Understanding the environmental factors that influence tree species composition is essential for suc-cessful management of biodiversity and sustainable use of community forest resources.This study aims to assess tree species composition and distribution in the deciduous Ban Mae Chiang Rai Lum Community Forest in Northern Thai-land and to analyze the influence of environmental factors on tree biodiversity in the forest.We conducted a stratified systematic sampling of the forest's total area of 3925 ha,and twenty-five 0.16 ha survey plots were established in three different stands of the deciduous forests to estimate and characterize the difference in biological diversity among the stands.Canonical correspondence analysis(CCA)was used to investigate the environment factors affecting such differ-ences in biodiversity of the stands.The results showed a high diversity of trees in the forest as 197 species,144 genera,and 62 plant families were recorded.The CCA ordination identified the environmental factors—the most important of which were elevation,distance to streams,soil moisture,organic matter,and distance to communities—that signifi-cantly influenced the diversity and distribution of tree spe-cies(p＜0.05)in the community forest.Our findings indi-cate that the implementation of drought reduction measures such as building check dams,fire protection,and monitoring community forest-product usage would be recommended to further biodiversity conservation and the sustainable use of community forest resources.