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Land degradation and desertification are major problems that are caused by natural factors (e.g., prolonged droughts) and by human activities-particularly overgrazing, uncontrolled cultivation, fuelwood gathering, inappropriate use of irrigation, uncontrolled urbanization, and tourism development (Kharin, 1995; IPCC 1996, WG II, Chapter 2; Schreiber and Shermuchamedov, 1996; UNEP, 1997). Urbanization and related activities (e.g., road construction) have resulted in losses of permanent pasture and increases in the agricultural use of marginal lands, leading to further degradation (UNEP, 1997). Dryland salinity and waterlogging, especially in low-lying countries in the Middle East and parts of central Asia (e.g., around the Aral Sea), also are contributing to land degradation (Kharin, 1997; UNEP, 1997).
The full extent of land degradation in the region is not known, although an estimated 10% of the arid and semi-arid land is classified as having some soil constraints (see Table 7-1). Future erosion risk is more likely to be influenced by increases in population density, intensive cultivation of marginal lands, and the use of resource-based and subsistence farming techniques than by changes in climate (IPCC 1996, WG II, Chapter 4).
Various options are available for reducing soil degradation by improving the carbon and water storage capacity of the soil (see below). Unfortunately, because of low surface-water availability, some of these practices might not be helpful for all of the countries in the region. However, other soil conservation and soil protection measures can be implemented in these areas.
Agro-ecosystems. Water availability is the main determinant of productivity; the use of reduced tillage and mulching to increase available water and reduce surface erosion can promote increased soil carbon. In areas where cropping and livestock are closely integrated, more-efficient use of manure and commercial fertilizer also can increase productivity and soil carbon. In temperate parts of the region, eliminating or reducing summer fallow through better water management in nonirrigated areas could significantly increase carbon and decrease soil erosion in semi-arid croplands (IPCC 1996, WG II, Section 23.2.2).
Reduction in animal density. In much of the semi-arid area, the predominant land use is pastoral, and grazing control is an important option for the maintenance of soil carbon. Reduction in animal numbers can increase carbon storage by enhancing plant cover. This practice can have a positive effect on the ecosystem if there is sufficient rainfall, but reductions in animal numbers on rangelands may require alternative sources of food for humans-and thus changes in national or regional food production policies.
Changing animal distribution. Changing animal distribution through salt placement, development of water sources, or fencing can lead to the more even use of pastures and consequently to increases in overall plant cover, improved status of the root system (as a consequence of less-intense grazing), and increased carbon sequestration. Appropriate animal-management practices will be specific to local and regional production systems; for example, fencing or salt placement may not be useful in herding systems and may interfere with wildlife migration.
Watershed-scale projects. Practices involving the development of dams with large-scale water-storage capacity may increase long-term carbon storage by improving animal management and food production systems. Such projects are expensive, however, and they can result in social and cultural dislocation, local extinctions of wildlife, and increases in human and animal population density. Because 6-89% of the region's cropland area already is irrigated (see Table D-5), watershed management with additions of dams may not be a suitable response.
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