Tree diversity’s impact on coarse woody debris biomass and spatial stability under different moisture stress levels in temperate forests, South Korea

• Tree diversity effects on CWDB and its spatial stability vary with moisture stress levels. • Under low moisture stress condition, CWDB is more significantly influenced by tree diversity. • Under high moisture stress condition, tree diversity plays a more significant role for the spatial stability of CWDB. Coarse woody debris (CWD) contributes significantly to forest ecosystems, influencing their structure, function, and stability. Despite its importance, the drivers of CWD dynamics, particularly under different moisture conditions, remain unclear. In this study, we examined the influence of species richness (SR), functional dispersion (FDis), structural complexity, forest age (Fage), and climate moisture index (CMI) on CWD biomass (CWDB) and its spatial stability across temperate forests in South Korea. Our findings revealed that aboveground biomass (AGB), influenced by tree diversity facets and Fage, significantly affects CWDB. Higher species and structural diversity contributed to increased AGB, thereby affecting CWDB due to niche complementarity effects. SR and FDis directly impacted CWD dynamics, with effects varying according to CMI levels. High CMI conditions showed a positive association between SR and CWDB, while this relationship diminished under low CMI conditions, highlighting the modulating effect of climate moisture stress. Furthermore, we found that species and functional trait diversity play more crucial roles in maintaining spatial stability in CWD distribution at low CMI levels than at high CMI levels. Our study emphasizes the importance of considering species, functional diversity, and climate moisture conditions in forest management and conservation efforts, particularly under moisture stress gradients. Adaptive management strategies that account for CWDB and its spatial variability in different moisture regimes are essential for enhancing ecosystem sustainability, health, and resilience in response to climate change.