Abstract: By the methods of correlation analysis and buffer analysis, and taking two main climate factors (air temperature and precipitation) and two main human activity areas (road and residential land) into account, this paper studied the effects of climate change and human activity on  grassland net primary productivity (NPP) in western Songnen Plain in 2000-2009. In the past ten years, the mean air temperature in the study area was 5.39 ℃, which increased from north to south, and the mean precipitation was 378 mm, which decreased from northeast to southwest. The grassland NPP increased with the increase of air temperature and precipitation. Compared with air temperature, precipitation affected NPP more obviously, which accorded with the special climate conditions of water shortage in western Songnen Plain. The difference in the NPP was not significant at yearly scale but extremely significant at monthly scale, indicating that time scale had remarkable effects on the statistical significance. The effects of road and residential land on the NPP were completely opposite. The closer to the road, the larger area the grassland with good plant growth, which could related to the appropriate management measures and the ways of local human activities; while the further to the residential land, the weaker the human activities intensity or their capabilities in affecting the grassland, the better the plant growth on the grassland. Compared with road, residential land had more obvious effects on the grassland NPP, possibly due to the higher density of residential land and the more frequent building construction, reclamation, and grazing caused by population increase.

Key words: leguminous green manure, rotation, summer fallow, winter wheat, soil water, soil fertility.