Cumberland ThrustBlock Sandstone Outcrop
Southern Appalachian Rocky Summit (NatureServe 2015)
Cumberland thrustblock sandstone outcrops are found in east Tennessee in Campbell County. They are limited to generally south-facing slopes of Pine Mountain and Cumberland Mountain, which are within the Central Appalachians Ecoregion.
These are small patch communities that can be distinguished from surrounding systems by bare or lichen-encrusted rocks. The vegetation of these areas are limited to low-growing plants, no more than 1 meter (less than 3 feet) in height, which grow in shallow soil pockets and crevices along the rocks. The rock surfaces support only non-vascular plants such as mosses and lichens.
Cumberland thrustblock sandstone outcrops are found within the Level IV Cumberland Mountains Ecoregion. They occur on summits and upper side slopes of low-elevation ridges along Pine Mountain and Cumberland Mountain in Campbell County. They are only found on southwest, southeast, and south facing slopes that are steeply sloping (30-65%). The elevation ranges from 1700-2300 m (5600-7500 ft.), although most occur around 2000 m (6500 ft.) above sea level. This community varies greatly in size and shape, although the average size is approximately 12 m x 5 m. The bedrock is Pennsylvanian aged sandstone, conglomerate, siltstone, and shale, with thin coal beds. The soil consists mostly of sandy loam, a residuum weathered from sandstone, which creates an acidic environment. Due to the steep slopes and bedrock surface it is somewhat excessively drained.
This community is formed by erosion of the soil, which exposes the sandstone bedrock and creates outcrops that limit plant growth. A combination of wind and rain weather the soil and rock, keeping it exposed to high amounts of solar insolation. These factors limit the ability for vascular plants to grow and result in the openness of the outcrops.
These outcrops have not been studied, therefore the dominant plants are not known at this time.
Corydalis sempervirens (pale corydalis)
Without a botanical survey, it is impossible to know what invasive species may be present in these communities.
Community Variation and Subtypes
This community consists of the characteristic bare or lichen-encrusted rock that may also include other non-vascular plants such as liverworts and mosses. The second subtype is comprised of small forbs and herbaceous plants that take root in the shallow soil pockets or crevices that occur along the rock surfaces. This community also supports a third subtype that includes the surrounding edges of the rocks which contain deeper soils and may support small trees and shrubs.
Associated Natural Communities
Cumberland sandstone mountain dry oak/pine forest
Presettlement Distribution and Size
The outcrops are believed to be virtually the same as pre-settlement times, although the distribution may have been more widespread during pre-settlement times.
This community type is rare, small in size, and limited to the ridges of Pine and Cumberland Mountains.
Campbell Co., Pine Mountain: (36.579703, -84.065024)
Campbell Co., Cumberland Mountain: (36.428851, -84.066236)
The encroachment of residential and commercial development of the mountain summits and slopes is the biggest threat to the preservation of Cumberland thrustblock sandstone outcrops.
If left undisturbed, these outcrops will be maintained by natural processes, although the surrounding forest may be fire dependent.
Future Research Needs
It is necessary to survey the outcrops to document the dominant and characteristic plants, and what, if any, invasive species occur there.
Hardeman, W.D., and others, 1966, Geologic map of Tennessee: Division of Geology, Tennessee Department of Environment and Conservation, scale 1:250,000
NatureServe. 2014. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1 NatureServe, Arlington, Virginia. Available http://explorer.natureserve.org
Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov/. Accessed February/2/2015.
Checklist of Plant Species known from this community