祁连山北坡中段植物群落多样性的垂直分布格局

Species diversity of plant communities along an altitudinal gradient in the middle section of northern slopes of Qilian Mountains, Zhangye, Gansu, China

利用DCCA排序和海拔高程排序相结合的方法 ,对祁连山北坡中段植物群落物种多样性垂直分布格局进行了初步研究。结果表明 :1)植物群落草本层和灌木层物种丰富度和多样性在环境梯度上呈单峰曲线变化趋势 ,乔木层的物种丰富度和多样性在环境梯度上无变化。物种丰富度和多样性对环境梯度变化敏感程度的次序是草本层 >灌木层 >乔木层 ;2 )植物群落各层次均匀度在环境梯度上没有表现出一定的变化规律 ,均匀度可能更多地受制于群落自身动态的影响 ,而独立于生境的资源水平 ;3)草地群落物种多样性在DCCA环境梯度上曲线的拟合效果优于按海拔高程排序效果 ,灌木群落则相反 ;4)低海拔、中低海拔和中海拔地带的草本层物种丰富度和Shannon Wiener多样性指数 (H′)显著高于灌木层 (p <0 .0 1) ;高海拔地带草本层仅丰富度指数显著高于灌木层 (p <0 .0 5 )。在整个海拔范围内 ,草本层和灌木层的均匀度无显著差异。就资源的可利用性而言 ,研究区域植物群落物种多样性在垂直环境梯度上的变化规律表达了物种多样性与资源生产力的单调关系内涵。

Measurements of species diversity of plant communities along both DCCA axis 1 and an altitudinal gradient in the northern slopes of Qilian mountains was carried out. The results showed that: 1) Both species richness and diversity in the herb layer significantly peaked at the intermediate elevations.The same trend was also suggested in the shrub layer, but the curves of both richness and diversity were not significant. Both richness and diversity in the tree layer showed no changes with increased altitude, suggesting that the order of sensitivity in terms of the responses of richness and diversity to altitudinal gradients was herb layer, then shrub layer and tree layer. 2) Evenness of the three layers showed no noticeable trend with altitude, suggesting that the dynamics of evenness of a given plant community may be strongly influenced by some fundamental characteristics of plant community rather than resource availability. 3) The fitted curve of both diversity and richness of herb layer with DCCA axis 1 was more significant than that fitted with altitudinal gradient, while that of shrub layer showed the opposite trend. 4) Of all the comparisons between shrub and herb layer in terms of richness, diversity and evenness, the differentiation was significant for both richness and diversity in the lower altitudinal zone (p<0.01), the mid-lower to mid-altitudinal zone (p<0.01)(excluding Simpson diversity index (D)) and in the high altitudinal zone (p<0.05)(excluding both Shannon-Wiener diversity index (H′) and Simpson diversity index). The differentiation of evenness between shrub layer and herb layer was not significant in any of the comparisons. The pattern of species diversity-altitudinal gradient reported here demonstrates a monotonic relationship between productivity and species diversity related to resource availability.