Throughout most of the world the worst enemy of the forest is considered to be fire. It has special uses, under expert control as a management tool (clearing fuel by control burning, removing debris from clearing operations, back-burning for fire suppression), but otherwise fire destroys wildlife, damages timber resources, weakens trees, paves the way for attack by insects and diseases, and increases soil deterioration and surface run-off of water. The burning of standing forest can release 10 to 80% of forest biomass to the atmosphere as heat - trapping carbon dioxide and particulate air emissions. Forest fires also threaten local communities, destroying lives and property. More indirectly, they damage watersheds and recreational resources.
A major consequence of forest fires is their potential impact on global atmospheric problems, including climate change. Only in the past decade have researchers realized the important contributions of biomass burning to the global budgets of carbon dioxide, methane, nitric oxide, tropospheric ozone, methyl chloride and elemental carbon particulates.
Forest fires have raged periodically throughout history. However, in the last couple of years, due to a variety of factors, including human activities, the prevailing weather and severe degradation of natural resources, their frequency and intensity seems to have increased, particularly in the Amazon and Southeast Asia.
Climate and the nature of the forest are important determinants of the incidence of forest fires. Coniferous forests burn much more readily than broad-leaved forests. The boreal forest region dominated by evergreen conifers regularly experiences some of the most extensive natural and human-caused forest fires on earth. For the period 1981-1989 an estimated 3.0 million ha burned annually in the former Soviet Union, nearly all in the taiga region of Russia. Satellite observations suggest this is greatly underestimated (since fires are monitored only on protected forest and pasture lands) and is more like 14.5 million ha for the 1987 season alone. In the same fire season about 1.3 million ha of forests were affected by fire in the montane-boreal forests of Northeast China, south of the Amur (Heilongjiang) River. During the 20th century Canada has experienced about 1 million hectares burned annually in forest regions, the great majority in the less accessible boreal forest in the north and west of the country. In Canada, over the past two decades, an average of 9000 fires have occurred yearly, burning an average of 2.8 million hectares annually, although annual area burned is highly episodic, and has varied by an order of magnitude (eg 0.67 million hectares in 1997, 7.28 million hectares in 1995). Likewise, in years with prolonged hot and dry periods of summer weather, Alaska experiences millions of hectares burned, mostly in a few very large fires.
Fires are common wherever there is a long dry season (such as in parts of Latin America and Africa) and especially where thunderstorms are accompanied by little rain (such as in parts of Asia and North America). Wildfire is most common in drier tropical forests, and uncommon where forests are divided into small, isolated units as in central Europe.
Natural wildfires are virtually unknown in the humid tropical evergreen forests and may, under exceptional circumstances, destroy tropical evergreen forests (as happened in Ivory Coast and Samoa). However in 1991-92 and again in 1995-97, hundreds of fires were alight for several months in Indonesia's tropical rainforests on Kalimantan (Borneo) and Sumatra, fuelled by burning underground peats and coal seams and highly inflammable debris from questionably managed logging operations (which may explain the Indonesian government's long silence before seeking help). The fires spread over 10 million hectares, causing losses of $9 billion. The fires recurred on a smaller scale in 1998 and cost Indonesia's neighbours an estimated $4 billion through disruption of tourism and transport as well as damage to public health. In 1999 the haze was still recorded at "extremely dangerous levels" in Sumatra.
In addition to the Indonesian fires, for six months in 1997 the fires blanketed an area of about 3 million square kilometres, which included Singapore, Brunei much of Malaysia, parts of Thailand, the Philippines and Australia. During 1997-98 the worst fires on record also raged in the Amazon rainforests of Brazil. They threatened the lives and crops of the Yanomami, who are also suffering from a lack of water. The damage to the environment was incalculable; it is estimated that the forest will take at least 100 years to recuperate.
The forests of Southeast Asia and of the Brazilian Amazon were especially vulnerable to fire in 1997 and 1998 because of a severe drought probably related to the strong El Niño of the same period and/or changing global weather patterns. After the severe El Niño of 1982, the largest fires then on record raged across Kalimantan. The 1997 and 1998 fires were far more extensive and coincided with an even more severe El Niño.
Despite the fact that hundreds of millions of dollars were spent to save the rain forest, burnings in Amazon region were up 28 percent in 1996, according to satellite data, and deforestation increased by 34 percent between 1991 and 1994. Roughly a fifth of the fires that rage annually between June and October cause new deforestation, and another 10th is burning off ground cover in virgin forests.
The recent prevalence of massive forest fires in certain countries is attributed to commercial logging, the rapid expansion of plantations and government sponsored transmigration programmes. Taking advantage of the dry conditions fires are started to clear land for agricultural use. There is a scramble for land at the forest frontier. Extinguishing the fires is costly and inefficient; the best solution is prevention. Effective reform is difficult in countries like Indonesia, where government rules are laxly applied or not enforced at all, especially in remote areas.
Extensive information on the incidence, causes and costs of forest fires is only available for the USA. Private, state and federal agencies spend US $300 million annually for controlling and preventing fire on 400 million hectares of forest and watershed lands. During the period 1957-66 in the USA, there were over 1 million forest fires covering more than 18.6 million hectares. Annually 100,000 - 150,000 fires burn 1.6 - 3.2 million hectares. The total damage is inestimable but timber losses alone are about $450,000,000 annually.
During 1996-98, fire swept through forests in Australia, Brazil, Canada, China's northeastern Inner Mongolian region, France, Greece, Indonesia, Italy, Mexico and several other countries in Latin America, the Russian Federation, Turkey and the United States. Satellite photos showed that about 3.3 million hectares of Brazilian forest were devastated as a result of the fires. More than 3 million hectares of forest in Mongolia were burnt in 1996. The fires in Southeast Asia in 1997 were the worst in 15 years, with at least 4.5 million hectares burnt, and smoke and haze affecting some 70 million people (Liew and others 1998). The fires in Indonesia threatened at least 19 protected areas, many of which are rich in biodiversity (WWF 1998).
According to a 2000 report, fires in 1997 and 1998 burned nearly 10 million hectares (24.7 million acres) of Indonesian forest, an area similar in size to Hungary or South Korea. Studies using satellite photographs showed that on Kalimantan, Sulawesi and Sumatra - three of the largest forested islands of Indonesia - more than 17 million hectares of forests disappeared in 12 years, from 1986 to 1997. The forestry ministry estimated that the nationwide annual deforestation rate was at least 1.5 million hectares, nearly twice the estimate published by the World Bank in 1994.
Getting within 10 metres of forest fires is difficult when using traditional firefighting tools like hoes, rakes and buckets.
During 1990's there were more and larger forest fires, caused by a combination of unfavourable weather conditions and land use that made susceptible areas more prone to burning; both forests and the health of inhabitants have been threatened over areas of millions of hectares.
Forest fires in Indonesia represented a massive environmental tragedy, and it was basically man-made. Many of the fires were deliberately set to clear land for plantations to produce palm oil and pulp for paper, enterprises that were encouraged by government subsidies. Indonesia's minister of agriculture said in 1997 that plantations caused some 80 percent of the forest fires.
Fires are also a serious threat to biodiversity, especially when protected areas are burnt.
Early warning and response systems are still weak, particularly in developing countries; there is an urgent need for improved information infrastructures and increased technical response capabilities. During rain forest fires in Southeast Asia in 1997, the governments of Indonesia, Malaysia and Singapore, the countries most affected by the haze, discussed possible remedial action, including trying to seed clouds and leasing aircraft to bomb the fires with water. However, no action was taken to put out the fires.
In Southeast Asia, fire also is the basic tool for trash disposal.
The Amazon rain forest may be reaching a critical level of dryness, in which standing forest could catch fire and burn out of control. The Amazon may be edging closer to catastrophic fire events with potentially enormous global consequences.
In the natural state, fire, started by lightning or other natural agents, has a beneficial effect and to some extent the forest is adapted to it. In the wild forest, fallen trees and branches may form a deposit many feet deep on the forest floor that provides shelter and nourishment for tree parasites, including insects, fungi and bacteria. This deposit, through which seedling trees have to push to reach light and air, also represents an accumulation of valuable minerals which are withheld from the living trees. Fire then plays a beneficial role as it sweeps through this tangled deposit, sterilizing, providing space in which new trees can thrive, and returning minerals to the soil. Indeed, fire is an essential agent in the regeneration of the forest in its natural state. Certain tree species have become so adapted to fire that it is unlikely that their cones will open to shed seeds without it. Fires which start naturally should therefore be allowed to run their course in the light of responsible conservation principles. In some cases, forest fires should even be started, to help forests to evolve back to natural state.
In Southeast Asia, for centuries rice farmers have used the dry season to burn off the stubble of the previous season's crop and refertilize their land with the ash. Haze in the dry season is normal there.
In Brazil, most fires are set by small farmers who would starve if they could not clear land for planting. Anyway, the environmental damage pales next to fossil fuel emissions in the USA.