Deforestation

Source: http://en.wikipedia.org/wiki/Deforestation

The conversion of forested areas to non-forest. Historically, this meant conversion to grassland or to its artificial counterpart, grainfields; however, the Industrial Revolution added urbanization and technological uses. Generally this removal or destruction of significant areas of forest cover has resulted in a degraded environment with reduced biodiversity. In developing countries, massive deforestation has accompanied mankind's progress since the Neolithic, and has shaped climate and geography.

Deforestation (whether deliberate or unintended) is the result of the removal of trees without sufficient reforestation. There are many causes, ranging from extremely slow forest degradation to sudden and catastrophic wildfires. Deforestation can be the result of the deliberate removal of forest cover for agriculture or urban development, or it can be an unintentional consequence of uncontrolled grazing (which can prevent the natural regeneration of young trees). The combined effect of grazing and fires can be a major cause of deforestation in dry areas. In addition to the direct effects brought about by forest removal, indirect effects caused by edge effects and habitat fragmentation can greatly magnify the effects of deforestation.

While tropical rainforest deforestation has attracted most attention, tropical dry forests are being lost at a substantially higher rate, primarily as an outcome of slash-and-burn techniques used by shifting cultivators.

Impact on the Environment

Deforestation alters the hydrologic cycle, potentially increasing or decreasing the amount of water in the soil and groundwater and the moisture in the atmosphere. Forests support considerable biodiversity. Forests are valuable habitat for wild mushrooms and medicinal conservation and the recharge of aquifers. With forest bioptopes a major, irreplacable source of new drugs (like taxol) and genetic variations (such as crop resistance) is lost irretrievably.

Shrinking forest cover lessens the landscape's capacity to intercept, retain and transport precipitation. Instead of trapping precipitation, which then percolates to groundwater systems, deforested areas become sources of surface water runoff, which moves much faster than subsurface flows. That quicker transport of surface water can translate into flash flooding and more localized floods than would occur with the forest cover. Deforestation also contributes to decreased evapotranspiration, which lessens atmospheric moisture which in some cases affects precipitation levels downwind from the deforested area, as water is not recycled to downwind forests, but is lost in runoff and returns directly to the oceans; in deforested north and northwest China, the average annual precipitation decreased by one third between the 1950s and the 1980s.

Long-term gains can be obtained by managing forest lands sustainably to maintain both forest cover and provide a biodegrable renewable resource. Forests are also important stores of organic carbon, and forests can extract carbon dioxide and pollutants from the air, thus contributing to biosphere stability and probably relevant to the greenhouse effect. Forests are also valued for their aesthetic beauty and as a cultural resource and tourist attraction.

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-- GeirThomasAndersen - 22 Sep 2006