Low-Elevation Basic Outcrop Barrens
This group comprises very sparse woodlands, scrub, and herbaceous vegetation of exposed, base-rich outcrops in the Piedmont and mountain regions. The majority of documented occurrences are on mafic (e.g., diabase, amphibolite, gabbro) outcrops of the Piedmont and southern Blue Ridge, and metabasalt (greenstone) outcrops of the northern Piedmont and Blue Ridge. A few examples on granitic rocks and calcareous sandstone have also been documented. Habitats generally have high cover of exposed bedrock, but often have more extensive organic or soil mats, and thus more vascular plant cover, than do acidic outcrops. Soils usually consist of thin veneers and vary from moderately acidic to circumneutral, with moderately high base status.
Vegetation is usually a patchwork of severely stunted trees, shrub thickets, herbaceous mats, and lithophytic lichens. Typical woody species include white ash (Fraxinus americana), eastern red cedar (Juniperus virginiana var. virginiana), fringetree (Chionanthus virginicus), common ninebark (Physocarpus opulifolius var. opulifolius), staghorn sumac (Rhus typhina), aromatic sumac (Rhus aromatica var. aromatica), and hoptree (Ptelea trifoliata var. trifoliata). Eastern prickly-pear (Opuntia humifusa var. humifusa) is present at most Piedmont sites. Typical herbs include nodding onion (Allium cernuum), roundleaf fameflower (Phemeranthus teretifolius), slender knotweed (Polygonum tenue), woodland sunflower (Helianthus divaricatus), hairy lip fern (Cheilanthes lanosa), rusty woodsia (Woodsia ilvensis), little bluestem (Schizachyrium scoparium var. scoparium), Pennsylvania sedge (Carex pensylvanica), hair-awn muhly (Muhlenbergia capillaris), whorled milkweed (Asclepias verticillata), Appalachian phacelia (Phacelia dubia var. dubia), hoary mountain-mint (Pycnanthemum incanum var. incanum), dwarf skullcap (Scutellaria leonardii), blue waxweed (Cuphea viscosissima), upland flatsedge (Cyperus lupulinus ssp. lupulinus), lacegrass (Eragrostis capillaris), false pennyroyal (Trichostema brachiatum), Virginia dwarf-dandelion (Krigia virginica), pale corydalis (Capnoides sempervirens), mountains and foothills only), and American alumroot (Heuchera americana). These small-patch communities are rare in Virginia and globally. Perhaps because of their more fertile substrates, basic outcrop barrens are more prone to invasion by non-native weeds than are acidic barrens.References: Copenheaver et al. (2004), Fleming (2002a), Fleming et al. (2007), Fleming and Coulling (2001), Fleming and Patterson (2004), Rawinski and Wieboldt (1993).
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Eastern red cedar (Juniperus virginiana var. virginiana) and lithophytic herbs on exposed metabasalt (greenstone) barrens at Cedar Cliffs, western slope of the Blue Ridge in Augusta County (George Washington and Jefferson National Forests). Gary P. Fleming / © DCR Natural Heritage.
Metabasalt (greenstone) barrens on the western slope Dickey Ridge, a Blue Ridge spur in Warren County (Shenandoah National Park). Gary P. Fleming / © DCR Natural Heritage.
Low herbaceous barrens on a massive diabase "flatrock" in the northern Virginia Mesozoic Basin. Near Elklick Run, Fairfax County (Fairfax County Park Authority lands). Gary P. Fleming / © DCR Natural Heritage.
Xerophytic herbaceous vegetation, lichens, and bryophytes on a massive exposure of actinolite schist, a metabasaltic rock of the southern Piedmont. Bald Knob, Franklin County. Gary P. Fleming / © DCR Natural Heritage.
Precipitous metabasalt barrens on the north flank of Little Devils Stairs, Rappahannock County (Shenandoah National Park). Clumps of little bluestem (Schizachyrium scoparium var. scoparium) dominate the herbaceous flora. Gary P. Fleming / © DCR Natural Heritage.