| The experiment designed by randomized of three blocks and four stocking ratess with sheep which conducted in Stipa breviflora desert steppe. It investigated and analyzed plant community characteristics by imitated summer grazing for continuous four years,the main results showed as follows:(1)The proper stocking rates in this area is between light grazing and moderates grazing. The standing crop, height, coverage of community and the main plants all decreased as stocking rates increased. Plants became clump fragmentation and smaller. (2)The plant community occurred the tendency of degradation which influenced by the grazing. Annuals and biennials forbs and other grasses ocurred in the plant community. (3)Moderates grazing has promoting effect in a short time, continuous grazing made the plant species biodiversity have the significance difference (P﹤0.05) between grazing and no grazing plots .Simultaneously, the increase of evenness was the main factor of the increase of biodiversity of functional groups with grazing. (4) The dissimilarity of community increased with years, and the plant community changed to the different directions. (5) In different years, the percentage of annuals and biennials plants, and perennial forbs increased in heavy grazing plot. The niche width of annuals and biennials were increased obviously. The niche overlap between annuals and biennials & perennial plants increased. It means that annuals and biennials will be the dorminant species if the heavy grazing continuously.
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