The application of fire in land-use systems and human-caused wildfires in forests and other vegetation in insular and continental South East Asia during the 1990s have reached unprecedented levels and have been leading to severe environmental problems and impacts on ecosystems and society. Traditional slash-and-burn agriculture (shifting cultivation) is still practiced in many countries of the region. During the 1990s an increase of fire application for large-scale conversion of primary and secondary forests into permanent agricultural systems and into tree plantations has been observed, particularly in Indonesia. Wildfires escaping from land-use fires are becoming more and more regular, especially during episodic droughts (inter-annual climate variability) associated with the El Niño - Southern Oscillation (ENSO) event.
A large variety of biogeographic features and climatic conditions within insular and continental South East Asia have created a high diversity of forest ecosystems and other wooded land with different fire regimes and vulnerabilities. The socio-economic conditions of wildland fires in SE Asia, including the underlying causes of fire application, and the ecological and environmental consequences of wildland fires in the region have been synoptically analyzed for the time period before the last ENSO (1997-98) by Goldammer and Seibert (1990), Goldammer and Peñafiel 1990, Stott et al. 1990, Goldammer 1993, Goldammer et al. 1996, AIFM 1997a). Several regional analyses have been published in the aftermath of the 1997-98 fire and smoke episode, notably by Schweithelm (1998, 1999), Chandrasekharan (1999), Suhartoyo and Toma (1999), BAPPENAS/ITTO/JICA (1999), Radojevic and Eaton. (2000), Barber and Schweithelm. (2000), Rowell and Moore (2000).
The following vegetation formations with distinct fire regimes are most typical in Southeast Asia:
Tropical lowland deciduous forests (based on Stott et al. 1990 and Goldammer 1996): This regime includes both monsoon and savannah forests, the latter having less tree cover and more grass. These forests occur in areas of South and Southeast Asia where the dry season is three to seven months long, total annual rainfall is usually less than 2,000 mm and the mean temperature in the coldest month is rarely less than 20 degrees centigrade. Monsoon teak (Tectona grandis) forests occur naturally in mainland Southeast Asia and have been planted elsewhere. Sal (Shorea robusta) forests occur in the northern part of the Indian Sub-continent. Dry dipterocarp savannah forests occur in mainland Southeast Asia, and open grasslands and thorn forests are spread in patches across drier parts of the region. The relatively dry Lesser Sunda Islands of eastern Indonesia contain monsoon and savannah forests with affinities to Australian flora.
These forests usually burn one or more times per year with low level litter and ground cover fires being the norm. Levels of fire adaptation vary among formations. Fires are typically ignited purposely or accidentally by humans, and increased frequency of burning places stress on these fire-adapted ecosystems. The primary objective of fire management is to control fuel loads through controlled burns, grazing, or cutting. Total fire exclusion is not practicable and prescriptions must be site specific.
Fire climax pine forests (based on Goldammer and Peñafiel 1990): Pine forests occur naturally on disturbed sites in the lower montane forests of tropical Asia, primarily in the Himalayan foothills, the mountains of mainland South East Asia, Sumatra (Indonesia), and Luzón (Philippines). Human disturbance of forests at lower and higher elevations have caused the altitudinal range of fire climax pine forests to expand. Pine plantations have been established at lower elevations in many parts of the region. Tropical pine species have various levels of fire adaptation and are prone to burning due to the volume and flammability of their litter. These forests are productive if fire frequency and intensity are stable, but tend to become degraded if fired too frequently or fire is combined with other disturbance factors. Most fires are ignited by humans through carelessness or escaped swidden fires, but may be started purposely to improve grazing or to facilitate hunting. Most pines will not regenerate if fired annually, so managers must try to reduce fire frequency to the period required for regeneration. Total fire exclusion usually results in broad-leaved species reclaiming the site.
Evergreen equatorial rain forest (based on Whitmore 1998, Goldammer and Seibert 1990, Goldammer et al. 1996, Schweithelm 1998): Tropical rainforests occur naturally over large areas of Southeast Asia and the tropical Pacific. These forests require abundant rainfall and high temperatures year round: drought conditions prevail when monthly rainfall drops below 100 mm. Insular Southeast Asia, New Guinea and the high islands of Melanesia were largely covered with species-rich forests until recent decades. Logging and agricultural expansion have now greatly decreased their quality and extent. Other than New Guinea and protected or remote parts of Southeast Asia, the lowland rain forests of the region are a mosaic of disturbed stands, fire climax grasslands, secondary vegetation and commercial crop plantations. Within this climate type, special vegetation types have their own fire regimes. During severe droughts peat swamp forests are susceptible to fire in desiccated organic layers, some of them burning sub-surface; and heath and limestone forests are more fire-prone than other forest types due to the limited water-holding capacity of their soils.
Undisturbed lowland rainforest is very resistant to burning, but scientific evidence indicates that Borneo's forests (and by inference, those elsewhere) have burned periodically over tens of millennia during extreme droughts. Humans have used fires as they settled the forests over thousands of years to create swidden plots and facilitate hunting. Traditional use of fire is thought to have had little long term ecological effect on the forests, but increased human population density, shortened fallow periods and cash cropping have made shifting cultivation a major agent of deforestation. Careless commercial timber harvesting has greatly increased fire hazard, and logging roads have provided agricultural settlers with access to remote forest areas, thereby increasing the risk that their land clearing activities will result in wildfires. Logged and otherwise disturbed forests are being cleared by “slash and burn” of waste wood in preparation for conversion to palm oil or pulp wood plantations.
Degraded/potential forest land (based on Goldammer and Seibert 1990, Goldammer 1993). A sequence of severe ENSO-related droughts over the last two decades, combined with human disturbance of rain forests and indiscriminate use of fire, have led to massive wildfires. This burning has produced dramatic changes in fire regimes and the overall size of degraded land area. Experience in East Kalimantan and other parts of the region have shown that important rain forest species are able to survive the irregular, non-uniform impacts of a single forest fire. However, because of altered microclimate, species composition, forest structure, and fuel availability the fire hazard in these damaged ecosystems has increased. A second and a third wildfire tend to burn with higher intensity and severity, thus leading to more complete destruction of the forest structure and the overall biodiversity of the flora and fauna (Goldammer 1999a). Similar observations were made regarding the Brazilian Amazon forest (Nepstad et al. 1999). In Southeast Asia, repeated wildfires in conjunction with land use impacts have led to the formation of large areas of degraded Imperata cylindrica grasslands. The majority of these grasslands are subjected to a one-year fire return interval, often purposely burned by local people to prevent the growth of woody and forest species.
The situation within the countries of the Southeast Asian region
During the 1990s the fire situation within the South East Asian nations was monitored by the ECE/FAO Team of Specialists of Forest Fire. National partner institutions and individuals were encouraged to provide analyses and statistical data that are published in the pages of International Forest Fire News (IFFN). For this regional review special country reports were delivered by individuals from Indonesia, Malaysia, the Philippines, and Thailand and provided below in full length.
The following short remarks on the fire situation in other countries of insular and continental South East Asia provide some major statements of interest and the information source. No information is available on Christmas Islands and East Timor; the small size of forest and other wooded land area in Singapore explains the lack of information in that country.