A dominant plant species and insects interactively shape plant community structure and an ecosystem function

Dominant plants and insects both structure plant communities and determine key ecosystem functions. However, dominant plants and insects can have opposing effects on plant community structure and ecosystem function. Critically, few studies have assessed the combined effects of these two drivers of plant community structure and ecosystem function. In this study, we factorially manipulated the presence of the dominant plant species Solidago canadensis (Canada goldenrod) and insects in an old field to quantify their independent and interactive effects on the plant community. Insect presence mediated the effects of S. canadensis removal on plant biomass and richness. Total plant biomass was ~32% lower following S. canadensis removal only when insects were present. In contrast, subdominant plant biomass was ~75% higher following S. canadensis removal, but only when insects were reduced. Subdominant species richness was ~37% higher following S. canadensis removal when insects were present, though the abundance of most subdominant species did not vary systematically with S. canadensis removal or insect reduction. Light availability was ~49% higher following S. canadensis removal with no effect of insect presence on light availability. Our results emphasize the interactive role of dominant plants and insects in determining the diversity and biomass of plant communities.