Comparative Evaluation Of Suitable Enclosure Years Of Desert Steppe In Inner Mongolia Based On Plant Community Characteristics

Grassland is one of the largest and most important terrestrial ecosystems,which plays a vital role in the survival and development of human beings.However,due to long-term human disturbance and climate change,grassland ecosystem has been seriously degraded and productivity has decreased significantly.Grazing is one of the most important factors causing grassland degradation.Since the 20^thcentury,with the rapid development of animal husbandry,the number of livestock has been rise rapidly in the western desert steppe area.Due to the poor nutrition,fragile vegetation and poor anti-disturbance ability in this area,overgrazing has made the unstable in structure and function of grassland ecosystem,which has brought huge pressure to the ecological environment.As one of the economical and efficient ecological restoration measurements,enclosure plays an important role in rational utilization of degraded grassland.Studying the relationship between enclosure and changes in plant community structure and diversity is helpful to clarify the mechanism of vegetation restoration process and provide theoretical support for sustainable utilization of grassland ecosystem.In order to reveal and evaluate the impact of enclosure on the grassland ecosystem,This study conducted with 2 treatments of enclosure and grazing,3 replications of each treatment.The quadrat method was used to determine some plant community indicators such as height,coverage,density and biomass in August every year in different plot,the quantitative analysis of plant community characteristics in different treatment was done in a long time series（2004-2020）,evaluated the relationship between the plant community structure and diversity under different enclosure years in the desert steppe,the main results as follows:（1）A total of 58 species of plants,belonging to 40 genera,19 families,appeared in the experimental area from 2004 to 2020.There were 55 species,belonging to 38 genera,18families in the enclosure treatment,while there were 44 species,belonging to 30 genera,17families in the grazing treatment,which were mainly Gramineae,Compositae,Chenopodiaceae,Legume and Liliaceae.（2）Enclosure significantly increased the number of plant species after 9 years of enclosures.The enclosure significantly increased the aboveground biomass of grassland plants.Enclosing is beneficial to increase the proportion of perennial herbs,shrubs and subshrubs,and annual and biennial herbs.After 9 years of fencing,the Margalef richness index,Shannon-Wiener diversity index and Simpson diversity index of grassland plants increased significantly.After 11 years of enclosure,the Pielou evenness index of grassland plants increased significantly.In summary,the enclosure treatment is beneficial to increase the plant diversity of Stipa breviflora desert steppe in Inner Mongolia,but the short-term or long-term enclosure has a certain limiting effect on the vegetation growth,and 9-12 years is the appropriate enclosure period in this type of grassland.