Influence of Seasonal Exclosure on Vegetation Restoration in Typical Steppe,Inner Mongolia

In order to discuss the restoration and reasonable utilization of degradation typical steppe,natural grasslands fenced in growing season for hay production then lightly grazed for the rest of the year were selected as research objects.Continuously grazed grasslands were selected as control.Vegetation restoration was investigated after seasonal exclosure.Results showed as follows: the biomass,coverage and density of vegetation in degraded typical steppe increased significantly after seasonal exclosure(P0.05),and reached the highest values after 13 years exclosure then decreased due to hay production developed continuously for many years.Dominant species changed significantly after seasonal exclosure.The community structure was changed from Potentilla acaulis+Artemisia frigida+Cleistogenes squarrosa to Leymus chinensis+Stipa krylovii+Artemisia frigida+Cleistogenes squarrosa after 20 years exclosure.The species richness,evenness,diversity and dominance increased significantly after 7 years exclosure.But the community was mainly dominated by signal or minority species and the species richness,evenness and diversity decreased then the dominance increased remarkably after 10 to 13 years exclosure.Then the community stabilized gradually,the species richness,evenness and diversity increased and the dominance decreased with the exclosure period prolonged to 20 years.In conclusion,seasonal exclosure was a feasible management method in Chinese pastoral areas.Comprehensive analysis of community structure,yield and species diversity indicated that 13 years exclosure is a reasonable exclosure period.And some problems such as reasonable mowing systems needed further study.