Invasive species, while currently ranked the second greatest threat to biodiversity, also challenge our classic ecological conceptions of intact ecosystems. Hairston, Smith, and Slobodkin famously asked, “Why is the World Green?” and predicted that consumers control the relative biomass of organisms in different trophic levels, including primary producers. However, invasive species may alter the structure of ecosystems through a number of pathways. For example, communities in which an invasive species experiences ‘enemy release’ may exhibit significant differences in trophic structure from natural communities. In this study we asked how biological invasions change the allocation of total biomass among primary producers and consumers. Garlic mustard (Alliaria petiolata), a noxious invader in the Eastern and Midwestern United States, commonly invades and dominates forest understories. In a replicated natural experiment we quantified the total biomass of producers and consumers in ecosystems both invaded and uninvaded by A. petiolata.

Results/Conclusions

Communities invaded by A. petiolata contained significantly more (presumably inedible) producer biomass and significantly less biomass of secondary consumers than uninvaded communities.  Our results demonstrate that the replacement of a dominant native plant with an invasive one can lead to dramatic changes in the trophic structuring of communities.