Characteristics and causes of changes of alpine grassland productivity in the source region of Yellow River

Vegetation productivity is one of the most important indicators for grassland health, which is also an important parameters for calculating the livestock carrying capacity. This research on alpine grassland productivity changes in the source region of Yellow River helps us comprehend the dominating driven factors on alpine grassland degradation and improve decision making by the government managers, optimize their management practices, and increase grassland productivity and profitability. Aboveground green biomass (AGGB), livestock carrying capacity, land use / land cover change and climate change, etc. in 1980 were compared with that in 2005. Results indicated that the grassland conditions became worse, with lower aboveground palatable grass yield, plant height, and cover in 2005 compared with the results obtained in 1981. Average AGGB in 1980s was 3605.25 kg/ha which decreased to 2954.44 kg/ha in 2005, the decreasing rate was 18.1%, among which areas of higher productivity grassland decreased while areas of low to middle productivity grassland increased. At the same time, regional climate become warm and humid which was conducive to alpine grassland´s recovery. In the meantime, however, although the actual livestock numbers decreased, they still exceeded the proper theoretical livestock carrying capacity, with and average overgrazing rate of 72.47%. Further investigations into the other impacting factors tells us that human activities were the main cause of alpine grassland degradation during the past 25 years.