Processes underlying the assembly of plant communities: The role of environmental filtering heterogeneity in a competition–dispersal experiment

• Published in: Journal of vegetation science Vol. 34; no. 2
• Main Authors: Alfonsi, Elsa, Benot, Marie‐Lise, Alard, Didier
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.03.2023; Wiley
• Subjects: above‐ground competition; Agricultural practices; Assembly; Availability; Biodiversity and Ecology; Canopies; canopy; Competition; competitive exclusion; conservation areas; Dispersion; environmental constraints; Environmental Sciences; Experiments; Filtration; Flooding; France; Heterogeneity; immigration; Meadows; Moisture effects; Molinia; Mowing; Natura 2000 6410 generic habitat; Nature reserves; Plant communities; Plant diversity; Plant species; seed addition; Seed dispersal; Seeds; Soil moisture; soil water; Spatial variations; species composition; Species diversity; Species richness; Stochasticity; wet meadow; France; pecies richness; seed addition; above-ground competition; mowing; flooding; Natura 2000 6410 generic habitat; wet meadow; heterogeneity; species composition; environmental constraints
• ISSN: 1100-9233; 1654-1103
• DOI: 10.1111/jvs.13186

Question Interspecific competition and seed dispersal are key mechanisms that may influence plant community assembly, but their relative importance remains difficult to disentangle as they can be affected by abiotic conditions (environmental filtering). We experimentally studied the balance between these processes in a Molinia wet meadow plant community in which abiotic constraints are mostly represented by flooding, while agricultural practices such as mowing prevent the dominance of a few competitive species. We hypothesized that (H1) mowing, by decreasing competitive exclusion and (H2) seed addition, by increasing immigration, both enhance plant species diversity, and that (H3) small variations in flooding intensity become secondary to these processes in determining species assembly. Location French National Nature Reserve “Etang de Cousseau”, Nouvelle Aquitaine, France. Methods In a three‐year experiment, we added seeds of 17 species characteristic of Molinia wet meadows and managed above‐ground competition through mowing. We measured spatial variations in soil moisture as an indicator of the flooding regime. We recorded species relative cover, species richness and evenness annually, and measured light availability, linked with canopy openness, twice. Results From the beginning of the experiment, small‐scale variations in soil moisture mainly affected species richness, composition and evenness, and canopy openness. Mowing significantly increased light availability and evenness, and affected the relative cover of several species, but not species richness. The addition of seeds did not influence any of the variables monitored during the experiment. Conclusion Our study helps to disentangle processes underlying community assembly in wet meadows. It demonstrates significant and rapid effects of mowing on canopy opening and on community assembly, while seed addition had only a slight effect, possibly explained by an insufficient decrease in competitive interactions through mowing or unmeasured processes. It also shows that abiotic heterogeneity remains a primary driver of community assembly, even on a small scale. Finally, our results suggest that the respective weight of the different filters (dispersion, environment, competition) is subject to interannual variability or environmental stochasticity. Interspecific competition and seed dispersal are key mechanisms that may influence plant community assembly, but their relative importance can be affected by abiotic conditions. Our study in a Molinia wet meadow shows rapid effects of mowing but a slight effect of seed addition, while abiotic heterogeneity remains a primary driver of community assembly, even on a small scale.