Invasive Plants
Exotic plant species are increasingly altering forest composition in ways that are both overlooked and unknown. Due to the importance of nonnative species worldwide and their historical and current significance to New England, the Harvard Forest has developed a number of integrated studies examining invasive organisms as well as their varied impacts on natural ecosystems.
We are investigating landscape, community, and population - level interactions between native and invasive plants in forest and coastal habitats. Our major objectives are to:
- identify links between land use and the presence/abundance of non-natives
- develop predictive models of invasion based on historical and present-day levels of anthropogenic and natural disturbance
- test the direct impact of invasive plant cover on the survival and performance of native flora
- identify evolutionary potential for further spread within invading populations
Our research of nonnative plant distribution across Cape Cod, MA, has revealed that nonnative species distributions and abundances in this largely invasion-resistant landscape are largely driven by soil nutrient conditions, rather than current biota or historical disturbances. Nonnative species richness and abundance values decrease away from typical natural disturbances (wind, salt spray) of the outer Cape, while native species richness and abundance values typify the 'intermediate disturbance' response to natural disturbances. We have documented that the invasive, nitrogen-fixing black locust tree, Robinia pseudoacacia, facilitates invasion by other nonnative plant species, most likely owing to the nutrient-rich soils found beneath this nonnative species.
Our research in central New England has been focused on the biennial herbaceous plant, Alliaria petiolata. This Eurasian exotic is a persistent invader in New England forests where it threatens native understory and tree seedling species. We have documented negative relationships between A. petiolata and key native tree seedlings, including sugar maple and beech. We have also determined that populations in high light habitats are more likely to spread than those in low light habitats, an important consideration for population dynamics in forests with different levels of canopy openness.
We have also begun investigating the distribution of nonnative species as a function of the geography of current and past habitat structure. This research utilizes newly available historical data collected by the Harvard Forest, with support from the State of Massachusetts and numerous conservation organizations, including The Nature Conservancy. These data comprise information on current vegetation, past land-use, and present and past forest harvesting. Using vegetation survey methods, are conducting spatial analyses to test for relationships between historical factors and the abundance of invasive plant populations, especially as regards the extent and locations of disturbed sites that could support potential source populations for understory invasion by exotic plants such as A. petiolata, Lonicera japonica, Berberis thunbergii. This work will provide insight into the role of historical and recent land use on regional landscape patterns of invasion.
Publications:
Von Holle, B., K. A. Joseph*, R. G. Lohnes*, and E. F. Largay*. 2005. Facilitations between the introduced nitrogen-fixing tree, Robinia pseudoacacia, and nonnative plant species in the glacial outwash upland ecosystem of Cape Cod, Massachusetts. Biodiversity and Conservation (In Press).
Stinson, K. A., S. Kaufman, L. Durbin*, and F. Lowenstein. 2004. Responses of a New England forest community to increasing levels of invasion by garlic mustard (Alliaria petiolata). Biological Invasion (submitted).
Orwig, D. A. 2002. Ecosystem to regional impacts of introduced pests and pathogens: historical context, questions and issues. Journal of Biogeography 29: 1471-1474.
Mack, R. N., D. Simberloff, W. M. Lonsdale, H. Evans, M. Clout, and F. A. Bazzaz. 2000. Biotic invasions: causes epidemiology, global consequences and control. Ecological Applications 10: 689-710.
Mack, R. N., D. Simberloff, W. M. Lonsdale, H. Evans, M. Clout, and F. A. Bazzaz. 2000. Biotic invasions: causes epidemiology, global consequences and control. Issues in Ecology. Ecological Society of America 5: 2-20.