Community biomass is driven by dominants and their characteristics - The insight from a field biodiversity experiment with realistic species loss scenario

Revealing the role of biodiversity in ecosystem functioning (BEF) has been a major focus of ecological research over recent decades. In general, results from artificially assembled communities point to the important role of biodiversity showing that loss of species has a negative effect on various ecosystem functions (mostly assessed by above-ground peak biomass). However, the evidence from manipulations of natural communities is scarce, and results are often contradictory between these two approaches. In particular, the importance of species dominance for ecosystem functioning remains poorly understood. We created a gradient of plant species richness in a meadow community following a realistic species loss scenario (removal of less abundant species) to test the effect of diversity on community biomass and assess the importance of subordinate species compared with dominants in a 5-year experiment. Contrasting with results of BEF experiments with artificial assembly, we did not find any relationship between plant species diversity and above-ground biomass across the timeframe of the experiment. We provide evidence that dominant species' identity and traits are the main drivers of community biomass because dominant species were able to maintain biomass production after substantial species loss. Furthermore, dominants prevented community biomass from declining and biomass was indirectly influenced not by species richness but through differences in functional diversity. Our results support the mass ratio hypothesis, showing much bigger effect of dominant species on community biomass production and hints to the rather minor importance of the complementarity effect between species. We emphasize that BEF research should more focus on the role of dominant species in maintaining various ecosystem functions. Synthesis. Species diversity is a poor predictor of community above-ground biomass production and dominant species can effectively compensate the total production after substantial loss of other species in a grassland community.

Automated summary

The role of biodiversity in ecosystem functioning (BEF) has been a major focus of ecological research. Results from artificially assembled communities point to the important role of biodiversity, showing that loss of species has a negative effect on various ecosystem functions. However, evidence from manipulations of natural communities is scarce, and results are often contradictory between these two approaches. This study found that species diversity is a poor predictor of community above-ground biomass production, and dominant species can effectively compensate for the total production after substantial loss of other species in a grassland community.