不同海拔关山草原群落的结构特征

以不同海拔梯度下（坡下、坡中、坡上）陕西关山草原群落为研究对象，利用幂乘方法则分析植被的空间分布特性及其群落的物种组成、物种多样性等。结果表明，坡下、坡中、坡上3个不同海拔梯度下，草地群落的组成物种对幂乘方法则具有很好的吻合性；草地群落的总物种数、物种多样性指数(H′)及群落整体的空间异质性指数（δc）都随海拔梯度的升高而增加；样方内的平均物种数、平均多样性指数亦随海拔梯度的升高而增加，但它们之间没有显著性差异（P>0.05）；坡上、坡中禾本科和豆科植物的出现频率较高，而草地退化的标志性植物火绒草（Leontopodium leontopodioides）在坡中的出现频率很高，蛇莓（Duchesnea indica）和毛茛（Ranunculus japonicus）在坡下的出现频率更高，表明坡下草地退化比较严重。

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 (P>0.05) 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.