Garlic mustard (Alliaria petiolata) is associated with an overall reduction in plant diversity, but is more likely to co-exist with native than alien species

Abstract

ABSTRACTBackground: Alliaria petiolata (garlic mustard) is a widespread allelopathic invasive species in North America, but despite extensive research we do not fully understand how it impacts plant communities.Aims: We tested the hypothesis that A. petiolata facilitates the introduction of additional alien species as predicted by the invasional meltdown hypothesis.Methods: We conducted co-occurrence surveys to compare the numbers of alien and native species in communities surrounding A. petiolata plants with those surrounding an allelopathic native species. We also conducted an experiment to compare recruitment of native and alien species in pots dominated by either A. petiolata or a native species.Results: A. petiolata plots in the co-occurrence surveys had relatively high proportions of bare ground, suggesting habitat modification, plus lower species richness and disproportionately fewer alien species. There was a greater tendency for native species than alien species to establish in A. petiolata pots.Conclusions: A. petiolata does not promote additional alien species, and in fact may be a more effective competitor against alien than native species in North America. This could help explain its invasive success in disturbed habitats, and illustrates the need to consider separately alien and native species when assessing the outcomes of competition.