Distribution of Pignut Hickory (Carya glabra) Along a Forest to Edge Transect, and Factors Affecting Seedling Recruitment

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Abstract
An examination of the distribution of pignut hickory (C. glabra (Mill.) Sweet, Juglandaceae) along a forest to forest edge transect (200 m .times. 40 m) in a southeastern Michigan [USA] forest revealed that few seedlings and saplings were located within the forest where adults were present but several were located on the forest edge. The goal of this study, after quantifying the hickory distribution along the transect, was to examine how factors affecting seed and seedling survival could explain seedling recruitment within the forest and forest edge. An experiment designed to compare post-dispersal survival of hickory nuts in different parts of the forest and forest edge indicated that more nuts buried on the edge survived than those buried within the forest. Germination experiments revealed that burial of nuts enhanced both germination and establishment of 1st year seedlings within the forest and that without burial, germination was nil in the forest edge. Information on growth rates, frequency of stem damage by vertebrate herbivores (probably deer), and general size characteristics of the individuals present, showed that seedlings located within transition and edge zones did better than seedlings within the forest. Comparison of size and age of saplings along the transect did not reveal any significant differences among vegetation zones. The information on overall seedling success supports the findings of other studies that pignut hickories do not reproduce well in an undisturbed forest. Seedling dynamics alone do not seem sufficient to explain the paucity of seedlings within the forest. It is possible that predation by vertebrates contributed to their low abundance within the forest and, more importantly, that seed dispersal by squirrels enabled seedling success along the forest edge. If true, then mammals may not only play a role in seedling recruitment of forest tree species but also in successional dynamics of forests.