Phylogenetic α- and β-diversity elevational gradients reveal consistent patterns of temperate forest community structure

Abstract

Phylogenetic data on species relatedness have increasingly involved in the analysis of community assembly mechanisms within the ecophylogenetic framework. Null-model analysis can detect patterns of phylogenetic clustering and overdispersion, corresponding to the leading roles of environmental filtering and biotic interactions in community assembly, respectively. Elevational gradients in montane communities are ideal systems for studying phylogenetic structure due to the existence of steep environmental gradients over short geographical distances. We analyze patterns of phylogenetic community structure in a montane temperate forest on Donglingshan Mountain, Beijing, China. We performed analysis based on both abundance-weighted and non-weighted α- and β-diversity metrics for three vegetation layers. We found layer-specific gradients of phylogenetic community structure. α- and β-diversity provided a consistent perspective on community assembly mechanisms. The elevational patterns of phylogenetic structure differ for woody and herbaceous plants. There is a linear transition from phylogenetic overdispersion at low elevations to phylogenetic clustering at high elevations in the tree and shrub layers. The herb layer is characterized by U-shaped relationships for abundance-weighted phylogenetic structure metrics. Low and high elevations are characterized by phylogenetic overdispersion, while mid-elevations show wide variation with no clear phylogenetic pattern. The greatest discrepancy between woody and herbaceous plants takes place at high elevations, where we observed phylogenetic clustering in the tree layer and overdispersion of the herb layer. This implies that different processes may determine the assembly of the species composition for woody and herbaceous species. We highly suggest that the combination of both phylogenetic and trait-based analyses can shed new light on our understanding of community assembly rules.