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Origin,
Incidence, and Implications of Amazon Fires |
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Updated
12 October, 2003
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Origin,
Incidence, and Implications of Amazon Fires USGCRP Seminar, 30 March 1998  |
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INTRODUCTION: Dr. William T. Sommers
SPEAKERS: Dr. Daniel Nepstad
Dr. Compton J. Tucker
Overview
More than 12% of the 2 million
square miles of Brazilian Amazonian forest has been deforested and converted
to crop- and pastureland. In 1995 alone, an area of forest the size
of Maryland was cleared and burned. In addition to this most extreme
form of forest alteration, large areas of Amazonian forest have been
selectively logged or burned beneath the canopy, beyond the view of
deforestation mapping exercises. Both deforestation and forest impoverishment
through logging and ground fire greatly increase the incidence of fire
in Amazonia, because these land-use activities replace the tall, dense,
naturally-resistant virgin forests with agricultural lands and degraded
forests that are highly flammable. During the seasonal drought that
affects half of Amazonia, many of these flammable ecosystems burn. When
seasonal drought is very severe, such as during the El Nino event of
1997/98, even virgin forests become more vulnerable to the ravages of
fire. Hence, a significant portion of the northern Amazonian state of
Roraima has burned in the 97/98 dry season, and continues to burn now,
in March. On a broader scale, the NOAA satellite detected 50% more Amazonian
fires in 1997 than in 1996.
Tropical forests also store
large amounts of CO2, and therefore play a key role in regulating
the world's climate. Mostly as a result of deforestation, Brazil now
accounts for nearly 10% of the world's greenhouse gases being emitted
into the atmosphere -- an amount comparable to many developed countries.
Burning half the Amazon, for example, would release roughly 35 billion
tons of CO2 into the atmosphere, the equivalent of approximately
6 years' worth of greenhouse gas emissions for the entire world. Unfortunately,
as a result of land-use influences and practices, much of the Amazon
is also losing its natural capacity to protect itself from fires, as
well as losing its capacity to store carbon and, therefore, limit future
climate warming.
Yes. The deforestation rates for the Brazilian Amazon that were recently released by the Brazilian Space Research Institute (Instituto Brasileiro de Pesquisas Espaciais - INPE) show that the area of forest cut and burned nearly doubled from 1994 (15,000 km2) to 1995 (29,000 km2). In 1996, the rate declined again, to 18,000 km2, and early analysis indicates that 1997 rates of deforestation were comparable to 1994 rates. All of these deforestation rates are much higher however, than the rates reported in 1992, when only 11,000 km2 of forest were cleared each year.
The INPE deforestation monitoring program provides the most reliable estimate of the areal extent of forest conversion to agriculture and ranchland in the Brazilian Amazon, which is the most extreme form of forest conversion. However, these estimates do not include alterations of the forest through selective timber harvest and forest ground fire. These land-use activities impoverish the forest by killing trees and animals, by releasing CO2 to the atmosphere, and by rendering the forest more vulnerable to fire. Studies conducted in the field indicate that the area of forest altered by timber harvest and ground fire may be similar in size to the area that is deforested during some years.
The Amazon Institute of Environmental Research (Instituto de Pesquisas Ambientais da Amazonia - IPAM) and the Woods Hole Research Center (WHRC) conducted a field survey in 1996 of five regions in the Brazilian Amazon where intensive deforestation and logging have taken place. This study provides the first detailed analysis of types of burning that are taking place in the region. This study indicates that the area of an average property burned each year ranged from 5% (properties less than 5,000 hectares) to 19% (properties greater than 100 hectares) in 1994 and 1995. Deforestation--the outright cutting and burning of mature forest--was responsible, on average, for only 16% of the total burned area, while 73% percent of the burning is on land that is already deforested and supports pastures, secondary fallow forests, and other types of non-forest vegetation. Eleven percent of the burning is beneath the canopy of standing forests. This last type of burning, which is called forest ground fire, is difficult to monitor using satellites. During years of intense drought, the areal extent of forest ground fire generally increases dramatically.
The virgin forests of Amazonia currently act as giant firebreaks through the landscape, preventing the spread of fires ignited in pastures and agricultural clearings. If virgin forests lose this fire-break function, then large Amazonian landscapes will burn periodically, killing fire-sensitive plants and animals, reducing the amount of biomass stored in these forests by 10Ð80%, and reducing the amount of water pumped into the atmosphereÑmoisture that is necessary to maintain the water and rainfall cycles. In addition to losing forest cover, fire also destroys timber and other "useful" plants such as vines (for construction), medicinal plants, and fruit trees. Each time a forest burns, it becomes more susceptible to future burning, because trees are killed and fuel is introduced to the forest floor. The major risk from fire is therefore the conversion of large areas of dense Amazonian forest into savanna-like scrub forest.
Both logging and drought are increasing the flammability of Amazonian forests. Each year, an area of Amazonian forest is logged that is similar in size to the area that is deforested (Source: IMAZON). Logging increases the flammability of these forests by opening up the leaf canopy, allowing sunlight to penetrate to the fuel layer on the ground, and by increasing the fuel load through the production of woody debris. Even virgin forests become flammable when drought is severe. Most forests in eastern and southern Amazonia (half of the 2 million square miles of closed canopy forest in Brazilian Amazonia) are subject to severe dry seasons each year, but grow on deep clay soils that store water which trees can tap during dry seasons to avoid drought-induced leaf shedding. These forests are at the "edge" of the rainfall regime that is necessary for them to be forests, and to resist fire, and are very sensitive to slight reductions in rainfall. Droughts in Amazonia are most severe during El Nino Southern Oscillation (ENSO) events, and El Nino's appear to be increasing in frequency and intensity. The most intense El Nino in recorded history is taking place right now.
One of the most promising approaches to reducing fires is to prevent or drastically reduce the number of accidental fires. Half of the area burned in 1994 and 1995 resulted from accidental fires. Accidental fires resulted in very large financial losses and extensive environmental damage. For example, in well-managed cattle pastures, cattle cannot be grazed on burned pastures until 2 or 3 months into the rainy season. Fires have damaged fences, killed livestock, burned fruit trees, and threatened human health. The owners of large ranches (greater than 1,000 hectares) in Amazonia invest an average of more than $2,000/year in bulldozing fire breaks to prevent their pastures and forests from catching fire. Accidental fires cost these ranchers more than $5,000/year in lost grazing and damaged fences. The owners of small properties (less than 100 hectares) incur proportionate costs associated with accidental fire. The 9,000-hectare Del Rei community, in eastern Amazonia, has come up with a very promising local approach to the prevention of accidental fire. This farm community has implemented its own fire ordinance, which requires community members to (1) use fire breaks before they burn in preparation for agriculture, (2) tell neighbors when they are burning their agricultural plots, and (3) compensate those neighbors who suffer losses because of their fires. Reductions in the occurrence of accidental fires can be achieved through good communication between neighboring landholders and through local forms of governance.
Dr. Daniel Nepstad is a tropical forest ecologist specializing in the effects of drought on Amazon forests, and in forest recovery following land abandonment. He has been a scientist at the Woods Hole Research Center since 1990. In 1995, he co-founded the Amazon Institute of Environmental Studies (Instituto de Pesquisas Ambientais da Amazonia) based in Belem, Brazil, which is now the largest non-governmental research institution in Amazonia. Dr. Nepstad has also been conducting field research in Amazonia since 1984, and during that time has documented the precarious water balance of vast areas of Amazonian forest. His current research efforts are focused on the prediction of fire risk in Amazonia, including the rainfall regime at which Amazon forests become vulnerable to fire, and the land-use patterns that are most likely to ignite fire-prone forests. Dr. Nepstad and his colleagues are also engaged in identifying possible solutions to the problem of Amazon burning, through research with farm communities and ranchers, and through dialog with government policymakers in Brazil. In recognition and support of this application of science to public affairs in Brazil, Dr. Nepstad was awarded a Pew Fellowship in Conservation and the Environment in 1994. Dr. Nepstad has a Ph.D. from Yale University, CT, an M.S. from Michigan State University, MI, and a B.A. from Kalamazoo College, MI.
Dr. Compton Tucker first came to NASA/Goddard in 1975 as a National Academy of Sciences post-doctoral fellow, and later joined NASA as a scientist in 1977. From 1975-1980, he concentrated on data collection and analyses using spectrometer data and hand-held radiometers. Since 1980, Dr. Tucker has used NOAA and Landsat satellite data for studying vegetation dynamics including deforestation, desert boundary determination, and terrestrial primary production. He is presently working on describing African and Asian arid and semi-arid vegetation dynamics using daily satellite data from 1981-1998; continuing work on deforestation and habitat fragmentation in the Amazon; studying the relationship between precipitation and grassland production in the Sahelian Zone of Africa; and studying higher northern latitude photosynthetic increases from 1981-1998. Dr Tucker received his B.S. in biological science in 1969 from Colorado State University in Ft. Collins, CO. He later received an M.S. (1973) and a Ph.D. (1975) from the Colorado State University's College of Forestry.
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