中文摘要：

江河源区高寒草甸退化日益严重，恢复治理已进行了大量工作，但收效甚微，主要是对退化机理认识不清．为阐明退化草地的形成机制，本文以江河源区高寒草甸为对象，分析退化序列土壤粒径的分布特征、分形维数，以及分形维数与土壤侵蚀模数的关系．结果表明：随着高寒草甸退化加剧，土壤的黏粒百分含量呈增加趋势，粉砂和极细砂呈减小趋势；退化序列土壤粒径分形维数与黏粒百分含量呈显著正相关，与极细砂和粉砂呈显著负相关；各粒级土壤侵蚀模数与分形维数呈二次函数关系，分形维数2．81为土壤侵蚀发生的阈值．以土壤粒径分形维数2．81作为草地恢复指标，选择使分形维数小于2．81的相应措施，是恢复退化草地的有力保证．

英文摘要：

The alpine meadow in the source region of the Yangtze and Yellow River is suffering serious deterioration. Though great efforts have been put into, the restoration for the degraded grassland is far from being effective, mainly due to poor understanding of the degradation mechanism of alpine meadow in this region. In order to clarify the formation mechanism of degradation grassland and provide the new ideas for restoration, degradation sequences of the alpine meadow in the source region of the Yangtze and Yellow River were taken as target systems to analyze the soil particle size distribution, the fractal dimension of the soil particle size, and the relationship between soil erosion modulus and fractal dimension. The results showed that, with increasing grassland degradation, the percentage contents of clay increased while the percentage contents of silt sand and very fine sand showed a decreasing trend. The fractal dimension presented a positive correlation with clay among the degradation sequences while negative correlations were found with very fine sand and silt sand. The curvilinear regression of fractal dimension and erosion modulus fitted a quadratic function. Judged by the function, fractal dimension 2.81 was the threshold value of soil erosion. The thre- shold value has an indicative meaning on predicting the breakout of grazing-induced erosion and on restoration of the degraded grassland. Taking fractal dimension of 2.81 as the restoration indicator, adoption of corresponding measures to make fractal dimension less than 2.81, would an effective way to restore the degradation grassland.