Deforestation and its effect on

Abstract: The focus of this paper is on the social causes and impacts of deforestation.
Some 500 million people live in or near forests worldwide. They rely on food, fuel and
other products from forests, and consequently the problem of forest destruction is
increasingly important as a development problem.           In addition to this, the global
significance of forests as carbon sinks and repositories of biodiversity is also considered.

       The world’s forests are considered to be a renewable natural resource because
they can regenerate under different ecological conditions.         Forests can be renewed
through the natural process of plant succession even when trees have been completely
removed from an area due to human and natural disturbances. In most developing
countries, however, the forests and woodlands are being cut and removed and are not
being replaced by an increasing number of people. This process, or the temporary or
permanent deterioration in the density or structure of vegetation cover or its composition
sometimes referred to as deforestation, is accelerating. Its causes are many, including the
quest for fuelwood; shelter, fodder, wood and wood chips for export, and pulp for paper.
The principal cause, however, is linked to the subsistence farmers of developing countries
and their efforts to gain space for food production and rural development
       Forests in many developing countries are not renewing themselves quickly enough
to sustain the adequate forest resource base, which is necessary to support the
environment and economic growth of the growing populations in these countries. The
“Global 2000 Report” issued to the president in July 1980, concludes:
       “Of all the environmental impacts implied by the Global 2000 stedy’s projections,
the forest changes (deforestation) pose one of the most serious problems, particularly for
the less developed regions of the world.”
       Other scientific studies have projected the rate at which forests are vanishing in
the developing regions of the world. The Food and Agriculture Organization (FAO)
estimate of 30 million acres a year is the most frequently cited estimate of forest loss.
Some scientific research studies estimate that some developing countries will lose their
remaining forests by the end of this century. The mounting concern over the impact of

deforestation on the long-term development of these countries has prompted many
bilateral and multilateral donors to give assistance for conservation, research, and

       Contemporary deforestation is primarily generated by human activities.          The
immediate processes and mechanisms generating forest clearance are observable and
fairly well documented. The same is true of many of its direct social and ecological
effects. The forces and relationships driving these immediate deforestation processes,
and that largely determine their social impacts, however, are much more complex,
speculative and controversial as are their indirect consequences. Linkages between local
level deforestation process and broader societies are frequently difficult to discern.
Moreover they tend to differ in divergent contexts.

Crop and Livestock Expansion
       Forest clearance for agricultural expansion is widely believed to be the biggest
immediate cause of deforestation in developing countries. The World Bank asserts that
“new settlement for agriculture accounts for 60 per cent of tropical deforestation” (World
Bank, 1992, p. 20). FAO estimated that 70 per cent of the disappearance of closed forests
in Africa, 50 per cent in Asia and 35 per cent in Latin America can be attributed to
conversion for agriculture (FAO, 1982).
       Clearance of forest areas by land speculators who can establish private property
rights by demonstrating conversion of forests to pasture or cropland is major direct cause
of deforestation in many countries.
       In areas of traditional agriculture, grazing pressures combined with the annual
burning of pastoral areas (to stimulate germination of fresh grasses) frequently results in
the failure of forests to regenerate. This is observed in areas where both human and
livestock populations are high and livestock production constitutes a vital part of the
household subsistence.

Other Direct Causes of Deforestation
       The excessive or careless exploitation of forests for wood and timber are other
proximate causes of deforestation.      Half of all the wood harvested in the world is
estimated to be used as fuel, primarily in developing countries (Grainger, 1990). In some
countries woodfuel fulfils nearly 90 per cent of the local fuel-energy demands (Eckholm
et al., 1984). In order to meet their minimum household energy requirements, in many
locations people tend to overexploit local forest resources.
       Commercial exploitation of old-growth or ‘primary’ forests for high value saw or
veneer logs accounts for much of the deforestation taking place in several developing
countries, as does commercial extraction of wood for pulp and paper production.
Estimates suggest that as many as 4.4 million hectares of tropical forests may be logged
each year to supply European, American and Japanese markets (Gregersen et al, 1989).
Logging, when carefully planned and carried out, does not necessarily degrade the forest.
Much depends on how it is done. Mechanized timber harvesting methods developed for
temperate forests have proved particularly damaging when used in tropical rain forests.
Logging roads are a major cause of increased soil erosion (Poore et al., 1989). Also,
logging opens the forest for other uses such as conversion to pasture or to tree crops,
settlement by poor migrants or land grabbing by wealthier and more powerful interests.
       Other less considered, but important, immediate causes of deforestation are urban
and industrial wood/timber demands. This is especially the case where urbanization is
rapid and wood and charcoal are the chief sources of household and industrial energy.
Likewise forest products provide most of the basic raw materials for several local and
national industries. In many developing countries, where there is a greater emphasis on
industrialization, forest-based industries not only acquire preferential treatment and
institutional subsidies but are also allowed or encouraged to extract forest resources in a
careless and exploitative manner, in order to maximize immediate profits.
       The destruction of forests to make way for urban settlements, mines and related
industries; large reservoirs, railroads and roads, all contribute directly to accelerating
deforestation.   These activities also stimulate deforestation indirectly by increasing

demands for wood, timber and agricultural products from forest areas and by making
them more accessible for exploitation.

Both selective and extensive deforestation has resulted in the loss of bio diversity,
depletion of extinction of valuable genetic resources, desertification of land, soil erosion,
and climate change.
        Countless species of plants and fauna found in forest ecosystems become
endangered or extinct with the destruction of their habitats.       Biological diversity is
described as ‘ the wealth of life on earth, the millions of plants, animals and micro-
organisms, the genes they contain and the intricate ecosystems they help build into the
living environment.’ Scientists have identified and classified some 1.4 million species,
but millions more remain unknown.
        The preservation of biological diversity is essential for many scientific advances
in industry, medicine, agriculture and other fields. Diminution of biodiversity reduces the
options for unborn generations, but no one knows which or by how much. For example, a
10 square kilometer (4 square miles) area of tropical rain forest contains more than 1500
plant species. Twenty-five per cent of the medicines prescribed in the United States also
come from tropical forest plants. Currently, about 120 prescription drugs that are used
worldwide contain plant-derived ingredients from the rainforests. It is estimated that only
1% of tropical plants have been tested by scientists for medical uses. This should be a
strong incentive to protect what remains of this potential medical resource.
Some plants that have been used to make medicines:
   Alkaloids from vines are used as muscle relaxant before surgery
   Active ingredients of hydrocortisone are used as an anti-inflammatory agent
   Quinine is used to fight malaria
   Digitalis is used to treat heart failures
   Diosgenin is used in birth control pills
   Ipecac is used to induce vomiting

   Madagascar periwinkle (now extinct in the wild) is used to treat childhood leukemia
   The National Cancer Institute identified 3000 plants to have anti-cancer agents and
    70% of those plants come from rainforests.
        Destruction of Biodiversity also leads to animal extinction because the forest is a
shelter to many animals as well as a source of food for them. For example, a 10 square
kilometer (4 square miles) area of tropical rain forest contains about 700 animal species
and thousands of insect species. Animals that live under the canopy of trees in the
rainforests have adapted to survive in the humid, tropical environment.                   When
deforestation claims the natural habitat of these animals, they are forced into more open
areas where they are less successful at survival. As one species declines, the food chain
exerts a domino effect on other animal species. Edward O. Wilson, Harvard’s Pulitzer
Prize-winning biologist, estimates that 137 plants, animals, and insects are lost everyday
as a result of deforestation.
                  Deforestation is the first step along the road to desertification. In dry areas
        where vegetation is sparse, trees and open woodlands play a vital role in
        stabilizing soil and water. When the trees are removed, the land becomes more
        exposed to the elements.
                  Desertification does not mean that deserts are steadily advancing or taking
        over neighboring land.          As defined by the United Nations Convention,
        desertification is a process of “land degradation in arid, semi-arid and dry sub-
        humid areas resulting from various factors, including climatic variations and
        human activities”.
        Desertification affects about one-sixth of the world’s population, 70% of all
        drylands, and one-third of the total land area in the world. The most tangible
        impact of desertification, in addition to widespread poverty, is the annual loss of
        3.5-4.0 million hectares of agriculturally used lands as a result of the various
        processes of land degradation around the world (United Nations, 1995).

       Desertification leads to the forced movement of people because their life-support
       system has deteriorated. It leads to a reduction in the world’s food-producing
       potential, the destruction of vegetation, and diminution of many plant and animal
       populations. Further, desertification can increase atmospheric dust, which can
       then act to modify the scattering and absorption of solar radiation in the
       atmosphere (Ahmed, 1993)
Soil Erosion
               Deforestation has caused severe soil loss. The removal of trees and shrubs
       exposes the soil, which leads to erosion. Erosion leads to the removal of the thin
       upper soil layers. This, in tun reduces organic matter content and vegetation
       growth. Soils that lose organic matter can no longer retain moisture between rainy
       seasons; when precipitation increases, the soil remains unproductive.
               The most significant type of soil loss is through landslides. Landslides
       induce soil loss by mass movement, and occur in natural forests and grasslands.
       Increased frequency of landslides often occurs in areas recently deforested. They
       remove soil and grasslands. They remove soil under indigenous forests and that
       new vegetation cover then replaces soil.
               Another form of soil loss is from intense rain after deforestation. When
       deforestation takes place the soil is left with nothing to protect it. Also, when
       trees exist the rain does not often reach the soil at full impact, so the soil is very
       loose and can be easily washed away. High intensity storms remove the eroded
       regolith. As less regolith is available to be removed, the frequency of landslides
       decreases. It is highly unlikely that the soil will accumulate to the same depth, as
       it was when forest cover was present. Allowing forests to grow in their natural
       state will prevent soil degradation, and will decrease the chance of landslides.

Climate changes
      Forest clearance often leads to desiccation of previously humid forest soils. Daily
      and seasonal temperature extremes usually increase dramatically following
      removal of tree cover. In many contexts deforestation changes a moist humid
      local climate to that of a virtual desert. Currently a much-debated issue is the

impact of deforestation, especially in the tropics, on global climate change. Large
quantities of carbon dioxide and other ‘greenhouse gases’ are being released into
the atmosphere from burning fossil fuels and other ‘modern’ industrial and
agricultural practices.      These ‘greenhouse gases’ trap thermal radiation,
redirecting some of the heat back to Earth, causing temperatures to rise
       Dense forests are found in the tropics in regions of ample rainfall, typically
more than 200 cm per year. The climate of these regions is more responsible for
the forests than the forests for prevailing climate. However, the presence of
forests also does have some influence on climate.
       In considering the effects of forests on climate, it is useful to distinguish
between microclimates, regional, and global climate. The forest microclimate is
the climatic conditions, i.e., the statistics of temperature; moisture, radiative
fluxes, and winds within the forest itself. Only for the microclimates can general
assertions be made about the effects of deforestation. The forest microclimate is
especially influenced by the shading of solar radiation and the mechanical
production of turbulence by the canopy of leaves and branches.
       The top of the forest canopy where the bulk of the solar radiation is
absorbed has a larger diurnal temperature cycle than does the air near the ground
surface, and the ground diurnal variation can be smaller yet. Averaged over the
day, near-surface and ground temperatures would usually be 1 to 2 degree
centigrade cooler under the forest canopy, and humidities somewhat higher. From
the viewpoint of living organisms, perhaps the most significant effect of the
canopy is the reduction of incident solar radiation to intensities less than 0.1 of
that incident on unshaded regions.
       It is important to discuss the more obvious local effects that deforestation
has. First, because changes in the local micrometeorological conditions are likely
to be much more severe than changes that occur on a large geographic scale;
second, because most of the means whereby forest removal could affect large-
scale climate involves the modulation, in various ways, of micrometeorological
energy transfer processes.

        One such means is by changes of surface albedo. The albedo of an area is
the ratio of reflected to incident solar energy. The surface albedo is especially
significant because it indicates not only how much solar radiation the surface
absorbs but also, to a large extent, how much solar radiation the combined
atmosphere-surface system absorbs, since most of the reflected solar radiation is
lost to space.
        Radiative energy absorbed by the forest canopy and ground is returned to
the atmosphere as sensible and latent heat. Sensible heat transfer is the cooling of
the surface by the dry ventilation of the surface by air passing over it. Latent heat
transfer refers to the energy the surface loses in transforming water from its liquid
to vapor phase through either evaporation or transpiration (which also involves
evaporation, but inside the leaf structure).
        The sensible heat energy transferred from the surface to the atmosphere
directly warms the lower layers of the atmosphere. The latent heat energy warms
the atmosphere only after it is released in rainfall processes. Because sensible and
latent energy are not lost from the surface-atmosphere system as a whole, global
temperatures are much less sensitive to differences in their exchange than to
changes in reflected solar radiation. However, changes in the ratio of sensible to
latent fluxes can be significant for the hydrological cycle and therefore modify the
frequency, amount, and location of tropical cloudiness and rainfall, and so change
regional climates.
        Deforestation can change the global balance of energy not only through the
above discussed micrometeorological processes but also by increasing the
concentration of carbon dioxide in the atmosphere. Carbon dioxide is one of the
more important absorbers of thermal infrared radiation in the atmosphere. Its
concentration in the atmosphere is currently increasing due to the burning of fossil
fuels, and to a lesser extent, tropical deforestation. This increase is of concern
because of its possible implications for changes in global climate.
        Deforestation is also responsible for the increase of Nitrous oxide in the

        Working in the Hubbard Brook Experimental Forest in New Hampshire,
Yale University forestry researchers William B. Bowden and F.H. Bormann have
been studying nitrous oxide (N.sub.2.O) emissions produced by two generic
classes of soil bacteria—nitrifiers and denitrifiers. Bacteria in the first group
create N.sub.2.O as they convert one plant nutrient, ammonium, into another plant
nutrient, nitrate.   Those in the second group convert nitrates into molecular
        Previously, research had shown that clear-cutting timber can encourage
production of nitrate—and therefore of N.sub.2.O—by the nitrifiers. However,
much of the concern over this focused on the nitrate, rather than on the N.sub.2.O,
Bowden says, because measurements showed that nitrate runoff in streams
accelerated dramatically after clear-cutting. And this loss of soil nitrogen—often
the primary factor limiting soil productivity—indicated that these soils ability to
nurture new trees might diminish after several cycles of clear-cutting.
        But N.sub.2.O loss, if it were high enough, would represent an additional
cause of soil-nitrogen depletion and therefore threaten the productivity of these
soils. And the Yale scientists reasoned that since the increased production of
nitrate after clear-cutting would also give N.sub.2.O producing denitrifiers a feast,
there would be a great deal of N.sub.2.O to lose through runoff.
        What this means, Bowden says, is that organisms in soil—especially in
soil that has been disturbed by deforestation or agriculture—appear to be a greater
source of N.sub.2.O than most people have expected. And “this may be important
on a global scale,” he believes.

        Tropical deforestation implies large changes for local microclimates. If
sufficiently extensive, the microclimatic changes can modify the climate of large
regions in the vicinity of the deforested areas. Extensive removal of tropical
rainforests also would change the global heat balance significantly. The radiateve
effects of increases in carbon dioxide from deforestation appear to outweigh the

effects of the potential increase in albedo, at least for several hundred years until
much of the carbon dioxide from loss of tropical forest biomass would be taken
up by the oceans.
       The global climate changes due to even complete tropical deforestation are
expected to be no larger than either natural climate fluctuations or the changes that
will result from past combustion of fossil fuels. Hence, it is unlikely that this
potential effect would deter tropical countries from exploiting their forest
resources. However, if in the future the climate change due to fossil fuel burning
were to stress the world economy, the additional contribution to atmospheric
carbon dioxide by destruction of tropical forests would exacerbate the situation.
Regional climate changes due to deforestation are likely to be considerably larger
than global changes and conceivably for some land use changes of greater cost to
some tropical countries than the benefits they might expect to receive from
exploiting their forestland.
       It is very important to find ways to conserve natural resources of global
importance while at the same time recognizing the sovereignty of the countries in
which the resources are found. We must take an integrated approach to land use
that encompasses agriculture, forestry, and the management of other resources and
       Our world is not as large as we may think. If we keep on using up our
resources at the current rate, it won’t be long until we run out of resources
especially at the current rat of population expansion.
       Literature cited
       1   L.s.Hingane 1996. Is a signature of socio-economic impact written on
           the climate? Climatic change, 91-103
       2   Pao-shin Chu, Zhi-ping Yu, 1994.Detecting climate change concurrent
           with deforestation. Bulletin of the American Meteorological Society,
       3   Robert E.Dickinson 1989. Predicting climate effects. Nature, 343-345

4   David pollard; Starley L.Thompson 1992. Effects of boreal forest
    vegetation on global climate. Nature, 716-719
5   P.R. Rowntree; M.F. Mylne 1992. Modelling the effects of albedo
    change associated with tropical deforestation. Climatic change, 317-
6   Mary H. Cooper 1991. The issues. CQ Researcher,683-690
7   B.L. Turner II; William B. Meyer 1991. Land use and land cover in
    global environmental change. International Social Science Journal,
8   Frank Rosillo-Calle 1992. Biomass energy, forests and global
    warming. Energy Policy, 124-137
9   Brahmananda Rao 1992. Climatic change due to land surface
    alterations. Climatic Change, 1-34
10 Philip M.Fearnside 1997. Greenhouse gases from deforestation in
    Brazilian Amazonia. Climatic Change, 321-361
11 Omar R. Masera; Maria J. Ordonez 1997. Carbon emissions from
    Mexican forests: current situation and long-term scenarios. Climatic
    Change 265-296
12 J.H.C. Gash; C.A. Nobre 1997. Climatic effects of Amazonian
    deforestation: some results from ABRACOS. Bulletin of the American
    Meteorological Society, 823-831
13 G.K. Walker; Y.C. Sud; R. Atlas 1995. Impact of the ongoing
    Amazonian deforestation on local precipitation. Bulletin of the
    American Meteorological Society, 346-352
14 Studies in third world societies 1981. Blowing in the wind:
    Deforestation and long-range implications, 411-443
15 Karen L.O’Brien 1998. Tropical deforestation and climate change. The
    professional Geographer, 140-154


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