Global Mapping of Forest Canopy Structural Complexity and Its Links to Ecosystem Productivity and Stability

Forest canopy structural complexity (CSC), the intricate arrangement and occupation of canopy elements in three-dimensional space, plays a critical role in shaping forest ecosystem productivity and stability by regulating light and water distribution within the canopy. However, the relationship between forest CSC and forest ecosystem productivity and stability remains controversial in current regional-scale studies, necessitating further investigation at broader spatial scales. Here, we introduce a novel entropy-based metric, canopy entropy, to quantify forest CSC from light detection and ranging (lidar) data. This metric effectively captures forest CSC variations arising from both horizontal and vertical arrangements and occupations of canopy elements. Notably, canopy entropy estimates from multiplatform lidar data demonstrate strong agreement, establishing its suitability for large-scale applications. Leveraging these advantages, as well as airborne lidar data from 4,000 forest plots worldwide and spaceborne lidar data from the Global Ecosystem Dynamics Investigation, we map the global distribution of forest CSC and investigate its relationships with forest ecosystem productivity and stability. We find climatic factors, especially water availability, play a critical role in driving the global distribution of forest CSC, while biotic factors exhibit a strong coupling impact with climatic and edaphic factors. From a global perspective, forest CSC predominantly enhances productivity and stability, although substantial variations are observed among forest ecoregions. The effects of forest CSC on productivity and stability are the balanced results of biodiversity and resource availability. These results offer valuable insights into understanding controversies in regional-scale studies. Furthermore, we found that managed forests generally exhibit lower CSC compared to intact forests but demonstrate stronger positive effects of CSC on ecosystem productivity and stability, underscoring the urgent need to incorporate CSC into forest management strategies to enhance climate change mitigation efforts.