A more efficient use of limited canopy space and, thus, a higher canopy space occupation (CSO) in forests can result in an increased absorption of photosynthetically active radiation, which in turn can promote productivity. Although there is some evidence for a positive relationship between tree diversity (TD) and CSO, the generality of this hypothesis is still under debate. Here, we propose a conceptual framework that accounts for both the spatial complexity of canopy space and size-dependent interspecific tree interactions and tested it using mobile laser scanning data across larger spatial scales. We assessed the CSO at high resolution with two diversity indices, tree species richness (TSR) and the effective number of species (ENS) along a TSR gradient ranging from monocultures to 8-species mixtures in a mature and structurally complex mixed-species temperate forest. We found that the direction and strength of the TD-CSO relationship largely depended on the way how canopy space is defined and which tree size classes are considered to calculate TSR. Using an broad deliniation of canopy space no significant relationship between TD and CSO was evident. In contrast, when considering only the upper canopy space, a significant effect of TSR on CSO emerged. Importantly, the direction of this relationship was critically dependent on the tree size threshold underlying the TSR determination. For all trees with a diameter at breast height > 7 cm, we observed a significant negative relationship, while the opposite was the case when considering only large-sized trees. Our novel conceptual framework demonstrates that accurate estimation of canopy space complexity and tree size dependence is key to better understanding the processes underlying CSO. However, further information on diversity-canopy space occupation relationships from studies in different forests and forest types is needed.

更有效地利用有限的冠层空间，从而提高森林中的冠层空间占用率（CSO），可以增加对光合有效辐射的吸收，进而提高生产力。尽管有一些证据表明树木多样性 (TD) 与 CSO 之间存在正相关关系，但这一假设的普遍性仍在争论中。在这里，我们提出了一个概念框架，该框架考虑了冠层空间的空间复杂性和依赖于大小的种间树相互作用，并使用移动激光扫描数据在更大的空间尺度上对其进行了测试。我们用两个多样性指数以高分辨率评估了 CSO，在成熟且结构复杂的混合物种温带森林中，树种丰富度 (TSR) 和沿 TSR 梯度的有效物种数量 (ENS) 范围从单一栽培到 8 种混合物。我们发现 TD-CSO 关系的方向和强度很大程度上取决于树冠空间的定义方式以及计算 TSR 时考虑的树大小类。使用对冠层空间的广泛划分，TD 和 CSO 之间没有明显的关系。相比之下，当仅考虑上部树冠空间时，TSR 对 CSO 的影响显着。重要的是，这种关系的方向严重依赖于 TSR 确定的树大小阈值。对于胸高 > 7 cm 的所有树木，我们观察到显着的负相关，而仅考虑大型树木时则相反。我们新颖的概念框架表明，准确估计树冠空间复杂性和树大小依赖性是更好地理解 CSO 基础过程的关键。然而，需要从不同森林和森林类型的研究中获得更多关于多样性-冠层空间占用关系的信息。