Carrying capacity of grasslands and its spatiotemporal change in Tibet, China

The carrying capacity of grassland and the carrying capacity of grassland with supplementary feeding were analyzed in Tibet, China. This analysis was based on identifying areas unsuitable for grazing or where grazing was not possible, correcting grass yield and calculating the demand for grass used for ecological protection, estimating the carrying capacity of grasslands at the county level. Also, the spatiotemporal change in the carrying capacity of grasslands over time, the effects of supplementary feeding of livestock on agricultural and forestry land on the trends and dynamics of the carrying capacity of grasslands, and the relationship between the carrying ratio of grasslands and the ecological status of counties were explored. Results showed that there was a significant regional difference in the spatial distribution of the carrying capacity of grasslands and the carrying capacity of grasslands with supplementary feeding of livestock in Tibet; these differences depended on water conditions and temperature, respectively. Although some counties in Southeast and Northwest Tibet had a grass surplus in 2011, grassland ecosystems of most counties and in Tibet as a whole were overstocked with livestock, shortages of adequate forage have become more serious since 2000. Furthermore, while the spatial autocorrelation of the carrying status of grasslands and its dynamic changes decreased, the spatial heterogeneity of the carrying status of grasslands increased. These characteristics were mainly the result of a rapid expansion of the stocking levels for livestock, and the spatial mismatch between the demand and supply of grass resources. By mitigating the quantitative and spatial mismatch between supply and demand for grass resources, the use of supplemental feeding on agricultural and forestry lands could improve the grassland carrying capacity of Tibet as a whole, especially for agricultural and semi-agricultural counties. However, such mitigation had a less significant effect on the dynamic trends of the carrying capacity of grasslands. In addition, the decreasing trend of the ecological quality in the counties was significantly correlated with the overstocking of grasslands with grazing animals and the decrease in the carrying ratio of grasslands in Tibet. Therefore, the main measures that are needed to improve the carrying capacity of grasslands and to mitigate the decreasing trend of the ecological quality of grasslands will include zoning areas suitable for grazing, controlling the stocking levels of livestock and optimizing the distribution of animal husbandry.