Climate Strengthens the Positive Effects of Stand Structure on Understory Plant Diversity in Chinese Temperate Forests

Stand structure, which links function and management, plays a crucial role in regulating forest ecosystems and influencing biodiversity. Nevertheless, knowledge of the effect of climate change on stand structure and plant diversity is still poorly understood on a large scale. To explore the effects of various climate conditions on stand structure-plant diversity, we conducted a comprehensive analysis of data from 1272 plots across China's temperate and subtropical forests. Leveraging the structural equation model (SEM), we explored the direct and indirect effects of climate, topography, and tree diversity on understory woody and herbaceous plants with respect to stand structure. Furthermore, we evaluated the effect size of stand structure on understory vegetation diversity under different climatic zones. Our results showed that tree size variation (CV DBH) and stem density (SD) were the key drivers for understory woody plants, while the stand structure complexity index (SSCI) was more important for understory herbaceous diversity. Furthermore, the positive effects of stand structure differed across various climate zones and were enhanced with an increase in the climatic gradient. For instance, the impact of SD on understory woody plants, as well as the influence of the SSCI on the diversity of understory herbaceous vegetation, were both strengthened. These findings raise our awareness of the pressing need to manage stand structure heterogeneity differently across different climate zones, and different management also needs to be implemented among different understory plant types. It becomes evident that distinct forest management measures must be applied under future climate change and forest management practices in order to preserve biodiversity.