Abstract Understanding how water use and drought stress in woody plants change in relation to compositional, structural and environmental variability of mixed forests is key to understand their functioning and dynamics. Observational and experimental studies have so far shown a complex array of water use and drought stress responses to species mixing, but progress is hampered by the costs of replicating measurements. A complementary approach consists in using in silico experiments with trait-based forest ecosystem models, which have the advantage of allowing the interpretation of the net mixing effect as the result of specific combinations of trait differences. We explore the potential of such an approach using a novel trait-based forest ecosystem model with a strong focus on plant hydraulics and data from 186 mixed forest inventory plots including holm oak (Quercus ilex L.) and eight co-occurring species. Sensitivity analyses focusing on the effect of differences in individual plant traits indicate that water use and summer drought stress of holm oak trees respond primarily to the variation in competitor's height, root distribution and xylem hydraulic efficiency and safety. Simulations of pure and mixed stands across different combinations of climate aridity and stand leaf area index indicate that differences in traits may compensate for one another, so that the influence of a given trait (e.g. tree height) on water use or drought stress can be decreased or offset by the influence of another one (e.g. hydraulic efficiency). Importantly, we show that species mixing does not always have positive effects at the stand level. Overall, our simulation study shows that the complexity of species- and stand-level mixing effects on water use and drought stress arises primarily as the result of differences in key functional traits of the competitor, although stand structure and climate aridity may modulate mixing effects.

中文翻译：

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揭示物种混合对地中海森林用水和干旱胁迫的影响：一种建模方法

摘要 了解木本植物的水分利用和干旱胁迫如何与混交林的组成、结构和环境变异相关的变化是了解其功能和动态的关键。迄今为止，观测和实验研究表明，对物种混合的一系列复杂的用水和干旱胁迫反应，但由于重复测量的成本而阻碍了进展。一种互补的方法包括使用基于特征的森林生态系统模型的计算机模拟实验，其优点是允许解释作为特征差异的特定组合的结果的净混合效应。我们使用一种新的基于特征的森林生态系统模型来探索这种方法的潜力，该模型重点关注植物水力学和来自 186 个混合森林库存地块的数据，包括圣栎（Quercus ilex L.）和八种共生物种。关注单个植物性状差异影响的敏感性分析表明，圣栎树的水分利用和夏季干旱胁迫主要对竞争者的高度、根系分布和木质部水力效率和安全性的变化做出反应。对不同气候干旱和林分叶面积指数组合的纯林和混合林的模拟表明，性状的差异可以相互补偿，从而可以减少给定性状（例如树高）对用水或干旱胁迫的影响或被另一个人的影响抵消（例如。G。水力效率）。重要的是，我们表明物种混合并不总是在林分水平上产生积极影响。总体而言，我们的模拟研究表明，尽管林分结构和气候干旱可能会调节混合效应，但物种和林分混合对用水和干旱胁迫的复杂性主要是由于竞争者关键功能性状的差异造成的。