Common buckthorn (Rhamnus cathartica L.) is one of the most abundant and ecologically harmful non-native plants in forests of the Upper Midwest United States. At the same time, European earthworms are invading previously glaciated areas in this region, with largely anecdotal evidence suggesting they compound the negative effects of buckthorn and influence the invasibility of these forests. Germination and seedling establishment are important control points for colonization by any species, and manipulation of the conditions influencing these life history stages may provide insight into why invasive species are successful in some environments and not others. Using a greenhouse microcosm experiment, we examined the effects of important biotic and abiotic factors on the germination and seedling establishment of common buckthorn. We manipulated light levels, leaf litter depth and earthworm presence to investigate the independent and interactive effects of these treatments on buckthorn establishment. We found that light and leaf litter depth were significant predictors of buckthorn germination but that the presence of earthworms was the most important factor; earthworms interacted with light and leaf litter to increase the number and biomass of buckthorn across all treatments. Path analysis suggested both direct and moisture-mediated indirect mechanisms controlled these processes. The results suggest that the action of earthworms may provide a pathway through which buckthorn invades forests of the Upper Midwest United States. Hence, researchers and managers should consider co-invasion of plants and earthworms when investigating invasibility and creating preemptive or post-invasion management plans.
Bibliographical noteFunding Information:
We thank the staff at Warner Nature Center for allowing us to collect soil and leaf litter for the experiment. We thank Cindy Buschena and Susan Barrott for their help throughout the experiment. We also thank the undergraduate student workers in the Reich lab for help planting and harvesting the experiment. Funding for this project was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR). Support was also provided by the Integrative Graduate Education and Research Traineeship: Risk Analysis for Introduced Species and Genotypes (NSF DGE-0653827); University of Minnesota Graduate School; the Wilderness Research Foundation; and the Dayton Fund of the Bell Museum of Natural History. N. E. gratefully acknowledges funding by the Deutsche Forschungsgemeinschaft (Ei 862/1, Ei 862/2).
© 2014, Springer-Verlag Berlin Heidelberg.
- Leaf litter
- Lumbricus terrestris
- Rhamnus cathartica