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item Havstad, Kris

Submitted to: Encyclopedia of Soil Science
Publication Type: Book / Chapter
Publication Acceptance Date: 9/25/2005
Publication Date: 10/15/2006
Citation: Havstad, K.M. 2006. Productivity and desertification. In: Lal, R., editor. Encyclopedia of Soil Science. New York: Marcel Dekker, Inc. p. 1375-1377.

Interpretive Summary: No Interpretive summary required

Technical Abstract: The United Nations Convention to Combat Desertification (UN-CCD) defined desertification as the degradation of land in arid, semi-arid, and dry sub-humid areas resulting from various factors, including climatic variations and human activities. These susceptible drylands cover approximately 40% of the world’s land surface. Desertification is not a new problem, but one that traces back to 2200 BC and the degradation of Mesopotamia. However, the estimated extent of degradation of the world's dry lands at the end of the 2nd millennium AD is substantial.. Though estimates of the magnitude of degradation vary widely, it is recently documented that soils of at least 12% of the world's 5169 m ha of drylands are at least moderately desertified. It should also be noted that these estimates often do not consider lands outside the world's subtropics. The UN-CCD estimates that over 250 million people are affected by desertification with about one-sixth of the world's population at risk. For some continents the numbers of people at risk are much greater. In Africa, Asia, and South America between 30-40% of the populations live within these susceptible drylands Generally, the effects of this land degradation are reductions in desirable plant production, alterations in biomass, lowered carrying capacities for livestock, increased soil erosion, and an overall increase in environmental deterioration. It is usually assumed that desertification has direct and measurable effects on either primary or secondary production from these lands. In very severely desertified situations, such as southern Kazakhstan, productivity has been dramatically reduced. For other regions of the world where desertification is certainly serious but not severe the relationships between degradation and productivity are less obvious and direct. These relationships need to be understood so that measures other than simply productivity reductions are employed to accurately assess rates, extent, and threats of degradation to these land resources.