The causes of desertification are numerous. Climatic change is an important cause for desertification, yet the increasing human pressure exerted through overgrazing, deforestation for fuel wood and expansion of agriculture are the main causes of desertification.
Although the sparsely populated arid and semi-arid lands cover about 33 per cent of the earth surface, they are supporting a population of over 700 million or nearly 8 per cent of the total world population.
The basic economic activity of these people is nomadic herding. In recent years, there has, however, been large-scale sedentarization and agricultural development.
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The development of irrigation and intensification of agriculture in the highly fragile ecosystems of the desert and semi-desert areas have brought radical changes in their environment.
In some cases of African, Asian and Latin American countries, land has become so degraded that it is worthless agriculturally and uneconomic for the pastoral activities.
Removal of the natural vegetation, overgrazing and over cropping have resulted in nutrient depletion, widespread soil erosion and desertification. The construction of dams for the development of canal irrigation has transformed the character of landscape.
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The mismanagement of canal water has created the problems of salinization and water logging that counteracts the beneficial effects. In extreme cases, irrigation systems have been abandoned, contributing further to land that is annually lost to agriculture.
Desertification is the long-term degradation of dry lands, resulting either from overuse by man and his animals or from natural causes such as Climatic fluctuations. It leads to loss of vegetation cover, loss of top soil by wind or water erosion, or loss of useful plant production as a result of salinization or excessive sedimentation associated with sand dunes, and sheets of torrents (Rapp, 1987: 425-43).
The spatial patterns of desertification show that the tropical and sub-tropical lands are more prone to desertification.
According to an estimate made by the United Nations, about 40 per cent of the African continent’s non-desert land is in danger of desert. Nearly 33 per cent of Asia’s land and about 20 per cent of Latin America’s land are similarly endangered.
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In countries where desertification is particularly extensive and severe (Algeria, Ethiopia, Iraq, Jordan, Lebnon, Mali, Chad, Sudan and Niger), per capita food production declined by 45 per cent between 1950 and 1990.
The resulting threat of starvation spurs population of the affected areas to increase their farming and livestock pressure on the denuded land, further contributing to their it has been suggested that Mali may be the first country in the world rendered uninhabitable by environmental destruction (Fellmann et al., 1990).