A Dominant Plant Species and Insects Independently and Interactively Shape Plant Community Structure and Ecosystem...

It is well-established that dominant plant species and insect herbivores independently shape community structure and ecosystem function in terrestrial plant communities. Critically, few studies have assessed the combined effects of these two drivers of plant community structure and ecosystem function above- and below-ground or tracked their effects over time. In this study, we factorially manipulated the dominant species Solidago canadensis (Canada goldenrod) and insects in an old field for 3 years and quantified their effects on plant diversity, biomass, functional traits, microclimate, and decomposition. Overall, S. canadensis and insect herbivores independently and interactively shaped aboveground plant biomass, richness, functional traits, microclimate, and the decomposition of soil organic matter. The biomass of the rest of the plant community was higher where S. canadensis was removed and where insects were reduced, in part due to the positive effect of S. canadensis removal on light availability and soil moisture. The highest estimated decomposition rate of soil organic matter occurred where S. canadensis was removed and insects were reduced. Furthermore, the community weighted mean (CWM) of multiple plant functional traits related to competition for light varied with S. canadensis removal and insect reduction; for example, the CWM of plant height was highest where S. canadensis was removed and insects were reduced. After 3 years of experimental manipulation, S. canadensis removal and insect reduction independently and interactively reduced the temporal stability of aboveground plant biomass but not species richness. Altogether, our results highlight the need to consider the potential interactive effects of dominant plants and insect herbivores above- and below-ground to improve our understanding of their role in structuring communities and ecosystems. Furthermore, we find that over 3 growing seasons insect herbivores prevent biomass compensation following S. canadensis removal, emphasizing the importance of insect herbivores in mediating community and ecosystem recovery after biodiversity loss.