The proliferation of invasive alien plants into local ecosystems--a disturbance predicted to become even more severe in the 21st century--is a major threat to species diversity and ecosystem functioning on a global scale. To mitigate the impacts of invasive plants on ecosystem structure and biodiversity, a fundamental understanding of the mechanisms by which plant invaders alter ecological communities and networks is essential. This research evaluated the changes plant invasions can elicit to woodland food webs and communities. First, a meta-analysis of the primary literature was used to evaluate the impacts of invasive plants on the trophic structure of terrestrial ecosystems. Second, using a widespread invasive plant (Alliaria petiolata [garlic mustard]) as a model system, we evaluated a mechanistically based hypothesis of how garlic mustard alters belowground food webs via reduction of mycorrhizal fungi. Lastly, we investigated how the presence and/or removal of invasive plants restores the structure of arthropod communities in woodland ecosystems.
Results/Conclusions
The meta-analysis revealed that invasive plants decrease abundances of major grouping of primary consumers (detritivores, bacterivores, fungivores, and/or herbivores) in both brown and green food webs of woodland ecosystems. Preliminary results from the manipulative field experiment with garlic mustard reveal no changes in arthropod primary- and secondary-consumer abundances in the first year of the invasive plant’s life-cycle. However, the adult stage of garlic mustard (second year of this biennial species) alters composition of the fungivore community. Our “natural experiment”, which was a collaborative study with the Chicago Wilderness Land Management Research Program, revealed that unmanaged woodland sites with high densities of invasive plants have a strikingly different community of detritivores and fungivores compared to high-quality restored (managed) sites, which have low densities of invasive plants. Overall, our findings indicate that invasive alien plants can engender considerable changes to the structure and composition of food webs in woodland ecosystems. Nevertheless, these effects can be mediated by removing invasive plants and re-introducing native vegetation.