关键词: 指标体系, 草场荒漠化, 评价, 毛乌素沙地

Abstract: The area of global desertified grass land occupies 93.6% of global desertified land's area. The proportion of desertified grass land in China to it's all grass land is 566%. Grass land is one of the main types in Mu Us Sandy Land, and it has also degraded in different degrees because of irrational economic activities. For evaluating the grass land desertification processes in Mu Us Sandy Land, 9 investigating sites were studied based on the interpretation of TM in 1994 and airphotos in different time, and considering the main desertification types and regional differentiation. On each site, 1-9 sample belts were choiced according to land types, landform characters, plant types and the degradation features. The sample belts are more than 500 m long and were arranged along degrading gradient direction. There is a small quadrate (1 m×1 m) for every 5 m on each sample belt, and 3-10 random typical quadrates (5 m×5 m for shrub community and 1 m×1 m for herb community) near sample belts. The measured subjects include vegetation coverage and the ratios, plant composition and height, as well as shrub density etc.. Moreover, typical soil sections under different vegetation types were unburied to investigate soil texture, structure, gardening degree, color, humidity and root system etc.. DCA sorting and TWINSPAN classification prove that grass land degraded in the direction from the fixed and the semifixed to the semishifing and the shifting; the stage of grass land degraded mildly is predominated by Sabina vulgaris Ant., moderately degraded stage by Artemisia ordosica Krasch, Caragana korshinskii Kom., severely degraded stage by Artemisia sphaoerocephala Krasch, Hedysarum laeve (Maxim.) B. Fedtsch and very severely degraded stage by Agriophyllum squarrosm (L.) Moq., Cynanchum komarovii Al. Iljin. Correlation analysis indicates that the degradation gradient of plant community is closely related to surface crust thickness, soil organic matter and soil texture. Biodiversity analysis proves that community biodiversity changes with one peak curve in the processes of grass land's degradation. Based on the analysis above, the indicator system of evaluating sandy grass land's degradation on community level are obtained:mildly degraded grass lands have the characteristics of surface crust thickness1 cm, soil organic matter1%, fine sand loam soil, S. vulgaris Ant. community type; moderately degraded grass lands have the characteristics of surface crust thickness between 0.5%-1%, sandy loam soil, A. ordosica community type; severely degraded grass lands have the characteristics of surface crust thickness0.5 cm,soil organic matter between 0.2%-0.5%, sandy soil, H.laeve community type; very severely degraded grass lands have the characteristics of no surface crust, soil organic matter 0.2%, sandy soil, A. squarrosm community type.

Key words: Indicator system, Grass land desertification, Evaluation, Mu Us Sandy Land