From: Meerman J.
C. & W. Sabido 2001. Central American Ecosystems Map:
Belize. Volume 1.
Fire as a threat to biodiversity and the status
of the vegetation, is not well understood. The frequency,
magnitude and effects that wildfires have had on biodiversity
in Belize have not been documented. However, the dimensions
of areas destroyed during these fires strongly imply major
destruction of flora and fauna" (Rosado in: Jacobs
& Castaneda, 1998). The ecological consequences of fire
in natural ecosystems are many and have been listed by Wade
et al (1980).
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Fires in broadleaf forests are often ignored
and bear no resemblance to the massive blazes that can
be seen in burning needle-leaf forests. The fire is
usually low, and slowly creeping through the leaf litter.
Often it is possible to walk close up to it and even
through it without too much danger. There is usually
little "media value" in such fires. Only in
areas with Cohune (Attalea cohune), the effects
can be more dramatic. The abundant leaf litter under
these palms explodes into flames, often igniting the
crown and spraying sparks over great distances. But
even in the case of these slow, low fires, the damage
can be profound. Trees, especially young trees may appear
unharmed but still die over time. The mortality either
being the result of direct damage or indirect damage
such as increased pathogen access through the fire damaged
bark. |
Tree mortality as the result of such slow
fires may continue for several years after the actual fire
(pers. obs.). Each fire, which leaves more dead or dying
trees behind makes the forest even more prone to fire damage.
Fire in broad-leaved forest is a relatively
rare phenomenon. It is argued that in Central America most
species of trees have evolved in the absence of fire and
thus developed little tolerance for it (Budowski, 1966,
Hopkins, 1983). Actual documentation of lowland broadleaf
forest fires started by lightning is rare (Middleton et
al., 1997). Consequently, fire in tropical lowland forests
has traditionally been considered as human induced (Janzen,
1986; Koonce & Gonzalez-Caban, 1990). This view was
also taken by the TFAP team when considering the causes
for fire in the Southern Coastal Plains (ODA, 1989). This
is also the reason why fires are treated here as part of
the human impact factor. On the higher peaks of the Maya
Mountains, however, lightning strikes appear to be the major
cause of forest fires. Nearly 2/3 of the fires recorded
in the Mountain Pine Ridge Forest Reserve are reportedly
caused by lightning strikes (ODA, 1989).
Wolffsohn (1967) suggested that about once
in every five or ten year the dry season in Belize is intense
enough to create hazardous conditions. The vegetation is
generally too damp to burn easily. This is especially the
case in "real" rainforest but evidence of rainforest
fires (dating many thousands of years back) has been collected
throughout the tropics (Bassini & Becker, 1990; Horn
& Sanford, 1992). Many of these large fires show a relation
to human presence and it is often assumed that early man
was directly or indirectly responsible for these fires (Horn
& Sanford, 1992).
It is generally accepted that once every one
or two centuries a series of abnormally dry years without
rainy seasons dramatically increase the fire hazard on otherwise
fireproof tropical rainforests (Jacobs, 1988). There are
indications that the incidence of rainforest fire is on
the increase worldwide. In 1982, 1983, 1992, 1993, 1997,
1998 and 2000, large surfaces of rain forest burned throughout
the tropics. This increase is most likely caused by increased
human encroachment on the forest and by the phenomenon of
global warming (which is expected to lead to more erratic
weather patterns including more frequent droughts). This
is especially worrisome since these wildfires are gaining
importance to the volatilization of gasses such as N2, N20,
CH4, CO2 and other greenhouse gasses, i.e. those that contribute
to global warming (Lugo, 1995). Fires are most devastating on hills where
an upward draft creates extremely hot fires towards the
top of the hill. Fire affected hills; therefore, show the
greatest damage towards the summit. Repeated hill fires
result in "bald" hills with no woody vegetation
but a cover of grasses or "Tigerbush" (the ferns
Dicranopteris and Pteridium caudatum).
The influence of fire is clearly greatest where there is
drought stress and highly inflammable vegetation is present.
Fire induced vegetation in hilly areas
are especially at risk since the fire resistant vegetation
has a lesser capacity of retaining the soil and increased
erosion is the result (Jacobs, 1989).
In the early days of the Forest Department it was noted
that fire kept broad-leaved forest species from invading
and replacing pine on soils which otherwise might have
carried high forest. Nevertheless, pines are liable
to be killed by fire when they are less than 3 m tall
and are liable to damage at any age and size. The old-growth
pines on the Southern Coastal Plain are frequently fire-scarred,
internally and externally. The damage allows the ingress
of wood-rotting fungi and termites and materially reduces
the net yield (ODA, 1989).
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Data from the Forest Department over the period
1963-1970 for the hills of the Mountain Pine Ridge Forest
Reserve (Cayo district) indicate that out of 46 recorded
fires during that period, 29 (63%) were reported to have
been caused by lightning. The remaining 17 fires (37%) were
caused by human agency. In the northern Coastal Plain of
Belize, the great majority of the lowland fires are caused
by arson, by hunters after game (ODA, 1989, pers. obs.).
In contrast, in the pine barrens of Florida, lightning strike
is a frequent cause of fire (Lugo, 1995).
The combination of infrequent lightning strikes
and a degree of fire adaptation in the savannah and needle-leaf
community indicates that fire is a natural part of the Belizean
savannah ecosystem, probably helped by the droughtiness
of the vegetation and naturally occurring more frequently
than in broadleaf forest. That said, the natural savannahs
would be much smaller in extent and not burnt so often as
is presently the case.
The Belizean Forest Department has had little
success in fire control, even in the pine plantations. The
staffing and equipment of the Forest Department have been
so reduced that the fire protection scheme (Johnson, 1974)
has never been implemented successfully. The priority areas
for fire control outlined in the fire protection scheme
have been so affected by wildfire that the stocking of healthy
live trees appears to have been reduced below any level
that would justify the expense (ODA, 1989).
Belize has experienced massive fires in broad-leaved forest
after hurricanes, which cause large amounts of debris. Initially,
these fires are usually started by farmers and may be accidental
escapes from farm clearings. The debris caused by the hurricane
is such that access and movement for firefighters is very
difficult. Consequently, these fires are difficult to suppress
unless they can be reached at a very early stage. Fire in
broad-leaved forest may stimulate the regeneration of mahogany
and cedar but more usually there is complete destruction
of forest and replacement by persistent bracken, which is
itself a fire hazard (Johnson & Chaffey 1973).
For the same reason selective logging practices
also create favorable conditions for the spread of wildfires.
Not only do the discarded crown and branches provide fuel
for fires, also the resulting scrubby growth following the
opening of the canopy is usually more incandescent than
the original forest.
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More than anything, slash and burn agriculture has
to be seen as the main culprit for fires in lowland
broadleaf forests. In general the subsistence farmer
has little consideration for the well being of the
forest and most farmers do not take escaped "milpa"
fires seriously. And the 1998 effort by PFA (1998)
clearly shows that most fires occurred near human
habitation (Figure left), this map also shows that
the fire intensity is higher in neighboring countries
where the human pressure is higher.
Observations in the field show that burned hill tops
are virtually always connected with agricultural clearings
in at the foot of the same hill. The only noteworthy
exceptions seem to be some fire damaged areas well
away from any activity on a hillcrest of the Maya
Mountains. Lightning strike is the most plausible
explanation for these burned areas although agriculture
is present at the feet of some of these same hills
and fire-creep below the canopy remains a distinct
possibility.
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Concluding, the importance of fire in the Belizean ecosystems
has largely been downplayed but is probably of major, and
increasing, significance. More investigations are needed
to establish the actual impact and possible measures to
prevent the damage caused.
Wildfire Risk: a model
In an effort to predict fire risk, a fire risk map was
developed using ecosystem characteristics. Recently this
first fire risk map was updated in 2004 as part of the National
Protected Areas Policy and Systems Plan (NPAPSP). This
update takes into account a larger number of variables such
as:
- High incidence of Cohune (Attalea cohune) palms
which are highly flammable (ecosystem factor)
- A 500 m buffer zone around (pine) savanna indicating
high risk of fire penetration in surrounding ecosystems
(ecosystem factor)
- Mechanized agriculture with 500 m buffer indicating
medium risk of fire penetration in surrounding ecosystems
(social factor)
- Non-mechanized agriculture with 1000 m buffer indicating
high risk of fire penetration in surrounding ecosystems
(social factor)
- Human settlements with 6 km buffer and fire risk class
value based on poverty data of 2000 population census
(social factor)
- Areas with slopes of > 10% (higher risk)
- Rainfall isohyets for Belize (high rainfall > lower
risk)
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This fire risk map (map to the left, click
for larger image) is highly theoretical but with the availability
of MODIS
fire data it was possible to test the theory
behind the fire risk map with the reality of annual fires
and the this comparison is presented above as well (map
to the right, click for larger image)(but this is changed as a result of hurricane damage as was the case in 2011). Clearly the actual
fire situation shows a very strong correlation with the
theoretical risk. Some "unexpected" fires do occur
in "low" and "medium" risk areas, but
it appears that in most of these cases, agricultural expansion
is the main driver behind this. Clearly the model does not
well in predicting agricultural expansion. Otherwise the
model seems to represent actual fire-risk very well.
Read on the 2005
fire season
Read on the 2006 fire season
Read on the 2007 fire season
Download report on the dramatic 2011 fire season
LITERATURE
Bassini, F. & P. Becker. 1990. Charcoal's occurrence
in soil depends on topography in terra firme forest near
Manaus, Brazil. Biotropica 22(4): 420-422.
Budowski, G. 1966. Fire in tropical lowland areas. Proceedings
of the annual tall timbers fire ecology conference. 5: 5-22.
Chazdon, R. L. 1998. Phoenix Rising? Fragility and resilience
of tropical forests. Tropinet 9(3)
Dwyer, J.D. & Spellman, D.L. 1981. A
list of the dicotyledoneae of Belize. Rhodora 83 (834) pp
161-235.
Hopkins, B. 1983. Succesional processes. In: F. Bourliere
(ed.). Tropical Savannas. Pp. 605-616. Elsevier, New York.
Horn, S. P. & R. L. Sanford. 1992. Holocene
fires in Costa Rica. Biotropica 24(3): 354-361.
Jacobs, M. 1988. The Tropical Rain Forest,
a first encounter. Springer Verlag. 295 pp.
Jacobs, N. D. & A. Castaneda.
1998. The Belize Biodiversity Strategy. Belmopan 2 vols.
Janzen, D. H. 1986. Guanacaste National
Park: Tropical ecological and historical restoration. Editorial
Universidad Estal A Distancia, San Jose, Costa Rica.Ef
Johnson, M. S. 1974. The Belize Forest Department Southern
Coastal Plain Fire Protection Scheme. Land Resources Division.
MoD, Misc. report 187.
Johnson, M. S., and D. R. Chaffey. 1973.
An inventory of the Chiquibul Forest Reserve, Belize. Land
Resource Study No. 14. Land Resources Division, Surrey,
UK.
Kauffman, J. B. 1991. Survival by sprouting following fire
in the tropical forests of the eastern Amazon. Biotropica
23(3): 219-224.
Koonce, A. L. & A. Gonzalez-Caban. 1990. Social and
ecological aspects of fire in Central America. In: J. G.
Goldammer (Ed.). Fire in tropical biota. Pp. 135-158. Springer
Verlag, Berlin.
Lugo. A. E. 1995. Fire and Wetland Management. In: Cerulean,
S. and R. T. Engstrom (eds.). 1995. Fire in wetlands: a
management perspective. Proceedings of the Tall Timbers
Fire Ecology Conference, No 19. Pp. 1-9. Tall Timbers Research
Station, Tallahassee, FL.
Middleton, B. A., E. Sanchez-Rojas, B. Suedmeyer
and A. Michels. Fire in a tropical dry forest of Central
America: A natural part of the disturbance regime? Biotropica
29(4): 515-517.
ODA. 1989. Belize Tropical Forestry Action
Plan. 273 pp.
PFA. 1998. Atlas Centroamericano de incendios.
Programma de desarollo sostenible en zonas de frontera agricola.
51 pp. Panama.
Wade, D., J. Ewel And R. Hofstetter. 1980.
Fire In South Florida Ecosystems. USDA Forest Service General
Technical Report SE-17. Southeastern Forest Experiment Station,
Asheville, North Carolina.
Wolffsohn, A. F. A. 1967. Post-Hurricane
Forest Fires in British Honduras. Commonwealth Forestry
Review 46(3): 233-238.
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