A multi-site comparison of invasion success in Alliaria petiolata (garlic mustard) in urban and rural environments

Background/Question/Methods

The establishment and proliferation of non-native plants is of great ecological concern because they can decrease biodiversity and significantly alter nutrient cycling in ecosystems. One of the most problematic invaders in North America is Alliaria petiolata (garlic mustard), a biennial herb of the family Brassicaceae that was introduced in 1868 from Eurasia. A. petiolata is now widely distributed throughout much of the United States and Canada.  In order to understand the mechanisms that influence invasion success, we need to examine factors operating at multiple spatial scales.  In this study, we examined plant and population traits at a landscape scale. Since nutrient availability and urbanization have both been suggested as driving factors behind the success of many invasives including A. petiolata, we compared dense populations of A. petiolata in rural and urban sites to determine if populations are more successful in urban sites, and whether this success is correlated with nitrogen availability. Dense populations of A. petiolata were randomly sampled in subplots located in edge habitats at three urban sites and three rural sites.  Plants were measured for leaf size and first-year rosettes were collected and analyzed for leaf nitrogen and shoot mass. These data were analyzed using a nested ANOVA design.

Results/Conclusions

A significant difference in shoot mass was detected between urban and rural sites (P < 0.001), with urban rosettes being significantly heavier than rural rosettes. The largest leaf width for each plot was found to be significantly higher in urban sites compared to rural sites (P = 0.009), and a significant difference in largest leaf width was also detected among individual sites within the two categories (P = 0.034). Leaf nitrogen did not differ significantly between urban and rural sites, but was found to differ significantly among individual sites within the urban and rural categories (P = 0.039). Urban populations do exhibit increased success in terms of rosette size and density, but leaf nitrogen was not correlated with this success. We are pursuing further studies to fully understand what drives the success of A. petiolata in urban sites.