AbstractWe analyzed patterns of plant species diversity along the northern slope of Mt. Xiaowutai based on 33 plots along an elevation gradient from 1250 m to 2850 m, at approximately 50 m intervals. Tree species richness decreased gradually with increasing elevation. However, α diversity index  distributed along the altitudinal gradient in a unimodal pattern, i.e., α diversity peaked at the middle elevation. Changes in β diversity corresponded with the transition of vegetation types, i.e., β diversity peaked at the ecotones between different vegetation types. Both the community dissimilarity index and Cody index peaked at 1400-1500 m, 2100-2200 m, and 2600-2700 m, corresponding to the transitional zones of shrubs to forests, broad forests to coniferous forests, and forests to subalpine meadows, respectively. Altitudinal replacement of congeneric species was apparent for the two most important broadleaf tree species, white birch (Betula platyphylla) and red birch (Betula albo-sinensis). At lower elevations, the deciduous broad-leaved forest was dominated by white birch, which was replaced by red birch at higher elevations.