Data from: Using a forest dynamics model to link community assembly processes and traits structure

1. Trait-based approaches have been increasingly used to understand the role of environmental and biotic filters on species assembly. However, our understanding of the relationships between traits and community assembly processes remain limited. Indeed, various assembly processes may lead to similar functional patterns, and the effects of a given process may vary with the considered traits. Especially, competition can result in trait divergence or convergence depending on whether the trait is related to niche differences or to species’ competitive abilities. 2. In this study, we used a process-based forest gap-model to explore the effect of environmental and biotic assembly processes on the functional diversity of tree communities along a productivity gradient of 11 sites across central Europe. In a simulation experiment, we (i) disentangled the effects of environmental and biotic filtering on community structure, and (ii) tested whether competition resulted in trait divergence or convergence. 3. Our results confirmed the expected decrease in species richness with decreasing site fertility. We detected environmental filtering for traits related to both species environmental requirements and species competitive ability, highlighting that environmental trait filtering can affect all aspects of tree life-history strategies. 4. We observed convergence of traits related to growth and light capture resulting from competition for light, suggesting that tree species assembly is mainly driven by differences in competitive abilities. Additionally, the observed trait convergence was stronger in more productive sites than in less fertile ones, reflecting the impact of environmental conditions on competitive interactions. 5. Synthesis. Our study shows that process-based forest models can help to test whether functional traits composition reveal the signature of community assembly processes. This process-based approach challenges the classical view on the links between traits and mechanisms driving community assembly.

1. 基于性状的研究方法（Trait-based approaches）正日益被用于解析环境与生物过滤因子（environmental and biotic filters）在群落构建（species assembly）中的作用。然而，当前学界对性状与群落构建过程间的关联认知仍较为有限。事实上，不同的群落构建过程可能催生相似的功能格局，且特定过程的效应会因所考量的性状而异。具体而言，竞争可引发性状趋异（trait divergence）或性状趋同（trait convergence），这取决于该性状关联的是生态位分化（niche differences），还是物种的竞争能力（competitive abilities）。
2. 本研究借助基于过程的林窗模型（forest gap-model），探究了中欧沿生产力梯度分布的11个样地中，环境与生物群落构建过程对树木群落功能多样性（functional diversity）的影响。在模拟实验中，我们（i）厘清了环境过滤与生物过滤对群落结构的作用效应，（ii）验证了竞争过程究竟会引发性状趋异还是性状趋同。
3. 研究结果证实了此前的预期：随生境肥力（site fertility）下降，物种丰富度（species richness）会随之降低。我们检测到与物种环境需求及竞争能力均相关的性状存在环境过滤（environmental filtering）现象，这表明环境性状过滤可影响树木生活史策略的所有维度。
4. 我们观测到，因光照竞争引发的与生长及光捕获相关的性状发生趋同，这暗示树木群落组装主要由物种间的竞争能力差异驱动。此外，在生产力更高的样地中，观测到的性状趋同程度较贫瘠样地更为显著，这反映了环境条件对种间竞争互作的影响。
5. 综合分析。本研究表明，基于过程的森林模型可用于验证功能性状组成是否能够反映群落构建过程的特征信号。这一基于过程的研究方法，对学界关于性状与驱动群落构建的机制间关联的传统认知提出了挑战。