Species-specific genotypic features, local neighbourhood interactions and resource supply strongly influence the tree stature and growth rate. In mixed-species forests, diversity-mediated biomass allocation has been suggested to be a fundamental mechanism underlying the positive biodiversity-productivity relationships. Empirical evidence, however, is rare about the impact of local neighbourhood diversity on tree characteristics analysed at a very high level of detail. To address this issue we analysed these effects on the individual-tree crown architecture and tree productivity in a mature mixed forest in northern Germany. Our analysis considers multiple target tree species across a local neighbourhood species richness gradient ranging from 1 to 4. We applied terrestrial laser scanning to quantify a large number of individual mature trees (N = 920) at very high accuracy. We evaluated two different neighbour inclusion approaches by analysing both a fixed radius selection procedure and a selection based on overlapping crowns. We show that local neighbourhood species diversity significantly increases crown dimension and wood volume of target trees. Moreover, we found a size-dependency of diversity effects on tree productivity (basal area and wood volume increment) with positive effects for large-sized trees (diameter at breast height (DBH) > 40 cm) and negative effects for small-sized (DBH < 40 cm) trees. In our analysis, the neighbour inclusion approach has a significant impact on the outcome. For scientific studies and the validation of growth models we recommend a neighbour selection by overlapping crowns, because this seems to be the relevant scale at which local neighbourhood interactions occur. Because local neighbourhood diversity promotes individual-tree productivity in mature European mixed-species forests, we conclude that a small-scale species mixture should be considered in management plans.

中文翻译：

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局部邻域多样性对成熟混合树种林冠结构和单株生产力的影响

特定物种的基因型特征，局部邻域相​​互作用和资源供应强烈影响树木的身材和生长速度。在混合物种森林中，已经提出了多样性介导的生物量分配是建立积极的生物多样性-生产力关系的基本机制。但是，经验证据很少涉及在非常高的详细程度下分析局部邻域多样性对树木特征的影响。为了解决这个问题，我们分析了这些对德国北部成熟混交林中单树冠结构和树生产力的影响。我们的分析考虑了范围从1到4的局部邻域物种丰富度梯度中的多种目标树种。我们应用了地面激光扫描技术，以非常高的精度对大量的个体成熟树木（N = 920）进行了量化。我们通过分析固定半径选择过程和基于重叠冠的选择来评估两种不同的邻居包含方法。我们表明，当地邻里物种多样性显着增加了目标树木的冠径和木材体积。此外，我们发现多样性对树木生产力（基础面积和木材体积增加）的大小依赖性，对大型树木（胸径（DBH）直径> 40 cm的树木）具有积极影响，而对于小型树木（胸径（DBH）> 40 cm）具有负面影响DBH <40厘米）的树木。在我们的分析中，邻居包含法对结果有重大影响。对于科学研究和增长模型的验证，我们建议通过重叠的冠状结构进行邻居选择，因为这似乎是发生局部邻居互动的相关尺度。由于当地社区的多样性提高了欧洲成熟的混合物种森林中单树的生产力，因此我们得出结论，在管理计划中应考虑使用小规模的物种混合。