Abstract Foliage clumping is a forest canopy structural feature influencing light interception, the inversion of light interception for estimating leaf area index, and photosynthesis rates. In this study we estimated clumping factor values at the branch level from different heights in broadleaf tree species at four sites in two climatic zones (two sites in dry climate and two sites in humid climate) using laser light. We found that branch level foliage distribution tends to be random at dry sites where water is the main limiting resource, and that foliage aggregation at the top of emergent canopy tops increases with branch height at humid site where competition for light is high. Our results suggest that high competition for light leads to the production of large amounts of leaves grouped together in high irradiance areas of the canopy, even though this significantly reduces the light interception efficiency on a per leaf area basis. A comparison of these results with foliage clumping factor values derived at larger spatial scales for two sites (one dry and one humid) revealed a crossover in the scales at which clumping arises: leaves are essentially clumped at the branch level but much less so at the plot level for the humid site, and leaves are clumped at the plot level but not at the branch level for the dry site. This suggests that the occurrence of foliage clumping may be related to the intensity of resource limitation (light or water in this case) and its availability in 3D space. Additional research is required to confirm the role of environmental conditions in determining foliage clumping across various forest biomes. Further confirmation and understanding of causal relations between abiotic stresses and canopy foliage clumping may lead to significant refinement in forest canopy radiative transfer modelling schemes.

中文翻译：

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树叶丛生是森林资源限制的结果吗？

摘要 丛叶是影响光截留、光截留反演以估计叶面积指数和光合作用速率的森林冠层结构特征。在这项研究中，我们使用激光估计了两个气候带四个地点（干燥气候中的两个地点和潮湿气候中的两个地点）的阔叶树种不同高度的树枝水平的丛生因子值。我们发现，在水分是主要限制资源的干燥地点，枝条水平的树叶分布往往是随机的，而在对光竞争激烈的潮湿地点，突顶冠层顶部的树叶聚集随着枝条高度的增加而增加。我们的结果表明，对光的高度竞争导致大量叶子聚集在树冠的高辐照度区域，尽管这会显着降低每个叶面积的光拦截效率。将这些结果与两个地点（一个干燥和一个潮湿）在更大空间尺度上得出的树叶丛生因子值进行比较，揭示了丛生发生的尺度上的交叉：叶子基本上在树枝水平上丛生，但在树枝水平上则少得多。潮湿场地的地块水平，而干燥场地的叶子在地块水平而不是在树枝水平上丛生。这表明树叶丛生的发生可能与资源限制的强度（在这种情况下是光或水）及其在 3D 空间中的可用性有关。需要更多的研究来确认环境条件在确定各种森林生物群落中的树叶丛生方面的作用。