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Ridge and Valley Sandstone Outcrop

* There is little published information on this community for Tennessee. The Virginia Natural Heritage Program, though admitting to the poor state of inventories of this community in the state of Virginia, has published a description that, due to its shared Ridge and Valley element, will largely be used to describe the communities here.


Southern Appalachian Rocky Summit Ecological System (NatureServe 2014)

Low-Elevation Acidic Outcrop Barrens (Fleming et al. 2013)


Northeastern Tennessee (Grainger, Hancock, Hawkins, Knox, and Union counties) where restricted to upper slopes of Clinch, House, and Stone Mountains in the Southern Sandstone Ridges Ecoregion of the Ridge and Valley physiographic province (Comer et al. 2003).

Vegetation Description

These small-patch outcrops are dominated by few trees, shrubs, and a mixture of perennial and annual grasses and forbs. Large expanses of bare rock are interrupted by soil pockets in crevices and organic mats that support vegetation as scattered, stunted trees, shrub thickets, and discrete patches of herbs (ranging from 0.1 – 2 m in height) adjacent to xeric pine-oak communities (Fleming et al. 2013).

Physical Characterization

These outcrops occur on shoulders of ridges in the Southern Sandstone Ridges Level IV Ecoregion on flat, south, southeast, and east-facing aspects of 25 to 75 percent slopes ranging from 365 m-762 m (1200- 2500 ft) in elevation, though most examples occur at 670 m (2200 ft). Soils are somewhat excessively-drained bouldery, cobbly residuum and/or creep deposits derived from interbedded sedimentary rock of the Wallen-Rock outcrop complex and have a pH of 5.3. uderlying bedrock is Silurian-aged, clean, white, well-sorted sandstone of the Clinch Formation. Examples range in size from __ to __ ha.

Natural Processes

Edaphic factors of shallow, oligotrophic soils and exposed bedrock are the most important natural processes for the development and maintenance of this community (Fleming et al. 2013). The position of these outcrops on shoulders of ridges and adjacent to xeric pine-oak communities makes them fire-prone, though the degree to which fire maintains the community is unknown.

Dominant Plants

The Low-Elevation Acidic Outcrop Barrens described by Fleming et al. (2013) and the description of plants for House Mountain State Natural Area (TDNA, 2015) lists the following dominant species: herbs- Andropogon virginicus var. virginicus (broomsedge), Carex pennsylvanica (Pennsylvania sedge), Danthonia sericea (silky oatgrass), Danthonia spicata (poverty oatgrass), Gaultheria procumbens (trailing arbutus), Hydatica petiolaris (cliff saxifrage), Mitchella repens (partridgeberry) and Schizachyrium scoparium var. scoparium (little bluestem).

Characteristic Plants

See “dominant plants” section.

Restricted Plants (expected)

Capnoides sempervirens (rock harlequin)

Invasive Species

There are no known invasive species for this community.

Community Variation and Subtypes

There are no studies that describe the variations of scrub and herbaceous components of this community, but the known association for this outcrop is:

Hydatica petiolaris Herbaceous vegetation (CEGL004524)

Associated Natural Communities

Ridge and Valley Xeric Oak-Pine Forest, Ridge and Valley Sandstone Cliff

Similar Communities

Cumberland Plateau Sandstone Outcrop (northern type), Blue Ridge Low-Elevation Sandstone Outcrop, Blue Ridge Low-Elevation Granite Outcrop

Presettlement Distribution and Size

These outcrops have the same distribution and size as presettlement conditions.

Present Status

Most examples occur on rugged, forested ridges with little anthropogenic disturbance or development.

Representative Sites

Hawkins Co.: North of Rogersville where TN-70 crosses Clinch Mountain, the outcrops are located upslope on the south and/or west side of the road (36.504613°, -83.025308°).

Knox Co.: House Mountain State Natural Area, on top of ridge (36.119201°, -83.759662°).


The rugged nature of these outcrops protects them from human interference, but they may be threatened by trampling by hikers (especially on House Mountain) and introduction of invasive species.

Management Considerations

Long-term protection of the high portions of ridges where these outcrops occur is important, but as edaphically-maintained communities in undisturbed areas of the state, they are in little need of management.

Future Research Needs

Baseline documentation of the flora on these outcrops is the most pressing research need.

Previous Studies

Little to no previous published studies focus on this community, though there few descriptions by NatureServe (2014) and Fleming et al. (2013). Communication with other agencies may yield unpublished technical reports that contain data relevant to this community.


Comer, P., D. Faber-Langendoen, R. Evans, S. Gawler, C. Josse, G. Kittel, S. Menard, M. Pyne, M. Reid, K. Schulz, K. Snow, and J. Teague. 2003. Ecological Systems of the United States: A Working Classification of U.S. Terrestrial Systems. NatureServe, Arlington, Virginia.

Fleming, G.P., K.D. Patterson, K. Taverna, and P.P. Coulling. 2013. The natural communities of Virginia: classification of ecological community groups. Second approximation. Version 2.6. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond, VA. [http://www.dcr.virginia.gov/natural_heritage/natural_communities/nctoc.shtml <accessed 29 April 29, 2015>]

Geology available at Tennesse Spatial Data Server which can be found at http://www.tngis.org/geology.html which links to a USGS Water Resources Division site: http://water.usgs.gov/lookup/getspatial?geo250k Tennessee Spatial Data Server site notes: Thanks goes to Jim Julian for researching this improved geology layer from the Tennessee Division of Geology. **Note** - The Tennessee Division of Geology does not endorse this coverage, stating this version is still incomplete and not fit for distribution.

NatureServe. 2014. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. Available http://explorer.natureserve.org. (Accessed: March 1, 2015).

Rawinski, T.J., K.N. Hickman, J. Waller-Eling, G.P. Fleming, C.S. Austin, S.D. Helmick, C. Huber, G. Kappesser, F.C. Huber, Jr. T. Bailey and T.K. Collins. 1996. Plant communities and ecological land units of the Glenwood Ranger District, George Washington and Jefferson National Forests, Virginia. Natural Heritage Technical Report 96-20. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond. Unpublished report submitted to the USDA Forest Service. 65 pp. plus appendices.

Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov/. Accessed [01/27/2015].

Tennessee Division of Natural Areas (TDNA). House Mountain. Nashville, TN: [http://www.state.tn.us/environment/natural-areas/natural-areas/housemtn/ <accessed 29 April 2015>]

Page created by Devin Rodgers and Dwayne Estes on 29 April 2015.

Suggested citation: Rodgers, D. M. and D. Estes. 2015. Blue Ridge High Elevation Gabbro Outcrop. Tennessee Plant Communities Database, Austin Peay State University, Tennessee.