中文摘要：

白水河国家级自然保护区位于四川省彭州市境内，地处龙门山脉东南部，从海拔1400～4800m依次覆盖着常绿阔叶林、常绿落叶混交林、落叶阔叶林、亚高山针叶林、高山亚高山灌丛、高山草甸和流石滩植被．通过对白水河保护区山地东南坡不同海拔高度的样方调查，研究了该区域植物群落a多样性及其沿海拔梯度的变化规律．结果表明，乔木层物种的丰富度及Shannon指数随海拔上升呈明显的线性下降趋势；灌木层和草本层物种丰富度及Shannon指数随海拔上升呈抛物线下降趋势．乔木物种从海拔1400m的12种至林线下降为2种；灌木和草本植物分别从35种和38种至山顶下降为5种和20种．乔木层物种的均匀度在2800～2900m由于出现单一的冷杉群落而突然降低；灌木层和草本层物种的均匀度则较为一致，波动不大．乔木层物种的优势度随海拔升高而逐渐上升，并在2900m急速升高；灌木层和草本层的优势度呈浅波状变化．乔木层物种随海拔升高在不同群落类型间出现明显的物种替代现象，表明海拔梯度包含了多种环境因子的梯度效应，影响着植物群落的分布、结构及物种多样性．

英文摘要：

The Baishuihe National Nature Reserve is located in the southeastern Longmen Mountains in Pengznou, Sicnuan, China. Eevergreen broad-leaved forests, deciduous broad-leaved forests, coniferous forests, subalpine and alpine shrubs, alpine meadows, and screes cover the southeastern slopes from foot to top of the mountains. From 1 400 to 3 900 m in the Nature Reserve, 52 plots were investigated with an interval of 100 m in altitude. Diversity of communities and their changes along altitude gradient were studied. The results showed that the richness and diversity of tree layer species decreased linearly with the increasing of altitude, while those of shrub layer and herb layer species decreased parabolically. Trees decreased from 12 at 1 400 m to only 2 species at timberline. Shrubs and herbs decreased from 35 and 38 at 2 000 m to 5 and 20 species at 3 800 m, respectively. Tree species are replaced obviously by others with the increase of altitude This shows that altitude contains many environmental factors, which affect the distribution, structure and species diversity of plant communities in the area.