Abstract
Songnen Plain in Northeast China is one of the most significantly altered biological hotspots on Earth. Based on the information from integrated topographic maps, Landsat MSS, TM/ETM images and geographic information systems, grassland cover change, grassland fragmentation, agricultural reclamation, and saline-alkaline wasteland expansion in the region were investigated for the period of 1954 to 2000. The results showed that the native grassland decreased by 44.6 × 10(4)ha and moderate density grassland decreased from 78.3 × 10(4) to 20.3 × 10(4)ha. Calculated from change dynamic model, the annual decrease rate of grassland was 1.1%.The distribution center of the grasslands illustrated a trend of shifting southeastward. The distance between centroids of grassland was 10.1km. The numbers of grassland patch increased by 1,378, while the patch size of grasslands declined. Grassland experienced substantial clearing and fragmentation. The decreased grassland was converted into cropland, wetland, and saline-alkaline wasteland. The loss and degradation of grasslands was closely related to regional climate during the past 47years. Population and livestock number increased significantly as grassland quality decreased. Intensive human activities including irrational reclamation and overgrazing may have accelerated the degradation of grasslands.
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