Vegetation cover change in desertified kerqin sandy lands, inner mongolia
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概要
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Historical and recent land degradation has been caused by human activities in semi-arid Kerqin Sandy Lands, Inner Mongolia. The purpose of the present study is to outline the process of land degradation in this area and to assess the efficiency of desertification control measures on recuperating process of vegetation cover. Historical documentation and field evidence suggest a long history of land degradation in the Kerqin Sandy Lands where Quaternary sand deposits with a depth of some 200m are widely distributed. Remnant forest patches dominated by Quercus mongolica and Pinus tablaeformis on isolated hills and Ulmus pumila on sand dune fields provide evidence of the previous landscapes in the forest-steppe transitional bioclimatic vegetation zone. In addition to the historical vegetation degradation, rapid expansion of denuded landscapes since World War II is obvious. Comparison of maps shows remobilized sand dune fields to have expanded 2.3 times in area in the last 50 years. Demographic data for the Wulan-Aodu settlement area at the center of the western Kerqin Sandy Lands shows that human and livestock population drastically increased in the 1950-60s, and this is thought to be the main cause of land degradation in this area. Livestock population has decreased since the 1970s but land degradation has continued because of a period of dry climate which started in 1971. Land use management such as grazing control is a most effective countermeasure against land degradation. Wulan-Aodu Grassland Ecosystem Research Station, Institute of Applied Ecology has set up fenced experimental fields on remobilized sand dunes and in interdune depressions within which grazing has been controlled. Remarkable vegetation restoration can be observed in fields conserved for about five years, though appearance of woody species is still insufficient even after 20 years' protection. Spatial variation in vegetation between sand dunes and interdune depressions can be observed in the protected area: Caragana microphylla and Artemisia holodendron are typically dominant on dunes and Thypa minima and Salix spp. are frequently dominant in interdune depressions. Well-devel-oped vegetation in protected lowlands comprises far more species than other vegetation in the study area does. In unprotected area Caragana microphylla and Setaria viridis dominate both on dunes and in interdune depressions, and also in flat lowlands. Therefore, the effectiveness of grazing control on vegetation restoration is indicated, though on dune ridges, where sand movement is very active, other strategies such as artificial revegetation works are also desirable to support and promote vegetation restoration.