Dominant ecological processes and plant functional strategies change during the succession of a subtropical forest

Understanding community assembly process could enhance forest conservation and restoration, while which dominant ecological process drives the community assembly during forest succession is still controversial. In this study, the phylogeny-based and functional trait-based indicators were used to investigate the community assembly processes during forest succession in southern China. 30 dominant species and 33 functional trait indicators related to plant competition, reproduction, and defense strategies, 7 environmental factors related to light availability and soil nutrients, and species richness were selected to explore the dominant ecological processes during succession via Monte Carlo method, structural equation model, multiple linear regression, and one-way ANOVA analysis. Results showed that both the community phylogenetic and functional trait structures changed during succession. Phylogenetic structure clustering and functional trait clustering were evident in early succession. In middle succession, the phylogenetic structure and functional trait structure were randomly dispersed. In middle and later succession, the phylogenetic structure clustering, functional trait clustering, and functional trait evenly dispersed were found. The environmental factors, especially the soil P content, and species richness were found to have significant effects on the community assembly processes during succession. Dominant species in early succession always occupied acquisitive strategies and had high light-use ability and low investment in defense, but dominant species in later succession showed more conservative strategies and exhibited diverse defense strategy, reproductive strategy, and light and nutrient resource-use strategy, apparently in order to adapt changing and more complex environments. The results demonstrate that the relative importance of ecological processes changed during succession. Environmental filtering mainly dominated in early succession, and its strength gradually decreased as succession progressed. Both environmental filtering and competitive exclusion had important effects on community assembly in later succession. The assessment of the relative importance of ecological processes during succession could be biased if only based on one plant functional strategy.