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Vegetation formations with distinct fire regimesare most typical in Southeast Asia


Tropical lowland deciduous forests (based on Stott et al. 1990 andGoldammer 1996): This regime includes both monsoon and savannah forests, thelatter having less tree cover and more grass. These forests occur in areas ofSouth 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 inthe coldest month is rarely less than 20 degrees centigrade. Monsoon teak (Tectona grandis) forests occur naturallyin mainland Southeast Asia and have been planted elsewhere. Sal (Shorea robusta) forests occur in thenorthern part of the Indian Sub-continent. Dry dipterocarp savannah forestsoccur in mainland Southeast Asia, and open grasslands and thorn forests arespread in patches across drier parts of the region. The relatively dry LesserSunda Islands of eastern Indonesia contain monsoon and savannah forests withaffinities to Australian flora.

Theseforests usually burn one or more times per year with low level litter and groundcover fires being the norm. Levels of fire adaptation vary among formations.Fires are typically ignited purposely or accidentally by humans, and increasedfrequency of burning places stress on these fire-adapted ecosystems. The primaryobjective of fire management is to control fuel loads through controlled burns,grazing, or cutting. Total fire exclusion is not practicable and prescriptionsmust be site specific.

Fire climax pine forests (based on Goldammer and Peñafiel1990): Pine forests occur naturally on disturbed sites in the lower montaneforests of tropical Asia, primarily in the Himalayan foothills, the mountains ofmainland South East Asia, Sumatra (Indonesia), and Luzón (Philippines). Humandisturbance of forests at lower and higher elevations have caused thealtitudinal range of fire climax pine forests to expand. Pine plantations havebeen established at lower elevations in many parts of the region. Tropical pinespecies have various levels of fire adaptation and are prone to burning due tothe volume and flammability of their litter. These forests are productive iffire frequency and intensity are stable, but tend to become degraded if firedtoo frequently or fire is combined with other disturbance factors. Most firesare ignited by humans through carelessness or escaped swidden fires, but may bestarted purposely to improve grazing or to facilitate hunting. Most pines willnot regenerate if fired annually, so managers must try to reduce fire frequencyto the period required for regeneration. Total fire exclusion usually results inbroad-leaved species reclaiming the site.

Evergreen equatorial rain forest (based on Whitmore 1998, Goldammerand Seibert 1990, Goldammer et al. 1996, Schweithelm 1998): Tropical rainforestsoccur 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. InsularSoutheast Asia, New Guinea and the high islands of Melanesia were largelycovered with species-rich forests until recent decades. Logging and agriculturalexpansion have now greatly decreased their quality and extent. Other than NewGuinea and protected or remote parts of Southeast Asia, the lowland rain forestsof 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 droughtspeat swamp forests are susceptible to fire in desiccated organic layers, some ofthem burning sub-surface; and heath and limestone forests are more fire-pronethan other forest types due to the limited water-holding capacity of theirsoils.

Undisturbedlowland rainforest is very resistant to burning, but scientific evidenceindicates that Borneo’s forests (and by inference, those elsewhere) have burnedperiodically over tens of millennia during extreme droughts. Humans have usedfires as they settled the forests over thousands of years to create swiddenplots and facilitate hunting. Traditional use of fire is thought to have hadlittle long term ecological effect on the forests, but increased humanpopulation density, shortened fallow periods and cash cropping have madeshifting cultivation a major agent of deforestation. Careless commercial timberharvesting has greatly increased fire hazard, and logging roads have providedagricultural settlers with access to remote forest areas, thereby increasing therisk that their land clearing activities will result in wildfires. Logged andotherwise disturbed forests are being cleared by “slash and burn” of wastewood in preparation for conversion to palm oil or pulp wood plantations.

Degraded / potential forest land (based on Goldammer and Seibert1990, Goldammer 1993). A sequence of severe ENSO-related droughts over the lasttwo decades, combined with human disturbance of rain forests and indiscriminateuse of fire, have led to massive wildfires. This burning has produced dramaticchanges in fire regimes and the overall size of degraded land area. Experiencein East Kalimantan and other parts of the region have shown that important rainforest species are able to survive the irregular, non-uniform impacts of asingle forest fire. However, because of altered microclimate, speciescomposition, forest structure, and fuel availability the fire hazard in thesedamaged ecosystems has increased. A second and a third wildfire tend to burnwith higher intensity and severity, thus leading to more complete destruction ofthe forest structure and the overall biodiversity of the flora and fauna(Goldammer 1999a). Similar observations were made regarding the Brazilian Amazonforest (Nepstad et al. 1999). In Southeast Asia, repeated wildfires inconjunction with land use impacts have led to the formation of large areas ofdegraded Imperata cylindricagrasslands. The majority of these grasslands are subjected to a one-year firereturn interval, often purposely burned by local people to prevent the growth ofwoody and forest species.

Source:
Goldammer, J.G. 2001. Asia region fire assessment. In: FRA 
Global Forest Fire Assessment 1990-2000. Forest Resources 
Assessment Programme, Working Paper 55, p. 115-131. FAO, 
Rome, 495 p.


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