The cause of grassland degradation in Golog Tibetan Autonomous Prefecture in the Three Rivers Headwaters Region of Qinghai Province

Grassland degradation was the deterioration of the grassland ecosystem function,such as structure,energy flow and material circulation,during its evolution process. This result is due to grassland coverage declining,yield of grass decrease and poison rank grass overgrowing,caused by human activities interference or adverse natural factors. Since the grim situation,the quality of grassland decline,Grassland productivity,economic potential and service function deteriorate,biodiversity complexity level descend,recovery function weaken or disappear,which threat region ecological security.Therefore,grassland degradation and its ecological impact have been an important research area of ecology. Located at the east of Tibet Plateau,the three rivers headwater region is the source region of Yangtze River,Yellow River and lancang River,and regard as the water tower of China. Under the influences of climate change and human activities,the grassland degradation presented a general situation in the Three Rivers Headwaters Region of Qinghai Province in last decades. Mainly located in the source region of Yellow River,the alpine meadow degradation and alpine steppe desertification were common phenomena. Grassland degradation was the result under joint action of long-term climate change and unreasonable grazing.By using long- term historical data,this paper investigated the cause of grassland degradation in the aspects of climate change effect and grazing influence to grassland productivity in Golog Tibetan Autonomous Prefecture since 1960s. The result showed that this region was sensitive to global warming. From 1961 to 2010,the annual average temperature ascending,annual precipitation slightly decreasing and moisture condition descending were the general trend. Nevertheless,the net primary productivity( NPP) was in the upward trend by the simulation of Miami Model,Thornthwaite Memorial Model and Synthetic Natural Vegetation Net Primary Productivity Model( Synthetic Model). The climate change improved the grassland productivity in generally. Hence,from macro point of view,climate change was not the cause of grassland degradation in the research area. The livestock amount at the end of year increased sharply in 1960s and reached the peak in1970s. Large grassland current carrying capacity meant grassland overload and overgrazing. After that,the grassland deteriorated. The livestock amount at the end of year had extremely significant correlation( P0.01) with NDVI condition.Therefore,long-term grassland overload and overgrazing was the cause of grassland degradation. The key points of degraded grassland recover and governance were controlling grassland current carrying capacity and relieving grassland livestock carrying pressure. Since 2000,with the declining of grassland current carrying capacity,degraded grassland began to recover.