Deforestation is the complete removal of a forest ecosystem and conversion of the land to another type of landscape. It differs from clear-cutting, which entails complete removal of all standing trees but leaves the soil in a condition to regrow a new forest if seeds are available. Humans destroy forests for many reasons. American Indians burned forests to convert them to grasslands that supported big game animals. Early settlers cut and burned forest to convert them to croplands. Between 1600 to 1909, European settlement decreased forest cover in the United States by 30%. Since that time, total forest acreage in the United States has actually increased. In Germany about two-thirds of the forest was lost through settlement. Food and Agriculture Organization (FAO) estimated that from 1980 to 1990, 0.9% of remaining tropical forests were deforested annually (65,251 mi2 [169,000 km2] per year), an area equivalent to the state of Washington. FAO defines forest as land with more than 10% tree cover, natural understory vegetation, nature animals, natural soils, and no agriculture. Analysis of deforestation is difficult because data is unreliable and the definitions for "forest" and "deforestation" keep changing; for example, clear-cuttings which reforest within five years have been considered deforested in some studies but not in others.
The major direct causes of topical deforestation are the expansion of shifting agriculture, livestock production, and fuelwood harvest in drier regions. Forest conversion to permanent cropland, infrastructure, urban areas, and commercial fisheries also occurs. Although not necessarily resulting in deforestation, timber harvest, grazing, and fires can severely degrade the forest. The environmental costs of deforestation can include species extinction, erosion, flooding, reduced land productivity, desertification, and climate change and increased atmospheric carbon dioxide. As more habitat is destroyed, more species are facing extinctions. Deforestation of watersheds causes erosion, flooding, and siltation. Upstream land loses fertile topsoil and downstream crops are flooded, hydroelectric reservoirs are filled with silt and fisheries are destroyed. In drier areas, deforestation contributes to desertification.
Deforestation can alter local and regional climates because evaporation of water from leaves makes up as much as two-thirds of the rain that falls in some forest. Without trees to hold back surface runoff and block wind, available moisture is quickly drained away and winds dry the soil, sometimes resulting in desert-like conditions. Another potential effect on climate is the large scale release into the atmosphere of carbon dioxide stored as organic carbon in forests and forest soils. In 1980, tropical deforestation released between 0.4 and 1.6 billion tons of carbon into the atmosphere, an amount equal to 10–40% of that from fossil fuels.
As a result of misguided deforestation in the moist and dry tropics, the rural poor are deprived of construction materials, fuel, food, and cash crops harvested from the forest. Species extinctions, siltation, and flooding expand these problems to national and international levels. Despite these human and environmental costs, wasteful deforestation continues. Current actions to halt and reverse deforestation focus on creating economic and social incentives to reduce wasteful land conversion by providing for wiser ways to satisfy human needs. Other efforts are the reforestation of deforested areas and the establishment and maintenance of biodiversity preserves.
Resources
Books
Rowe, R., N. P. Sharma, and J. Browder. "Deforestation: Problems, Causes and Concerns." In Managing the World's Forests, edited by N. P. Sharma. Dubuque, IA: Kendall Hunt, 1992.
Periodicals
Monastersky, R. "The Deforestation Debate." Science News 144 (July 10, 1993): 26-27.
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