The high peaks of the southern Appalachians (Latitude 35°-37°N, Longitude 81°-84°W) range up to 2,037 m (6,684 ft) in elevation, but lack an alpine treeline. Because some species with alpine affinities persist on high elevation rock outcrops in these mountains and because of our interest in the potential impacts of past and future climate changes on rare plants, we sought answers to the following questions: At what elevation would climatic treeline occur in these mountains under current climatic conditions if the mountains were higher and how variable are predictions based on different methods and assumptions? We compared sixteen estimates based on geographic, vegetational, floristic, and climatic lines of evidence in order to bracket the potential treeline. At 36°N in eastern North America these estimates showed considerable variation, ranging from 2,009 m to 3,237 m (28 m lower to 1,200 m higher than the highest summit). World-wide latitude averages probably overestimate treeline because of differences in continentality among sites, while extrapolations from the northern Appalachians underestimate it because of importance of particular climatic factors in northern latitudes. Non-linear or site-specific methods using extrapolation of vegetation zones, alpine species distributions, or temperature correlations give estimates that lie between these extremes. The range of the four independent methods that we considered the most appropriate for the southern Appalachians was 2,285 to 2,600 m, with an average of 2,417 m (7,930 ft). We believe that the most realistic prediction of treeline elevation in the southern Appalachians, combining local summer temperature regime with the best treeline isotherm from maritime east Asia (11.9°C), is 2434 m (7,985 ft), 397 m (1,301 ft) above the highest southern Appalachian peaks.