Changes of community structure and species diversity in different succession stages in typical steppe.

In order to discuss the restorative process and reasonable utilization of degraded typical steppe,natural grasslands fenced in growing season(April to September)for hay production then light grazing in the rest of the year were chose as the research objects.At the same time open grazing land was chose as the control to carry out the research on the changes of community structure and species diversity in different succession stage in typical steppe.The results were as follows:The species composition of typical steppe in different succession stage was basically identical,but the dominant position of main species changed significantly.In open grazing land,the dominant species were Potentilla acaulis,Artemisia frigida and Cleistogenes squarros;after the utilization of seasonal exclosure,the dominant position of excellent forages such as Leymus chinensis and Stipa klmenzii increased,the degraded typical grassland developed positive,the coverage,density,biomass and proportion of palatable forage increased,the structure of community optimized and the species diversity increased.But if hay production was continued for many years(13 years or more),and then the recovered grassland might appear the second retrogressive succession.Through the research we concluded that seasonal fencing could ensure the restoration of degraded grassland to some extent,and it also could avoid the waste of forage resources caused by completely fencing at the same time.Seasonal fencing was one of the feasible management methods in Chinese pastoral areas,but some problems such as suitable forbidding season and reasonable mowing systems need further study.