Effects of Yaks Grazing Methods on the Community Characteristics of Kobresia pygmaea Meadow in Tibet

Effects of yaks grazing intensity and grazing years on the plant community dynamics and aboveground biomass of Kobresia pygmaea meadow in Tibet were studied using sampling methods in order to provide a theoretical basis for recovering and increasing the productivity of degraded grasslands in alpine pastoral region.The results showed that heavy grazing(HG) negatively influenced plant community diversity and aboveground biomass,whereas moderate grazing(MG) increased diversity,richness,evenness,aboveground biomass and reduced vegetation coverage.These values in delayed-moderate grazing(DHG)were higher than those in HG.Correlation analysis showed that coverage and evenness,richness,plant density,diversity and aboveground biomass were positively correlated.In addition,the functional groups of Kobresia pygmaea meadow significantly differed from different grazing intensities.The coverage and aboveground biomass of perennial rhizome grass(Kobresia pygmaea and Carex rnoorcroftii) and perennial bunch grass(Stipa purpurea),which constituted the dominant species of the ecosystem,decreased with the increase of grazing intensity.