Human-mediated spread of an invasive forest grass and what to do about it
Even though it is known that human activities typically play a large role in invasions, many studies that do investigate invasive species spread are focused on small-scale natural mechanisms that do not explain regional spread. My current research on Microstegium vimineum (Japanese stiltgrass), an aggressive invader threatening forest regeneration and native plant diversity in Pennsylvania, focuses on human-mediated spread through road maintenance activities. David Mortensen and I developed these research ideas together, and we co-wrote a USDA-NRI grant. First, we analyzed local growth from fine-scale experiments and discovered that it was too slow to account for regional spread (Rauschert et al. Biological Invasion 2010). In collaboration with the Center for Dirt and Gravel Road Studies, we did further experiments examining the effects of road maintenance, which we found can move seeds more than two orders of magnitude further than natural spread (Rauschert et al, in review). We also developed simulation models incorporated multiple mechanisms for spread, and we were able to show that this behavior can account for the corridor-like spread patterns that we observe (Rauschert and Mortensen, ESA 2011, also covered by Scientific American podcast, Discovery News, NPR and Penn State Live).
Having gained an understanding of spread, we are currently using the models to explore how to best mitigate this problem. When working with invasive species, particularly ones which have already invaded large areas, it is important to be very explicit about what management goals are feasible. Additionally, which techniques are most effective can vary considerably depending on the goals. We are currently using the model to contrast various management scenarios, either targeted at slowing further spread or at protecting ecologically sensitive areas from invasion. It appears that the creation of managed buffer areas best protects sensitive areas, and reducing the frequency of grading best slows the spread. Janel Hoffman, who recently completed her undergraduate degree at Penn State, and I have been working on experiments investigating the effects of the timing of chemical and mechanical control of stiltgrass, which will further inform these models.