LTREB RENEWAL: The population dynamics of forest understory invasion: mechanistic experiments with generalist herbivores, natives, and invaders

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Invasive species threaten the integrity of native ecosystems and cause billions of dollars in economic losses in the US annually. This long-term project will identify the mechanisms that allow some species to be invasive, and some communities to be invaded, while others are not. It is an exciting example of a public-scientist partnership in research and management, as the investigator works collaboratively with local and regional officials on the conservation of their natural areas, outreach to public visitors of these areas, and developing and assessing a virtual field trip that engages middle school students who are unable to visit the research site directly. The project will continue to provide training for undergraduate and graduate students, with a particular emphasis on recruiting students from groups under-represented in field ecology. This award supports Phase II of a decadal project to understand the population- and community-level dynamics of invasion by garlic mustard. The investigator will collect vital rate data on seven focal species, including three native herbaceous perennials that are highly palatable to deer, two native herbaceous perennials unpalatable to deer, a native winter annual, and the highly invasive garlic mustard. A Life Table Response Experiment will include two fully crossed treatments: plots are either open or fenced to exclude deer, and plots divided between garlic mustard presence and its removal. Demographic matrix projection analyses and Integral Projection Models analyses will be used to project population growth rates and the long-term fates of focal species under the deer and invader scenarios generated by the experiment. Demographic analyses will be complemented by experiments exploring the hypothesized mechanisms of invasion success. Results from Phase I of this project indicated that chemicals released by garlic mustard suppress physiological function and carbon storage of the focal natives by disrupting the native plant-mycorrhizal mutualism. In Phase II, additional data on the physiological status of plants the four treatments will be compared. Instantaneous photosynthetic and transpiration rates, stomatal conductance and fluorometric measurements of focal plants will provide insights into carbon stress as a mechanism of native decline and invader domination.