Can functional identities and geo-topographical differences predict the subtropical forest phylogenetic diversity variations? Conservation and management implications

Enhancing tree diversity through forest management remains a key ecological challenge, yet limited attention to phylogenetic diversity has hindered comprehensive biodiversity enhancement strategies. In this study, we analyzed 570 plots (≈36,000 trees) across subtropical non-commercial forests in eastern China, calculating five phylogenetic diversity indices. Using Pearson correlations, redundancy analysis, and structural equation modeling, we identified functional identities as the strongest predictor of phylogenetic diversity (45.54 % variance), outperforming forest age/density (36.97 %) and geo-topography (20.23 %). Key drivers included conifer percentage (17.6 %), evergreen percentage(6.4 %), elevation (4.1 %), and ectomycorrhizal (ECM) tree abundance (3.6 %). Plots with higher proportions of conifers, evergreens, and ECM trees exhibited significantly higher MNTD(Mean Nearest Taxon Distance), SesMPD(Standardized Mean Pairwise Distance), and SesMNTD(Standarized MNTD) values (1.70 times, 6.82 times, and 501.86 times, respectively) than low-proportion plots. Higher elevations correlated with increased Faith’s PD (phylogenetic diversity) but clustered phylogenetic structures (reduced SesMPD and SesMNTD). Older, low-density forests showed 1.28–25.08 times higher MNTD than younger, dense stands. Structural equation modeling demonstrated that preserving functional identities (conifers, evergreens, ECM trees) directly increased phylogenetic overdispersion, particularly in high-elevation, deep-soil regions. These findings highlight that functional identities serve as robust predictors of phylogenetic diversity in subtropical forests, offering actionable insights for conservation strategies aimed at maximizing community evolutionary potential.