Integrating phylogenetic community structure and phylogenetic beta diversity to infer community formation in Pinus rigida plantations

Abstract Background Recent accelerated environmental changes have highlighted the vulnerability of single-species plantations, and a demand to switch plantations closer to natural forests has increased. However, research on community assembly mechanisms in plantations is scarce compared to those in natural forests. In this study, we identified the key factors controlling phylogenetic diversity (PD) and community assembly mechanisms and established an ecological basis for converting planted coniferous forests into forests with abundant structures and functions. Method This study targeted Pinus rigida plantations in the central and southern regions of South Korea, identifying factors controlling PD and phylogenetic community structure [net relatedness index (NRI) and nearest taxon index (NTI)] across forest strata (whole strata, upperstory, and understory). We also constructed a model encompassing abiotic (topographical and climatic conditions) and biotic (taxonomic diversity, stand structural diversity, age class, and community-weighted proportion) factors, and conducted an analysis using piecewise structural equation modeling. Furthermore, phylogenetic beta diversity (PBD) was decomposed into turnover and nestedness, and distance matrix-based simple and multiple regression analyses were applied to test the main factors at the distance dimension (geographical and climatic distance, pairwise stand age difference). Results Controlling factors for PD, NRI and NTI varied depending on forest strata and phylogenetic depth. PD in the upperstory was controlled by stand structural diversity, PD in the understory was controlled by topographical, climatic, and biotic factors. NRI and NTI were influenced by various factors; NRI was particularly affected by climatic factors, and NTI was notably affected by biological factors. The contribution of turnover was found to be large in PBD, which had a high correlation with climatic distance, whereas nestedness exhibited a high correlation with geographical distance. This study employed NRI, NTI and PBD to identify the process whereby assembly signals within communities were transferred as differences between communities, suggesting a mechanism for how local assembly processes scaled up large-scale patterns. Conclusions Our findings attempt to fill the knowledge gap in plantation assembly mechanisms and suggest the need for an integrated approach to understanding community formation.