海拔梯度包含了多种环境因子的梯度效应，因而研究山地植物区系的海拔梯度格局对揭示植物区系的环境梯度变化规律、了解生物适应性和生物多样性沿海拔梯度的变化趋势等具有重要意义。为了探讨山地植物区系构成特征及其海拔梯度的生态意义，该文根据对大围山国家级自然保护区植被线路调查和垂直样带调查，并结合文献研究等获得的植物区系资料，分析了该保护区种子植物区系构成的基本特征及其随海拔梯度的变化趋势；利用系统聚类的方法寻找和研究大围山植物区系沿海拔梯度变化的断点位置。研究结果表明：1)大围山大多数热带成分分布的上限位于海拔1 500 m左右，以此为界划分热带雨林和常绿阔叶林是合理的。 2)湿润雨林分布于海拔700 m以下；山地雨林分布于海拔700～1 500 m；季风常绿阔叶林分布于海拔1 300～1 800 m；山地苔藓常绿阔叶林分布于海拔1 800 m以上；在海拔2 100 m以上的迎风坡面、土层瘠薄的地段分布有不甚典型的山地苔藓矮林。
Altitudinal gradients incorporate multiple resource gradients which vary continuously in different fashions. Studies of mountain floristic patterns along altitudinal radients has revealed regular patterns of the flora along envir onmental gradients, changing trends in biodiversity along altitudinal gradients as well as a better understanding of biological fitness. To explore the floristic compositional characteristics and the ecological significance of floristic patterns along altitudinal gradients in the China National Natural Reserve of Dawei Mountain in southeast Yunnan, the flora was uantified along two transects, one on the southwest slope and the other on the northeast slope of the reserve, including a vertical vegetation transect. Further investigations were conducted on the flora of Dawei Mountain which have ever been accounted for in the literature , such as Flora of Yunnan, The Seed Plant in Yunnan and so on. The structural characteristics of the flora and the altitudinal distribution patterns of its floristic components were analyzed. Systematic cluster analysis was applied to the data to determine how composition changed with changes in altitude and climate. The conclusions can be summarized as follows: 1) There was a strong boundary that ifferentiated tropical floristic elements from evergreen broad_leaved forests at an altitude of approximately 1 500 m; 2) Cluster analysis showed that humid rain forests occurred below 700 m a.s.l, mountain rain forests were between 700 m and 1 500 m, monsoon evergreen broad_leaved forests were between 1 300 m and 1 800 m, and the mountain mossy evergreen broad_leaved forest occurred above 1 800 m a.s.l. Non_representative mountain mossy dwarf forests (above 2 100 m) in the area are distributed on windward slopes and barren land on the mountain slopes.