Historic field systems and the structure of maritime oak forests, Cumberland Island National Seashore, Georgia

BRATrON, S. P. AND S. G. MiLER (Institute of Ecology, University of Georgia, Athens, GA 30602). Historic field systems and the structure of maritime oak forest, Cumberland Island National Seashore, GA. Bull. Torrey Bot. Club 121: 1-12. 1994.-Understory structure and composition for the maritime oak and oak-pine forests on Cumberland Island National Seashore varies from dense palmetto thickets to open understories with few shrubs. The purpose of this project was to investigate the possibility that understory composition was primarily an artifact of past agricultural activity, rather than a product of anthropogenic burning or of soil moisture gradients. Historic maps were utilized to select areas of forest that had: 1) no history as agricultural fields, 2) use as cotton fields during the plantation era of the late eighteenth and the first half of the nineteenth century, 3) use for grazing during the era of private estates from 1881 to 1916, and 4) combinations of 2 and 3. The canopy and understory of 27 sample fields or non-agricultural areas were sampled by at least four randomly selected 50 m line-intercept transects. Sites with no known history of agriculture had dense understories of saw palmetto, Serenoa repens, had relatively high dominance indices for red bay, Persea borbonia, had few vines and almost no grass and forb cover. Fields with a history of grazing during the late nineteenth century had very open understories with greater dominance of grasses and forbs and widely scattered rings of saw palmetto. Sparkleberry, Vaccinium arboreum, and pines, particularly loblolly, Pinus taeda, were also characteristic of these sites. Fields utilized for cultivation during the plantation era, but not shown as fields on the late nineteenth century map had intermediate densities of palmetto, including some sabal palm, Sabal palmetto, and high covers of grasses, forbs and vines. The non-agricultural sites had significantly greater depths of soil litter and duff, but there were no significant differences in litter or duff depth among the agricultural field types. The results imply that the open understories in the maritime oak forest have not historically been maintained by either anthropogenic or natural fire, but are artifacts of cultivation and human land management extending back to aboriginal settlement of the island.