| General Description |
This habitat is associated with rock formations located close to the surface, producing thin, circumneutral to basic soils. Where they exist as clearings in open woodlands, they are referred to as glades; where they occur as more extensive open areas, with only scattered trees, they are termed barrens. The openness that is characteristic of this habitat is partially due to edaphic conditions: the thin soils do not hold much water and are prone to drought; trees also have difficulty taking root and the vegetation usually consists of herbs and sparse shrubs. Due to the seasonally dry conditions and the build-up of dry plant material, these sites were once frequently swept by wildfires. The plant species belonging to this habitat include the herbaceous and shrubby species associated with the openings themselves. Patches of stunted trees may also be present but belong to other intersecting habitats, particularly Rich Dry-Mesic Hardwood Forests.
In North Carolina, most of these habitats are associated with mafic rock formations, which include igneous rocks such as Basalt, Gabbro, and Diabase. All three are rich in iron and magnesium and also have a higher calcium content than found in felsic rock formations, the more prevalent igneous rocks found in North Carolina. Soils weathered from mafic rocks are both mineral-rich and fairly high in pH, although usually in the circumneutral range rather than truly basic (i.e., pH > 7). Some metamorphic rocks, such as Amphibolite, shale, and serpentine, produce similar circumneutral, mineral-rich soils that support examples of this habitat, as do the small inclusions of limestone that occur in some ares of the Mountains. This particular habitat contains the most generalized species associated with these formations. Species that are more limited to certain rock or soil types are treated in separate habitats.
In all of these cases, the habitats are naturally fragmented into small units, existing as inclusions within the prevalent matrix of forested habitats growing on deeper, wetter, and more acidic soils. In addition to their adaptations to certain types of soils and their drought- and fire-prone habitats, species belonging to this habitat typically are able to persist in insular conditions for very long periods of time. Plants are particularly well adapted to these situations and make up the majority of the Determining Species of this habitat. Due to their insularity, many of these species are quite rare and consequently receive high Global and State Ranks from the Natural Heritage/NatureServe Network.
In North Carolina at least, only one specialized herbivore is known to be associated with the plant species in this habitat. The Barberry Geometer (Coryphista meadii), a native moth that feeds on Berberis species, was probably confined to this habitat originally, feeding only on the native Berberis canadensis. However, it now feeds on introduced species of barberries and shows up in developed areas far from basic glades. Other species may not be able to cope with the fragmented nature of these habitats. Papaipema silphii, for example, is associated with populations of Prairie Dock growing in the widespread calcium-rich prairies of the Midwest, but has yet to be found in the small prairie-like barrens that occur on our side of the Appalachians.
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