中文摘要：

通径分析是研究变量间复杂关系的一种有效方法。在沿海拔梯度进行群落调查的基础上，对贺兰山针叶林物种密度进行通径分析，结果表明：1）贺兰山东西坡针叶林物种密度的海拔格局基本一致。物种密度的主要影响因子是海拔，而海拔反映了综合的气候梯度。2）针叶林的物种密度明显随着海拔的升高而降低，表层土壤有机质含量的增高对于物种密度有促进作用。3）针叶林的物种密度主要由草本种类的多少决定。草本和灌木层物种密度都明显受到海拔和土壤有机质含量的影响。坡向对于灌木层物种密度也有一定影响。

英文摘要：

Path analysis is an effective method to analysis the complex interactions among variables. Based on plant communities investigations in coniferous forest of Mr. Helan along altitude, path analysis has been conducted on the relationship between species denstiy in coniferous forest and environmental factors. Then, several conclusions has been obtained. Species denstiy changes along altitude between the east and west sides are similar. Dominant factor which influencing species density is altitude, reflecting the climatic gradient in fact. Species density decreases with altitude significandy, and the more content of organic matter in topsoil could increase the species density in coniferous forest. The species denstiy of coniferous forest is mainly determined by herberous species, as over 70% of species are herbs. The species densities on shrubby and herbaceous layers are both influenced by altitude and organic matter content. However, the species density on shrubby layer would be varied when the slope aspect changes.