Abstract: Investigating the phylogenetic structure of communities can provide insights into the mechanisms of community assembly from both evolutionary and ecological perspectives. Based on the survey data from four forest plots at different elevations within the Meigu Dafengding Nature Reserve in Sichuan, the phylogenetic relationships were constructed to analyze the community phylogenetic structure across various temporal and spatial scales by using the net relatedness index (NRI). Results showed that the NRI values of all the four plots were less than zero, indicating phylogenetic overdispersion within the communities. The degree of dispersion increased with increasing spatial scale, but exhibited an initial decrease followed by an increase and then another decrease as small scale. Communities with small DBH-class exhibited phylogenetic clustering dominated by habitat filtering (NRI>0) at smaller spatial scales. In contrast, communities with larger DBH-class demonstrated phylogenetic overdispersion (NRI<0) driven by competitive exclusion, with the degree of dispersion increasing alongside both DBH-class and spatial scale. Our results indicated that competitive exclusion mediated by niche theory played a significant role in the assembly of forest communities in Sichuan Meigu Dafengding Nature Reserve.

Key words: forest community, phylogenetic divergence, spatial scale, diameter class