青海三江源区果洛藏族自治州草地退化成因分析

本文利用长期历史资料，通过分析气候变化和人类放牧活动对草地生产力的影响，探讨1960s以来青海三江源区果洛藏族自治州草地退化主要原因，结果显示：研究区是全球变暖的敏感地区，1961-2010年研究区气温升高、年降水略有下降、湿润程度下降，Miami模型、Thornthwaite Memorial模型和综合自然植被净第一性生产力模型（综合模型）模拟的该区植被净初级生产力（NPP）均具有上升趋势，近50年来研究区气候变化总体上有利于该区草地生产力改善；研究区家畜年末存栏数60年代剧烈上升，至70年代达到顶峰，家畜年末存栏数与植被NDVI呈极显著负相关关系(P<0.01)，草地实际载畜量过大造成牲畜对草地过度啃食，导致草地退化。研究区退化草地恢复治理的重点应放在减轻载畜压力、控制草地现实载畜量方面。

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 in 1970s. 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 (P < 0.01) 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.