中文摘要：

贺兰山是针叶林分布的交错区,为我国油松林分布的西界和青海云杉林分布的东界。通过沿海拔梯度设计样带,系统布设样方,对贺兰山针叶林进行了野外调查。结果表明,贺兰山针叶林的平均树高和总胸高截面积随海拔升高而增加,同时立木组成中胸径大的树木增多,表明其生长状况逐渐变好。随着海拔升高,群落的物种丰富度不断降低,但种类组成的变化是连续的。林下土壤的土层深度、有机质和全氮质量分数随海拔升高而增加,土壤pH值则随着海拔升高而降低。土壤因子随海拔的变化,是研究区针叶林变化的生态梯度,反映了气候因子的作用。

英文摘要：

As a typical ecozone,Mt.Helan locates in the western boundary of Pinus tabulaeformis forests and the eastern boundary of Picea crassifolia forests in China.A field survey on the coniferous forests was conducted,with selective elevational gradients and systematic sampling plots.Results show that the mean heights of trees and the total trunks’ area at breast height increase with elevation,and the trees in large diameter classes occupy a large proportion in the species composition,indicating that the coniferous forests grow better at higher elevations.However,the species richness declines with elevation,and there is a gradual change in species composition.The soil depth,organic matter and total nitrogen content increase with elevation,while the pH value decreases.The changes in soil features with elevation result in the ecological gradients influencing the coniferous forests in the study area,which indicates that the climatic gradient is associated with elevation.