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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 |
