Demography and distribution of the invasive Rhamnus cathartica in habitats of a fragmented landscape

MCCAY, T. S. (Department of Biology, Colgate University, Hamilton, NY 13346), D. H. MCCAY (Department of Geography, Colgate University, Hamilton NY 13346), A. V. CARAGIULO (Department of Biology, Colgate University, Hamilton, NY 13346), AND T. L. MANDEL (Department of Geography, Colgate University, Hamilton, NY 13346). Demography and distribution of the invasive Rhamnus cathartica in habitats of a fragmented landscape. J. Torrey Bot. Soc. 136: 110-121. 2009.-Forest fragmentation and abandonment of lands managed for agriculture are widespread processes in eastern North America that might promote the expansion of exotic pests. We studied populations of Rhamnus cathartica L. (European buckthorn), an invasive alien plant in North America, in maple-beech forests, abandoned agricultural fields, and unmanaged conifer plantations in central New York State. Surveys and neighborhood functions were used to examine demography and spatial distribution. Populations of R. cathartica in maple-beech forests were sparse (112 ha(-1)), dominated by seedlings and saplings, and strongly aggregated in space. Populations of R cathartica in plantations, by contrast, were dense (7,717 ha(-1)), not strongly concentrated at the low end of the diameter distribution, and less strongly aggregated than those in other habitats. Old fields included a high density of R. cathartica plants (5,912 ha(-1)), which were predominantly seedlings and strongly aggregated. Seedling density was positively related to availability of light at our forested plots, and plants were clustered near walking trails at three of four maple-beech plots. At all old field and two of four plantations, seedlings were spatially associated with fruiting R. cathartica, suggesting that they served as recruitment foci. Further, seedlings also were associated with non-fruiting adult R cathartica at 2 of 3 old-field and 2 of 4 plantation plots. Unmanaged conifer plantations with numerous canopy openings may permit colonization and population growth of R cathartica. Management for closed-canopy forest and the elimination of plants, particularly fruiting conspecifics, serving as recruitment foci are potentially successful approaches toward control of R. cathartica.