Forest environments of the Southern Appalachian Mountains and their characteristic plant communities are among the most varied in the Eastern United States. Considerable data are available on the distribution of plant communities relative to temperature and moisture regimes, but not much information on fertility as an environmental influence has been published; nor has anyone presented a map of the major, broad-scale ecosystems of the region, which could be used for planning and management of biological resources on forestlands. Our objectives were to identify predominant ecological units, develop a grouping of geologic formations related to site fertility, and model and map ecological zones of the Southern Appalachians. We synthesized 11 ecological units from an earlier analysis and classification of vegetation, which used an extensive database of over 2,000 permanent, 0.10-ha, intensively sampled plots. Eight lithologic groups were identified by rock mineral composition that upon weathering would result in soils of low or high availability of base cations.