Vertical forest structure is closely linked to multiple ecosystem characteristics, such as biodiversity, habitat, and productivity. Mixing tree species in planted forests has the potential to create diverse vertical forest structures due to the different physiological and morphological traits of the composing tree species. However, the relative importance of species richness, species identity and species interactions for the variation in vertical forest structure remains unclear, mainly because traditional forest inventories do not observe vertical stand structure in detail. Terrestrial laser scanning (TLS), however, allows to study vertical forest structure in an unprecedented way. Therefore, we used TLS single scan data from 126 plots across three experimental planted forests of a large-scale tree diversity experiment in Belgium to study the drivers of vertical forest structure. These plots were 9–11 years old young pure and mixed forests, characterized by four levels of tree species richness ranging from monocultures to four-species mixtures, across twenty composition levels. We generated vertical plant profiles from the TLS data and derived six stand structural variables. Linear mixed models were used to test the effect of species richness on structural variables. Employing a hierarchical diversity interaction modelling framework, we further assessed species identity effect and various species interaction effects on the six stand structural variables. Our results showed that species richness did not significantly influence most of the stand structure variables, except for canopy height and foliage height diversity. Species identity on the other hand exhibited a significant impact on vertical forest structure across all sites. Species interaction effects were observed to be site-dependent due to varying site conditions and species pools, and rapidly growing tree species tend to dominate these interactions. Overall, our results highlighted the importance of considering both species identity and interaction effects in choosing suitable species combinations for forest management practices aimed at enhancing vertical forest structure.

中文翻译：

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树种同一性和相互作用决定了通过地面激光扫描测量的幼龄人工林的垂直森林结构

垂直森林结构与多种生态系统特征密切相关，例如生物多样性、栖息地和生产力。由于组成树种具有不同的生理和形态特征，在人工林中混合树种有可能创造出多样化的垂直森林结构。然而，物种丰富度、物种同一性和物种相互作用对垂直森林结构变化的相对重要性仍不清楚，这主要是因为传统的森林清查没有详细观察垂直林分结构。然而，地面激光扫描（TLS）允许以前所未有的方式研究垂直森林结构。因此，我们使用来自比利时大规模树木多样性实验的三个实验人工林的 126 个样地的 TLS 单次扫描数据来研究垂直森林结构的驱动因素。这些地块是树龄 9-11 年的幼龄纯林和混交林，其特点是树种丰富度有四个级别，从单一栽培到四种树种混合，跨越 20 个成分级别。我们根据 TLS 数据生成了垂直植物剖面，并得出了六个林分结构变量。使用线性混合模型来检验物种丰富度对结构变量的影响。采用分层多样性相互作用建模框架，我们进一步评估了六个林分结构变量的物种同一效应和各种物种相互作用的影响。我们的结果表明，除了冠层高度和树叶高度多样性之外，物种丰富度对大多数林分结构变量没有显着影响。另一方面，物种身份对所有地点的垂直森林结构产生了重大影响。由于场地条件和物种库的不同，物种相互作用的影响被观察到是依赖于场地的，并且快速生长的树种往往在这些相互作用中占主导地位。总的来说，我们的结果强调了在选择合适的物种组合进行森林管理实践以增强垂直森林结构时考虑物种同一性和相互作用效应的重要性。