Résumé
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.