Influence of exclosure year on community structure and species diversity on a typical steppe

To investigate the restoration process and reasonable utilization of degraded grassland,we chose as research objects natural grasslands which were exclosed during the growing season for hay production then subjected to light grazing for the rest of the year.Continuous grazing land was used as a control.Comparative research on the influence of different exclosure years on the community structure and species diversity was carried out.The plant species and diversity of degraded grassland increased and the community structure and dominance of species changed greatly after seasonal exclosure.With increased periods of exclosure,coverage and density reached a maximum at year 14 then declined.Community yield and height continued to increase up to year 25.The community changed from Potentilla acaulis+Artemisia frigida+Stipa krylovii to Leymus chinensis+Cleistogenes squarrosa+Serratula centauroides.After 5 years of exclosure,the species richness,evenness and diversity increased.With increased periods of exclosure,the species richness increased continuously and reached its highest after year 14,but the community was mainly dominated by L.chinensis and the species evenness and diversity decreased.Along with the increase of exclosure year,the community gradually stabilized,the species evenness and diversity increased.The analysis of community similarity showed that the similarity between the exclosed sites and the control decreased,which showed that seasonal exclosure had a great impact on changing the environment of the community.We concluded that growing season exclosure for hay production followed by grazing through the rest of the year enabled the grassland to recover to some extent.After comprehensive consideration of the community structure,yield and species diversity,we consider that 14 years of seasonal exclosure appears a reasonable compromise.