Data and code for: A Height-Independent Metric Reveals the Dominant Role of Internal Structural Complexity in Forest Diversity

This release contains the current version of the data and analysis code for the manuscript, which is currently under peer review and has not yet been published. Detailed information are described in README.md file.ABSTRACT Understanding the relationship between forest structural complexity and tree species diversity is fundamental for biodiversity conservation, yet empirical evidence remains contradictory. A key methodological limitation is that most structural complexity metrics inherently confound canopy height (representing vertical niche volume) with internal structural complexity (representing vertical niche differentiation). To address this gap, we developed a novel height-independent metric for quantifying internal structural complexity based on normalized vertical canopy entropy. Using high-density UAV-LiDAR data from 11 ForestGEO plots across China and ground-based diversity measurements covering 240 ha and 899,063 individual trees, we disentangled the independent effects of canopy height and internal structural complexity on tree species diversity. Our results reveal that internal structural complexity generally outperforms canopy height as a predictor of species diversity at the 20 m scale, showing significant positive relationships with species richness and Shannon diversity, while canopy height exhibited no significant overall effects. This pattern supports the niche differentiation mechanism, where heterogeneous vertical structure creates diverse microhabitats for species specialization. The relationship was scale-dependent, strongest at 20 m and diminishing at 50 m, highlighting the importance of spatial resolution in detecting structural effects on diversity. Our methodological innovation provides a height-independent metric that advances beyond existing approaches, while our findings challenge the reliability of canopy height as a local-scale biodiversity proxy and emphasize the critical role of internal structural complexity in supporting tree species coexistence through vertical niche differentiation.