Research on characteristics of vegetation community structure at different altitudes in Guanshan grassland

A field investigation was made to clarify community characteristics,including species composition,species diversity and spatial distribution,on a slope of the Guanshan grassland in Shaanxi Province.The surveys were conducted at the lower(2 092 m),middle(2 112 m) and upper(2 132 m) altitudes on the slope,and the data collected were analyzed using the power law.The results indicated that each plant species composition of the three different communities followed the power law.The total species richness,the species diversity index value(H′) and the spatial heterogeneity index value of the entire community(δc) at each altitude tended to increase with the altitude raise.The average values of species number and the species diversity index per quadrat also increased with increasing altitude,and there were no significant differences(P0.05) among three altitudes.The occurrence of Gramineae and Leguminosae plants were more at the upper and middle altitudes than at the lower one.The occurrence of Leontopodium leontopodioides was the highest at the middle altitude;and quantities of Duchesnea indica and Ranunculus japonicus were larger at the lower altitude than at the other ones.L.leontopodioides,D.indica and R.japonicus are the characteristic species of deteriorated grassland in this area.These phenomena indicate that the grassland degradation is more serious in the lower altitude than in the middle and upper ones.