Pine - Oak / Heath Woodlands
This group contains species-poor, fire-influenced, mixed woodlands of xeric, exposed montane habitats. Communities in this group occur in the Appalachians from New York south to northern Georgia. Sites are typically located on convex, south to west facets of steep spur ridges, narrow rocky crests, and cliff tops. Pine - Oak / Heath woodlands are widespread throughout both the Ridge and Valley and Blue Ridge provinces in western Virginia. They occur at elevations from below 300 m (1,000 ft) to more than 1,200 m (4,000 ft) on various substrates, but most commonly on acidic, sedimentary and metasedimentary substrates, e.g ., sandstone, quartzite, and shale. A few stands occur on Piedmont monadnocks and foothills. Soils are very infertile, shallow, and droughty. Thick, poorly decomposed duff layers, along with dead wood and inflammable shrubs, contribute to a strongly fire-prone habitat. Short-statured table-mountain pine (Pinus pungens) and pitch pine (Pinus rigida) are usually the dominants forming an open overstory, often with co-dominant chestnut oak (Quercus montana, = Quercus prinus). Less important tree associates include scarlet oak (Quercus coccinea), Virginia pine (Pinus virginiana), and sassafras (Sassafras albidum). Except in the Piedmont stands, bear oak (Quercus ilicifolia) is characteristically abundant in the shrub layer, along with various ericaceous species. Colonial shrubs usually pre-empt available microhabitats for most herbaceous species, but bracken fern (Pteridium aquilinum var. latiusculum) and turkey-beard (Xerophyllum asphodeloides) are often competitive enough to achieve significant cover.
Periodic fire is an important ecological process that provides opportunities for regeneration of both pines and less competitive herbaceous species, while setting back successional encroachment of potential overstory oaks (especially chestnut oak). On cliffs and other very rocky sites, the vegetation is self-perpetuating due to extreme edaphic conditions. Fire reduction and the native insect pest, southern pine beetle (Dendroctonus frontalis) are the most serious threats to communities of this group, although historically, pine beetle-induced mortality followed by stand-replacing fire was a principal mechanism for pine regeneration. The globally rare variable sedge (Carex polymorpha), the state-rare northern pine snake (Pituophis melanoleucus melanoleucus) and several rare moths, all bear oak feeders, are locally associated with these woodlands. More common and conspicuous animals often found in these dry, rocky, semi-open habitats include the northern fence lizard (Sceloporus undulatus hyacinthinus) and the five-lined skink (Eumeces fasciatus).
A subset of northern and central Appalachian Pine-Oak / Heath communities that occurs on exposed, high-elevation summits of sedimentary ridges are sometimes referred to as montane or Appalachian "pine barrens." Although these communities are fire-influenced, the vegetation retains a dwarfed, shrubland (< 6 m [20 ft] tall) physiognomy even during long absences of fire due to extremely shallow, xeric soils and constant exposure to severe winds and ice. Only one occurrence of such a "pine barren" is documented in Virginia, covering about 60 ha (150 ac) on Warm Springs Mountain (Bath County), at elevations between 1,100 and 1,200 m (3,600 and 4,000 ft). Larger examples occur in nearby West Virginia at elevations from 1,200 to 1,375 m (4,000 to 4,500 ft) on the summit of North Fork Mountain (Pendleton County). The singular Virginia occurrence is characterized by dense, nearly impenetrable thickets of Catawba rhododendron (Rhododendron catawbiense), bear oak (Quercus ilicifolia), mountain-laurel (Kalmia latifolia), black huckleberry (Gaylussacia baccata), and late lowbush blueberry (Vaccinium angustifolium), with scattered emergent (but still shrub-sized) pitch pines (Pinus rigida). The average height of the barrens vegetation varies from knee-high in years following intense burns to about 5 m (16 ft). Compositionally and environmentally, the Central Appalachian "pine barrens" can be considered part of the Pine - Oak / Heath Woodlands ecological group, but more study is needed to determine whether the Virginia stand represents a distinct community type.References: Fleming (2002a), Fleming (2002b), Fleming and Coulling (2001), Fleming and Moorhead (2000), Groeschl et al . (1992), Leahey et al. (2006), Martin et al . (1982), Olson and Hupp (1986), Rawinski et al. (1994), Rawinski et al. (1996).
Click on the images below to open a larger image in a separate window.
|Central Appalachian Pine-Oak/Heath Woodland (Pitch Pine Type) on a thin-soiled quartzite ridge. DCR Bull Run Mountains Natural Area Preserve, Fauquier County. Photo: © Gary P. Fleming|
|Severely stunted pines and an exceptionally dense ericaceous shrub layer characterize this "pine barrens" variant of Pine-Oak/Heath Woodland on The Nature Conservancy's Warm Springs Mountain Preserve, Bath County. Photo: Gary P. Fleming|
|Turkeybeard (Xerophyllum asphodeloides) blooming in an open pine-oak/heath woodland on Rocky Mountain, Rockingham County (Shenandoah National Park). Gary P. Fleming / © DCR Natural Heritage.|
|Table-mountain pines (Pinus pungens) dominate a xeric woodland on quartzite cliffs of the Bull Run Mountains, Fauquier County. Photo: © Gary P. Fleming.|
This group is represented by 69 plot samples from mostly northwest and west-central Virginia (map). Central Appalachian stands of this group have been extensively sampled and robustly classified through several regional analyses of plot data. Examples of this vegetation in southwestern Virginia, which represent a type with Southern Appalachian floristic affinities, have not yet been adequately sampled. The status of the dwarfed "pine barrens" variant also remains unclear. Click on any highlighted CEGL code below to view the global USNVC description provided by NatureServe Explorer.
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