Decoupled Drivers of Phylogenetic Diversity and Community Assembly Signals Across Forest Types in a Temperate Forest, South Korea

Phylogenetic metrics can separate two complementary biodiversity dimensions: the amount of evolutionary history retained in a community (Faith’s phylogenetic diversity, PD) and community assembly signals expressed as departures from null expectations in phylogenetic relatedness (standardized effect size of mean pairwise phylogenetic distance, SES.MPD). However, at the individual-forest scale—where conservation and management decisions are implemented—the key drivers and linked pathways controlling these two dimensions often remain unclear. Here, PD and SES.MPD were quantified for 96 20 × 20 m forest plots spanning broadleaved, conifer, and subalpine forests on Mt. Gariwang, South Korea. Community phylogenies were generated and related to elevation, stand age class, soil fertility, species richness, and community-weighted mean (CWM) traits (specific leaf area, SLA; wood density, WD) using information-theoretic multimodel inference and piecewise structural equation modeling. PD and SES.MPD differed significantly among forest types, but were governed by distinct controls. PD was most strongly and negatively associated with CWM.WD, indicating that dominance by high–wood-density strategies coincided with reduced retained evolutionary history. In contrast, SES.MPD was primarily negatively associated with CWM.SLA and species richness, with soil fertility influencing SES.MPD indirectly via SLA; stand age class showed limited explanatory power. Overall, these results demonstrate decoupled drivers of evolutionary-history retention versus assembly-related coexistence structure and identify management-relevant levers at the individual-forest scale, highlighting the importance of trait dominance and soil–trait pathways in addition to forest type.