Livestock-carrying capacity and overgrazing status of alpine grassland in the Three-River Headwaters region, China

The Three-River Headwaters region in China is an ecological barrier providing environmental protection and regional sustainable development for the mid-stream and downstream areas, which also plays an important role in animal husbandry in China. This study estimated the grassland yield in the Three-River Headwaters region based on MODIS NPP data, and calculated the proper livestock-carrying capacity of the grassland. We analyzed the overgrazing number and its spatial distribution characteristics through data comparison between actual and proper livestock-carrying capacity. The results showed the following: (1) total grassland yield (hay) in the Three-River Headwaters region was 10.96 million tons in 2010 with an average grassland yield of 465.70 kg/hm(2) (the spatial distribution presents a decreasing trend from the east and southeast to the west and northwest in turn); (2) the proper livestock-carrying capacity in the Three-River Headwaters region is 12.19 million sheep units (hereafter described as SU), and the average stocking capacity is 51.27 SU [the proper carrying capacity is above 100 SU/km(2) in the eastern counties, 60 SU/km(2) in the central counties (except Madoi County), and 30 SU/km(2) in the western counties]; and (3) total overgrazing number was 6.52 million SU in the Three-River Headwaters region in 2010, with an average overgrazing ratio of 67.88% and an average overgrazing number of 27.43 SU/km2. A higher overgrazing ratio occurred in Tongde, Xinghai, Yushu, Henan and Zkog. There was no overgrazing in Zhiduo, Tanggula Township and Darlag, Qumerleb and Madoi. The remainder of the counties had varying degrees of overgrazing.