Limestone and Dolomite Barrens
Exposed, carbonate rock outcrops and associated xeric rocky slopes provide the requisite habitats for the herbaceous communities of this group. These calcareous barrens are scattered throughout the western Virginia Ridge and Valley region, usually occurring on steep, south- to west-facing slopes. In The Cedars region of Lee County, "flatrock" limestone barrens are present on gently rolling topography. The degree of exposed bedrock cover is variable, and many occurrences have considerable development of thin soils and gravel. Soils typically have high pH (> 7.0) and calcium levels; in addition, dolomitic soils have relatively high magnesium levels.
Warm-season prairie grasses, including big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium), indian grass (Sorghastrum nutans), side-oats grama (Bouteloua curtipendula var. curtipendula), and rough dropseed (Sporobolus clandestinus) characterize the largely herbaceous vegetation. Ebony sedge (Carex eburnea) is also an abundant, sod-forming graminoid at some sites. Associated perennial forbs include western silky aster (Symphyotrichum pratense, = Aster pratensis), false boneset (Brickellia eupatorioides var. eupatorioides), eastern indian-paintbrush (Castilleja coccinea), Canada bluets (Houstonia canadensis), tall gay-feather (Liatris aspera var. intermedia), false aloe (Manfreda virginica), southern obedient-plant (Physostegia virginiana ssp. praemorsa), white blue-eyed-grass (Sisyrinchium albidum), hairy wild-petunia (Ruellia humilis), and stiff goldenrod (Oligoneuron rigidum var. rigidum, = Solidago rigida ssp. rigida). Pitcher's stitchwort (Minuartia patula var. patula), wiry panic grass (Panicum flexile), sheathed dropseed (Sporobolus vaginiflorus), and other calciphilic annuals are characteristic of exposed, gravelly areas and rock crevices. Stunted trees and shrubs such as chinkapin oak (Quercus muhlenbergii), eastern red cedar (Juniperus virginiana var. virginiana), and Carolina buckthorn (Frangula caroliniana) are scattered in the barrens.
Communities in this group are highly localized, small-patch units that are considered state-rare and, in some cases, globally rare. Threats include quarrying, grazing, and invasive introduced weeds.Reference: Ludwig (1999).
Click on the images below to open a larger image in a separate window.
|A Ridge and Valley limestone barren dominated by prairie grasses. Tall gay-feather (Liatris aspera var. intermedia) is blooming in the foreground. Cleveland Barrens Natural Area Preserve, Russell County. Photo: Chris Ludwig.|
|Gravelly Limestone / Dolomite Barren (Southern Ridge and Valley Type) near Dry Creek, The Cedars Natural Area Preserve, Lee County. Photo: Chris Ludwig.|
The two classified community types in this group are clearly distinct, but supporting data (14 and 11 plots, respectively) were collected from only a few discrete landscapes (map) . Wider geographic sampling of this group is needed to firm up characterization and resolve problems in crosswalking the units to similar vegetation outside of Virginia. However, due to the rarity of this vegetation, it is unlikely that many more sites will be found. Click on any highlighted CEGL code below to view the global USNVC description provided by NatureServe Explorer.
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