关键词: 土地退化, 土地沙漠化, 人类驱动力, 农牧交错区, 陕北长城沿线地区

Abstract:

Through the analysis of historical natural settings in the farming and grazing interlocked zone along the Great Wall in northern Shaanxi Province of China, this study has ascertained that its land degradation is both natural and anthropogenic. The overlay of desertification severity layers interpreted from multi-temporal remotely sensed materials in a GIS, in conjunction with field investigation, has revealed that the spatial extent of desertified land in the area has drastically expanded during the 13-year period in certain localities. Both natural and anthropogenic factors in this study are realistically considered to assess land degradation severity. It is found that desertified area of most of the counties in the study area has exceeded 50% of each county's total area. The percentage is even higher in a few counties. The overall severity of land degradation has worsened during the last 13 years with extremely serious and serious degraded areas accounting for 88.5% of the total study area in 1998. The spatial distribution of the desertified land is uneven in terms of degrees. A comparison of the recent satellite image with historical aerial photographs reveals that the extent of degraded land in the study area has expanded while the overall severity of land degradation has worsened. Confirmed by the field investigation, the desert front in the vicinity of Xincheng, Jingbian County has encroached by over 10 km. In the worst affected region between Yulin and Hengshan, the encroachment is as far as over 40 km. Because of the expansion of the Mu Us Desert and the impact of sandstorms, the Great Wall is no longer the divide between sandy land and loessial area. The worsened desertification is attributed to the intensified conflicts among mounting population pressure, limited land resources, and the fragile ecosystem. Inappropriate human activities such as excessive exploitation of natural resources and malmanagement of land, to a certain extent, have inevitably resulted in the destruction of the environment. Mining activities have been identified as the sole cause of rapid spread of desertification in the vicinities of coalfields. The findings in this study have profound implications on how to reduce the severity of desertification hazard in the study area. As the cause of this problem is both natural and anthropogenic in origin, any measure must deal with problems of rural economic development, especially development of agriculture and animal husbandry for increasing farmer's income. A mechanism should be established to compensate for farmers whose income has dropped as a consequence of diminished land productivity caused by mining-induced degradation in the vicinity. Secondly, environmental laws aimed at controlling desertification and protecting environment should be formulated to mitigate the detrimental influence of human economic activities on land. For instance, in severely degraded, poverty-stricken regions the scattered small villages must be shifted to areas with relatively richer water resources so as to enable natural vegetation to recover, thus reversing the trend of desertification.

Key words: land degradation, land desertification, human driving, farming-grazing ecotone, the zone along the Great Wall in northern Shaanxi Province