Analysis of NDVI distribution and limiting factors of alpine grassland in permafrost area of the upper Shule River

The most direct impacts of global warming on permafrost are ground temperature rising and active layer thickening, which will reduce moisture content of surface soil, and then, influence vegetation of permafrost zone. In this study, we studied distribution and changes of NDVI of the alpine grassland and built relationships between NDVI and land surface temperature (LST) to infer the limiting factors (water and energy) of vegetation growth on the source region of Shule River basin, a semiarid zone, which locates in the western of Qilian Mountain. The result showed that the distribution of NDVI was in the shape of reversed U from extreme stable permafrost zone to seasonal frost zone. Second, Since 1995, NDVI has increased slightly in extreme stable and stable permafrost zones and the increase were more significant in substable and transition permafrost zones. However, NDVI has decreased in unstable permafrost zone and seasonal frost zone. Moreover, limiting factor of vegetation growth was transfered from energy in extreme stable permafrost zone to water in seasonal frost zone.