Effects Of Disturbance Regimes On Vegetation Community Structure In Typical Steppe Of Yunwu Mountain

We study the effects of different disturbance regimes(fire,grazing and fencing)on the community characteristics,niche and spatial heterogeneity of typical steppe in Yunwu Mountain,to provide the theoretical basis for the rational utilization of grassland resources and the restoration of degraded grasslands.The results showed that:1 Fire affected the species composition,structure and succession process of the community.Fire decreased the importance value of Stipa grandis and increased the importance value of species Stipa przewalskyi,Chrysanthemum lavandulifolium and Artemisia sacrorum Ledeb.var.messerschmidtiana.Fire significantly decreased the importance value of perennial grasses,and significantly increased the importance value of perennial forbs,and had no effect on the importance value of annual or biennal herbs and shrubs or subshrubs(P>0.05).For the species composition of the functional groups,fire significantly increased the percentage of shrubs or subshrubs and decreased the percentage of annual or biennal herbs,and did not significantly affect the percentage of perennial forbs and perennial grasses(P>0.05).The species richness,diversity and evenness of the community and functional groups did not differ significantly between burnt and unburnt plots(P>0.05),except that the species richness of annual or biennal herbs significantly decreased and shrubs or subshrubs significantly increased in burnt grasslands compared with unburned grasslands.Fire significantly decreased the aboveground biomass of perennial grasses and increased the aboveground biomass of perennial forbs.2 Species Potentilla bifurca was the generalist in this region,and had higher niche breath in all sites.The niche breadths of Carex aridula was largest than that of other species in unburnt grassland.The niche breadths of species Potentilla bifurca both was the largest in 1-year and 2-year burnt grasslands.The niche breaths of Viola dissecta was the largest in 5-year burnt grasslands.Fire significantly increased the niche breath of species Stipa przewalskyi,and significantly decreased the niche breath of species Thymus mongolicus and Leymus secalinus.Species having high niche overlap with other species didn't have large niche breath.The species richness,the niche width and management and use of resources improved significantly during the grassland in the national succession of restoration after burning.The pairs of species with the highest niche overlap in the grasslands with were,respectively,Saussurea japonica var.pteroclada and Thymus mongolicus,Stipa grandis and Carex aridula,Stipa przewalskyi and Chrysanthemum lavandulifolium.The average values of niche overlap to the dominant species was highest in the grasslands with one year after a fire,and obviously decreased in the 5-year burnt grasslands.Species diversity significantly decreased in the grasslands with one year after a fire,and significantly increased in 2-year and 5-year burnt grasslands.These findings indicated that the grassland ecosystem was gradually restored and interspecific competition was also decreased with increasing the restoration time after a fire.3 Under different disturbances,the dominant species of the community changed;The spatial distribution of community had good concordance with function law,and all population had strong spatial heterogeneity under different disturbances;The spatial heterogeneity was species-specific in different disturbance regimes.The spatial heterogeneity in burned plots was higher than fenced plots,and the spatial heterogeneity in fenced plots was lower than grazed grasslands,and the uniformity of fenced plot was better than other two grasslands;The species richness and ShannonWiener diversity index in grazed plots and burned plots were significantly higher than that in fenced plot,while the Pielou evenness index in fenced plots was significantly higher than that in grazed plots and burned plots;It can be seen that the spatial heterogeneity of the community in the typical grassland on Loess Plateau,grazing and burning has increased the spatial heterogeneity.They also make the spatial heterogeneity of plant population change obviously.