Long-term changes in species composition in heavily invaded plant communities

Background/Question/Methods   A key gap in invasion biology has been our understanding of the long-term impact of species invasions on local communities. In particular, it has been unclear whether ecosystems with many exotic species are likely to become increasingly dominated by them over time or instead whether coexistence between native and exotic species is likely to occur. We examined this question by assessing changes in species composition over 11 years (1998-2009) in the strandline plant communities of Narragansett Bay, RI and MA. These communities are ideal for examining the long-term impact of invasions on local communities as they have been heavily invaded for over two hundred years.

Results/Conclusions   In this study, we determined that the strandline plant communities of Narragansett Bay have become increasingly dominated by exotic species within the last decade. In particular, we showed that the ratio of exotic-to-native richness and percent cover has significantly increased at local sites from 1998-2008 and 1998-2009. Our findings indicate that the long-term fate of these strandlines may still be in flux and that communities that have been heavily invaded historically should be of considerable concern to conservation biologists in the future.