Regional Patterns of Floristic Diversity and Composition in Forests Invaded by Garlic Mustard (Alliaria petiolata)

Abstract

The impacts of invasive species on native plant communities are often studied on small spatial scales but may vary across regionally heterogeneous landscapes. Comparisons of vegetation across several similar sites with and without an invasive species present can be logistically challenging but highly informative to both scientists and land managers. We examined regional geographic variation in the diversity and composition of 8 replicate northeastern forest-understory plant communities invaded by the non-native species Alliaria petiolata (Garlic Mustard). Despite variation in underlying soil conditions and horizon development, several native species and their associated functional groups were either negatively or positively associated with Garlic Mustard invasion at the regional scale, and soil moisture and pH were higher in invaded plots across all sites. Most tree species were less common at invaded sites, but high tree-seedling abundances at some sites led to regionally higher seedling abundance in the presence of Garlic Mustard. Our study highlights the importance of species-specific responses, as well as site-specific soil conditions, for better understanding potential impacts of invasion.