中文摘要：

生物多样性沿海拔梯度的变化是多样性环境梯度格局研究中的一个热点问题。在对滇西北玉龙雪山2900m～4200m间沿海拔梯度进行的群落调查基础上，对植物物种多样性和群落结构的垂直分异格局进行了分析。结果表明：1）在16个样地中共记录植物物种261种，分属78科，158属，其中木本植物36种，灌木植物71种，革本154种。2）沿海拔梯度，森林群落的最大树高、最大胸径、平均树高和平均胸径等群落结构指标均呈单峰分布格局。3）随着海拔的升高。木本和草本的物种丰富度，先增加后下降；而灌木层的物种丰富度随着海拔的上升呈明显下降格局。4）木本层和灌木层的β多样性（Cody指数）随海拔升高，总体呈减小趋势，而草本层β多样性显示出单峰分布的垂直格局。

英文摘要：

The changing pattern of plant diversity along the environment gradients was the important topic in ecology. Because the elevational gradients comprised the combining effects of temperature, moisture and sunlight et al. , and the changing of temperature in elevational gradients was 1 000 times faster than that of latitude gradients, therefore, the pattern of plant diversity on elevational gradients was the hotspot in plant ecology. It was often thought that the changing of plant diversity on elevational gradient shared similar patterns with that of latitude gradients. In other words, plant diversity decreased with the increase of elevation, But other studies found that plant diversity increased first and then decreased at reaching their maximum, showing a unimodal pattern against elevation. So, it may indicated the patterns were different in different mountains and it was necessary to make some case studies in typical mountains to reveal some rules on the elevational patterns of plant diversity. Yulong mountain was located in the northwest part of Yunnnan province, and was the core region of plant diversity, linking the plant distribution between the northwest part and central part of Yunnan. And great elevation gradient was found in Yulong mountain, although it was in the region with low latitude, so it was a model to make a case study on the elevational pattern of plant diversity. However, until now, there was little research on the plant diversity there. In this study, we analyzed changes in species diversity of plant communities on Mt. Yulong using data from 16 plots ,which were mainly investigated along an altitudinal gradient at 100 m intervals, through cluster analysis, community structure, diversity index. Major results were summarized as follows ：A total of 261 species were recorded, including 36 tree species, 71 shrub species and 152 herb species from 158 genera in 78 families. With the increase of altitude,the forest communities were Pinus yunnanensis forest, Picea likiangensis forest, Larix pot