Abstract: The mechanism of species coexistence, as a core theme in community ecology, is critical for understanding community structure features, as well as for predicting community dynamics. We examined community assembly characters and influencing factors through the integration of phylogenetic information and leaf functional traits in semi-humid evergreen broad-leaved forests (SEBFs) in Yunnan, China. Eight leaf functional traits of five dominant tree species of SEBFs were examined along with phylogenetic data. To quantify the effects of deterministic and stochastic processes on leaf functional traits, the factors were categorized into environmental and environmental + spatial variables (representing niche-based processes) and spatial variables (representing stochastic processes). Functional trait changes along environmental gradients were analyzed. Leaf structural traits exhibited phylogenetic signals (Blomberg’s K>1 for dry matter content, specific leaf area, leaf mass per area, and leaf thickness, with P=0.05 for dry matter content), suggesting their formation and development are primarily determined by genetic variation. Leaf chemical traits showed weak phylogenetic signals (K<1, P>0.05 for leaf nitrogen, leaf phosphorus, and carbon-to-nitrogen ratio), indicating the traits of different tree species maintain optimal performance by tradeoff strategies across different habitats. Community assembly in SEBFs is a result of the combined effects of deterministic and stochastic processes. Water conditions are pivotal environmental factors shaping leaf functional traits of dominant tree species. Wetness and aridity explained 19.1% and 10.8% variations of leaf functional trait, respectively. In areas with less precipitation, dominant species in SEBFs tend to increase specific leaf area to enhance water use efficiency and increase carbon storage.

Key words: semi-humid evergreen broad-leaved forest, leaf functional trait, phylogeny, community assembly, environmental gradient