CAUSES OF DEFORESTATION - Pace University



Deforestation and its effect on Environment

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.

INTRODUCTION

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 education.

CAUSES OF DEFORESTATION

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.

CONSEQUENCES OF DEFORESTATION

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.

Biodiversity

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.

Desertification

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 atmosphere.

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 nitrogen.

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.

Conclusion

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 conservation.

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, 579-584

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, 317-341

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, 669-680

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

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download