Comparative study of the alpine grassland communities in varying degradation in Zoige County,Sichuan Province

The monitoring of species diversity and evenness of alpine grassland along the degradation gradient was conducted to characterize changes of the community structure in varying degradation and suggest possible causes in Zoige County in both 2008 and 2009.The results showed that:(1)the coverage,species richness,Shannon-Wiener and Pielou indexes of species diversity of communities were decreasing from the non-degradation to the highest degradation;(2)The aboveground biomass was decreasing from the non-degradation to the highest degradation,with 836.78 g/m2,726.37 g/m2,and 542.78 g/m2 in fresh weight for non-degraded,moderate degraded and heavy degraded communities.The weight of dry biomass of moderate degraded communities was quite close to non-degraded communities and obviously higher than heavy degraded communities;(3)Excavating discharge ditches in 1965-1973 might be the main driving factor of community degradation.Other driving factors included overgrazing,highway construction and tourism.