Abstract: The β-diversity characteristics of four Stipa communities (S.baicalensis, S.grandis, S.krylovii and S.klemenzii) were studied using comparable plots methods. As a measurement of species turnover within communities, Whittacker's index(β_ws) was size dependent, and reduced gradually with the increasing quadrat size.Under the same scale,β_ws indices of the communities were similar.Cody's index (βc)was also affected by sampling size.βc increased initially as quadrat size enlarged,then stabilized over the size of 0.5m² for S.baicalensis and S.grandis communities, and 2 m² for S. krylovii and S.klemenzii communities. S.baicalensis community had the highest Cody index, while S.klemenzii community had the lowest one. In most cases, the within community distance interval had a relatively high effect on Cody index; From S.baicalensis to S.klemenzii community,the functional group diversities of forbs,perennial bunch and rhizome grasses decreased greatly,the diversity of intermediate xerads reduced significantly,and the diversity of xerads increased firstly, and then declined for S.klemenzii community.The changes in species composition of four Stipa communities could give a reflection to the degrees of community replacement along ecological gradients,and Cody indices between the communities reduced gradually.The Morisita Horn similarity coefficient between S.baicalensis and S.grandis community was significantly higher (0.72) than those between S.grandis and S.krylovii communities (0.55),and between S.krylovii and S.klemenzii communities(0.42).

Key words: Inner Mongolia Plateau, Sitpa communities, β-diversity