Compensatory effects stabilize the functioning of Baltic brackish and salt marsh plant communities

Abstract The variation in plant species abundances and in community composition appears to be a basic ecological trigger that determines changes in community functionality and resilience. Particularly, fluctuations in abundance of dominant species might indicate major changes in resource use and ecosystem functioning. Here we use quantitative surveys of Baltic brackish and salt marsh plant communities to infer how variability in species abundances and environmental conditions influence plant assimilation rates and whether compensatory effects in abundance mask variability in functionality. The variability in species richness and assimilation rates was negatively correlated with average soil organic matter content and moisture and positively correlated with soil pH. It was independent of the variability in soil conditions. The abundances of rare species and species of intermediate abundances increased with increasing community wide assimilation rates. Our findings indicate that the strength of compensatory mechanisms that stabilise assimilation rates in salt marsh environments heavily depend on soil conditions. In the present study sites benign soil conditions stabilized assimilation rates while more stressful conditions caused synchronous fluctuations in total abundance and assimilation.