Fire has been a source of disturbance for thousand of years. Forest and wild land fires have been taking place historically, shaping landscape structure, pattern and ultimately the species composition of ecosystems. The ecological role of fire is to influence several factors such as plant community development, soil nutrient availability and biological diversity. Forest and wild land fire are considered vital natural processes initiating natural exercises of vegetation succession. However uncontrolled and misuse of fire can cause tremendous adverse impacts on the environment and the human society.
Forest fire is a major cause of degradation of world’s forests. While statistical data on fire loss are weak, it is estimated that the proportion of forest areas prone to forest fires annually ranges from 33% in some states to over 90% in others. Forest fires cause wide ranging adverse ecological, economic and social impacts. In a nutshell, fires cause: indirect effect on agricultural production and loss of livelihood for the tribals as approximately 65 million people are classified as tribals who directly depend upon collection of non-timber forest products from the forest areas for their livelihood.
A combination of edaphic, climatic and human activities account for the majority of wild land fires. High terrain steepness along with high summer temperature supplemented with high wind velocity and the availability of high flammable material in the forest floor accounts for the major damage and wide wild spread of the forest fire. The contribution of natural fires is insignificant in comparison to number of fires started by humans. The vast majority of wild fires are intentional for timber harvesting, land conversion, slash – and – burn agriculture, and socio-economic conflicts over question of property and land use rights. In recent years extended droughts (prolonged dry weather), together with rapidly expanding exploitation of tropical forest and the demand for conversion of forest to other land uses have resulted in significant increase in wild fire size, frequency and related environmental impacts. Recent wild fires have an immense impact in Indonesia, Brazil, Mexico, Canada, USA, France, Turkey, Greece, India and Italy. Large-scale fires and fire hazards were also reported in eastern parts of the Russian Federation and in China north-eastern Mongolia autonomous region. There has been a continuous increase of application of fire in land use system in forest of South East Asian region. This has resulted in severe environmental problems and impacts on society. Wild fires often escape from land use fire and take unprecedented shape causing problems of trans boundary pollution. According to a classification of forest fires by type and causes, three types of forest fires are prevalent;
a) Ground fires: Ground fires occur in the humus and peaty layers beneath the litter of undecomposed portion of forest floor with intense heat but practically no flame. Such fires are relatively rare and have been recorded occasionally
b) Surface fires: Surface fires occurring on or near the ground in the litter, ground cover, scrub and regeneration are the most common type in all fire-prone forests of the country.
c) Crown fires: Crown fires, occurring in the crowns of trees, consuming foliage and usually killing the trees are met most frequently in low level coniferous forests.
Forest fires controlled or uncontrolled have profound impacts on the physical environment including: land cover, land use, 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.
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 radioactively 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. 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 centre” of the planet. Biomasses 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.
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, behaviour 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 and impact on soil. Basic tropical and subtropical fire regimes are determined by ecological and anthropogenic (sociocultural) 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 as well as occasionally in the rain forest. Today the contribution of natural forest to the overall tropical wild land fire scene is becoming negligible. Most tropical fires are set intentionally by humans and are related to several main causative agents:
- 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);
- wild land/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.
Increasing population pressure with multiplied demand for the domestic needs have carved out separate fracture in the biosphere by modifying the forest ecosystems. In the process we have been loosing green cover at faster rate than expected. Sustainable management of forest resources has become key agenda of the century. The assessment of the forest fire and degradation is one of the important factors to be considered for better management of the forest resources. However, the lack of reparative analysis with synoptic coverage has been one of the limitations in the conventional assessment techniques which can be potentially over come by using geospatial approach. Hence, satellite remote sensing has provided holistic view to the planet Earth.
Extensive areas are burnt and deforested every year, leading to widespread environmental and economic damage. The impact of this damage involves not only the amount of timber burnt but also environmental damage to forested landscapes leading, in some cases, to land and forest degradation and the prevention of vegetation recovery. However, further more improvement required to enhance the process of better assessment, monitoring and management of the forest resources of the planet earth.
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