AbstractThe patterns of biodiversity along altitudinal gradients are well-documented ecological phenomena. Community composition and structure are important factors affecting diversity patterns in plant communities. Furthermore, species diversity along altitudinal gradient differs in different layers at different scales. In this paper, we analyzed the composition and structure of communities on the northern slope of Mt. Changbai based on TWINSPAN classification. The patterns of plant diversity for tree, shrub and herb layers were described by indices of species richness, α diversity and β diversity. Four community groups characterized by different dominants in the tree layer were distinguished: (1) mixed coniferous and broadleaved forests (700 -1065 m a.s.l.) dominated by Pinus koraiensis, Tilia amurensis, Fraxinus mandschurica, and Acer mono, including secondary birch forest (1150 m a.s.l) dominated by Betula platyphylla, which developed from natural pine and deciduous forests due to disturbance; (2) transitional forests of mixed coniferous and broad-leaved forest and sub-alpine coniferous forests (1100-1300 m a.s.l.); (3) sub-alpine coniferous forests (1300-1780 m a.s.l.) dominated by Picea jezoensis, Abies nephrolepi and Larix olgensis; and (4) alpine birch forests (1800-2000 m a.s.l.) dominated by Betula ermanii. Distribution of importance values of dominants explicitly indicated a vertical pattern of these four forest types. Frequency distribution of DBH classes suggested major forest types in Mt. Changbai were regenerating at a healthy pace. Species richness in the tree and shrub layers declined with altitude, while herb layer species richness showed no significant trend along the altitudinal gradient. With increasing altitude, α diversity, represented by the Shannon-Wiener index, decreased for both tree and shrub layers, with no clear trend for herb layer. Pielou evenness index in the three layers showed no noticeable change with increasing altitude. β diversity, indicated by the Cody index, declined with increasing altitude for all three layers.