Managing tree species diversity and ecosystem functions through coexistence mechanisms

Key message A better transfer to managers of studies examining the functional role of tree species diversity would be achieved by explicitly addressing two missing links: the effect of management interventions on coexistence mechanisms and the relationships between coexistence mechanisms and ecosystem functions. Context Plant species diversity has been shown to promote a wide array of ecosystem functions and ecosystem services. However, scientific results concerning relationships between species diversity or species mixing and ecosystem functions have not been well transferred to management practices so far. Part of the problem lies in the difficulty of assessing whether interesting species mixtures can persist over the long term and how management influences ecosystem functions. Aims We argue that a better transfer of knowledge to managers would be achieved by addressing two missing links: (i) the effect of management interventions on coexistence mechanisms and (ii) the relationships between coexistence mechanisms and ecosystem functions. Methods To do so, we first provide a brief overview of the recent scientific results on relations between tree diversity (or two-species mixing) and ecosystem functions, focusing on studies dealing with productivity and stability in forests. We further introduce the key question of whether mixed stands are transient or permanent. We then briefly present key elements of modern coexistence theory and illustrate them with three examples in forest ecosystems. We finish by discussing how management interventions in forests can affect coexistence mechanisms and by addressing some methodological perspectives. Results We provide examples of management actions (e.g. gap-based silviculture, preferentialselection of the most frequent species, preferential selection of the most competitive species, plantingweakly competitive species) that may increase the strength of coexistence mechanisms. Conclusion Analysing long-term management impacts on species coexistence and ecosystem functions with a combination of long-term monitoring of large permanent plots and mechanistic dynamic model simulations will be useful to develop relevant practices favouring mixed forests in the long term.