James Runkle (Advisor)
Master of Science (MS)
Species that form forest understory layers affect canopy tree seedling establishment worldwide. In the Eastern United States, shrub understories like Rhododendrom maximum, a native evergreen species, and Lonicera maackii, an exotic, invasive species, diminish tree seedling survival. I compared the density and survival of canopy tree seedlings under and outside patches of the native shrub, Asimina triloba (L.) Dunal (Annonaceae) (pawpaw). I also conducted a manipulative experiment to determine whether above ground or below ground competition was more important in seedling growth and survival. Above ground competition was manipulated by tying back the leaves of the pawpaw and below ground competition was manipulated by trenching the perimeter of the study plots. Tree seedling density was approximately three times greater outside pawpaw patches than under pawpaw over the range of sites. Seedlings under pawpaw were both younger and shorter than those outside of pawpaw. Survival varied by species. Acer saccharum seedlings were about one and a half times more likely to survive outside pawpaw than under pawpaw. Prunus serotina seedlings were about three times more likely to survive outside pawpaw than under pawpaw. In contrast, pawpaw did not affect the survival of Fraxinus spp. seedlings. Differing survival rates may reflect characteristics related to the species shade tolerance. Light (measured by canopy densiometer) was greater outside pawpaw than under pawpaw. No significant differences in moisture levels were detected; however, at three of the four sites, moisture was greater under pawpaw than outside of pawpaw. The combination of above ground and below ground factors was more important in the survival and growth (measured by biomass) of planted A. saccharum seedlings under pawpaw than either above ground or below ground factors alone. Given that conditions such as elevated deer herbivory and tree diseases may provide opportunities for pawpaw to expand, continued attention to the pawpaw understory is warranted.
Department or Program
Department of Biological Sciences
Year Degree Awarded
Copyright 2007, all rights reserved. This open access ETD is published by Wright State University and OhioLINK.