Cumberland Riverscour Ecological System (NatureServe 2015)
Sandbar riparian shrub-herb habitat (Estes and Fleming 2008)
Eastern Middle Tennessee (Cumberland and Morgan counties) where restricted to alluvial bars on the Obed River, Clear Creek, and Daddy’s Creek in the Cumberland Plateau.
This small patch community is a riparian woodland dominated by scattered trees, perennial grasses, forbs, and scattered shrubs that ranges in height from 0.1-10 m. It occurs on the elevated, slope-adjacent periphery of alluvial bars containing other Cumberland Plateau Riverscour communities, especially at the borders of deep pools and inside bends of stream meanders. Groundwater influence on certain bars may support seeps. This community is a woodland with a semi-open, short canopy, scattered shrub-layer, and an herb layer dominated by perennial grasses, herbs, and unvegetated patches of fine sand.
In the Cumberland Plateau Ecoregion, this community occurs on flat or gently-sloping alluvial bars of deeply-entrenched river gorges ranging in elevation from 290-440 m (950-1450 ft). While most examples occur on south-facing aspects, some occur on east- or west-facing aspects. This woodland occurs on bars composed of deep sandy alluvium and embedded cobble. Geology is composed of Pennsylvanian-aged coarse- to fine-grained conglomeritic sandstones of the Rockcastle formation and Crab Orchard Mountains group. Soils, one of the diagnostic characteristics of the community, are Ultisols of sandy or silty alluvium derived from Gilpin-Bouldin-Petros Complex, Jefferson-Varilla-Shelocta Complex, Pope-Philo Complex, and/or Ealy-Craigsville Complex that are well-drained to excessively-drained.
This community is maintained by a combination of intense flooding in spring and winter with occasional summer floods, well-drained acidic soils, and high sunlight. Unlike the riverscour shrubby grasslands, edaphic factors of large amounts of coarse-particle (sand) deposition, rather than intense scouring, characterizes the sandy woodland. As slightly more-elevated sites, trees are typically established, but the edaphic factors of sandy soils supports many species typical of adjacent riverscour grasslands and shrublands. The extent of fire’s impact on examples of this community adjacent to dry south- to southwest-facing slopes is unknown.
Trees: Betula nigra (River Birch), Juniperus virginiana (Eastern red cedar) and Platanus occidentalis (Sycamore). Shrubs: Amorpha fruticosa (False indigo bush), Cornus amomum (Silky dogwood), Hypericum prolificum (Shrubby st. johnswort), Physocarpus opulifolius (Ninebark), Viburnum alabamense (Alabama arrowwood), and Yucca flaccida (Weak-leaf yucca). Herbs: Andropogon gerardii (Big Bluestem), Coreopsis tripteris (Tall coreopsis), Sorghastrum nutans (Indiangrass), Solidago arenicola (Sand Goldenrod), and Symphyotrichum aff. dumosum (Bushy Aster), Vitis rotundifolia (Estes and Fleming 2008).
Conradina verticillata (Cumberland rosemary), Euphorbia pubentissima (False flowering spurge), Polygonella americana (Southern jointweed), Sorghastrum nutans (Indiangrass), Solidago arenicola (Sand Goldenrod), and Symphyotrichum aff. dumosum (Bushy Aster).
Clematis sp. nov. (Cumberland Leatherflower; Rodgers and Estes in prep.), Conradina verticillata (Cumberland Rosemary), Marshallia grandiflora (Barbara’s Buttons), Polygonella americana (Southern jointweed), Rhynchosia aff. tomentosa (Twining snoutbean), Solidago arenicola (Sand goldenrod), Symphyotrichum aff. dumosum (Bushy Aster), Tridens chapmanii (Chapman’s Tridens) (Estes and Fleming 2008).
Albizia julibrissin (Persian silk tree), Elaeagnus umbellata (Autumn olive), Lespedeza cuneata (Sericea lespedeza), Microstegium vimineum (Japanese stiltgrass), Rosa multiflora (Multiflora rose), Spiraea japonica (Japanese spiraea).
Community Variation and Subtypes
Woodlands, Dry Shrubland, Sand Barrens
Associated Natural Communities
Cumberland Plateau Riverscour Shrubby Grassland, Cumberland Plateau Riverscour Sandy Shrubland, Cumberland Plateau Riverscour Seep, Cumberland Plateau Sandstone Riverscour Outcrop
Presettlement Distribution and Size
Current distribution is the same as presettlement distribution.
Data and descriptions of this community are lacking, thus it is difficult to assess present status for a poorly understood vegetation. However, Estes and Fleming (2008) discuss campsite disturbance on these sand bars as both a possible reason for keeping the community open and a possible threat to the rare species of the community. This is perhaps the rarest of all the riverscour communities, generally hosting more likeness to coastal plain vegetation than other riverscour communities.
Clear Creek, 250m downstream of Lily Bridge.
The disturbance regime critical to this community is not yet well-understood, but suppression of that disturbance regime may threaten the open nature of this community, such as changes in flood regime or fire regime (if applicable). Smith (1991) lists hikers, fishermen, whitewater enthusiasts, off-road vehicles, accidental chemical spills, and poor water quality as threats to these open, sandy habitats.
Once baseline information is collected to understand the maintenance of this community, management techniques such as thinning or fire may enhance the open nature of this community. Limiting trampling and off-road vehicle use on this community will protect the rare species occurring there from being trampled.
Future Research Needs
The abiotic factors of the sandy woodland are not well-understood. Also, the sandy woodland needs to be fully surveyed on all riverscour systems to understand the variation in the community and the breadth of rare taxa that inhabit the community.
Estes and Fleming (2008) is the only study to specifically mention “sandbar” habitats that support a high amount of rare species on riparian habitats of deep, fine sands.
Estes DE and Fleming C. 2007. T&E and exotic invasive vascular plant survey of the Obed Wild and Scenic River: Obed Junction to confluence of Clear Creek, Morgan County, Tennessee. Unpublished report presented to the Obed Wild and Scenic River (NPS). 49 p.
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.
Smith, R.N. 1991. Endangered and threatened wildlife and plants; Conradina verticillata (Cumberland Rosemary) determined to be threatened (50 CFR Part 17; RIN 1018-AB52). Federal Register 56 (230): 60937-60941.
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].
Wolfe WJ, Fitch KC, Ladd DE. 2007. Alluvial bars of the Obed Wild and Scenic River, Tennessee. USGS and NPS report.