Abstract: A study was carried out on seasonal variation of species composition,biomass and distribution of alpine meadow plant communities with different grazing intensity in Hongyuan County,Sichuan Province. With increasing grazing intensity,dominancy of the plant community shifted from grasses(Roegneria nutans and Elymus nutans) to sedges (Kobresia pygmaea and K. setchwanensis). Over the growing season from June to September,aboveground biomass was the highest in Treatment NG (non-grazing plot) and the lowest in Treatment HG (heavily grazed plot),while belowground biomass showed an rising trend with increasing grazing intensity and it was significantly higher in Treatment HG and Treatment MG (moderately grazed plot) than in Treatment NG and Treatment LG (lightly grazed plot). Total plant biomass averaged over the growing season was 1 543.3,1 621.6,2 294.7,and 2 448.5 g·m^-2 in Treatments NG,LG,MG and HG,respectively. The proportion of belowground biomass to total plant biomass was 87.8%,81.8%,76.2%,and 69.2%,in Treatments HG,MG,LG and NG,respectively,which shows adaptation of the plants in the meadow to grazing.

Key words: grazing, plant species composition, biomass, Qinghai-Tibet Plateau