Although snow cover plays an important role in structuring plant diversity in the alpine zone,there are few studies on the relationship between snow cover and species diversity of alpine meadows on the eastern Qinghai-Tibetan Plateau.To assess the effect of snow cover on plant species diversity of alpine meadows,we used ten parallel transects of 60m×1m for this study and described the changes in species diversity and composition associated with snow depth.With the division of snow depth into six classes,the highest species richness(S)and species diversity(H')occurred with an intermediate snow depth,i.e.,class III and class IV,showing a unimodal curve with the increase in snow depth.The relationship between snow depth and plant diversity(both richness and Shannon index)could be depicted by quadratic equations.There was no evident relationship between diversity(both S and H')and soil water content,which implied that other more important factors influenced species diversity.The patterns of diversity found in our study were largely attributed to freeze-thaw alteration,length of growing season and disturbances of livestock grazing.Furthermore,snow depth affected species composition,as evaluated by the Srensen's index of similarity.In addition,almost all species limited to one snow depth class were found only in class III and class IV,indicating that intermediate snow depth was suitable for the survival and growth of many alpine species.
