Land degradation is the loss of production capacity of the land. Degraded land is a land, which due to natural processes or human activity is no longer able to sustain properly an economic function and/or the original natural ecological function. Land degradation refers to the temporary or permanent reduction in the productive capacity of land. It is a dynamic, interactive process that evolves and differs over time and space. It is the cumulative effect of the interaction of various biophysical, socio-economic and institutional factors over time and space.
Extent - Global
In 1950, some 115 million km2 of the Earth's surface was un-degraded, vegetated land. Just 40 years later, almost nine million km2 - an area as large as China - were classified as "moderately degraded", with greatly reduced agricultural productivity. A further three million km2 were "severely degraded", having lost almost completely their original biotic functions. About 100,000 km2 are beyond restoration. Deforestation
Vast reserves of forest have been degraded by large-scale logging and clearing for farm and urban use. Between 1975 and 1990, more than 2.2 million km2 of tropical forest were destroyed, mainly to provide new land for food production. Worldwide, tropical forests are being cleared at a rate of about 'one percent each year, with annual losses of as high as two percent in West Africa. About 5.8 million km2 of land has been degraded by deforestation. Overgrazing
Overgrazing has damaged 20 percent of the world's pasture and rangelands. Recent losses have been most severe in Africa and Asia. Typically, animal herds compact soil around waterholes and strip the land of vegetation, reducing its capacity to retain moisture and exposing soil to wind and water erosion. As rangeland productivity declines in developing countries, more forests and farmland are being converted to grazing. Overgrazing has degraded about 6.8 million km2 of land.
Fuelwood and charcoal are the primary sources of energy in many parts of the world. Each year an estimated 1,730 million m3 of fuelwood is taken from forests and plantations. As population pressure mounts, rural people are removing vegetation from higher and steeper areas, exposing more and more land to erosion. Fuelwood extraction has degraded about 1.37 million km2 of land.
Soil nutrient loss occurs when land is farmed beyond its capacity. This is increasingly the case in areas of shifting (or "slash-and-burn") cultivation, where population pressure has reduced fallow periods to virtually zero. Soil salinization and waterlogging are caused by poor drainage of irrigated land. Agricultural mismanagement has degraded about 5.5 million km2 of land.
Urban growth, road building, mining and industry are degrading land worldwide. Often, valuable agricultural land is lost - during 1967-75, almost 30,000 km2 of good cropland disappeared under concrete in the United States alone. Associated problems include pollution of soil by industrial and urban wastes, acid rain, overuse of inputs in feedlots, and oil and chemical spills. About 2.4 million km2 has been degraded by chemical degradation.
Water and Wind Erosion
Water erosion affects mainly steep land or unprotected sloping areas. It causes soil losses estimated at 25,000 million tonnes every year. Wind erosion degrades land left bare of vegetation. It affects more than a third of land in the Near East and almost a quarter of Africa north of the equator. According to an estimate, about 11 million km2 are affected by water erosion, 5.5 million km2 by wind erosion, and 0.8 million km2 by physical soil degradation; at least 2.25 million km2 of land affected by water erosion is degraded to such an extent that it is no longer suitable for agricultural land use.
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