The distribution of heath balds in the Great Smoky Mountains, North Carolina and Tennessee

We used remote sensing and a geographic information system to model the distribution of evergreen shrub communities, called 'heath balds', in the Great Smoky Mountains, North Carolina and Tennessee, USA. The 421 heath balds averaged 1.8 ha in size and covered 0.3% of the landscape. They reached their greatest importance on upper slopes (92% had relative slope positions > 80), convex topography (82% occurred on sites with a curvature greater than 2.6), and elevations between 1100 and 1600 m (94% of the balds). although heath balds were found in old-growth watersheds, the two watersheds with the greatest number of balds burned extensively after logging in the early 1900s. Bald occurrence was positively correlated with burned sites, old growth condition, and a highly acidic rock type. Heath balds showed a striking geographic pattern, with 88.1% of the area of this community found in six watersheds comprising only 35.4% of the study area. Despite similar topography, geology, and history, the eleven other watersheds had only 11.9% of the bald area while comprising 64.4% of the study area. Multivariate models showed that this community occurs on only 0.4 to 9.0% of the seemingly appropriate sites. Once established, this shrub community, with its dense evergreen canopy and thick leaf litter, is resistant to tree invasion. Both forest and shrub communities are stable on sites that are seemingly ideal for heath bald occurrence.