The Ecology and Control of Invasive Exotic Plants in Urban Parks

James N. McNair
Patrick Center for Environmental Research
Academy of Natural Sciences of Philadelphia

Numerous species of introduced plants are now considered to be problematic in the United States. Examples include Japanese knotweed (Polygonum cuspidatum, photo above left), Norway maple (Acer platanoides), and the infamous kudzu (Pueraria lobata)—“the plant that ate the South”. These aggressive exotic species are characterized by an ability to spread rapidly, out-compete native species, and eventually establish near monocultures in areas that formerly possessed a diverse flora. Habitat quality for many native animal species also often declines in areas where these plants come to dominate.

The purpose of this project was to rigorously assess potential management techniques for controlling two aggressive exotic plant species in the extensive natural lands of Philadelphia’s Fairmount Park system, the largest urban park system in the United States. The species chosen for study—Japanese knotweed and Norway maple—were selected after discussions with district managers from the park system, who ranked these as two of their most serious vegetation-related problems.

Though certainly an applied problem, I believe that assessment of strategies for controlling aggressive species should be approached in essentially the same way that one would approach a basic research problem in plant ecology. I and my former postdoctoral fellows, Dr. Margot Bram and Dr. Robert Witmer, designed rigorous field experiments and used statistical analyses of their outcomes as the main basis for comparing the efficacy of different management techniques. Greenhouse and laboratory experiments with both species were also conducted to answer basic questions about the biology of these species that where stimulated by our field studies. I am also in formulating mechanistic population models of the two species to aid in identifying key factors that determine their rate of spatial spread and to assist in evaluating the likely effectiveness of different management practices.

Field and laboratory experiments for this project have now been completed. Most of the basic statistical analyses of alternative management practices have also been completed, and the results have been shared with park managers. We are still in the process of publishing results of our studies, and of developing and implementing the population models. Additional information can be found at the project web site.)

We gratefully acknowledge funding for this project from the William Penn Foundation.

Selected Publications

Bram, M.R. & McNair, J.N. 2004. Seed germinability and its seasonal onset in three populations of Japanese knotweed. Weed Science 52: 759–767.