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2006 Harvard Forest REU Student Symposium Abstracts

Jessica Woltz - North Carolina State University at Raleigh

Garlic mustard population demographics differ among forest habitats at the Harvard Forest LTER.


Invasive species can severely affect ecosystems by displacing natives, disrupting trophic interactions, and altering natural processes such as nutrient cycles. Garlic mustard (Alliaria petiolata), an invasive biennial plant that ranges over much of the Northeastern and Midwestern US, is known to invade a vast range of habitat types. This experiment investigated garlic mustard population dynamics in forest edge, intermediate, and understory habitats at the Harvard Forest LTER. We predicted that only the edge populations would be self-sustaining. We monitored garlic mustard populations in three study sites, each consisting of contiguous forest edge, intermediate and understory habitats that had been invaded with garlic mustard prior to our study. Twice per summer from 2003 to 2006, we counted all garlic mustard individuals within 10 1 m2 quadrats placed in each habitat within each site. This census data was used to construct population matrices for each full garlic mustard life cycle in each habitat, for a total of 9 matrices. Using MatLab computer software, we calculated population growth rates (λ) and sensitivity values for each matrix. Sensitivity values measure how much a change in a given matrix element will affect λ. The edge populations were increasing over all three time periods, while the intermediate populations were decreasing over all three time periods. The understory populations, which were initially increasing, decreased over the last time period. These results indicate that only the edge populations are self-sustaining, and may in fact be supplying individuals to the other populations. Also, in all 9 matrices, the transition from rosette to adult had the greatest sensitivity, indicating that changes to this transition would have the greatest impact on λ. Our results suggest that management efforts should be focused on populations in edge habitats and on reducing over-winter survival of rosettes to achieve maximum management efficacy.

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