Factors Influencing Species Composition in Canopy Gaps: The Importance of Edge Proximity in Hueston Woods, Ohio* John A. Kupfer George P. Malanson University of Memphis University of Iowa James R. Runkle Wright State University In this research, we attempt to quantify the factors structuring woody species composition within forest gaps in the interior of Hueston Woods Nature Preserve, Ohio. Our results indicate that composition is related not only to factors commonly cited in other studies, including disturbance history, topographic position, and environmental factors (e.g., gap age, soil pH, slope, and aspect), but also to the proximity of forest edge communities. Partitioning of species variation to environmental factors, spatial factors, and spatially structured environmental factors reinforces the importance of both environment and edge proximity in explaining gap composition. These findings underscore the need for a more complete understanding of the potential impacts of edge effects in fragmented landscapes. Key Words: edge effect, gap succession, Ohio, forest fragmentation, seed dispersal. Introduction I n extensively modified areas such as agricul- tural landscapes, forest fragmentation repre- sents a large-scale but external (i.e., outside of a forest remnant) disturbance that may impact the floral and faunal dynamics in remnant forest patches and reserves (e.g., Burgess and Sharpe 1981; Hanson et al. 1990; Saunders et al. 1991). Within the mosaic of patches created by forest clearing and observed at coarse scales, individual remnant forest patches are subjected to natural disturbances such as tree mortality. Manage- ment goals have recently recognized the need to accommodate or perpetuate natural distur- bances in remnant natural or seminatural areas (Baker 1992; Grumbine 1994). It has not, how- ever, been widely recognized that even the maintenance of natural disturbance regimes in remnant forests will be insufficient to maintain existing or desired species patterns if key eco- logical processes (e.g., species establishment or succession) within the remnant are disrupted, directly or indirectly, by external large-scale disturbances. The death of one or a few canopy individuals from windthrow, pathogens, lightning, or other factors represents a vital internal disturbance in many remnant forest communities. Regrowth and filling of the opening created by the death of a canopy tree, termed gap succession, is the primary process that determines forest structure and composition in many temperate and tropical forest communities (Runkle 1985; Veblen 1992), including beech-maple forests (Runkle 1990; Poulson and Platt 1996). Regeneration after gap creation is determined by the probabilities of both arrival and survival (Pickett et al. 1987; Schupp et al. 1989). Research, however, has tended to focus on the latter, with researchers relating species composition to the environ- mental conditions present on a site. Because the competitive abilities of species within gaps are determined by their physiological adaptations and life history traits (e.g., shade tolerance), gap researchers have particularly emphasized the importance of gap size and age, variables that directly influence the microclimate, especially light, in the forest understory and on the forest floor (e.g., Brokaw 1985; Whitmore 1989). *We would like to thank Marc Armstrong, Steve Hendrix, and three anonymous reviewers for their constructive comments, which greatly improved the quality of this paper, and Joel Udstuen, Park Manager at Hueston Woods, for his permission to carry out research within the preserve. Tammy Wambeam and Joy Mason assisted in data preparation; Todd Blankenbeckler assisted in map preparation. As always, O.E. Jakes provided much needed inspiration. This work was supported in part by a grant from the Biogeography Specialty Group of the Association of American Geographers to Dr. Kupfer. Professional Geographer, 49(2) 1997, pages 165–178 © Copyright 1997 by Association of American Geographers. Initial submission, April 1996; revised submissions, August 1996, September 1996; final acceptance, September 1996. Published by Blackwell Publishers, 350 Main Street, Malden, MA 02148, and 108 Cowley Road, Oxford, OX4 1JF, UK. ARTICLES