In tropical forests as much as 50% of the original extent may have been lost to deforestation in the last two decades, primarily as a result of agricultural expansion. Global estimates of tropical deforestation range from 69,000 km2 year in 1980 to 165,000 km2 year in the late 1980s; 50 to 70% of the more recent estimates have been attributed to deforestation in the Brazilian Amazon, the largest continuous region of tropical forest in the world (Skole and Tucker, 1993).
Tropical deforestation is a major component of the carbon cycle and has profound implications for biological diversity. Deforestation increases atmospheric CO2 and other trace gases, possibly affecting climate. Conversion of forests to cropland and pasture results in a net flux of carbon to the atmosphere because the concentration of carbon in forests is higher than that in the agricultural areas that replace them.
While covering less than 7% of the terrestrial surface, tropical forests are the home to half or more of all plant and animal species. The primary adverse effect of tropical deforestation is massive extinction of species including large numbers of vascular plant species.
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Deforestation affects biological diversity in three ways: destruction of habitat, isolation of fragments of formerly contiguous habitat, and edge effects within a boundary zone between forest and deforested areas (Skole and Tucker, 1993).
As the boundary zone extends some distance into the remaining forest, there are greater exposures to wind; dramatic micrometeorological differences over short distances; easier access for livestock, other non forest animals, and hunters; and a range of other biological and physical effects. The result is a net loss of plant and animal species in the edge areas (Skole and Tucker, 1993).