Balance between actual number of livestock and livestock carrying capacity of grassland after added forage of straw based on remote sensing in Tibetan Plateau

Abstract: In order to quickly and accurately know grassland productivity and the balance between the actual livestock and carrying capacity of the grassland, to promote the rational use of grassland and ensure the sustainable development of ecological environment and animal husbandry on the Tibetan Plateau, it is necessary to estimate the stock capacity of natural grassland and grassland after supplementing feed, as well as understand grassland balance situation supplementing feed before and after among different administrative regions in the Tibetan Plateau. The study estimated the grass yield on the Tibetan Plateau and analyzed the yield's spatial distribution of natural grassland using an improved model of CASA combined with the data of NDVI from MODIS, grassland type maps, meteorological data, soil texture on the Tibetan Plateau. The paper adopt the method of straw-to-grain ratio to estimate the volume of straw forage among different administrative regions in the Tibetan Plateau and then to calculate the carrying capacity of the available straw resources of each county. According to the grass yield, carrying capacity of straw resource and the real number of livestock, the paper identified the overgrazing of all counties and cities with grass build balance model. The results showed that the annual grass yield of different regions in the Tibetan Plateau varied a lot in 2010, and the maximum was in Tibet with the largest grass yield of 26 428 890 tons, followed by Qinghai Province with the yield of 23.08 million tons, and Yunnan was the lowest, only 373 600 tons. The total livestock carrying capacity of natural grassland in the Tibetan Plateau was 83 630 365 (standard sheep unit, the same below), in which, the livestock carrying capacities of Qinghai, Tibet, Sichuan, Gansu and Yunnan were 28 890 963, 27 893 522, 18 540 968, 7 964 236 and 340 946, respectively. The overgrazing among each county and city in the Tibetan Plateau was very common. Without adding feed by straw forage, the quantities of the county and city with the overgrazing rate more than 5 times, between 2 and 5 times, less than 1 time accounted for 7.69%, 28.84% and 38.82% of total county and city, respectively. And the counties in which the actual number of livestock did not exceed the local maximum carrying capacity only accounted for 11.19%. In case of adding straw forage, the proportion of the counties without overgrazing remained the same, however the situation of overgrazing county improved. The proportions of the county with overgrazing rates more than 5 times, between 2 and 5 times, between 1 and 2 times decreased by 3.2%, 4.49%, 5.49%, respectively, and the proportion of the county with overgrazing rate less than 1 time increased by 2.2%. Therefore, it is necessary to strictly control the volume of cattle and sheep to match the carrying capacity of natural grassland and feeding straw resources, and to achieve sustainable development of ecological environment and animal husbandry.