Variations of forage yield and forage-livestock balance in grasslands over the Tibetan Pla-teau, China.

An in-depth understanding of variations in grassland productivity and forage-livestock balance is the basis of ecological barrier construction and ecosystem conservation in the Qinghai-Tibetan Plateau. Using an ecohydrological process-based model VIP with remotely sensed vegetation index and leaf area index, we simulated the spatial and temporal variations of grassland productivity in the Tibetan Plateau in 2000-2018. The variations in the status of forage-livestock balance at the county level were analyzed, combining with agriculture and animal husbandry statistics in the same period. The results showed that the mean annual net primary productivity (NPP) of grassland in the Tibetan Plateau was 158.4 g C·m·a, which had increased significantly in the past 20 years, with a significant increase in 44.7% of the total area. Climate warming, increased precipitation, prolonged growing season, and elevated carbon dioxide concentration were main driving forces for grassland productivity. The mean theoretical livestock carrying capacity estimated based on pasture yield was 1.17 SU·hm, with a growth rate of 0.011 SU·hm. The situation of overgrazing in the Tibetan Plateau had generally improved since 2000. The proportion of counties with severe overgrazing had dropped to less than 20%. In areas with more severe overgrazing, animal husbandry's maintenance and development mainly relied on supplementation of crop straw. The results could provide a scientific basis for regional agricultural and animal husbandry structural adjustment and environmental protection.