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Hiwassee River Phyllite Bedrock Riverscour

Synonyms

Southern Appalachian Bedrock Scour Herbaceous Vegetation (NatureServe 2015)

Hiwassee / Ocoee River Boulder Scour Vegetation (NatureServe 2015)

Hiwassee / Ocoee Bedrock Scour Vegetation (NatureServe 2015)

Rocky Bar and Shore (Schafale and Weakley 1990)

Distribution

Southeastern Tennessee (Polk County) in the Hiwassee river gorge.

Vegetation Description

This is a linear, small patch community that can be dominated by shrubs or graminoids (NatureServe 2015).  Vegetation typically reaches 1.5 meters in height at most in the shrub type and just over a meter where graminoids dominate.  On the greywacke bedrock scour bars of the Ocoee River, in cases where bedrock or boulder is submerged, Podostemum ceratophyllum dominates, forming mats over rocks (NatureServe2015). Scour bars occur between the aquatic zone of the river and the forested terraces and low-slopes of the surrounding gorge. 

Physical Characterization

Phyllite bedrock and boulder riverscour are restricted to the Southern Sedimentary Ridges EPA level IV ecoregion in the Blue Ridge Mountains (Griffith et. al 1998).  This system is situated in the low (260-295 meters above sea-level) flat areas of the Hiwassee River Gorge along the margins of the river where high-water events infrequently scour inhabiting vegetation. The exposed metamorphic slate, or phyllite, bedrock is regularly fractured by weathering and cracks and fissures collect fine particles of substrate where vegetation can take root.  The geology is of the Cambrian age and is part of the Licklog Formation (Hardeman et. al 1966).  Soils are likely alkaline.  This system is severely restricted in size with less than 3.5 river miles of available habitat remaining.  

Natural Processes

High-energy flooding events maintain this system.  It is unknown whether the unique phyllite geology has a pronounced chemical effect on vegetation.

Dominant Plants

Unknown.

Characteristic Plants

Mostly unknown.

Herbs

Pityopsis ruthii (Ruth’s golden aster)

Restricted Plants

Pityopsis ruthii (Ruth’s golden aster)

Solidago sp. nov. (Hiwassee Goldenrod)

Invasive Species

Unknown.  On the Ocoee greywacke bedrock scour, Microstegium vimineum and Polygonum caespitosum var. longisetum among others have been observed (NatureServe 2015).

Community Variation and Subtypes

NatureServe Associations:

Hiwassee / Ocoee River Boulder Scour Vegetation: Schizachyrium scoparium - Andropogon ternarius - Liatris microcephala - (Pityopsis ruthii) Herbaceous Vegetation

Hiwassee / Ocoee Bedrock Scour Vegetation Schizachyrium scoparium - Schoenoplectus americanus - Juncus marginatus - Eupatorium serotinum Herbaceous Vegetation

Rocky Bar and Shore (Alder - Yellowroot Type)

Rocky Bar and Shore (Twisted Sedge Type) 

Rocky Bar and Shore (Riverweed Type) 

Associated Natural Communities

Blue Ridge Phyllite Cliff, Blue Ridge Slate Cliff, Blue Ridge Dry/Xeric Calcareous Phyllite Woodland, Blue Ridge Dry/Xeric Acidic Phyllite Woodland, Blue Ridge Low-Elevation Calcareous Phyllite Outcrop , Blue Ridge Low-Elevation Acidic Phyllite Outcrop

Similar Communities

The Bluffs of Hiwassee Glades (NatureServe 2015)

Presettlement Distribution and Size

This system likely occurred along an estimated 5 mile section of the Ocoee River and 6.5 miles along the Hiwassee River in areas where exposed phyllite crops out along the river bed.  The instillation of dams in both rivers has since eliminated all representative habitat in the Ocoee and drastically reduced the quality and size of habitat in the Hiwassee. 

Present Status

Perhaps less than 40 scour bars remain in just 1.9 miles of the last remaining suitable habitat.  The four dams upstream of the Tennessee section of the Hiwassee have altered the hydrology of the river to such an extent that predictable, seasonal flooding no longer takes place.  Sensitive endemics like Pityopsis ruthii have been observed in rapid decline -- a census by the Tennessee Valley Authority (TVA) of P. ruthii in 2010 showed losses in 5 of 6 sites sampled in the range of 20-60% over the previous 12 year period (Call 2012).  Cruzan (2001) estimated a 50% increase in woody vegetation in the Hiwassee floodplain since the late 1940’s, indicating loss of scoured habitat.

Representative Sites

Polk Co.: Cherokee National Forest, confluence of Deep Branch, West Fork Butler Branch with the Hiwassee River.

Threats

Altered hydrological inputs impact this system more than any other factor, although there are a number of threats.  The region has historically been heavily mined for copper, best remembered by the terrible environmental tragedy that occurred in nearby Ducktown.   In order to move copper from the hills, roads were constructed along the rivers and trees were cut in the surrounding hills to fuel smelting furnaces.  Resulting erosion of the surrounding hills resulted in the siltation of waterways (Shaw and Estes 2012).  Modern recreational boaters may pose a minor risk to riverscour vegetation through trampling.

Management Considerations

Efforts to increase populations of Pityopsis ruthii on the Ocoee and Hiwassee have been ineffective due to low seed and seedling viability (Cruzan and Beaty 1998).  Dam release times should be considered as the timing of high and low-water events are crucial to maintaining the system.

Future Research Needs

 A floristic inventory and plot work are required.  Floristic comparisons between the nearby and physiognomically similar greywacke bedrock scour bars and this system should be made to investigate possible geochemical effects unique to phyllite. 

Previous Studies

Cruzan (2001), Cruzan and Beatty (1999), Clebsch and Sloan (1993) and Call (2012) have collected or assimilated data on the ecology and status of this system to build a context for studies on Pityopsis ruthii.  Most of the relevant work done has been to document the extent of remaining riverscour habitat suitable for the species.

References

Call, G.  2012. Ruth's Golden Aster (Pityopsis ruthii) 5-Year Review: Summary and Evaluation.  U.S. Fish and Wildlife Service, Southeast Region, Tennessee Ecological Services Field Office.

Clebsch, E. E. C. and A. Sloan. 1993. Final Report, Contract Between the University of
Tennessee and the Tennessee Department of Environment and Conservation for the study
of various aspects of the ecology and life history of the endangered plant species Ruth’s
Golden-Aster (Pityopsis ruthii). Report to Tennessee Department of Environment and Conservation, October 8, 1993. 19 pp.

Cruzan, M. B. 2001. Ecological genetics of Pityopsis ruthii: Final Research Report I.
Reproductive Ecology. Unpublished report to Tennessee Department of Environment and
Conservation/Division of Natural Heritage. 3 pp.

Cruzan, M. B. and P. Beaty. 1998. Population Biology of Ruth’s Golden Ater (Pityopsis ruthii): Final Report (Tennessee Department of Environment and Conservation/Division of Natural Heritage ID-96-05937-6-00). March 7, 1998. 5 pp.

Griffith G, Omernik J, Azevedo S.  1998. Ecoregions of Tennessee (color poster with map, descriptive text, summary tables, and photographs): Reston, VA., U.S. Geological Survey (map scale 1:1,000,000).

Hardeman, W.D., and others, 1966, Geologic map of Tennessee: Division of Geology, Tennessee Department of Environment and Conservation, scale 1:250,000

 Schafale, M. P., and A. S. Weakley. 1990. Classification of the natural communities of North Carolina. Third approximation. North Carolina Department of Environment, Health, and Natural Resources, Division of Parks and Recreation, Natural Heritage Program, Raleigh. 325 pp.

 Schafale, Mike P. Personal communication. Ecologist, North Carolina Department of Environment, Health, and Natural Resources, Division of Parks and Recreation, Natural Heritage Program, Raleigh.

 Shaw, J., and D. Estes. 2012. Botanical survey and ecological systems mapping of the Ocoee River Gorge, Polk County, Tennessee. Prepared for the Tennessee Department of Transportation under a contract from URS Inc.

Statement from Mitchell B. Cruzan, Ph.D., University of Tennessee, Recorded RCWG Meeting Minutes (August 23, 2000).

Checklist of Plant Species known from this community

Uknown