Effects of over-grazing on vegetation degradation of Kobresia pygmaea meadow in Nagqu, Tibet

In this paper, investigation and analysis of vegetation of Alpine Kobresia meadow (Kobresia pygrnaea) in different grazing densities were conducted in the middle region of Nagqu. Results showed that the grasslands of Alpine Kobresia meadow in the region have suffered from intensive grazing, over-grazing rates around the residential areas have reached 260% and the lowest over-grazing rate was also 69%. The over-grazed grasslands have significant lower diversity index, coverage percentage and standing biomass yields than those of the enclosed grasslands. With the increased stocking rates, the number of species of the Sedge family, drought-resistant weeds and grasses inedible for livestock shows an increasing trend. According to the changes in the vegetation features and compared with the classified index of degradation grasslands of Alpine Kobresia meadow, we found that the Alpine Kobresia meadow in Nagqu exhibited a degrading tendency and is in the process of heavy-to-middle level degradation. The extremely over-grazed grasslands are undergoing very serious degradation stages and the grasslands in high and medium over-grazed status are in the medium-degradation stages. The ratios have reached 9% and 91% respectively, which were more than those of 1996.