Diversity comes at a cost: multifaceted diversity reduces plant community stability in peatlands

Heikel Balti , Alexandre Buttler, Lise Pinault, Guillaume Bertrand, Philippe Binet, Daniel Gilbert, Geneviève Magnon, Pierre Agnola, Arnaud Mouly, Cyrille Violle

1.     Aim: Understanding how ecological stability relates to diversity is of crucial importance under global change. Greater biodiversity is expected to stabilize aggregate community properties through compensatory dynamics, yet diversity-stability relationships can vary across ecosystems, particularly in wetlands where strong abiotic filters shape community assembly and temporal dynamics. We examined how multiple facets of diversity (taxonomic, functional, and phylogenetic) and functional trait identity relate to temporal stability (invariability) and species asynchrony in peatland vegetation.

2.     Location: Forbonnet peatland, Jura Mountains, northeastern France.

3.     Methods: We used a 17-year field experiment in a montane peatland complex spanning a bog and a transitional poor fen, combining passive open-top chamber warming with natural hydrological contrasts.

4.     Results: Water table depth was the dominant environmental filter of plant communities, explaining 46 % of total compositional variance, whereas experimental warming had no detectable effect. Community temporal stability and species asynchrony were higher under drier conditions (deeper water table), consistent with moisture-driven constraints on peatland vegetation dynamics. Contrary to insurance hypothesis predictions, temporal stability decreased with multiple biodiversity facets, particularly phylogenetic diversity and species richness, but increased with deeper-rooted plant strategies and functional redundancy, after controlling for experimental conditions. Species asynchrony was largely unrelated to biodiversity, except for functional redundancy, which was negatively associated with asynchrony. The stability-asynchrony association weakened substantially after controlling for hydrology.

5.     Conclusions: Our results suggest that in peatlands, hydrology simultaneously structures biodiversity patterns, temporal stability and species asynchrony, yielding negative diversity-stability relationships that contradict classical insurance hypothesis predictions. Stability arises primarily from hydrological constraints, with limited contribution from compensatory dynamics among plant species. In strongly constrained, species-poor ecosystems, conservation may therefore prioritize maintaining or restoring the key abiotic conditions that favor functionally adapted communities over increasing diversity to sustain stable ecosystem functioning under global change.