Changes of Productivity and Grazing Capacity of Grassland in Middle Arid Zone of Ningxia during 20 Years

[Objective] The study aimed to explore the vegetation regressive succession law of the middle arid zone of Ningxia.[Method] Based on the investigation data of seven plots in this region from 1982 to 2001,grassland type, vegetation characteristics,productivity and grassland quality were analyzed.[Result] During nearly 20 years,the grassland type of Middle Arid Zone of Ningxia had been changing;the dominant species were being replaced by other species;the vegetation coverage and the number of species in community reduced persistently; the grazing capacity decreased by 114% and the grassland quality deteriorated seriously.[Conclusion] This study should provide basic data for the sustainable utilization of typical grassland.