Effect of grazing intensity on species richness and biomass of alpine meadow in northwest Sichuan

This study aimed to elucidate the effects of yak (Bos grunniens) grazing intensity on aboveground biomass and identify the optimum grazing intensity of alpine meadow in northwest Sichuan area. Three grazing intensities were considered, namely light grazing (0.71 yak·ha-1), moderate grazing (1.19 yak·ha-1), and heavy grazing (1.60 yak·ha-1), which were selected based on the food intake of the yaks and the average annual biomass of the meadow. The grazing experiment lasted for 3 years. The species richness of the plants and the aboveground biomass were determined. The results showed that the species richness tended to decrease as the grazing intensity increased. In the third year of grazing, the annual aboveground biomass of the meadow under moderate grazing was the highest, followed by that of the meadow under light grazing, and that of the meadow under heavy grazing was the lowest. In the third year, compared with the first year, there was a decrease in the proportion of forbs and an increase in that of grass among the annual biomass in the meadows under light and moderate grazing. In contrast, there was no change in the proportion of forbs and a decrease in that of grass in the meadow under heavy grazing. Meanwhile, the proportion of sedge increased in all meadows irrespective of the grazing intensity. In conclusion, moderate grazing (1.19 yak·ha-1) is best due to its beneficial effects on yield and the growth of grass and sedge.