Mountain / Piedmont Acidic Woodlands
Coniferous , mixed, or less commonly deciduous woodlands of xeric, edaphically stressful habitats constitute this ecological group. These woodlands are uncommon but are found in the Piedmont of the southeastern United States, as well as in the southern Appalachians and westward in the Ozark and Ouachita Mountains. Stands are scattered throughout the Virginia mountains and inner Piedmont, occupying somewhat heterogeneous habitats that are characterized by rock outcrops and shallow, drought-prone, highly oligotrophic soils. Included are outcrops and pavements of sandstone and other acidic rocks in the northern Blue Ridge, Ridge and Valley and Cumberland Mountains; xeric, low-elevation terrain formed on massive alluvial fans along the western foot of the Blue Ridge; and massive bedrock terraces flanking the Potomac River in the fall zone west of Washington, D.C.
Most expressions of the group in Virginia could be characterized as pine-oak woodlands. Virginia pine (Pinus virginiana), pitch pine (Pinus rigida), and shortleaf pine (Pinus echinata) are each co-dominant in one or more classified types. Chestnut oak (Quercus montana, = Quercus prinus), post oak (Quercus stellata), and blackjack oak (Quercus marilandica var. marilandica) are representative oak components. In some cases, Montane Acidic Woodlands are floristically similar to Pine-Oak/Heath Woodlands, but are maintained primarily by drought stresses associated with outcrop environments or extremely dry soils rather than by fire. They also tend to have a sparser representation of heath shrubs and a more diverse herb layer, with a larger component of graminoids such as little bluestem (Schizachyrium scoparium var. scoparium), Pennsylvania sedge (Carex pensylvanica), poverty oatgrass (Danthonia spicata), and starved panic grass (Dichanthelium depauperatum). Most of the community types in this group are considered state- or globally rare, but their relationships to vegetation on a regional scale needs further investigation.
References: Fleming (2007), Fleming et al. (2007).
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Mountain laurel (Kalmia latifolia), bearberry (Arctostaphylos uva-ursi), and wavy hairgrass (Avenella flexuosa) in an acidic woodland opening at Miller's Head, Page County (Shenandoah National Park). This is the only known Virginia site for the creeping ericad bearberry, a boreal disjunct. Gary P. Fleming / © DCR Natural Heritage.
Virginia Pine (Pinus virginiana), blackjack oak (Quercus marilandica var. marilandica), and Pennsylvania sedge (Carex pensylvanica) in a Central Appalachian xeric sandstone woodland. James River Face Wilderness, Rockbridge County (George Washington and Jefferson National Forests). Photo: Tom Rawinski.
Sparse woodland of Virginia Pine (Pinus virginiana) and lowbush blueberry (Vaccinium pallidum) on xeric rimrock of bedrock terraces along the Potomac River downstream from Great Falls, Fairfax County. Periodic catastrophic floods scour these terraces and tend to eliminate or reduce hardwood competitors. Photo: Karen D. Patterson / © DCR Natural Heritage.