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Vol. 4 No. 2 - April 1998

Forest Fire and Ecosystem-Health

By Anil K. Gupta1  and M. Yunus2

 Concept of ecosystem health can be better illustrated through "forest health" as forests are the most productive among natural ecosystems. Most recent definitions of forest health range between utilitarian and ecosystem perspectives. From a utilitarian perspective, a desired state of forest health can be considered "condition where biotic and abiotic influences on forests (e.g. pests, pollution, silvicultural treatments, harvesting) do not threaten management objectives now or in the future". "A healthy forest is one that is resilient to changes". The term "Ecosystem-Health" thus, could be defined as the structural and functional stability of an ecosystem and its ability to bounce back after stress.

Ecosystem-Health Problems of Forest

World forests and woodlands at present occupy more than three million hectares. These forests have been steadily receding ever since the earliest Palaeolithic times, but the pace of retreat has accelerated since the Neolithic age and has become particularly rapid over the last 100 years as population has exploded. Deforestation has arisen from four principal causes, often in combination with each other : excessive felling of trees for timber, overgrazing, fire and clearance of land for cultivation and pasture.

Ecosystem management, the term, is described as keeping the ecosystems functioning well over long-term changes. Integrated forest management thus re-evaluates the approaches to managing ecosystem-health issues, and consider more fully their effects on the sustainability of forest ecosystems.

Forest Fire

Fire is one of the significant causes of deforestation throughout the world. In the earliest cultural stages of development it was the only effective tool for clearing land (slash and burn technique) and keeping it open for grazing.

Forest fires cause the degradation of forests by exerting potential impact on forest crop, regeneration, productivity, protective power, soil, wildlife and aesthetics. The overall damage to the forest crop by fire depends upon (1) the species forming a part of the crop or composition of the forest, (2) condition of the crop, (3) time and season during which the fire occurs, (4) age of the crop, water, and the nutrient status of the soil is adversely affected. The decomposition of organic and even inorganic compounds of nitrogen by the heat causes an extra loss of nutrients. Forest fires cause extensive loss of wildlife by burning the eggs, destroying the young ones, and damaging their habitat which is an intergal part of the forest ecosystem.

Biomass Burning and Global Change

Biomass burning is recognized as a significant global source of emissions, contributing as much as 10 per cent of gross carbon dioxide and 38 per cent of tropospheric ozone. While in the case of traditional shifting agriculture the gases released by burning and rottening is resequestered during the recovery phrase, permanent cleaning of the forests create a net flux of carbon into the atmosphere.

The vast majority of the world's burning is human-initiated, with lightening-induced natural fires accounting got only a small percentage of the total. The immediate effect of burning is the production and release of gases and particulates into the atmosphere. the instantaneous combustion products of burning vegetation include carbon dioxide, carbon monoxide, methane, non-methane hydrocarbons, nitric oxide, methyl chloride, and various other gases which are released and returned to the atmosphere in a matter of hours. The burning of forest also destroys an important sink for atmospheric carbon dioxide. Hence, burning has strong role in world carbon dioxide budget. If the burned ecosystem regrows, the carbon dioxide is eventually removed from the atmosphere via photosynthesis and is incorporated into the new vegetative growth. Other gaseous emissions, however, remain in the atmosphere.

The gases produced by biomass burning are environmentally significant. The green house viz., carbon dioxide and methane influence global climate. Combustion particulates affect the global radiation budget and climate. Methane, non-methane hydrocarbons and nitric oxide are all chemically active gases that affect the oxidizing capacity of the atmosphere and lead to the photochemical production of ozone in the troposphere. Recently it was discovered that biomass burning is also an important global source of atmospheric bromine in the form of methyl bromine. Bromine leads to the chemical destruction of ozone in the stratosphere and is about 40 times more efficient in the process than is chlorine on a molecule-to-molecule basis. Burning also enhances the biogenis emissions of nitric oxide, and nitrous oxide from soil. Biomass burning affects the reflectivity and emissivity of the earth's surface as well as hydrological cycle by changing rates of land evaporation and water runoff. For these reasons, it appears that biomass burning is a significant driver of global change.

Fire as a Management Tool

Fire and ecosystems have interacted throughout time, establishing fire as an influence in such ecosystem function as:

         recycling of nutrients

         regulating plant succession and wildlife habitat

         maintaining biological diversity

         reducing biomass, and

         controlling insect populations and diseases.

Fire can either kill forest pest or alter their habitat. Outright mortality of pets and pathogens varies with fire behavior and/or fuel characteristics. Prescribed burning is the knowledgeable application of fire on a specific area to attain predetermined objectives. To accomplish a prescribed burn safety, managers must write a prescribed burn plan detailing how the burn will be executed.

Conclusion

Understanding the relationship between fire and forest health requires a clear distinction between prescribed fire and wildfire. Forest managers must have knowledge of how fire behaves under specific atmospheric conditions. A thorough understanding of past stand history and an ability to judge potentially dangerous conditions is invaluable and can make difference between successful and disastrous use of prescribed, managers must weigh negative influences against positive ones. For example, fire may result in the loss of photosynthetic tissue but produce a competition free site. In addition, fire may eliminate some pathogens form a site but create additional points for infection, such as developments of fire scars on tree boles. Recent fire may also limit the effectiveness of insecticide.

A prescribed burn will also be safer and more successful if the perimeter of the treated are is extended to natural boundaries such as lakes, rivers, and marshes. Narrow roads on single-blade bulldozed firelines are not wide enough to prevent the fire from crossing the fire brands. It is now obvious to consider the "fire ecology" as an important attribute in "integrated approach to ecosystem-management", in order to efficiently plan and manage our natural ecosystems.

1DMI, Bhopal, 2DDAU, Lucknow


This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.


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