Effect of grazing intensity on characteristics of alpine meadow communities in the eastern Qinghai-Tibetan Plateau.

A comparative study on community characteristics with different grazing intensitie was conducted in alpine meadows of the eastern Qinghai-Tibetan Plateau(Maqu county,Gansu province).With increased grazing intensity,vegetation height,total cover and above-ground biomass all showed a significant decrease.The importance of species of Cyperaceae and Gramineae families fell and their dominances were replaced by some forbs species(Ligularia virgaurea and Leontopodium leontopodioides).For plant functional groups,the biomass proportions of the germinal species group and the sedge species group were significantly reduced by increased grazing intensity,but the biomass proportions of leguminous species group,forbs species group and noxious species group were significantly increased.Richness index(R),Shannon-Wiener diversity index(H) and Evenness index(E) of alpine meadow communities reached a maximum under the middle grazing intensity in the moderately-grazed plotheavily-grazed plotnon-grazed plot.Results suggest that with increased grazing,alpine meadow communities will undergo a succession from "dominated by tall germinal and sedge species" to "dominated by tall germinal and sedge species+middle forbs species",then to "dominated by middle and lower forbs species".