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Current Ph.D. Research

I am currently conducting three studies pertaining Rhamnus cathartica (European buckthorn) invasions in Chicago-area woodlands. This exotic shrub reduces the abundance of native understory plants where it invades (Figure 1) and is hypothesized to cause changes in belowground community structure and ecosystem processes that may persist after its removal.

Figure 1. The effect of buckthorn on abundance of native understory plants. The photograph on the left shows an understory in a woodland that is
uninvaded by buckthorn. The photograph on the right shows the understory of a buckthorn-invaded woodland.

Study 1: This landscape-level, "natural experiment" will differentiate between the causes and consequences of buckthorn invasions by measuring multiple belowground factors hypothesized to either promote and/or respond to buckthorn invasions including total soil C and N; soil pH; soil moisture; soil Ca; leaf litter mass; decomposition; earthworm abundance; and fungal:bacterial ratios at buckthorn-invaded and adjacent buckthorn-free points. The relationship between invasion severity and the differences in values for factors at invaded and uninvaded points will reflect whether or not these factors respond to or promote buckthorn invasions (Figure 2).

Study 2: This experiment is in collaboration with Dr. Liam Heneghan and Lauren Umek from DePaul University's Environmental Science Program. The objective of this experiment is to 1) determine if amending soils with buckthorn mulch after buckthorn removal will reduce reinvasion and enhance restoration outcomes and 2) determine if reduced reinvasion results from microbial immobilization of N caused by the addition of high C:N amendments (mulch) or through burying the existing remnant buckthorn seedbank through tilling of the mulch into the soil (Figure 3).

Figure. 2. Possible relationships between the severity of buckthorn invasion and the differences in between invaded-uninvaded points-pairs in measured factors (∆ Response Variables).

· Relationship A suggests that buckthorn invasions affect the measured factor and the magnitude of this effect is positively correlated with invasion severity.

· Relationship B suggests that the factor is not affected by buckthorn, but instead influences where buckthorn establishes.

· Relationship C suggests a combination of Relationships A and B, i.e., a positive feedback.

· Relationship D suggests that the factor neither influences nor responds to buckthorn invasion.

Study 3: This study is in collaboration with Dr. Moira Zellner from the College of Urban Planning and Public Affairs at UIC, and is part of a larger NSF-funded project investigating how social interactions between individuals affiliated with ecological restorations influence biological diversity. For this study I am constructing a computational, agent-based model to gain insight into how canopy-gap related variability in age of first reproduction, fecundity, and dispersal patterns influences the spread of exotic shrubs through light-limited woodlands. This model will then be expanded to investigate how various restoration strategies (e.g. burning, seeding native species) influence reinvasion after initial shrub removal.

Figure 3. Setting up Study 2. The photograph on the left shows the incorporation of the mulch.
The photograph on the right shows the the crew who was brave enough to be outside all day
on multiple days throughout the winter to remove buckthorn from the study plots. The shrub in the background of both photographs is buckthorn.

Past Master's Research:

I worked on my master’s degree at the University of Minnesota as a member of Dr. Susan Galatowitch’s lab group. My research focused on the restoration of sedge meadow wetlands. In particular, I determined if reducing light by sowing native cover crops and/or reducing soil nitrogen by incorporating high C:N amendments would limit Phalaris arundinacea L. (reed canarygrass) invasions of restored sedge meadow wetlands. Phalaris is an extremely fast-growing, perennial grass that invades newly formed wetlands and prevents the establishment of native plant communities. We found that reducing light by sowing cover crops limited the establishment of desired species more than Phalaris, resulting in a Phalaris-dominated community. We also concluded that reducing nitrogen, even for short periods, decreased Phalaris invasion, increased natural colonization, and resulted in a graminoid-rich community similar to natural sedge meadows. Lastly, we determined that the most important step in limiting Phalaris invasions of restored sedge meadows was the rapid establishment of a perennial plant community that could sequester both light and nitrogen.


From left to right: Phalaris arundinacea and three other common sedge meadow species- Carex pseudocyperus, Mimulus ringens, and Pycnanthemum virginianum.