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Synonyms

Cumberland Riverscour Ecological System (NatureServe 2015)

Distribution

Eastern Middle Tennessee (Cumberland and Morgan counties) where restricted to alluvial bars on the Emory River, Obed River, Clear Creek, and Daddy’s Creek in the Cumberland Plateau.

Vegetation Description

This linear community is a riparian matrix dominated by various gradients of perennial grasses, forbs, shrubs, and stunted trees. Shrubs and small trees dominate the periphery of riverscour communities closest to the stream channel. Between this periphery and the adjacent slope forest, vegetation takes on either two major physiognomies, or variable combination of the two. These tentative associations, to be studied with plot data, are as follows:

Riverscour grassland: This vegetation is a grassland with a diverse mixture of perennial grasses, sedges, and forbs with the occasional small tree or shrub. Vegetation height ranges from 0.1-1.5m.

Riverscour shrubland: This community is a dense shrubland of riparian woody species, lianas, low-growing herbs, and the occasional tall forb. Vegetation height ranges from 1.0- 2.5m.

Riverscour shrubby grassland: This community describes the gradient of successional mixture of the riverscour grassland and shrubland that commonly occurs as an open, rather than dense, shrubland. Vegetation height ranges from 0.5-2.5m.

Physical Characterization

In the Cumberland Pateau Ecoregion, this community occurs on flat or gently-sloping alluvial bars of deeply-entrenched river gorges with no particular aspect, from 243- 460 m (800-1512 ft). This grassland occurs on stony bars composed of imbricated sandstone boulders and cobble embedded in sandy alluvium (Wolfe 2008). Geology is composed of Pennsylvanian-aged coarse- to fine-grained conglomeritic sandstones of the Rockcastle formation and Crab Orchard Mountains group. Soils 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. 

Natural Processes

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. The extent of fire’s impact on examples of this community adjacent to dry south- to southwest-facing slopes is unknown.

Dominant Plants

Riverscour grassland:

Andropogon gerardii, Coreopsis major, Dichanthelium spp., Liatris microcephala, Ionactis linariifolius, Oenothera fruticosa, Rhododendron arborescens, Rhynchospora capitellata, Salix caroliniana, Schizachyrium scoparium, Solidago arenicola, Sorghastrum nutans, Symphyotrichum sp. nov., and Veronicastrum virginicum.

Riverscour shrubland:

Alnus serrulata, Amorpha fruticosa, Andropogon gerardii, Betula nigra, Cephalanthus occidentalis, Cornus amomum, Hammamelis virginiana, Hypericum prolificum, Ilex verticillata, Itea virginica, Lyonia ligustrina, Osmunda spectabilis, Physocarpus opulifolius, Platanus occidentalis, Salix caroliniana.  

Riverscour shrubby grassland:

Shrubs of Alnus serrulata, Betula nigra, Cephalanthus occidentalis, Cornus amomum, Crataegus spp., Hypericum prolificum, Physocarpus opulifolius, Platanus occidentalis, and Salix caroliniana, grow in sparse to dense shrublands with patches dominated by Andropogon gerardii, Coreopsis major, Dichanthelium spp., Ionactis linariifolius, Liatris microcephala, Oenothera fruticosa, Schizachyrium scoparium, Solidago arenicola, Sorghastrum nutans, Symphyotrichum sp. nov., Veronicastrum virginicum, and Yucca flaccida.

Characteristic Plants

Andropogon gerardii (Big Bluestem), Calamovilfa arcuata (Cumberland Sand Reed), Conradina verticillata (Cumberland Rosemary), Ionactis linariifolius (Flax-leaf Whitetop Aster), Liatris microcephala (Dwarf Blazing Star), Sorghastrum nutans (Indiangrass), Rhynchospora capitellata (Brownish Beaksedge), Solidago arenicola (Sand Goldenrod), and Yucca flaccida (Weak-leaf Yucca).

Restricted Plants

Amelanchier sanguinea (Roundleaf Serviceberry), Calamovilfa arcuata (Cumberland Sand Reed), Clematis sp. novum (undescribed species of Clematis), Conradina verticillata (Cumberland Rosemary), Eubotrys racemosa (Swamp doghobble)Helianthus aff. eggertii (Eggert’s Sunflower), Hieracium scabrum (Rough hawkweed)Marshallia grandiflora (Barbara’s Buttons), Oenothera perennis (Small sundrops), Physostegia virginiana var. virginiana (Obedient plant), Polygonella Americana (Southern jointweed), Rhynchosia aff. tomentosa (Twining snoutbean), Solidago arenicola (Sand goldenrod), Sporobolus junceus (Pineywoods dropseed), Symphyotrichum aff. dumosum (Bushy Aster), Tridens chapmanii (Chapman’s tridens), (summary provided by Estes and Fleming 2008)

Invasive Species

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

As a riparian community, microtopography and flood-regime play major roles in variation of vegetation, especially on a small-scale. Along this note, these grasslands demonstrate lateral zonation, so that the dominant plant species changes depending on how close a particular site is to the river channel or the base of the adjacent slope above the alluvial bar. For example, a single alluvial bar, going from stream channel to adjacent slope, may have an emergent aquatic vegetation, wet sandy seep, alluvial shrubland or woodland, riverscour grassland, xeric sandy shrubland, and riverscour sandy woodland. The distribution of these communities can change depending on the local availability of water, exposure to flooding, soil particle size, and sunlight.

Associated Natural Communities

Cumberland Plateau Riverscour Sandy Woodland, Cumberland Plateau Riverscour Xeric Sandy Shrubland, Cumberland Plateau Sandstone Riverscour Outcrop, Cumberland Plateau Streamside Seep.

Similar Communities

Though data to verify the extent of the concept are being collected now, collections made in different watersheds show differences in vegetation that may yield interesting biogeographic differences between riverscour systems, especially through differences in endemic and rare taxa. If this is true, on a local scale, then each river system might be considered a different entity. However, on a large scale, separations between the Obed Gorge, Big South Fork Gorge, and New River Gorge (TN, TN/KY, and WV, respectively) show some degree of variation that certainly separates major drainages, for which there may be 3 systems, the Emory River, the Big South Fork, and the Caney Fork. However, this particular community describes the types of vegetation in the Emory River system.

Presettlement Distribution and Size

Current distribution is the same as presettlement distribution.

Present Status

Like other associated riverscour natural communities, this community is intact because of its flood-prone nature, lack of dams, and rugged, remote locations. 

Representative Sites

Antioch Bridge, Devil’s Breakfast Table, Cumberland Trail along Daddy’s Creek, Obed Junction, Lilly Bridge, Nemo Bridge.

Threats

Invasive species, streamside campsites, climate change, and major changes to stream hydrology, such as damming or municipality water-use that could change flooding that maintains this community.

Management Considerations

Maintaining free-flowing nature of Cumberland Plateau headwater streams, ensuring no development of streamside environments where this community exists, and removing invasive species from becoming well-established will ensure the health of this community.

Future Research Needs

Rare species biology of cobble bar species, especially those endemic to this community; role of fire on cobble bars; ecological succession on cobble bars and fluvial biogeomorphology (Corenbilt et al. 2007); numerous problematic taxa in need of taxonomic study; phylogeographic connections of different river systems.

Previous Studies

J.K. Small collected plants along riverscour habitats of the Emory River system, but never published a report on the riverscour habitats (Dwayne Estes pers. comm.). Schmalzer (1985) conducted a flora of the Obed Wild and Scenic River (Clear Creek, lower Daddy's Creek, and the Obed River), which reported rare plants from herbaceous vegetation of "gravel bars", but focused strongly on the upland communities of the gorge system. Estes and Fleming (2008) conducted a rare and invasive species report for the main stem of the Obed River from Daddy's Creek confluence to the Clear Creek confluence, but failed to conduct any vegetation analysis outside of qualitative habitat descriptions. Wolfe et al. (2007) provided much-needed hydrogeomorphological insight into the formation and maintenance of alluvial bars containing these riverscour communities. Natureserve's Cumberland Riverscour Ecological System combines all examples of riverscour from river systems of KY, TN, AL, and GA, with preliminary plot data informing a list of associations occurring in the system, but is based on limited available data. The National Park Service, specifically the Appalachian Highlands Network, is conducting ongoing vegetation and rare plant monitoring of cobble bars containing riverscour vegetation in the Obed Wild and Scenic River.

References

Bailey CJ and Coe FG. 2001. The vascular flora of the riparian zones of the clear fork and new river in the big south fork national river and recreation area (BSF-NRRA). Castanea 66(3):252–274. 

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.

Corenbilt D, Tabbachi E, Steiger J, and Gurnell AM. 2007. Reciprocal interactions and and adjustments in fluvial landforms and vegetation dynamics in river corridors: a review in complimentary approaches. Earth-Science Reviews 84 (2007): 56-86.

Evans R and Pyne M. Cumberland riverscour. 2013 In: NatureServe. International ecological classification standard: terrestrial ecological systems of the United States. Arlington, VA: http://explorer.natureserve.org, printed on March 27, 2014

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.

Schmalzer PA, Patrick TS, DeSelm HR. 1985. The vascular flora of the obed wild and scenic river, Tennessee. Castanea 50(2): 71-88.

Schmalzer, PA. 1989. Vegetation and flora of the obed river gorge system, cumberland plateau, Tennessee. Journal of the Tennessee Academy of Science 64(3): 161-168. 

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.

Checklist of Plant Species known from this community