Desertification is a process of continuous, gradual ecosystem degradation, during which plants and animals, and geological resources such as water and soil, are stressed beyond their ability to adjust to changing conditions. Because desertification occurs gradually, and the processes responsible for it are understood, it can often be avoided by planning or reversed before irreparable damage occurs. The physical characteristics of land undergoing desertification include progressive loss of mature, stabilizing vegetation from the ecosystem, or loss of agricultural crop cover during periods of drought or economic infeasibility, and a resulting loss of unconsolidated topsoil. This process is called deflation. Erosion by wind and water then winnows the fine-grained silt and clay particles from the soil; dramatic dust storms like those observed during the 1930's Dust Bowl in the American mid-west, and in northern Africa, were essentially composed of blowing topsoil. Continued irrigation of desertified land increases soil salinity, and contaminates groundwater, but does little to reverse the loss of productivity. Finally, ongoing wind and water erosion by eDeals" style="color: rgb(0, 0, 153); border-style: none !important; display: inline-block !important; float: none !important; font-weight: bold !important; height: auto !important; min-height: 0px !important; min-width: 0px !important; text-transform: uppercase !important; width: auto !important; background: transparent !important;">LEADS to development of gullies and sand dunes across the deflated land surface.
The forces causing these physical changes to occur may be divided into natural, human or cultural, and administrative causes. Among the natural forces are wind and water erosion of soil, long-term changes in rainfall patterns, and other changes in climatic conditions. The role of drought is variable and related in part to its duration; a prolonged drought accompanied by poor land management may be devastating, while a shorter drought might not have lasting consequences. As such, drought thus stresses the ecosystem without necessarily degrading it permanently. Rainfall similarly plays a variable role that depends on its duration, the seasonal pattern of its occurrence, and its spatial distribution.
The list of human or cultural influences on desertification includes vegetation loss by overgrazing, depletion of groundwater, surface runoff of rainwater, frequent burning, deforestation, the influence of invasive non-native species, physical compaction of the soil by livestock and vehicles, and damage by strip-mining. Desertification caused by human influences has a long historical record; there is evidence of such damage caused around the Tigris and Euphrates rivers in ancient Mesopotamia. Administrative influences contributing to desertification include encouragement of the widespread cultivation of a single crop for export, particularly if irrigation is required, and the concentration of dense human populations in arid lands. Poor economic conditions, like the Great Depression in United States in the 1930s, also contribute to degradation of croplands. During that crisis, American farmers were simultaneously confronted with bankruptcy and a decade-long drought, and they left millions of acres of plowed, bare cropland unplanted. According to the 1934 Yearbook of Agriculture, "Approximately 35 million acres of formerly cultivated land have essentially been destroyed for crop production.... 100 million acres now in crops have lost all or most of the topsoil; 125 million acres of land now in crops are rapidly losing topsoil."
Considering these factors together, desertification can be viewed as a process of interwoven natural, human, and economic forces causing continuous degradation over time. Therefore, ecosystem and agricultural degradation caused by desertification must be confronted from scientific, social and economic angles. Fortunately, scientists believe that severe desertification, which renders the land irreclaimable, is rare. Most desertified areas can be ecologically reclaimed or restored to agronomic productivity, if socioeconomic and cultural factors permit restoration.
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