Grell, A. G. (Arkansas Forest Resources Center, School of Forest Resources, University of Arkansas-Monticello, Monticello, AR 71656-3468), M. G. Shelton (USDA Forest Service, Southern Research Station, Monticello, AR 71656-3516), and E. Heitzman (Arkansas Forest Resources Center, School of Forest Resources, University of Arkansas-Monticello, Monticello, AR 71656-3468). Changes in plant species composition along an elevation gradient in an old-growth bottomland hardwood-Pinus taeda forest in southern Arkansas. J. Torrey Bot. Soc. 132: 72–89. 2005.—Old-growth bottomland hardwood-Pinus taeda L. forests are rare in Arkansas, and the complex relationships between plant communities and environmental conditions have not been well described in these forests. To investigate these relationships, a digital elevation model was developed for a 16.2 ha old-growth bottomland hardwood-Pinus taeda forest in southern Arkansas. Overstory trees, saplings, seedlings, and herbaceous plants were analyzed in three 0.5 m elevation classes and by using indirect gradient analysis. Information was also collected on site factors (canopy cover, forest floor litter cover, and elevation), soil physical factors (bulk density and soil texture), soil moisture, and soil chemical factors (pH, electrical conductivity, organic matter, N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, and Na). Importance values for 35% of seedling species, 30% of overstory species, 22% of herbaceous species, and 8% of sapling species differed significantly by elevation class. Significant differences by elevation in species diversity, richness, and evenness were identified in the seedling stratum, while only sapling evenness differed by elevation. Seventy-four percent of the environmental characteristics produced significant differences by elevation except for soil texture (sand, silt, and clay), September soil moisture content, Mn, and Cu. Seventy percent of environmental variables were significantly correlated with elevation. Dominant environmental influences on species composition in all strata included elevation as well as many other correlated variables such as Fe, forest floor litter cover, bulk density, and Na. Results from this study suggest that differences in vegetation were primarily the result of subtle elevational variations. Restoration or management of these forests should carefully consider microtopographical influences.