Mutualists and Invasion
In collaboration with Dr. Jennifer Rudgers (Rice University), I am conducting research on mutualistic endophyte fungi (EF) and mycorrhizal fungi (AMF) in Great Lakes sand dune plant communities dominated by the grass Ammophila breviligulata. Dune systems provide unique opportunities to examine the role of microbial mutualisms as they are one of the few natural systems where plant and soil communities develop from initially sterile conditions. Fungal mutualists can help infected plants in stressful environments by increasing resistance to herbivores, drought tolerance, and nutrient uptake. These symbionts can additionally alter competitive interactions between species, and so may have important impacts on dune invasion dynamics. Further, dune restorations provide ideal opportunities to study how changes in AMF and EF affect plant community structure, as restoration activities often alter microbial biota unintentionally. I am using a combination of surveys and field and greenhouse experiments to address the following questions:

1) Are AMF and EF more abundant in restored dunes than in natural dunes?
2. Are restored dunes more or less susceptible to exotic species invasion and native species colonization because of changes in these mutualists?
3. Do interactive effects of AMF and EF differ from their individual effects on community invasibility?
Community and Ecosystem Impacts of Invasive Species Gypsophila paniculata (baby’s breath) is a serious invader of the sand dune systems in the greater Sleeping Bear Dunes National Lakeshore region. It is widely believed that G. paniculata creates problems for the dunes by over-stabilizing habitat, making it unsuitable for native species such as the federally-threatened Cirsium pitcherii (Pitcher’s thistle) which thrive in active dunes, and may be capable of out-competing native matrix species (e.g., Schizachyrium scoparium and Ammophila breviligulata) for resources due to its incredibly deep root system. The Nature Conservancy (MI) and the National Park Service are actively managing their properties with the goal of G. paniculata eradication by hiring field crews to mechanically remove plants by cutting the plant below the root crown. While some data indicate that this method of removal is effective, there has been little long-term monitoring of the impact these removal efforts have on community and ecosystem properties. In collaboration with TNC-MI and Sleeping Bear Dunes National Lakeshore, I am monitoring the effects of large-scale removal of G. paniculata on primary productivity, native plant diversity, insect communities, soil microbes, sand stabilization, and nutrient cycling.  

Dominant Species and Community Invasibility Developing a better understanding of the role of biodiversity for community functions, such as invasibility, has been a driving focus of ecological research over the past 50 years. However, much of the theory and experiments developed about the role of biological diversity have focused solely on aspects of species richness in communities. Although very little of theory or empirical work has addressed the importance of other aspects of biodiversity for community functioning, recently there has been a call to acknowledge and better understand the role of other aspects of biodiversity, such as species evenness and species composition/identity. In particular, while dominant species are believed to exert strong influence over community dynamics, very little research has addressed how dominant species affect invasibility. In my dissertation work, I examined whether there was an effect of the identity and relative abundance of dominant species on invasibility of communities using a field seed-addition experiment and a more controlled mesocosm experiment in oldfield communities at the Kellogg Biological Station. The identity of the dominant species was always a significant predictor of invasibility (Emery and Gross, 2007), though relative abundance of these dominants rarely affected invasion.

Invasive Species Population Dynamics
Many management decisions regarding invasive species are based on studies that only consider short-term population or community responses. Modelling approaches, such as transition matrix models, account for the responses of all life stages of a species and improve predictive power in management decisions. As part of my dissertation, I used matrix population models to examine the effects of prescribed burns on populations of invasive spotted knapweed, Centaurea maculosa, in a prairie restoration project in Michigan. The frequency and season of burn differentially affected the populations of C. maculosa (Emery and Gross 2005), and models suggested annual summer burns were most effective in reducing growth rates.