This document summarizes a study on the effects of fire as a recurrent disturbance in tropical forests of eastern Amazonia. The key points are: 1) Burned forests were found to be extremely heterogeneous, with substantial variation in forest structure and fire damage over small distances. Canopy cover, biomass, and stem densities decreased with increasing fire intensity/frequency. 2) Even light fires removed over 70% of sapling and vine populations. Abundance of pioneer species increased dramatically in more severely damaged areas. 3) Species richness was inversely related to burn severity but no clear pattern of species selection was observed. 4) Fire appears to be a cyclical, recurrent event in the region.

1. BIOTROPICA 31(1): 2-16 1999
Fire as a Recurrent Event in Tropical Forests of the Eastern
Amazon: Effects on Forest Structure, Biomass, and Species
Composition'
Mark A. Cochrane2
lnstituto do Homem e Meio Ambiente da Amazonia (IMAZQN), Caixa Postal 1015, Belem, Para 66.000, Brazil
and
Mark D. Schulze
Biology Department, Pennsylvania State University, University Park, Pennsylvania 16802, U.S.A.
ABSTRACT
'I'hc effects of fire on forest structure and composition were studied in a severely firc-impacted landscape in the eastern
Amazon. Extensive sampling of area forests was used to compare structure and compositional differences between
burned and unburned forest stands.
Hurned forests were extremely heterogeneous, with substantial variation in forest structure and fire damage recorded
over distances of <50 in. Unburned forest patches occurred within burned areas, but accounted for only six percent
of the sample area. Canopy cover, living biomass, and living adult stem densities decreased with increasing fire
intensiry/frequeiicy, and were as low as 10-30 percent of unburned forest values. Even light burns removed >70
percent of rhc sapling and vine populations. Pioneer abundance increased dramatically with burn intensity, with
pioneers dominating the understory in severely dainaged areas. Species richness was inversely related to burn severity,
hut no clear pattern of species selection was observed.
Fire appears to be a cyclical event in the study region: <30 percent of the burned forest sample had been subjected
to only one burn. Based on estimated solar radiation intensities, burning substantially increases fire susceptibility of
forests. At least 50 percent of the total area of all burned forests is predicted to become flammable within 16 rainless
days, as opposed to only 4 percent of the unburned forest. In heavily burned forest subjected to recurrent fires, 95
percent of thc area is predicted to become flammable in <9 rain-free days. As a recurrent disturbance phenomenon,
fire shows unparalleled potential to impoverish and alter the forests of the eastern Amazon.
RESUMO
0 s impactos sobrc a estrutura e composigzo florestal foram estudados em uma irea severamente impactada pelo fog0
na Amazbnia oriental. Amostragcns extensivas de partes da floresta foram utilizadas para comparar as diferengas de
estrutura c de composig8o em trechos queimados c nso-queimados.
As florestas queimadas eram extremamente heterogeneas, com uma significativa variagzo na estrutura florestal, e
os dams causados pelo fog0 foram registrados em intervalos de menos de 50 metros. 'Trechos de floresta intacta
ocorreram cntre as ircab queimadas, mas constituiram apenas 6 porcento da Area amostrada. A cobertura do dossel, a
biomassa viva, c as densidades de individuos adultos vivos diminuiram coin o aumento da frequEncialintensidade das
ocorrhcias de fogo, chegando a constituir apenas 10 a 30 porcento dos valores relativos hs florestas intactas. Mesmo
as queimadas menos intensas chegaram a remover mais de 70 porcento das populag6es de pldntulas e cipos. A
abunddncia de espkcies pionciras aumentou dramaticamcnte, sendo que essas espkcies dominaram o sub-bosque nas
ireas mais severamentc afetadas. A riqueza de espkies foi inversamente proporcional gravidade da queimada, mas
1150 se observou um padrzo claro de selegzo de espkcies.
0 fog0 parece scr uma ocorrencia ciclica na regizo em cstudo-menos de 30 porcento das amostras de florestas
queimadas havia sofrido uma queimada. Com base em estimativas sobre a intensidade da radiagiio solar, as queimadas
aumcntam substaiicialmente a susceptibilidadc das florestas ao fogo. Estima-se que pelo menos 50 porcento do total
da irea de todas as florestas queimadas venha a sc tornar inflamivel, caso ocorra um periodo de 16 dias sem chuva,
o que contrasta coin a cifra de apenas 4 porcento no caso das florestas intactas. Em florestas fortemente afetadas pelo
fog0 em queimadas repetidas, estima-se que 95 porcento da irea se tornari inflamivel em menos de 9 dias sem chuva.
Como uma perturbagzo recorrente, o fogo apresenta urn potencial sem paralelos para empobrecer c alterar as florestas
da Amazbnia oriental.
Keywords:
.sb$s; succession; tropicul ruinforest.
biomass; cyclical disturbance; eastern Amazon; $re; j r e susceptibility;forest degrudution;jorest ecology; species
' Kcceived 14 March 1997; revision accepted 3 October 1997.
Woods Hole Research Center (WHRC), PO. Box 296, Woods Hole, MA 02543, U.S.A
2

2. Fire as a Recurrent Event in Tropical Forests 3
As EARLY AS 1785, THERE WERE WARNINGS HAT FIRE
was being promoted in the forests of eastern Ama-
zonia by a “disturbing synergism” between cattle
ranching and selectivelogging (Uhl & Buschbacher
1785). Reported flammability of selectivelylogged
forests in this region has been borne out by sub-
sequent studies (Uhl & Kauffman 1770, Hold-
sworth & Uhl 1797) and reports of large burns in
previously logged forests, including a 1000 km2
burn near Paragominas (1788) and a 7000 ha burn
around the community of Del Rei (1771-72; Le-
febvre & Stone 1774).
Although undisturbed tropical forest has been
shown to be resistent to fire (Uhl et al. 1788), fire
has been recognized as a historical element in the
Amazonian landscape (Sanford et al. 1785, Saldar-
riaga & West 1986) and may occur in natural for-
ests after multiple year periods of low rainfall (Nep-
stad et al. 1774, 1795). Fire may even have been
adequately prevalent during the last two millenia
to have displaced Amerindian cultures at 300-500
year intervals (Meggers 1774). Kauffman and Uhl
(1770), however, have shown that regional forest
vegetation has few evolutionary adaptations to fire.
Fire is therefore expected to be a rare event and
tree mortality is expected to be high even during
light ground fires.
The causes of fire in some Amazonian forests
are well understood. Forest disturbances such as
logging cause an increase in the amount of woody
debris and fine fuels (e.g., vines and herbaceous
growth) present at a site (Kauffman et al. 1788,
Uhl & Kauffman 1770) while concurrently induc-
ing significant changes in the microclimate (q.,
decreased canopy cover, increased daily maximum
temperatures, increased wind speeds, and increased
vapor pressure deficits; Kauffman & Uhl 1770),
such that fuel dry-down rates are accelerated and
fire susceptibility is achieved in as little as five or
six days (Uhl & Kauffman 1770, Holdsworth &
Uhl 1777). These factors, when combined with the
frequent use of fire for clearing slash, weed control,
and conversion of forest to pasture (Uhl & Busch-
bacher 1785, Fearnside 1770) lead to frequent fires
in those areas where logging has occurred.
Evidence of fire in logged forests is common
and widespread. Throughout Brazilian Amazonia,
200,000 km2 of land area may burn in a given year
(Setzer & Periera 1971). Estimates of the amount
of forest involved vary widely, from Nelson’s (1794)
report of 500 km2 of forest fire scars in 1783Land-
sat T M prints to Setzer’s (in Fearnside 1770)report
that, in a single year (1787), as much as 80,000
km2 of forest had burned in the BrazilianAmazon.
At a more local level, the story is equallyprofound.
Near Paragominas, 8 of 15 ranchers experienced
forest fires on their lands shortly after logging (Uhl
& Buschbacher 1785), while in 1775 alone it is
estimated that 21 percent of ranches in southern
Pari burned, with the area of standing forest af-
fected by fires exceedingnew deforestation by more
than three-fold (Alencar et al. 1997).
At present, selectivelogging is the most rapidly
growing land-use activity in the eastern Amazon.
Furthermore, it is expected to increase in impor-
tance during the coming years (Verissimo et al.
1772). As Asian timber stocks decline, the quantity
of Amazonian timber supplied to the international
market is expected to increase (ca 10%/yr; Verfs-
simo & Amaral 1776). Already, it is estimated that
each year 10,000 km2 of forest are selectively
logged yearly in the Brazilian Amazon (Verissimo
& Amaral 1776). As such, the scene is being set
for fire to become an increasingly important dis-
turbance in the eastern Amazon.
The potential for large-scale fires in logged for-
est was graphically illustrated during 1782-83 in
East Kalimantan, Indonesia when fires escaped
from agricultural activities and burned 25,000 km2
of Bornean forest (Malingreau et al. 1785, Leigh-
ton & Wirawan 1786,Woods 1787). This scenario
also is becoming more likely in the easternAmazon
as the forest becomes increasingly fragmented. In a
selected area of ParagominasCounty (24,700 h2),
standard imagery analysis shows that two-thirds of
the land area is still forested, but if areas that have
been selectivelylogged or have experiencedground
fires are accounted for, only six percent of the area
can be considered as supporting primary forest
(Alencar et al. 1777).
Given the large amount of previously burned
forest already existing and that burned forests will
become a larger element of the future landscape,
the time has come to study this ‘‘new’’landscape
element. We thus selected an area known to have
been severely impacted by uncontrolled forest fires
during recent years. We opted for an extensivesam-
pling design to incorporate areas subjected to both
single and multiple fire events as well as different
fire intensities. Our objectives in this preliminary
study were to: (1) determine the effectsof fire upon
forest structure, (2) investigate changes in species
composition caused by fire, and (3)characterizethe
heterogeneous nature of repeatedly burned forest.
STUDYAREA
This study was conducted within ca 100 km2 area,
roughly centered on the community of Olho

3. 4 Cochrane and Schulze
D’Agua, Pad, 30 km south of the logging town of
’railpndia. The area is bisected by a two lane north-
south road (PA-150) and further subdivided by
perpendicular secondary roads at ca 2-km intervals.
On the west, the area is bounded by the Moju
River and on the east by a large land holding. The
Electronorte high voltage power line runs roughly
parallel to the west side of the main road (PA-150)
at 1.O-1.5 km distance. Over the years, the flam-
mable herbaceous vegetation under this power line
has reportedly acted as a 100-m-wide fire corridor,
spreading many fires on the west side of the road.
At present, only small fragmentary sections of
burned forest remain between the power lines and
the road.
The Taillndia region, described as the Ama-
zonian frontier at the beginning of the 1770s (Uhl
et al. 1771), has since matured with all land now
being privately held by a combination of small
landholders and ranchers. The remaining forests
within the immediate region have all been logged
to some degree and most also have burned in re-
cent years. The landscape in this area is a mosaic
of pastures, small agricultural plots, second growth
forest, logged-unburned, and logged-burned for-
ests. The forest of this region is tropical moist ev-
ergreen on latosol soils. The region is subject to a
strong dry season June-November, averaging
1500-1 800 mm annual rainfall (Silva 1776).
METHODS
PART ~-MAPPINC,TRANSITIONS IN VEGETATION COVEIi
WITI-IIN A 100 K M ~LANDSCAPE BLocK.-Using a por-
table Global Positioning System (GPS), we mapped
the vegetation along 40 km of secondary and ter-
tiary roads within a ca 17 x 6 km block. The
network of roads within the study area was such
that no forested areas were >I km from a road.
The differentiated vegetation classes were: pasture,
active agricultural plot, secondary forest, burned
forest, and unburned forest. In areas with pasture
adjacent to the road, forest type beyond the pasture
was recorded. We relied on this extensive sampling
to obtain a rough estimate of the amounts and
distributions of burned and unburned forestswith-
in the study area.
PAR I‘ 2-INTENSIVE SAMPLING OF FOREST STRUCTURE
AND SPECIES coMPosITioN.-we established 10 belt
transects in forest (8 burned forest, 2 unburned
forest) scattered throughout the study area. Site lo-
cation was occasionallylimited by fearful landown-
ers who refused permission to conduct studies on
their land. As such, seven transects (6 burned, I
unburned) were established on the west side of the
main road (PA-150) and three (2 burned, 1 un-
burned) on the east side. All sites had been logged
with intensity estimated (from cut stumps) as rang-
ing from 2-8 trees/ha removed. While transect
starting locations were not selected randomly, the
use of long transects helped minimize bias due to
the fact that most of the transect not being seen
from the starting point (Brown et al. 1975). Tran-
sects were started 50-500 m from the road, well
away from the forest edge (50 m minimum), and
directed so as to avoid running within 50 m of
transitional vegetation. A total of 5 ha of forest was
sampled in this manner.
All transects were 500 x 10 m, subdivided into
25-m units. All stems 2 1 0 cm DBH were mea-
sured, classified as live or dead, scored for vine pres-
ence, and identified to species or higher taxon (ge-
nus or family for some groups). All small stems
(<lo cm DBH) >2 m tall were sampled in 100
m2plots centered on each 25 m point (20/transect)
for a sample size of 0.2 hahransect (2.0 ha overall).
Saplings were divided into two classes (<5.0 cm
and 25.0 cm). For each plot, the total number of
living and dead stems were recorded by size class.
Live stems were further divided into pioneer and
non-pioneer classes (the “pioneer” class being lim-
ited to well documented pioneer genera such as
Cecropia, Solanum, Vitmia, and Trema). In addi-
tion, the presence or absence of small (<2.5 cm)
and large (22.5 cm) vines was scored for each 5
x 5 m quadrant of every 100 m2 plot to provide
a frequency estimate.
On all transects, canopy cover was estimated by
taking four spherical densiometer readings (one per
quadrant) at each 25-m point. One observer took
all measurementson all transects to reduce sampling
bias. To provide for correlation of densiometerread-
ings with light intensity, we sampled four transects
(one in unburned and three in burned forest) rep-
resentative of the full range of fire damage recorded
in the study area, every 50 m (11 pointshransect)
along the transect with hemispherical photographs.
Canopy photos were digitized and then analyzed us-
ing Winphot (ter Steege 1776) to estimate the solar
radiation at camera level (1 m). A regression was
then performed to relate densiometerreadingsto ex-
pected solar radiation levels.
PART 3-DELINEATION OF BURNED FOREST CUSSES.-
Due to the high degree of variation in fire damage
and even fire history at small scales along transects,
additional analyses of the effects of fire on forest

4. Fire as a Recurrent Event in Tropical Forests 5
TABLE 1.
'1i.ansccr 2 8 6 10 5 4 3 7 1 9
Comparison of burned and unburnedforest traizsects, Olbo DZgua, Park
Burned, Unburned, or
Partially Burned
(13, u, 1%) 1J U PB B B B B B B B
Steins 2 10 cm DBH (no./ha)
Live non-pioneer stems 514 506 408 288 240 168 140 124 106 8
Live pioneer stcms 6 8 6 58 38 106 78 56 28 10
Dead stems 54 26 76 68 132 186 184 200 236 302
574 542 490 414 410 460 402 380 370 320lotal sccms
,.
Biomass (iiietric toidha)
Living 2 10 cm DRH 250 256 186 178 202 75 151 89 81 24
Standing dead 75 26 69 46 76 78 56 140 106 104
Vines 2 10 crn DBH 1 0 2 2 6 0 0 2 0 0 2 0
Number of rnorphospecies
Vines (no./ha)
Species richncss
(species or genera) 49 33 35 39 24 22 21 21 21 5
structure were conducted at the sub-transect level.
We divided all transects into 25-m sections (20/
transect) and regrouped the sections into four dis-
turbance classes: (1) areas of high intensity/high
frequency burning, (2) areas of moderate intensity/
frequency burning, (3) lightly burned areas (only
burned once), and (4) unburned forest including
islands. Areas placed in classes one and two had
been burned more than once. While this grouping
is a simplification of what is really a continuum of
fire damage, it provides a means for examining the
relationship between fire intensity/frequency and
structural and compositional variation. Sub-tran-
sect sections were assigned to burn classes using
information from reference stands with known fire
histories. Specifically, the lightly burned class cri-
teria were based on samples of areas known to have
burned only once while the heavily burned class
criteria were based on data from areas reported to
have burned many times in recent years. Transect
subsections for which reliable fire histories did not
exist were assigned to a burn class based on simi-
larity to the reference areas. Sections with damage
intermediate between the lightly and heavily
burned classes were assigned to a moderately
burned class. Sample area was relatively equal be-
tween the four classes: 1.53 ha (30.6%) heavily
fire-damaged forest, 1.26 ha (25.2%) moderately
burned forest, 0.96 ha (19.2%) lightly burned for-
est, and 1.25 ha (25%) unburned forest.
RESULTS
FIRHL>ISTRIBUTION AND FREQUENCY.-ke has af-
fected forest throughout the 100 km2 study area.
Of 43 forest patches in our 40 km mapping, only
3 were not yet burned. Unburned forest accounted
for <5 percent of the total transect length. Two
unburned patches were on large land holdings
where the owner had constructed 5-m-wide fire
breaks with a bulldozer. The third stand was a large
fragment of unburned forest within a matrix of
burned forest.
Although fire frequency in our study area can-
not yet be quantified, we were able to reconstruct
a rough history of burning through interviewswith
landowners and several long-term residents of Olho
D'Agua. Virtually all forest that burned did so dur-
ing the dry season of 1995. In this severe dry sea-
son, fire swept through many areas more than once.
At the time of sampling (October 1996) none of
the areas we sampled, and virtually no forest in the
study area as a whole, had burned during the dry
season of 1996, owing to unusually high rainfall
during this period. Prior to 1995, fire occurrence
was less spatially uniform; some stands burned re-
peatedly, while many apparently remained un-
burned.
COMPARISONSBETWEEN BURNED AND UNBURNED FOR-
EsT.-Burned stands displayed substantially re-
duced living biomass. On both unburned forest
transects, the density of live stems >10 cm DBH
was >500/ha (Table 1). In only one of the burned
forest stands, in which unburned forest islands ac-
counted for 50 percent of the sample, was the liv-
ing stem density >400/ha. On the remaining tran-
sects, living stem density ranged 18-346/ha (Table
1).Moreover, these densities included large pioneer

5. 6 Cochrane and Schulze
stems, most of which had invaded the sites follow-
ing the burns. When pioneers are removed from
calculations, living stem densities in the unburned
forest stands remain >500/ha, while densities in
the burned stands range from 8-288 (excludingthe
transect with a high percentage of unburned forest
island habitat). Dead standing stem density was
negatively correlated with living stem density
(-0.97). All the burned transects, however,showed
lower total stem densities than the unburned con-
trols (as low as 55.6%) , indicating that a large
percentage of the stems killed by fire had either
fallen over or were consumed entirely by the blaze.
We observed numerous fallen stems, fire-hollowed
bole fragments and bole-shaped holes in the
ground during the sampling.
COMPARISONSAMONG BIJRNED FOREST CATE,GORIES.-
Patterns of fire damage cannot be explained by
stand-level fire history alone; very small-scale
(50.05 ha) variation in intensity and burning in-
terval result in dramatic differences in forest struc-
ture. Variation in numbers of standing dead trees
within the two unburned transects was low; how-
ever, most burned forest transects consisted of mo-
saics of lightly to heavily damaged patches and even
small islands of unburned forest, displaying sub-
stantial variation in structure and fire damage at
scales of 50-100 m. Of the eight transects in
burned forest, only two intersected forest that had
burned only once. Three of the six remaining sam-
ples intersected forest that was reported to have
burned virtually every dry season over the previous
5-10 years. Some of this variation may have been
due to preburn differences in disturbance history.
The majority of this small-scalestructural variation,
however, was due to differences in fire intensity.
Clear boundaries between lightly burned or even
unburned forest and heavily fire-damaged forest
were visible within several of the transects. Un-
burned forest remnants accounted for 6 percent of
the burned forest sample; lightly fire-damaged for-
est represented 24 percent, moderately burned for-
est 31.5 percent, and heavily burned forest 38.5
percent of the sample.
CANOPYOPENING AND UNDERSTORY MOISTURE CON-
-rPNT.-with increased fire intensity/frequency for-
est canopy opening increased linearly. Average can-
opy cover, as measured with a spherical densiom-
eter, ranged from an averageof 14 percent in heavi-
ly burned forest to 87 percent in unburned forest.
All transected areas were previously subjected to
logging, so the increases in canopy opening asso- ~ ” ,,
ciated with this activityshould have been consistent
among forest classes.
Densiometer readings were highly correlated
with canopy cover as calculated for a subset of sam-
ple points using hemispherical photographs. Re-
gression of canopy cover in the 180 degree hemi-
sphere on densiometer readings was highly signifi-
cant (P< 0.000, R2 = 92.1). Densiometer read-
ings, however corresponded more tightly with
overhead canopy cover, as measured by a 45 degree
conical subsample of the total hemisphere (P<
0.000, R2 = 94.1).
The differences in canopy cover between
burned and unburned forest translate into dramatic
differences in daily solar radiation reaching the un-
derstory. Using Winphot we estimated average dai-
ly photon flux density at each photo station based
on site characteristics (latitude, altitude), an as-
sumed T value of 0.4 corresponding to a diffuse
radiation component equal to 40 percent of total
radiation (4ter Steege 1996), and clear skies. Giv-
en these assumptions, calculateddaily radiation val-
ues averaged 13 percent of the total above-canopy
photon flux density beneath unburned forest can-
opy, 33 percent under lightly burned forest canopy,
64 percent in moderately burned forest, and 71
percent in heavily fire-damaged forest understories.
We were unable to correct for the effectsof overcast
skies; therefore, our estimated PPFD (photosyn-
thetic photon flux density) values are applicable
only to days with clear skies, conditions common
in our study area during the dry season.
Using the aforementioned regressions of den-
siometer readings and calculated canopy cover, we
estimated the direct photon flux density (min of
mol/m’/d) for each 25-m segment of the various
transects. This enabled us to use Holdsworth and
Uhl’s (1997) established relationship between di-
rect solar radiation intensity and the number of
rainless days necessary to reduce understory fuel
moisture content below the 12 percent flammabil-
ity threshold to predict which locations were likely
to become flammable. The distribution of sites
within each forest class according to different rates
of direct photon flux density are given in Figure 1.
Holdsworth and Uhl’s (1997) relationship between
flammability and direct photon flux density does
not apply at rates <150 min of mol/m2/d,and sites
with these rates can be considered as being resistent
to lire. Conversely, all sites with rates >150 min
of mol/m2/d are expected to become flammable
within 16 rainless days. Locations receiving >300
min of mol/m2/d will become susceptible to fire
within onlv 9 rainless davs. From our data (Fig. 1).

6. Fire as a Recurrent Event in Tropical Forests 7
80
v)
Y
2 60
4.
0
40
B
$a
20
0
Fire resistant Fire susceptible Fire susceptible
9-16rainless days <9rainless days
FIGURE 1. Rate of direct photon flux density (PFD in minutes of mol/m2/d). Bar height relates the percentage of
plots in each forest type to three separate ranges of PFD values. The three PFD ranges correspond to different fire
susceptibilities (4Holdsworth & Uhl 1997).
only 4 percent of unburned logged forest sites are
expected to become flammable within 16 rainless
days. This increases to 51 percent after only a single
light burn and is nearly 100 percent for more se-
verely burned forests. In moderately burned areas,
53 percent of the sites are expected to become sus-
ceptible to fire within 9 rainless days. In heavily
burned areas, a sobering 95 percent is expected to
become flammable in less than 9 rain-free days, and
50 percent in less than a week. Although site-spe-
cific calculations of dry-down rates would be pref-
erable, we feel that these estimates are conservative
because they do not account for the expected in-
crease in forest dry-down rates caused by air move-
ment within these extensively thinned forests.
FIREEFFECTS ON TREm-The live tree density (ex-
cluding pioneers) in lightly burned forest patches
was on averageonly 62 percent of that in unburned
forest areas. These densities dropped to 36 percent
of unburned densities in moderately burned forest
and 10 percent in areas of high frequency and/or
intensity burning. Total stem densities (living and
dead 210 cm) in the three classes of burned forest
were lower than in unburned forest but not dra-
matically different from each other (range 375-
449/ha; Table 2). Thus, the dramatic decrease in
live stem density with increased fire intensity/fre-
quency cannot be attributed to pre-disturbance
variation in stem density among sites,and is almost
certainly due to increased mortality in more heavily
burned areas.
By comparing tree size-class distributions
among forest classes, it is possible to gain insight
into size-class specific impacts of burning on sur-
vival. The unburned forest exhibits a reverse-J dis-
tribution curve for the tree community as a whole.
Using this distribution as a standard, it is possible
to compare presumed mortality rates among size
classes within a burn-intensity type. In lightly
burned forest, small stems (10-30 cm DBH) ap-
pear to suffer disproportionate mortality, presum-
ably because larger stems are better able to survive
fire contact than smaller ones (Fig. 2). These find-
ings are consistent with other studies of tropical
forests subjected to a single burn (Woods 1989,
Holdsworth & Uhl 1997). In areas subjected to
high intensity blazes or recurrent fire events, how-
ever, large trees appear to be nearly as susceptible
to fire induced mortality as smaller stems (Fig. 2).
In the case of repeat burns, this increasedincidence
of large stem mortality possibly may be attributable
to already fire-weakened trees.
SAPLINGSAND SEEDLINGs.-The effects Of fire On the
forest understory were more immediate and more
pronounced than on trees (stems 2 1 0 cm DBH).
Although total sapling stems densities were essen-
tially equal in all four forest categories, live stem
densities in the three burned forest classes were
only 59-66 percent of densities in unburned forest.
Multiple regressionof non-pioneer saplingdensities
on canopy cover and forest class (as three indicator
variables) showed a significant positive correlation

7. 8 Cochrane and Schulze
TABLE 2. Comparisons between unburnedforest and three burned forest classes, Olho DXqua, Pard.
Unburned Lightly Moderately Heavily
(control) burned burned burned
forest forest forest forest
Sample size (ha)
Number of sampling plots
Average canopy cover (Yo)
Standard deviation canopy cover
Stems 2 10 cm DBH (average no./ha)
Live non-pioneer stem density
Live pioneer stem density
Dead stem density
Total stem density
Biomass (metric tons/ha)
Living biomass
Dead biomass
Total biomass
Saplings (avg. per 0.01 ha understory plot)
Dead saplings 2 5 cm DBH
Live non-pioneer saplings 2 5 DBH
Live pioneer saplings 2 5 cm DBH
Dead saplings 2 2 m tall, < 5 cm DRH
Live non-pioneer saplings 2 2 m tall, < 5 cm
Live pioneer saplings 2 2 m tall, < 5 cm DBH
Sapling total
Freq. (% plots w/vines) of vines 2 2.5 cm DBH
I’ercent stems 2 10cm supporting vines (all sizes)
Density of vines 2 10 cm diameter (no./ha)
DBH
Vines
Species composition
Total no. of taxa (species or genera) recorded
No. of taxa adjusted bv samDle size (no./ha)
1.3
50
87.1
2.9
509
6
42
557
242
53
295
0.2
11.1
0.4
3.7
39.2
0.5
55.1
83.0
45.5
15.2
66
58
1.o
39
61.0
8.8
317
27
105
449
220
50
270
3.2
3.1
1.3
24.3
10.4
15.0
57.3
19.5
39.5
1.o
49
49
1.3
50
33.9
10.0
183
54
147
384
129
71
200
4.6
1.5
1.9
15.7
2.7
25.4
51.8
11.3
43.6
0
48
43
1.5
61
13.8
5.1
52
64
259
375
47
116
163
5.7
0.2
1.7
17.5
0.6
30.9
56.6
0
42.4
0.7
24
19
with canopy cover and significant negative corre-
lation with burn category (P< 0.000 for all x
variables, R2 = 75). The majority of live stems in
all three burned forest classes were pioneers, vir-
tually all of which had colonized the site subse-
quent to burning. After adjusting densities for all
four forest categories to exclude pioneers, densities
of mature forest species < 10 cm DBH were as
low as 1.4 percent of densities in the unburned
forest for heavily burned sites, and only 26.6 per-
cent of densities in the lightly burned areas (Table
2). If similar initial densities of non-pioneers are
assumed for all four forest classes, this translates to
sapling mortality rates of 73.4 percent in lightly
burned, 92 percent in moderately burned, and 98.6
percent in heavily burned forest.
Large saplings (5 cm SDBH <10 cm) did not
appear to be dramatically more resistant to fire than
small saplings (2 m tall-4.99 cm DBH). In lightly
burned forest, the ratio of live small non-pioneer
saplings to live large non-pioneer saplingswas iden-
tical to that in unburned forest (77% small; Table
2), and in more intensely/frequently burned patch-
es the ratio was only slightly lower than in un-
burned forest (65 and 73%). In some areas that
were only lightly burned in 1995, however, we ob-
served that all the small saplings had been killed,
while a small portion of large saplings were still
living. It is possible that a percentage of the small
non-pioneer saplingsare not advancedregeneration
survivors of burning, but rather faster growing ma-
ture forest species that colonized the burned forest
from seed or by sprouting.
PIONEERsPEcIEs.-Forest fires clearly resulted in in-
creased abundance of pioneers, at least in the short
term (1-10 yr after burning). The density of large
(>lo cm DBH) pioneer stems increased with fire
intensiqdfrequency (6.4lha unburned-64lha heavi-
ly burned; Table 2). Pioneer stem densities in the

8. I
Dl Heavily burned
Fire as a Recurrent Event in Tropical Forests 9
17.-
~~
0 10 20 30 40
Diameter (cm)
FIGURE 2. Comparison of relative diameter distributions between burned and unburned forest classes. Lightly
burned forest clearly shows that tree survival after fire is diameter dependent. Enhanced survival of larger size class
trees, however, appears to decline or disappear with greater fire intensity/frequency.
understory were positively correlated with both
canopy opening and forest class (linear regression
canopy opening P < 0.000, R2 = 47.8; forest class
as indicator variables P < 0.000, R2 = 44.1). In
the extreme case, pioneers accounted for 97.7 per-
cent of all live sapling stems in the heavily burned
forest. Pioneer juveniles, however, did not appear
to be any more likely to survive burning than sap-
lings of non-pioneer species. In frequently burned
areas, virtually all dead standing saplings were pi-
oneers that had colonized the site between fires,
rather than stems present before the first burn. This
is indicative of high turnover in dead understory
stems.
VINES.-AS a group, vines appeared highly suscep-
tible to fire damage. Whereas in trees there ap-
peared to be a substantial increase in fire resistance
with increased stem diameter, mortality was high
in all vine size classes. The density of living vines
>10 cm diameter dropped from 15.21ha in un-
burned forest <l/ha in moderately and heavily
burned forest. The frequency of living vines >2.5
cm diameter in understory samplesfell dramatically
from 83 percent of all plots in unburned forest to
only 20 percent of plots in lightly burned forest,
with no living vines of this size recorded in heavily
burned forest. In all burned areas, dead vines of
this size class were common, precluding the possi-
bility that differences were merely artifacts of pre-
disturbance variation in densities.
In contrast, small vines (<2.5 cm diameter)
were present in virtually all understory plots in all
forest categories. In unburned forest and in forest
burned only once, these vines were generally a rel-
atively minor component of the vegetation, while
in more intensely burned forest areas, small vines
frequently formed a dense mat at the height of the
upper surface of the regenerating vegetation. In
heavily burned areas, the vine community was
dominated by a handful of aggressive, pioneering
species (including Curcurbitaceae, Passzjlora, Mal-
phigiaceae, Mimosa and Poaceae).
It is partly due to this invasion of burned areas
by weedy vine species that frequencies of vines on
adult trees were relatively constant among forestclas-
ses (range 3746% of stems with vines; Table 2).
We conducted a more detailed point-centered-quar-
ter sampling of vine abundance on adult trees, on
one burned and one unburned transect, in which
the actual numbers of small and large vines were
recorded for each tree. With all size classes lumped,
the two area showed no difference in vine frequen-
cies (41 and 43% of trees with vines). However,
19.6 percent of trees in unburned forest supported
large vines (22.5 cm), compared to only 2.4 percent
in the burned area. The average number of large

9. 10 Cochraneand Schulze
81%
Moderately Burned HeavilyBurned
FIGURE 3. Vine patch size distribution in each of the forest classes. Percentages reference the quantity of patches
for each size class encountered. Solid = no live vines >2.5 cm; vertical lines = 25 m2 patch; stipple = 50 m2 patch;
clear = 75 In2 patch; horizontal lines = 100 m2patch.
vines per tree in unburned forest was nearly thirty
times that in the burned area (0.59 vs. 0.02hee).
We hypothesize that the presence or absence of
live large vines (22.5 cm) also can be used to gain
insight into the percentages of the sample area in
each forest class actually contacted by the most re-
cent fires (1995). Due to the uneven spread of fire
through a stand, even in an area where fire has
passed, there may be small (5-100+ m2) pockets
without fire damage. Vines, being highly susceptible
to fire damage, are a good surrogate for mapping
very small-scale burn variation. Vine frequency in
our understory samples was categorized at each 25-
m point of every transect by the number of 25-m2
quadrants in each 100-m2 plot with vines present,
on a scale of 0-4. For the purpose of this analysis,
the presence of one or more large vines in a single
quadrant was considered as forming a vine patch of
25 m2. Therefore, at each 25-m point a vine patch
size 0-100 m2 was calculated. For example, if two
quadrants had vines present, this equated to a 50-
m2 patch; for three quadrants a 75-m2 patch, and
four quadrants a 100-m2patch. The distribution of
vine frequencies (Fig. 3) clearly shows that not only
are vines increasinglybeing killed by higher frequen-
cyhntensity fires, but that the size of livingvine clus-
ters is decreasing. This suggests that the size of un-
burned patches within burned forest decreases with
increased fire frequencylintensity. Using data from
the unburned forests as a crude standard, it is pos-
sible to calculate the percentage deviation from ex-
pected vine frequency. Because there is no reason to
assume that fire seeks out these vines, we propose
that the inverse of this deviation is a rough estimate
of the minimum percent of the area actually con-
tacted by fire. For our data, we calculated that fire
contact ranged from ca 77 percent in lightly burned
forests to very nearly 100 percent in heavily burned
forests, with respective maximum unburned patch
sizes of >lo0 m2 and <25 m2. This hypothesis
should be experimentally tested, but we expect that
it will provide crude but easily measurableestimates
of total ground fire contact area after relatively re-
cent burns (51 yr). Interestingly, data from Hold-
sworth and Uhl (1997) showed that fire contacted
78 percent of the trees in their study area subjected
to a single burn. Although not an actual test of the
hypothesis, this contact percentage is remarkably
close to what we would have predicted (77%) for a
single burn.
SPECIEScoMi~osImoN.-Our data show that while
light burning did not appear to dramaticallyreduce
tree species diversity, high intensity or repeat burns

10. Fire as a Recurrent Event in Tropical Forests 11
70
60
50
40
# of
SPP
30
20
10
0
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61
d a t i v en m k r oftrstsectsegenmts
FIGURE 4.
selected randomly. Each “plot” equals 0.025 ha.
Species-area curves for samples in four forest categories, Olho D’Agua, Par& Transect segments were
drastically reduced the number of species present/
ha of forest. A total of 84 taxa (identified to species
or genus) were recorded in our sample as a whole.
In unburned forest 66 taxa were recorded, which
when adjusted for sample area (adjusted for small-
est sample size of 0.96 ha), gives an average of 58
species. In lightly burned forest the number of taxa
recorded per sample area was 49, but the adjusted
frequency drops to 43 and 19 taxa respectively in
moderately and heavily burned forest (Table 2).
Species area curves suggest that our samples for all
four forest categories were at or near their asymp-
totes (Fig. 4). The percentage of species in each
burned forest category also recorded in the un-
burned sample was uniformly high (71-87%), and
increased with increasing burn intensitylfrequency.
This strongly suggests a trend toward species extir-
pation with burning.
A critical question in understanding the effect
of forest fires on forest composition and regional
biodiversity is: do fires select for certain species or
groups of species?Mortality rates among large stems
appear to be roughly equal for all species. This in-
dicates that advantages conferred to individual spe-
cies by fire resistent characteristicssuch as thick bark
(Uhl & Kauffman 1990) were largely swamped by
stochastic factors controlling the spatial distribution
and fire intensity within our study site. It is possible
that fire resistent species traits are significant only
for relatively light burns or at larger spatial scales
than in this study. Of the fourteen most common
non-pioneer speciesencountered in unburned forest,
all except one accounted for roughly the same per-
centage of live non-pioneer stems in burned forest
as in unburned (Table 3). One taxon, Leythis sp.,
increased slightly in relative abundance in burned
forest, although it decreased in stem density. Given
equal mortality rates, rare species will be more prone
to local extirpation than common species.
In attempting to understand the erosion of eco-
nomic resources directly caused by forest fires, the
fate of Mapranduba (Manilkara huberi) in our
study area is illustrative. This species is an impor-
tant and common timber species in the study re-
gion, with a relatively balanced population struc-
ture amenable to management (ie., with a large
juvenile and pole-sized population). In addition, it
is relatively thick-barked and is therefore predicted

11. 12 Cochrane and Schulze
TABLE 3. Relative ubundunces and densities of the fourteen most common tuxu in f.ur forest classes of Olho D X p u
region.
~~ ~ ~~~ ~~
Lightly Moderately Heavily
Unburned burned burned burned
Specics forest forest forest forest
Coupeiu guiunensis percent 2.2 4.3 3.5 5.0
no.lha 11.2 13.6 6.4 2.6
Eschweilera sp. percent 18.2 18.1 19.4 17.5
no.lha 92.6 57.4 35.5 9.1
Hieronymu sp. percent 1.6 0.7 3.5 1.3
no.lha 8.1 2.2 6.4 0.7
Ingu sp. percent 3.1 1.o 1.8 0
no./ha 15.8 3.2 3.3 0
Luuruceue sp. percent 9.6 16.1 6.6 6.3
no.lha 48.9 51.0 12.1 3.3
Lecythis lurida percent 5.5 6.6 9.7 5.0
no./ha 28.0 20.9 17.8 2.6
Lecythis spp. percent 13.4 17.4 14.5 26.3
no./ha 68.2 55.2 26.5 13.7
Licuniu sp. percent 3.0 1.3 1.8 0
no./ha 15.3 4.1 3.3 0
Munilkuru huberii percent 0.9 1.6 0 1.3
no.lha 4.6 5.1 0 0.7
Pouteriu spp. percent 7.2 5.6 5.7 5.0
no.lha 36.6 17.8 10.4 2.6
Rhinoreu sp. percent I .4 1.6 0 0
no./ha 7.1 5.1 0 0
huucupou americunu percent 3.1 6.3 5.7 5.0
no.lha 15.8 20 10.4 2.6
to be somewhat resistent to fire (Uhl & Kauffman
1990). Densities of large MaGarandubastems (>lo
cm DBH) in logged, unburned forest were 5/ha on
average. These densities were unaffected in lightly
burned forest (average 6/ha), but dropped dramat-
ically in more intensely burned forest (0 and 0.5/
ha in moderately and heavily burned forest, re-
spectively). As we observed a number of dead Ma-
Faranduba stems on the burned forest transects,
and as forest classes were intermixed along tran-
sects, these differences in density are unlikely the
result of pre-disturbance site variation. Saplings
(<lo cm DBH) of this species showed much high-
er susceptibility to fire. From a density of 37.5Iha
in unburned forest, MaGaranduba sapling density
dropped to 3.3/ha in lightly burned forest. No liv-
ing saplings were found in either moderately or
heavily burned forest. Thus, while adults showed
some tolerance to light burning, even one light
burn was enough to drastically reduce the sapling
pool, greatly increasing the time required for re-
placement of large individuals. High intensity
burns have the potential to reduce the local pop-
ulation to highly scattered adult trees, with no ad-
vanced regeneration and drastically reduced local
seed production.
BIOMASScHANGEs.--Whileprecise estimates of bio-
mass are not possible with our data, it was clear
that burning dramatically reduced livingforest bio-
mass. Using Brown et al.’s (1989) equation to con-
vert diameter measurements to estimates of above-
ground biomass, data from the ten transects suggest
that burned transects contained 30-80 percent of
the living biomass in unburned forest (Table 1).
When average biomass was calculated for the four
forest categories, lightly burned forest was shown
to contain roughly 90 percent of the livingbiomass
in unburned forest. Moderately and heavily burned
forests, however, averaged only 50 and 20 percent
respectively of the living biomass in unburned for-
est. The amount of dead standing biomass in-
creased from unburned through heavily burned
forest, but did not completely account for the dif-
ferences in living biomass among forest classes. To-
tal standing biomass in heavily fire-damaged forest
was still only 55 percent of that in unburned forest.
DISCUSSION
Forest fires in the study area have drasticallyaltered
forest structure. High postfire tree mortality rates
have significantly reduced canopy cover and have

12. Fire as a Recurrent Event in Tropical Forests 13
led to substantial increases in the density of small
pioneers and weedy vines. Species richness of all
but the most lightly burned forest patches has been
dramatically reduced, as has overall living biomass.
These results are consistent with other studies of
stand-level fire effects in the eastern Amazon (Uhl
& Kauffman 1990, Holdsworth & Uhl 1997)),
and the tropics as a whole (Woods 1989). Our
relatively extensive sampling approach, however,
has revealed the high degree of spatial variability
within the “burned forest class,” both among forest
patches and within a stand at small spatial scales.
In the study area, spatial variability can be at-
tributed to the following factors: (1) uneven spread
of fire through a stand, (2) variation in burn in-
tensity within a single burn (3)differences in burn
frequency between stands, and (4)postfire succes-
sional stage of stand. This extreme heterogeneity
within burned forests must be explicitly addressed
in any effort to model regional fire dynamics or to
estimate the consequences of fire to forest well-be-
ing.
Previous studies have focused on fires as a one-
time forest disturbance, either quantifying the role
of logging in increasing fire susceptibility of stands
(Uhl & Kauffman 1990) or measuring the effects
of single fires on forest structure and composition
(Woods 1989, Holdsworth & Uhl 1997). In our
study area, fire clearly has become a regular com-
ponent of the disturbance regime. While lack of
precise oral histories makes quantification of fire-
return rates impossible at this point, stands obvi-
ously are being subjected to repeated burning. Fire
susceptibility of these forests is in fact increasing
after the initial burn. If fire is considered a single
disturbance incident, predictions of the future of
burned forest areas are considerably more optimis-
tic than if fire is viewed as a cyclical disturbance
(Fig. 5).
According to our data, in areas subjected only
to a single low intensity burn, the forest can be
expected to lose the majority of its saplings and
vines, but only a small percentage of the canopy
trees. If fire-contacted living trees continue to re-
produce normally, seed input from mature forest
species should not be reduced substantially.There-
fore, assuming mature forest seedlingscan compete
with, or persist underneath, invading pioneer and
weed species, shade tolerant tree species may par-
tially restore the advanced regeneration pools with-
in a few years (if the area does not reburn). More
light demanding canopy species may even experi-
ence short-term increases in seedling densities fol-
lowing the burn. Even after a single light burn,
pioneer speciesappear to dominate regeneration for
at least the first year or so.
The above scenario is highly optimistic for the
Olho D’Agua region because of two reasons. First,
fire sources are constant or increasing from year to
year. Second, our data strongly suggest that burned
areas become more susceptible to repeat burns as
canopy cover decreases, understory moisture de-
creases, and fuel loads appear to increase.The high
frequency of forest patches that have burned mul-
tiple times within our study area supports the hy-
pothesis of a positive feedback loop between burn-
ing and fire susceptibility. Thus, without modifi-
cation of land-use practices in this area, it can be
expected that most stands that burn once will be
subjected to additional burns, with subsequent ero-
sion of forest structure and resources. We do not
yet know how representative the Olho D’Agua area
is of the eastern Amazon as a whole; it may be that
this region is anomalous or the extreme example in
a gradient of regional fire intensity and frequency.
However, it points to the critical need to charac-
terize the fire regime of the eastern Amazon. This
will require a regional assessmentof fire impact and
return rates and should ideally be linked to causa-
tive agents (e.g., climate, rainfall, economic incen-
tives, population density, fragmentation).
At a minimum, the Olho D’Agua region serves
as a sobering example of the potential for fire, in
concert with other disturbances, to impoverish and
transform forests on a grand scale. It is clear that
fire has become the dominant disturbance force in
the Olho D’Agua landscape. Virtually all forest in
this region has been subjected to selectivelogging,
which on average severely damages or kills 11.6
percent of the trees (>lo cm DBH)/ha and de-
creases average canopy cover by 8.1 percent (Uhl
et al. 1991).This disturbance, although substantial,
pales in comparison to damage caused by uncon-
trolled forest ground fires. After adjusting for av-
erage preburn logging damage, burning results in
an average stem mortality of 41 percent, reduces
canopy cover by over 40 percent, and destroys vir-
tually all of the understory vegetation.
A critical factor determining the capacity of
these forests to rebound from fire disturbance is the
stand-levelfire return interval (Fig. 5). If fire return
rates are high enough, this will result in near com-
plete replacement of the individuals in the regen-
eration layer following every fire, thus effectively
preventing any new regeneration from reaching re-
productive stature. As adults trees are culled with
every burn, local seed sources will disappear, ma-
ture forest species will be eliminated locally, and

13. 14 Cochrane and Schulze
,,
currently little understandingof
burning frequency in unlogged
_ - _ _
UnloggedUnburned
Forest
- -~ - -- time after logging
-- -&- --,;it at 70years
LoggedForest - - - - -
I~-- - - - ___
Early Successional
Vegetation *3
1
additional burning
within 1-5 years
I
forest recovery
estimatedat 70-100
years
A
forest recovery time
unknownconjectured
minimumof 150years
??
forest recovery time will
depend on burn size *b
L - - _ _ _ _ _ _ _ J
additional burningwithin
_ _ - _ _ _ - - ??
,/,'
, deflected succession77
Scrub Savanna77
- - - - - __
4 GOld Fields Dominated by
PantropicalWeeds '4
- _ _ ~ _
FIGURE 5. Conceptual model of fire impacts on Amazonian forests. Solid arrows represent forest degradation
catalyzed by fire. Unfilled arrows show forest recovery from fire damage assuming no additional fire disturbance. *1:
sapling layer destroyed, majority of vines killed, increase in pioneer seedling abundance, canopy cover and live adult
stem density reduced by 30-40 percent, mature forest seed sources still present. "2: sapling layer destroyed, canopy
cover and live stem density reduced by 70-80 percent, pioneers dominate understory, appearance of invasive vine and
grass species, availability of mature forest propagules dramatically reduced. *3: Canopy virtually destroyed, pioneer
species dominate and achieve reproductive status between burns, density of invasive species increases? *4: canopy
destroyed, pioneers do not reproduce prior to re-burn, seed bank is destroyed, pioneer colonization rates dramatically
reduced, invasive species proliferate? *a: based on calculations for sustainable rotation times using traditional logging
practices (Barreto et al. 1993) "b: for large burns, seed dispersal into burned area is predicted to be a limiting factor.
For smaller burns, recovcry should roughly be equal to recovery of abandoned agricultural plots (200-400 yr).
the pool of postfire colonizers will be reduced to
those species with long-range dispersal. Under this
scenario, the forest quickly degrades to a succes-
sional status equivalent to young, second growth
forest. For burns that cover large areas, succession
may be even slower than for second growth forest
on abandoned agricultural plots because of the
greater distance to mature forest seed sources. If
burns are frequent and intense enough, even pio-
neer species may be temporarily extirpated from
stands, as the seed bank is destroyed (4Uhl et al.
198l), and any seedlings present after burning are
killed prior to attaining reproductive status. At this
extreme, burned forest areas would be highly sus-
ceptible to colonization by invasive non-forest
plants (eg, grasses and weedy vines), and may
eventually resemble scrub-savanna. These highly
degraded areas already occur in our study area, as
typified by transect nine, having had virtually no
overstory and several dense patches of grass.
If fire return intervals are longer (.g,10-20
years), then some seedlings will be able to recruit
to size classes in which the chances of surviving a
burn are higher. Assuming that size-class specific
mortality rates are consistent among species, we
would expect faster growing species that achieve
reproductive stature rapidly will dominate the
stand, as adult stocks are depleted and slow-grow-

14. Fire as a Recurrent Event in Tropical Forests 15
ing seedlings and saplings are selected against. In
this scenario, forest structure and composition
might not be completely eroded, but composition
would shift dramatically in favor of pioneers and
light demanding canopy species.
To understand the effects of fire on regional
biodiversity, it will be important to determine the
relative roles of species characteristics (Uhl &
Kauffman 1990) and fire stochasticity in control-
ling species mortality rates. In our study area, the
high degree of spatial variability in fire intensity
may have dampened the evidence of species-level
fire resistence since the total number of stems in
the moderately and heavily burned areas is consid-
erably lower than in the lightly burned and un-
burned areas. Nevertheless, uncommon species
without effective long-range seed dispersal will be
the most likely to experience local extirpation due
to forest fires.
Other questions warranting attention are: what
are the size and landscape distributions of un-
burned forest fragments within areas subjected to
fire, and to what degree is the biotic integrity of
these “habitat islands” maintained? If these un-
burned fragments are common enough and of suf-
ficient size, they may play a key role as refugia for
at least a portion of the disturbance-sensitive, for-
est-dwelling animal species unable to inhabit fire-
damaged areas. In addition, burned forest adjacent
to unburned forest islands will be expected to ex-
perience more seed rain than areas distant from
mature forest seed sources, and subsequently,faster
rates of recolonization by “climax” tree species.
Future research on fire in the eastern Amazon
should concentrate on linking plot-based infor-
mation on fire history, damage, and vegetation re-
sponse with large-scale data from satellites (e.g.,
Landsat TM, SPOT, AVHREUNOAA). Only in
this manner will researchers be able to determine
the true magnitude of fire disturbance in the Am-
azon and model the effects of this new fire regime
on future forest structure, composition, and func-
tion.
We would like to stress the apparent positive
feedback between forest burning and fire suscepti-
bility. The findings of our study support the con-
ceptual model by Nepstad et al. (1995) showing a
potential positive feedback among deforestation,
drought, and fire. With regional precipitation ex-
pected to decrease because of deforestation (Salati
& Nobre 1991), the increasing importance of se-
lective logging (Verissimo et al 1932),and the al-
ready established fire susceptibility of logged forest
(Uhl & Kauffman 1990, Holdsworth & Uhl
1997), the stage is set for fire to become a serious
disturbance factor in the eastern Amazon. As more
areas burn, the chances for continued reburning
will increase. Olho D’Agua illustrates one outcome
of current land-use practices in the easternAmazon
and may foreshadow the future of the region’s for-
ests if these practices continue unabated.
ACKNOWLEDGMENTS
This research was funded by a grant from the PPG7-
“Programa de Pesquisa Dirigida” (MMA/MCT/FINEI’)
to the Instituto do Homem e Meio Ambiente da Ama-
zonia (IMAZON). We gratefully acknowledge Bruno Ri-
beiro da Silva, Orlando Lopes de Souza, and Raimundo
Antonio Pereira for help with data collection and Rai-
mundo Sugre Filho for help with logistics in Olho
D’Agua. We would also like to acknowledge Christopher
Uhl for commentary on earlier drafts of this manuscript.
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