Abstract: We investigated species composition, spatial distribution, biodiversity, and community structure of tree layer in an evergreen broad-leaved forest at low elevation in Dagang Mountain Ecological Station in Jiangxi Province. The results showed that: (1) Plant density was 1667 individuals·hm^-2 and there were 22 families, 34 genera and 41 species. Lauraceae, Fagaceae and Theaceae were most abundant, accounting for 52.49% of the total abundance. In addition, each species had a regular spatial distribution under the influence of environmental factors, disturbance factors and biological characteristics. (2) Simpson index, Shannon index, Pielou evenness index and Menhinick richness index were 0.896, 2.674, 0.725 and 0.978, respectively, which were lower than other evergreen broad-leaved forests in subtropical regions. (3) The height and diameter classes of trees showed an inverted “J” type distribution, which represented a typical heterogeneous forest structure and a relatively stable community structure. For each species, the height class and diameter class of trees had several distribution forms. For example, diameter distribution of Machilus pauhoi followed Poisson distribution, while Castanopsis fargesii followed multi-peak distribution. (4) This community was in the near climax community stage, with constructive species of C. fargesii, M. pauhoi and Symplocos sumuntia. In terms of tree height class and diameter class distribution, these three species had stable population structure, which was beneficial to the stable development of the whole community. Our results were helpful for understanding the variation of resource competition in the succession process of multispecies composition, providing scientific support for exploring forest community succession and its maintenance mechanism and the enhancement of ecosystem services.

Key words: factor diagnose., agroecosystem health, spatial-temporal pattern