Human activity profoundly transforms the natural landscape, with dramatic consequences for biological communities. Across the eastern United States many species are relegated to forest fragments embedded within cities and sprawling suburbs. These forests typically exhibit a striking lack of native plants (including tree seedlings), but have thriving populations of non-native plant species and dense populations of white-tailed deer. This project will examine how these phenomena are related, by investigating the joint effects of two important co-invading plant species and deer on the invasion process and the native plant community. The plants are garlic mustard and Japanese stilt-grass, two co-occurring species that pose serious threats to the native community. The study will address key questions concerning plant invasions in the suburban landscape: do invasive plants facilitate each other's invasions, and is invasiveness promoted by intensive deer impact on the native plant community, by their strong competition with natives, or by both acting together? The study will be a multi-year field experiment in 240 plots spread across six forests of central New Jersey. Half of the plots will be unfenced, and half will be fenced to exclude deer. Experimental treatments will include addition of seeds of garlic mustard, stilt-grass, both species, or neither species added. All invasive plants in the plots will be removed at the end of the study. The response of the plant community will be studied in each plot for five years, by measuring garlic mustard and stilt-grass population growth and changes in the herb layer plant community.
Most people live in or near cities and towns, so this study of suburban forests will be of interest to many citizens, including the many conservation groups and local agencies that need to manage suburban forests to conserve native biodiversity. It also will enhance plant science and ecology education at a primarily undergraduate public college. Eighteen students will each engage in mentored research teams for two years and one summer, which will encourage them to pursue ecology and conservation-related graduate school and professions.