varied with diameter classes. Conclusions Species compositional changes were caused by changes in the abundance of species with similar functional traits through time. Temporal functional turnover in small trees was random in most quadrats, suggesting that the recruits came from the equal proportions of surviving trees and new individuals of fast-growing species, which increased rapidly after fires. On the other hand, functional composition in big trees was more likely determined by surviving trees which maintained higher functional similarities than small trees through time. Fire disturbance is important for ecosystem functions, as changing forest fire frequency may alter forest turnover, particularly in functional composition in the new recruits of this forest.
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... Dry season conditions provide the fuels necessary to carry low-intensity surface fires. In deciduous forests, these fires can spread throughout the landscape, primarily killing understorey vegetation, but occasionally wounding or killing large trees [16,19]. ...
... Because fire-induced mortality is typically size-dependent, low-intensity surface fires typically kill seedlings, saplings, and small trees and have little impact on medium-and large-sized trees. This fire-induced mortality across species varies among sizes of trees [16] and fire intensity [21]. As a consequence, fire may drive changes in tree species abundance due to species-specific size distributions. ...
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The effects of forest fires on tree recruitment dynamics in tropical forests is important for predicting forest dynamics and ecosystem function in Southeast Asia. To our knowledge, no studies have examined the effects of fire intensity on community-level recruitment patterns in tropical forests due to the rarity of long-term observation datasets in fire-impacted tropical forests and the difficulty of quantifying fire intensity. We addressed two questions: (1) is tree recruitment among species affected by fire intensity? and if so, (2) are there specific plant functional traits associated with these responses? We used data from a long-term forest dynamics plot at the Huai Kha Khaeng (HKK) Wildlife Sanctuary in Thailand. The HKK plot occurs in a strongly seasonal tropical environment and has experienced several fires since its establishment in 1994. We found 46 tree species (52% of the 89 species analysed) showed evidence of reduced recruitment rates with increasing fire intensities during the most recent fire in 2005. Tree species in this flammable landscape have various leaf and wood functional traits associated with fire. Spatial and temporal variability in fire activity may lead to alterations in long-term taxonomic and functional composition of the forest due to selection on fire-related traits.
... The dominant dipterocarp tree species show morphological adaptations to fire such as thick barks, and germination and seed dispersal are also adapted to fire (Baker and Bunyavejchewin, 2006). Consequently, a study in the aftermath of the El Nino -Southern Oscillation (ENSO) event of 1997/1998 that had devastating consequences of logged lowland dipterocarp forests in Indonesia (Siegert et al., 2001), did not find substantial impacts in mixed and dry deciduous dipterocarp forests in our study area (Baker, Bunyavejchewin and Robinson, 2009;). However, high fire frequencies or intensities may be critical as slow growing tree seedlings are vulnerable to fire (Wanthongchai, Bauhus and Goldammer, 2014), and a fire mediated tree-recruitment bottleneck has been postulated for DDF making them very similar to savannas (Nguyen, Murphy and Baker, 2019). ...
... Forest fires in this area are typically surface fires. The HKK Wildlife Sanctuary regularly witnesses a long period of continuous burning, sometimes lasting up to two months (Baker, Bunyavejchewin and Robinson, 2009). Fires occur from mid-December to late April with the peak fire season in March. ...
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Dry broad-leaved seasonal forests are widespread in Southeast Asia. They are characterized by drought deciduous tree species, which are adapted to a severe dry season that lasts several months each year. Forest fires are frequent in this vegetation type. To further understanding of fire behavior and fire impact, a series of fire field experiments implemented in the Huay Kha Khaeng (HKK) Wildlife Sanctuary (Uthai Thani Province, Thailand) between 2008 and 2016 was analyzed. A fire behavior model based on the Canadian Fire Behavior Prediction System (Prometheus) was calibrated using the experimental data for the deciduous dipterocarp forest fuel type. The model was then tested on a remotely observed large wildfire in Thailand. Our results confirm the slow fire spread and low to moderate fire intensities observed for this forest type in earlier studies. The fire spread model performs well compared to satellite observations but tends to overestimate area burned and fuel consumption and, consequently, fire emissions when used in air pollution models. Our results indicate that widely used global databases may substantially overestimate fuel consumption and hence fire emissions for this forest type.
... The southern plains and foothills (100 − 2000 masl) are subtropical with heavy rainfall occurring during the summer monsoon, while the valleys of the central region of the inner Himalayan (2000 − 4000 masl) have a temperate climate and typically receive less rainfall than the surrounding slopes and ridges (Stewart et al. 2017). In many areas of South and Southeast Asia that experience a monsoonal climate, fire is a key disturbance agent that shapes forest dynamics (Baker et al. 2008;Baker and Bunyavejchewin 2009). Within the Asian monsoon region, large areas of forests with grassy understories experience a 4-6-month annual dry season followed by a 3-6-month wet season. ...
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Background Chir pine ( Pinus roxburghii Sarg.) forests are distributed in the dry valleys of Bhutan Himalaya. In the past, these forests have been heavily influenced by human activities such as grazing, burning, resin tapping, and collection of non-timber forest products. Bhutan’s Forest Act of 1969, which shifted forest management from local community control to centralized governmental control, greatly restricted these activities. To understand the implications of the Forest Act on the chir pine forests, we used tree-rings and fire scars to reconstruct the fire history of a chir pine forest in eastern Bhutan. This provided an opportunity to characterize the fire regime before and after the Forest Act of 1969 was implemented and assess the scale and magnitude of changes that have occurred. Results We developed a 120-year chir pine fire chronology from nine sites within a single forested landscape. Between 1900 and ~ 1970, fires were small and patchy. When fires occurred, they were limited to one to two sites within the larger study area. After 1970, there was a distinct shift in fire activity, with fires in 1985, 1989, 1996, 2000, and 2013 burning > 90% of sample plots. Fire activity was positively associated with La Niña conditions (wetter, cooler) in the preceding year. This is likely the result of increased accumulation and connectivity of fuels on the forest floor in wetter years. Conclusions Prior to 1970, the fire regime in the studied chir pine landscape in eastern Bhutan was dominated by patchy, low-intensity fires indicating that the fire regime was fuel limited. After 1970, fires became larger and more frequent. This shift was associated with the enactment of the Bhutan Forest Act in 1969, which regulated grazing and implemented a policy of strict fire exclusion in government-reserved forests. This likely led to a large buildup of fuels, particularly after La Niña years. Historical patterns of grazing and low-intensity fires prior to the Forest Act kept fuel loads low and disconnected. The cessation of most human activities in these forests after 1969 resulted in an increase in fuel loads and connectivity within the landscape. This has greatly reshaped fire regimes in the chir pine forests of eastern Bhutan over the past half century.
... The single or combined effect of these conditions can trigger reductions in carbohydrate reserves, limitations in stomatal and photosynthetic activity as well as dysfunctions in cambial production (Gričar et al., 2020;Hood et al., 2018). Thus leading to a reduction of tree vigor, growth (Schweingruber, 1993;Stahle et al., 1999) and, in some cases, even death several years after fire (Baker et al., 2008;Barlow et al., 2003;Barlow and Peres, 2008). Although many studies on the post-fire effects on forests are available (Beghin et al., 2011;Breece et al., 2008;Kobziar et al., 2006;Sieg et al., 2006;Valor et al., 2018), intra-annual studies on post-fire effects are lacking. ...
Article
The increase in frequency and intensity of wildfires is seriously affecting forest ecosystems, especially in drought-prone areas. Trees’ recovery after fire is related to direct tree damage and is influenced by climate conditions, such as warm temperature and water shortage. In this study, we evaluate the post-fire effects on a Pinus pinaster Aiton forest growing in a hot and dry area of the Mediterranean region by comparing burned trees with severe crown reduction against unburned and not-defoliated trees. Inter-annual analyses of dendrochronology and stable isotopes in tree rings were combined with xylogenesis monitoring to investigate the effects of fire on tree growth, ecophysiological processes and wood formation. Tree-ring and isotope data showed a growth reduction and a decrease in photosynthetic activity in the burned trees, compared to control individuals, in the three years after fire. Further, the monitoring of cambial activity demonstrated a negative influence of warm and dry periods on wood formation, low xylem production, a delay in phenology and a reduction in xylem plasticity in burned trees. Our findings suggest that substantial photosynthetic limitations caused by crown defoliation and recurrent drought events could lead to severe growth decrease and reduction of trees ability to regain the pre-disturbance productivity rates.
... Therefore, common species in these forests are deciduous tree species that shed their leaves during the driest time of the season [4]. Distinct dry periods, combined with a large volume of fuels from deciduous trees, lead to annual low-intensity, short-lived surface fires in these forests, and all are human-caused fires consisting of prescribed burning (early burning) and burning for crop preparation by local people along the forest edge [5,6]. One consequence of the frequent, low-intensity burns is the annual supply of fresh herbaceous plants for large herbivores, including Bos javanicus birmanicus (banteng, an endangered species to these deciduous forests in mainland Southeast Asia [7,8]), Rusa unicolor (sambar deer), Rucervus eldii (eld's deer,) and Muntiacus muntjak (red muntjac) etc. (Figure 1). ...
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Forage plants, as primary producers, play an essential role in maintaining populations of large herbivores. The availability and quality of these forage plants can affect the health and viability of these animals. Seasonally dry forests of Huai Kha Khaeng Wildlife Sanctuary and Huai Thab Salao-Huai Rabum Non-Hunting Area are recognized as one of the largest contiguous pieces of forests in mainland Southeast Asia and serve as a home to many large herbivore species, particularly banteng (Bos javanicus birmanicus). However, our understanding of forage plants and their dynamics is still limited. Therefore, the current study was undertaken to understand the dynamics of forage plants, prescribed burning effects, and the associated environmental factors. During 2018–2019, the results showed that the highest forage availability was in June after the prescribed burns at 156.2–252.6 kg ha−1 and the lowest in February before the burning at 16.8–39.8 kg ha−1. Environmental factors that impacted the forage availability include canopy cover, tree density, tree basal area, soil bulk density, soil pH, and topography. However, the impacts of these factors varied among the studied plant life forms, suggesting the importance of active habitat management through prescribed burns and stand improvement to maintain sufficient forage for large herbivores in the future.
... There are many works on post-fi re forest recovery in various biomes in Brazil, such as the Amazon (Cochrane and Laurance, 2002;Prestes et al., 2020;Silvério et al., 2019) and the Cerrado (Souchie et al., 2017;Zanzarini et al., 2019), as well as in other forest areas around the world (Keyser et al., 2017;Svátek et al., 2018;Richardson et al., 2018;González-De Vega et al., 2018). However, the after-eff ects of forest fi res on vegetation, as well as their impacts on species diversity and seedling establishment in humid tropical forests are still highly questioned (Baker et al., 2008;Bhadouria et al., 2017). ...
Article
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Forest fire is considered a relevant environmental and ecological issue worldwide, as it causes population, ecosystem, and economic impacts, making monitoring and additional research necessary to understand post-fire forest recovery. Thus, the aim of this study was to evaluate the changes that occurred in the natural regeneration stratum in a fragment of Atlantic Forest in the municipality of Viçosa (MG), with and without the occurrence of fire. The phytosociological parameters and the functional diversity of the plant community were evaluated through 20 plots, 10 in the burnt area and 10 in the unburnt area, in 2018 and 2019, to follow the natural regeneration. There were collected, in the burnt and unburnt areas, respectively, 113 and 126 individuals, 23 and 16 species, and 13 and 9 botanical families. Piper sp.1, showed the highest values for the parameters: relative density, absolute frequency, and cover value, occurring in 100% of the plots. Areas with occurrence of fire present higher species richness. Species of the genus Piper occur frequently in areas of Semideciduous Seasonal Forest with signs of disturbance. The highest Shannon diversity and Pielou equitability indexes were found in the burnt area. The Jaccard index and the cluster analysis confirm the formation of groups with low similarity, showing floristic heterogeneity between the two areas, and the disturbance caused by fire is considered an important aspect for this floristic differentiation to occur. Therefore, the occurrence of forest fire in areas of Atlantic Forest increased the diversity values of species, with an increase in the equitability index, showing low floristic similarity between burnt and unburnt areas. Keywords: Degradation; Forest Fires; Recovery
... To our knowledge there has been no regional-level assessment of the distribution of savannas across SE Asia. Forest-savanna mosaic landscapes are widespread in this region (Stott 1990, Baker et al. 2008, Bunyavejchewin et al. 2011, Khaing et al. 2019, and represent an opportunity to study how the distribution and spatial characteristics, such as patchiness, of naturally occurring landscape mosaics are shaped by climate and disturbance. ...
Article
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Forest–savanna mosaics exist across all major tropical regions. Yet, the influence of environmental factors on the distribution of these mosaics is not well explored, limiting our understanding of the environmental constraints on savannas especially in Southeast Asia, where most savannas exist in mosaics. Despite clear structural and functional characteristics indicative of savannas, most SE Asian savannas continue to be classified as forest. This designation is problematic because SE Asian savannas are threatened by both fragmentation and forest‐centric management practices. By studying forest–savanna mosaics across SE Asia, we aimed to parse out how landscape mosaics of forest and savanna may be constrained by fire, climate and soil characteristics. We used remotely sensed data to characterize the distribution of tree cover and forest–savanna mosaics. Using regression models, we quantified the relative effects of precipitation, fire frequency, seasonality and soil characteristics on average tree cover and landscape patchiness. We found that low tree cover, indicative of savannas, occurs in drier, seasonal subregions that experience frequent fire. Further, our results demonstrate that fire and precipitation strongly shape landscape patchiness. Landscapes were patchiest in subregions with low precipitation and intermediate fire frequency. These results demonstrate that the environmental factors important in delineating the distribution of savannas globally shape the distribution of tree cover and landscape patchiness across SE Asia. Fire especially drives patterns of tree cover across scales. In a region where fire suppression is a common management strategy, our results suggest that further research studying vegetation response to fire and fire suppression is needed to improve management and conservation of these mosaic landscapes. More broadly, this work demonstrates a useful approach for studying the environmental drivers that influence the distribution of forest–savanna mosaics.
... Su et al. (2015) found that over 90% of common woody species were resprouters in the central Yunnan Plateau region. The dominance of resprouters was consistent with other studies in the monsoon region of East China, Thailand and India (Wang et al., 2007;Baker et al., 2008;Mondal and Sukumar, 2015). Collectively, resprouting is the dominant pathway of regeneration under a monsoon climate, with its role in post−fire plant community assembly enhanced by the efficiency for community recovery in response to the monsoon precipitation, which normally arrive several weeks after the wildfires. ...
Article
Understanding the determinants of post–fire regeneration is critical for determining an appropriate restoration program following fire disturbances. However, studies addressing the drivers of post–fire regeneration of forests in monsoon climate are rare. This study explored the temporal and spatial variations of post–fire forest regeneration in the Central Yunnan Plateau of Southwest China, and disentangled the direct and indirect effects of the environmental factors via structural equation models (SEMs). We found that the overall post–fire regeneration density was generally greater for the habitat with higher values of elevation, pre–fire abundance, and soil pH. Post–fire regeneration was mainly composed of resprouts; seedlings were less relevant and appeared later. The SEM approach showed more variation of recruitment in resprouting (R2=0.66) than seeding (R2=0.33), and revealed different direct and indirect pathways. Resprouts were widely distributed, and significantly influenced by pre–fire abundance, elevation, soil pH, and years since the last fire. In contrast, seedlings preferentially occurred in infertile habitats, andweremainly influenced by topographic position and soil nutrients, showing distinct distribution from that of resprouts. Overall, forests under the subtropicalmonsoon climate in the Central Yunnan Plateau were resilient to fire mainly due to rapid post–fire resprouting. These findings indicate the complementary roles of resprouting and seeding in post- fire regeneration, and help to understand themechanisms that regulate post-fire plant regeneration in a spatially heterogeneous landscape. Our results should contribute to improving the post–fire management of forest ecosystems under the influence of a semi–humid monsoon climate.
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Large portions of the rain forests of Borneo (mainly in Indonesian Kalimantan and in the Malaysian state of Sabah) were heavily damaged by fire in 1982 and 1983. Accurate and timely assessments of the extent and dynamics of the 'Borneo fires' have been difficult, however, owing to the size and geography of the area. The authors report on a series of observations made using the Advanced Very High Resolution Radiometer (AVHRR) carried on-board the NOAA-7 satellite. Such observations obtained daily by this sensor provide valuable information on the occurrence of the fires and on their impact on the vegetation.-from Authors
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Each dry season from January onwards the litter on the jungle floor ignites spontaneously and creeping ground fires clear away old matted vegetation, making way for the new season’s growth. Some of these fires reach considerable size and provide one of the most impressive of jungle sights when viewed from a distance on a dark night. Long, jagged fronts of flame advance across the black backdrop of hillsides, exploding into pyrotechnics as clumps of dry bamboo are engulfed by the everchanging scarlet patterns of destruction….
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Are the effects of fire good or bad for Earth's ecosystems? The weight of the evidence is tilting toward the bad side, as explained by [Goldammer][1] in his Perspective. He describes the need for precise data to assess fire's effects--such as that provided in two recent studies of the negative influence of fire in tropical rainforests (one, [ Cochrane et al .][2], in this issue)--and outlines the challenge presented by another paper in this issue ([ Keeley et al .][3]) to the popular ecological management tool of fire suppression and controlled burning. [1]: http://www.sciencemag.org/cgi/content/full/284/5421/1782a [2]: http://www.sciencemag.org/cgi/content/short/284/5421/1832 [3]: http://www.sciencemag.org/cgi/content/short/284/5421/1829
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The ecological significance of fire is reviewed, particularly in relation to the savanna forest of mainland South East Asia, a community, in which dry season burns occur annually or at least every 2-3 years. It is argued that this tropical deciduous formation is basically an edaphic climax which is well adapted physiognomically, physiologically and phenologically to fire and which in consequence has been gradually spread into the more fire-sensitive adjacent associations, such as tropical semi-evergreen rain forest, by cutting and burning. A careful examination is made of the forest fire environment, of the fuels involved, of the life forms and their adaptive capacity, and of the origins and characteristics of the fires themselves. A case is presented for the prescribed application of fire in this type of habitat and suggestions for appropriate future work are given.
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This paper reports the first stage of a research project to investigate the vertical and horizontal spatial pattern of temperatures in the fires which are common throughout the dry deciduous dipterocarp forests of north and northeast Thailand from December to March every year. The work was carried out by using 'Thermocolor' mica pyrometers in experimental burns at three localities. The construction, calibration, field deployment and limitations of the pyrometers are fully described. It is shown that there are two basic types of vertical temperature profile, for which characteristic curves are provided. These occur in different forms in four main types of burn, namely: (1) typical litter burns; (2) extreme litter burns; (3) typical groundcover burns; (4) extreme groundcover burns. The fire characteristics of each are described in detail. Extreme groundcover burns may attain temperatures of between 700 and 900⚬ C at 0.5-1 m above the ground and spread at rates exceeding 3.0 cm/s even in near windless conditions. Unfortunately, a policy of fire exclusion leads to the groundcover associations that give rise to this dangerous type of wildfire and a policy of prescribed burning is preferable. The insulating properties of both the sandy loam soils and the bark of savanna forest tree species are demonstrated and it is concluded that the dry deciduous dipterocarp forest ecosystem is well adapted to fire. Suggestions for further work are given.
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Southeast Asia has the highest relative rate of deforestation of any major tropical region, and could lose three quarters of its original forests by 2100 and up to 42% of its biodiversity. Here, we report on the current state of its biota and highlight the primary drivers of the threat of extinction now faced by much of the unique and rich fauna and flora of the region. Furthermore, the known impacts on the biodiversity of Southeast Asia are likely to be just the tip of the iceberg, owing to the paucity of research data. The looming Southeast Asian biodiversity disaster demands immediate and definitive actions, yet such measures continue to be constrained by socioeconomic factors, including poverty and lack of infrastructure. Any realistic solution will need to involve a multidisciplinary strategy, including political, socioeconomic and scientific input, in which all major stakeholders (government, non-government, national and international organizations) must participate.