Impact of the Forest Fire on the Global Environment

Forest fires controlled or uncontrolled have profound impacts on the physical environment including: landcover, landuse, biodiversity, climate change and forest ecosystem. They also have enormous implication on human health and on the socio-economic system of affected countries. Economic cost is hard to quantify but an estimate by the economy and environment can be provided. The fire incidence problem for South East Asia put the cost of damages stemming from the Southeast Asian fires (all causes) at more than $4 billion. Health impacts are often serious. As per one estimate 20 million people are in danger of respiratory problems from fire in Southeast Asia.

Most pronounced consequence of forest fires causes their potential effects on climate change. Only in the past decade researchers have realized the important contribution of biomass burning to the global budgets of many radiatively and chemically active gases such as carbon dioxide, carbon monoxide, methane, nitric oxide, tropospheric ozone, methyl chloride and elemental carbon particulate. Biomass burning is recognized as a significant global source of emission contributing as much as 40% of gross Carbon dioxide and 30% of tropospheric ozone (Andreae, 1991).

Most of the world burnt biomass matter is from savannas, and because 2/3rd of the earth savannas are in Africa, that continent is now recognized as

"burnt center" of the planet. Biomasss burning is generally believed to be a uniquely tropical phenomenon because most of the information we have on its geographical and temporal distribution is based on the observation of the tropics. Because of poor satellite coverage, among other things, little information is available on biomass burning in boreal forests, which represent about 29% of the world's forests.

Table 1. Global estimates of annual amounts of biomass burning and resulting release of carbon into the atmosphere

Source of burning (Tg dry matter/year)

Biomass burned

Carbon released (TgC/year)

Savannas

3690

1660

Agricultural waste

2020

910

Tropical forests

1260

570

Fuel wood

1430

640

Temperate and boreal forests

280

130

Charcoal

20

30

World total

8700

4000 3500 3000

2500

8 2000 w

H 1500 1000 500 0

Biomass burned (Tg dry matter/year)

Source of Burning

Figure 5: Global estimates of annual amounts of biomass burning and of the resulting release of carbon into the atmosphere (Andreae et al., 1991). Where, 1. Savannas; 2 Agricultural waste; 3. Tropical Forests; 4. Fuel Wood; 5. Temperate & Boreal Forest and 6. Charcoal.

Knowledge of the geographical and temporal distribution of burning is critical for assessing the emissions of gases and particulates to the atmosphere. One of the important discoveries in biomass burning research over the past years, based on a series of field experiments, is that fires in diverse ecosystems differ widely in the production of gaseous and particulate emissions. Emissions depend on the type of ecosystem; the moisture content of the vegetation; and the nature, behavior and characteristics of the fire.

Fire regimes in tropical forests and derived vegetation are characterized and distinguished by return intervals of fire (fire frequency), fire intensity (e.g. surface fires vs. stand replacement fires) and impact on soil. Basic tropical and subtropical fire regimes are determined by ecological and anthropogenic (socio-cultural) gradients.

Lightning is an important source of natural fires which have influenced savanna-type vegetation in pre-settlement periods. The role of natural fires in the "lightning-fire bioclimatic regions" of Africa was recognized early (e.g. Phillips 1965; Komarek 1968). Lightning fires have been observed and reported in the deciduous and semi-deciduous forest biomes as well as occasionally in the rain forest. Today the contribution of natural forest to the overall tropical wildland fire scene is becoming negligible. Most tropical fires are set intentionally by humans (Bartlett 1955, 1957, 1961) and are related to several main causative agents (Goldammer 1988) :

• deforestation activities (conversion of forest to other land uses, e.g. agricultural lands, pastures, exploitation of other natural resources);

• traditional, but expanding slash-and-burn agriculture;

• grazing land management (fires set by graziers, mainly in savannas and open forests with distinct grass strata [silvopastoral systems]);

• use of non-wood forest products (use of fire to facilitate harvest or improve yield of plants, fruits, and other forest products, predominantly in deciduous and semi-deciduous forests);

• wildland/residential interface fires (fires from settlements, e.g. from cooking, torches, camp fires etc.);

• other traditional fire uses (in the wake of religious, ethnic and folk traditions; tribal warfare) and

• socio-economic and political conflicts over questions of land property and land use rights.

Comparatively little is known empirically about the vegetation fire regime of Southeast Asia when viewed at larger scales. This is despite the importance of fire as an agent of regional land cover change and in modifying atmospheric chemistry. Fire is widely used in rice cultivation in Asia where 94 % of the world's crop is grown (Nguyen et al., 1994). It also has a high incidence within forests in tropical Asia (Hao and Liu, 1994) where it is mainly associated with shifting cultivation (McNeely et al., 1991). As with the tropics and the African tropics, Southeast Asian tropical forests are of considerable ecological and economic importance and make up about 20% of the world's tropical forest resource (after FAO, 1993). Information on biomass burning within the Indo-Malayan region is needed to assist in the modelling of large-scale atmospheric pollution and climate change phenomena and for regional use by landuse managers, habitat conservationists, and national and regional policy makers. Mainland Southeast Asia is the focus of the Southeast Asian fire, since it is more strongly seasonal and less humid than many parts of insular South-east Asia (Nix, 1983) and thus both favour the use of fire as a land management tool and support more fire-prone ecosystems (54% of forest formations are tropical seasonal forest compared to 4% within insular regions, FAO, 1993). The mainland Southeast Asian product offers an analysis of the spatial and temporal distribution of vegetation fire in mainland Southeast Asia using AVHRR 1 km resolution data for the period of single dry season (that chosen is from November 1992 to April 1993).

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