Effects of over-grazing on vegetation degradation of the Kobresia pygmaea meadow and determination of degenerative index in the Naqu Prefecture of Tibet

In this paper, the investigation and analysis of vegetation of the Kobresia pygmaea meadow under different grazing intensities was conducted in the middle region of the Naqu Prefecture. Results showed that the grasslands had suffered from over-grazing ranging from 69% to 260% in areas near residential locations. The over-grazed grasslands were shown to have a significantly lower diversity index, coverage percent, and standing biomass yield than that of enclosed grasslands which are protected from grazing. With increasing stocking rates, the number of sedge family species which are drought-resistance and inedible by livestock showed increasing numbers. Using the degenerative index based on the change in vegetation features, the K. pygmaea meadow was classified as having areas ranging from mid-level to heavy degradation, with areas showing a tendency towards further degradation. The grasslands in extremely over-grazed areas have reached the serious degradation stage and the grasslands in medium to high over-grazed areas have reached the medium degradation stage, the percentage of these stages being 9% and 91%, respectively. This figure was more severe than that recorded in 1996.