Spatial and temporal variation of net primary productivity in Inner Mongolian grassland from 1981 to 2001

With remote sensing and climatic data, CASA model was applied to simulate spatiotemporal variations of grassland net primary productivity (NPP) in Inner Mongolia from 1981 to 2001. Impacts of climatic factors and human activities on the grassland NPP were primarily distinguished via statistical analysis. The results showed that from 1981 to 2001, approxmiately 69% of the grassland NPP had no significant change, while about 30% of the grassland obtained NPP increment and only about 1% of the grassland experienced a process of NPP decrease. Spatially, the NPP in northeastern, southeastern and southern part of Inner Mongolia significantly increased, but in boundary areas of the desert steppe and typical steppe in the central region of Inner Mongolia, the grassland degraded in term of NPP change. For the whole region, NPP of Inner Mongolian grassland showed a slightly increasing but not statistically significant trend; the long term averaged seasonal NPP between July and August is 192.0 g/m2 (150.5-255.5 g/m2). There was a significant positive correlation between NPP and precipitation, but increased temperature had the effect to cause NPP decreasing. The solar radiation in this region showed no obvious correlation with the grassland NPP. Human activities had determinative impacts on grassland NPP on local scale. While grazing strength represented by livestock density intensified during the two decades in Tumote Left Banner and Tumote Right Banner, the grassland NPP there decreased rapidly and remarkably.