Since 2005, undergraduate students at Ohio Wesleyan University have collected data on the community level effects of the invasive biennial herb Alliaria petiolata in two mesic forest fragments in central Ohio. The objectives of this ongoing study are to determine if the cover, abundance and/or diversity of native understory plant species are being influenced by A. petiolata over time. We established fourteen transects in a forested nature preserve that had a substantial A. petiolata population (the invaded preserve) and nine in a preserve where A. petiolata was present, but rare (the uninvaded preserve). Each transect contained five to eight 2x2 m plots (175 plots total) spaced 5m apart. In May and June of 2005 and 2007, one randomly chosen 1x1 m section was selected in each plot and surveyed for percent cover and stem counts of all species. 

Results/Conclusions

Plots in the invaded preserve, where A. petiolata was the second most abundant species as measured by stem counts, showed no significant differences in overall species diversity and composition between plots containing A. petiolata and plots that did not for both 2005 and 2007.  In contrast, in 2005 plots in the uninvaded preserve that contained A. petiolata were significantly less diverse and compositionally distinct from plots without A. petiolata. One interpretation of these data is that unusual microsites may be providing “access” points for the invasive species in this relatively pristine community. A. petiolata populations were very small in the uninvaded site in 2007, which reduced the numbers of plots available for comparisons.  Seedlings of the most common woody species Acer saccharum tended to be less abundant in plots with A. petiolata in the invaded preserve in 2007, but this difference was not statistically significant. Because A. petiolata is known to suppress mycorrhizal development for woody seedlings, it will be interesting to determine if this trend strengthens over time. While these data are interesting on their own, they would have much greater scientific relevance as part of a regional pattern. This work will be discussed as a potential starting point for a collaborative research project among small colleges using college nature preserves as a network of study sites in a long-term experiment on fragmentation. This project could eventually link with the future National Ecological Observatory Network to study the effects of fragmentation on factors such as invasion dynamics and carbon sequestration at regional to continental scales.