Brush fire in Tanzania. (Photo by R. Butler)
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FIRES IN THE RAINFOREST
By Rhett Butler | Last updated July 27, 2012
Rainforests are increasingly susceptible to forest fires today due to degradation from selective logging, fragmentation, and agricultural activities. Scientists are concerned that much of the Amazon is at risk of burning, and that in the future we could see fires similar to those that so damaged Indonesia in recent el Niño years.
Today most rainforest fires originate in nearby pasturelands and agricultural fields where fires are used for land clearing and crop maintenance. Every year, during the burning season, tens of thousands of fires are set by land speculators, ranchers, plantation owners, and poor farmers to clear bush and forest. Under dry conditions these agricultural forests can easily spread into neighboring rainforest.
Low-level fires in the rainforest are not unusual. Even in "virgin" forests, fires may burn across thousands of acres of forest during dry years. The distinction between these fires and the fires that forests are increasingly experiencing today is the frequency of occurrence and level of intensity. Natural fires in the Amazon generally do little more than burn dry leaf litter and small seedlings. Typically these fires have flames that only reach a few inches in height and have virtually no impact on tall trees or the canopy itself. However, in passing, the fire sets the path for recurrent fires and subsequent forest loss. Once-burned forests are twice as likely to be deforested as unburned forests, largely because the initial fires—however small—thin out the canopy, allowing more desiccating sunlight to reach the forest floor. Previously burned forests, in addition to having more combustible material, are also often adjacent to fire-maintained pastures and therefore are frequently exposed to sources of ignition. Subsequent fires burn with increased velocity and intensity and cause higher tree mortality. Fires intervals of less than 20 years may eliminate all trees in the forest stand.
Under "normal" rainfall and humidity conditions most of these fires are extinguished by the arrival of the rainy season or monsoon. Usually virgin forests serve as a sort of humid barrier which prevents the spread of agricultural fires. However, under dry conditions—such as those of an el Niño year—fires can spread from pastures and fields into primary forest. In the 1990s, 90 percent of burning in the Brazilian Amazon occurred in El Niño years.
The unusually strong El Niño of 1997-98 contributed to massive forest fires. In the Amazon, humidity in the Basin was 45-55 percent lower than usual and the Woods Hole Research Center estimated that 400,000 square kilometers of forest could go up in smoke during the burning season.
In early 1998, some of these fears materialized as 13,200 square miles (34,000 square km) of Roraima state in northern Brazil burned. The fires, started by subsistence farmers, spread rapidly across the dry savanna and advanced into rainforest usually too humid to burn. As many as 3,800 square miles (10,000 sq km) of intact rainforest were damaged or destroyed by these fires. The government firefighting efforts had virtually no effect and it was only freak heavy showers that extinguished the flames.
Dry conditions again returned in 2005, when the Amazon experienced the worst drought in recorded history. As rivers went dry and communities were left stranded, tens of thousands of fires burned. That calamity was topped in 2010 by an even worse drought that affected a million square kilometers of Amazon forest. In both of these droughts, dry conditions were linked not to El Niño but to warm temperatures in the tropical Atlantic Ocean, raising fears that climate change could worsen droughts in the Amazon.
Besides destroying the rainforest ecosystem and killing wildlife, these fires create other environmental problems. The "burnings" release thousands of tons of carbon into the atmosphere and the smoke produced causes local airport closings and hospitalizations for smoke inhalation. These fires are significant sources of greenhouse gases. For example, in a four-month period (July-October) in 1987, about 19,300 square miles (50,000 sq. km) of the Brazilian Amazon burned in the states of Para, Rondonia, Mato Grosso, and Acre. The burning produced carbon dioxide containing more than 500 million tons of carbon, 44 million tons of carbon monoxide, and millions of tons of other particles and nitrogen oxides.
The tropical forest fires that have made headlines of late will only worsen as more forest is degraded and the area of previously burned forest expands. A study by IMAZON (the Institute for Man and Nature in the Amazon) found that for every acre burned or cleared which shows up on satellite, at least one-acre burns undetected under the forest canopy. These leaf-litter fires can burn for months with warm temperatures and little rain, and subsequent fires in these previously burned areas are more intense and destructive.
Other studies have warned that climate change could significantly dry forests in the Amazon Basin and Africa, increasing their risk of burning. In light of this potential scenario and to better understand the impact of extended drought in the Amazon and the resilience of the forest to fire, the Woods Hole Research Center and NASA are have conducted an extensive series of large-scale experiments in the Brazilian rainforest. Separate findings from NASA suggest that heavy smoke from Amazon forest fires inhibits cloud formation and reduces rainfall. This conclusion, combined with other NASA studies suggesting that deforestation can affect regional climate, means that the Amazon rainforest may be on the verge of a significant environmental transformation—one that will increasingly leave the ecosystem vulnerable to fire.
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Indigenous tribes say effects of climate change already felt in Amazon rainforest
(04/30/2013) Tribal groups in Earth's largest rainforest are already being affected by shifts wrought by climate change, reports a paper published last week in the British journal Philosophical Transactions of the Royal Society B. The paper, which is based on a collection of interviews conducted with indigenous leaders in the Brazilian Amazon, says that native populations are reporting shifts in precipitation patterns, humidity, river levels, temperature, and fire and agricultural cycles. These shifts, measured against celestial timing used by indigenous groups, are affecting traditional ways of life that date back thousands of years.
Frequent understory fires change rainforest community composition
(04/24/2013) Frequent understory fires change the composition of rainforest plant communities, potentially altering the capacity of forests to regenerate, finds a study published in special issue of the journal Philosophical Transactions of the Royal Society B.
Burned rainforest vulnerable to grass invasion
(04/24/2013) Rainforests that have been affected by even low-intensity fires are far more vulnerable to invasion by grasses, finds a new study published in special issue of the journal Philosophical Transactions of the Royal Society B. The findings are significant because they suggest that burned forests may be more susceptible to subsequent fires which may burn more intensely due to increased fuel loads.
Forests under fire: Australia's imperiled south west
(03/05/2013) In the far southwestern corner of Western Australia, beyond the famed wineries in the shadow of the Margaret River, lies an ecosystem like no other, the South West ecoregion. This part of Australia has been identified as one of 34 global biodiversity hotspots, home to rare endemic flora and fauna like the Carnaby's black cockatoo, numbat (banded anteaters), woylie (brush-tailed bettong), mainland quokka and over 1500 plant species, most found nowhere else. Unfortunately, this unique habitat is being increasingly fragmented and its inhabitants threatened by a number of forces, including climate change, dieback, fires and logging. And, on the eve of the Western Australia's state elections, the future of the South West hangs in the balance.
Forests worldwide near tipping-point from drought
(11/23/2012) Forests worldwide are at 'equally high risk' to die-off from drought conditions, warns a new study published this week in the journal Nature. The study, conducted by an international team of scientists, assessed the specific physiological effects of drought on 226 tree species at 81 sites in different biomes around the world. It found that 70 percent of the species sampled are particularly vulnerable to reduction in water availability. With drought conditions increasing around the globe due to climate change and deforestation, the research suggests large swathes of the world's forests — and the services they afford — may be approaching a tipping point.
More news on forest fires
More rainforest news
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(06/03/2010) While rates of forest loss in the Brazilian Amazon have been on the decline since 2004, the incidence of fire is increasing in the region, undermining some of the carbon emissions savings of reduced deforestation rates, report researchers writing in the journal Science. The paper argues that REDD, a global plan to reduce deforestation and forest degradation, must include measures to eliminate the use of fire from land management in the Amazon.
(03/05/2009) Drought in the Amazon is imperiling the rainforest ecosystem and global climate, reports new research published in Science. Analyzing the impact of the severe Amazon drought of 2005, a team of 68 researchers across 13 countries found evidence that rainfall-starved tropical forests lose massive amounts of carbon due to reduced plant growth and dying trees. The 2005 drought — triggered by warming in the tropical North Atlantic rather than el Niño — resulted in a net flux of 5 billion tons of carbon dioxide (CO2) into the atmosphere — more than the combined annual emissions of Japan and Europe — relative to normal years when the Amazon is a net sink for 2 billion tons of CO2.
(02/22/2009) Destruction of rainforests and peatlands is making Indonesia more susceptible to devastating forest fires, especially in dry el Niño years, report researchers writing in the journal Nature Geoscience. Constructing a record of fires dating back to 1960 for Sumatra and Kalimantan (on the island of Borneo) using airport visibility records to measure aerosols or "haze" prior to the availability of satellite data, Robert Field of the University of Toronto and colleagues found that the intensity and scale of fires has increased substantially in Indonesia since the early 1990s, coinciding with rapid expansion of oil palm plantations and industrial logging.
(03/26/2008) Remote sensing is increasingly used as a tool for conservation management. Beyond traditional satellite imagery popularized by Google Earth, new sensing applications are allowing researchers located anywhere in the world to track fires, illegal logging and mining, and deforestation in some of Earth's most isolated regions using a computer or handheld device. The Fire Alert System is one example of an application that is harnessing the power of satellites to deliver key data to conservation managers. Developed by Madagascar's ministry of Environment, the International Resources Group, conservation International using data from the University of Maryland and NASA, the Fire Alert System enables near real-time monitoring of fires anywhere on the island of Madagascar, a hotspot of biological diversity. The system, which sends subscribers regular email alerts on newly-detected burning, will eventually be expanded to include all the world's protected areas, allowing managers to detect not only fires but potentially related activities like road building, logging, and even hunting.
(02/27/2008) More than half the Amazon rainforest will be damaged or destroyed within 20 years if deforestation, forest fires, and climate trends continue apace, warns a study published in Philosophical Transactions of the Royal Society B. Reviewing recent trends in economic, ecological and climatic processes in Amazonia, Daniel Nepstad and colleagues forecast that 55 percent of Amazon forests will be "cleared, logged, damaged by drought, or burned" in the next 20 years. The damage will release 15-26 billion tons of carbon into the atmosphere, adding to a feedback cycle that will worsen both warming and forest degradation in the region. While the projections are bleak, the authors are hopeful that emerging trends could reduce the likelihood of a near-term die-back. These include the growing concern in commodity markets on the environmental performance of ranchers and farmers; greater investment in fire control mechanisms among owners of fire-sensitive investments; emergence of a carbon market for forest-based offsets; and the establishment of protected areas in regions where development is fast-expanding.
(11/07/2007) While the mention of Amazon destruction usually conjures up images of vast stretches of felled and burned rainforest trees, cattle ranches, and vast soybean farms, some of the biggest threats to the Amazon rainforest are barely perceptible from above. Selective logging -- which opens up the forest canopy and allows winds and sunlight to dry leaf litter on the forest floor -- and 6-inch high "surface" fires are turning parts of the Amazon into a tinderbox, putting the world's largest rainforest at risk of ever-more severe forest fires. At the same time, market-driven hunting is impoverishing some areas of seed dispersers and predators, making it more difficult for forests to recover. Climate change -- an its forecast impacts on the Amazon basin -- further looms large over the horizon.
