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Fraxinus americana / Andropogon gerardii - Sorghastrum nutans - Schizachyrium scoparium - Pycnanthemum tenuifolium Riverscour Wet Meadow
Translated Name: White Ash / Big Bluestem - Indiangrass - Little Bluestem - Narrowleaf Mountainmint Riverscour Wet Meadow
Common Name: Piedmont-Central Appalachian Riverside Outcrop Prairie
Unique Identifier: CEGL006478
Classification Approach: International Vegetation Classification (IVC)
Summary: This association is known only from scattered sites along the Potomac River in Maryland and Virginia, and possibly the Shenandoah River in Virginia. The type occupies steeply sloping riverside outcrops and eroded bedrock terraces along high-gradient, rocky river reaches where depositional features are very poorly developed. These habitats are exposed to considerable scouring during major floods and are seasonally xeric. Bedrock parent material of sites in the fall-line gorge of the Potomac River includes metagraywacke and schist, with local mafic and ultramafic intrusive bodies. An additional site on the upper Potomac (Allegany County, Maryland) is on shale, and another potential site on the Shenandoah River is located on an exposure of dolomite. This vegetation occupies sites ranging from about 2 to 15 m above mean water level, and the flooding-return interval has been estimated at 2.5 to 7 years. Fifteen to 90% of the substrate consists of exposed bedrock, and soils are sandy loams or loamy sands with relatively high base status. Stands are dominated by warm-season grasses, with moderate to locally dense total herbaceous cover. Andropogon gerardii is the most abundant species, with Sorghastrum nutans, Schizachyrium scoparium, and Panicum virgatum each occurring constantly and achieving codominance in a subset of stands. Other characteristic, but less constant, graminoid associates include Sporobolus clandestinus, Aristida purpurascens, Dichanthelium depauperatum, Dichanthelium dichotomum, Chasmanthium latifolium, Danthonia spicata, Eragrostis spectabilis, Tripsacum dactyloides, Scleria triglomerata, and Muhlenbergia capillaris var. capillaris. The type also contains a number of characteristic xerophytic forbs, the most constant of which are Pycnanthemum tenuifolium, Solidago simplex var. racemosa, Symphyotrichum patens var. patens (= Aster patens var. patens), Euphorbia corollata, Allium cernuum, Cerastium arvense, Phlox subulata, Coreopsis tripteris, Ionactis linariifolius, Lespedeza virginica, Potentilla canadensis, Veronicastrum virginicum, Lathyrus venosus, and Helianthus divaricatus. Other noteworthy herbs occurring less frequently include Asclepias verticillata, Cheilanthes lanosa, Dichanthelium laxiflorum, Eupatorium hyssopifolium (two vars.), Galactia volubilis, Helianthus occidentalis ssp. occidentalis, Lespedeza capitata, Lespedeza violacea, Liatris spicata var. spicata, Onosmodium virginianum, Paronychia virginica, Physostegia virginiana, Selaginella rupestris, Solidago nemoralis, Stylosanthes biflora, and Tridens flavus. Scattered, stunted, flood-damaged trees and shrubs occasionally achieve 25% aggregate cover in an individual 400-square-meter plot. Species richness of this community is typically high to exceptional, averaging 88 taxa per 400 square meters (range 51 to 138 taxa) in 16 plots.



Classification

Classification Confidence: Moderate
Classification Comments: The classification is supported by data analysis of 15 plots from metamorphic outcrops of the Potomac Gorge (Maryland and Virginia) and one from a shale outcrop in Allegany County, Maryland. This vegetation is probably best characterized as "wooded herbaceous," but the most appropriate alliance placement is in the herbaceous class. Although this community has some affinities to certain upland "barrens" vegetation types, its strongest affiliation is clearly with the periodically flood-scoured prairies in Andropogon gerardii - Sorghastrum nutans Appalachian Gravel Riverscour Alliance (A2069).

Vegetation Hierarchy
Class 2 - Shrub & Herb Vegetation
Subclass 2.C - Shrub & Herb Wetland
Formation 2.C.4 - Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland
Division 2.C.4.Nd - Eastern North American Temperate & Boreal Freshwater Marsh, Wet Meadow & Shrubland
Macrogroup Eastern North American Riverscour Vegetation
Group Central Interior-Appalachian Riverscour Barrens & Prairie
Alliance Appalachian Riverine Gravel Wash Prairie

This is the revised vegetation hierarchy. For more information see Classification Sources and usnvc.org.

Similar Associations
Unique Identifier Name
CEGL006283 Andropogon gerardii - Panicum virgatum - Baptisia australis Riverscour Wet Meadow
CEGL006491 (Hypericum prolificum, Leucothoe racemosa) / Schizachyrium scoparium - Solidago simplex var. racemosa - Ionactis linariifolius Riverscour Sparse Vegetation
CEGL008471 (Salix caroliniana, Rhododendron arborescens) / Andropogon gerardii - Baptisia australis - (Solidago simplex ssp. randii) Riverscour Wet Meadow



Related Concepts from Other Classifications

Related Subnational Community Units
These data are subject to substantial ongoing revision and may be out of date for some states.
In the U.S., contact the state Heritage Program for the most complete and up-to-date information at: http://www.natureserve.org/natureserve-network.
Information from programs in other jurisdictions will be posted when they are made available.
Subnation Concept Name Relationship to Standard Confidence Reference
Maryland Fraxinus americana / Andropogon gerardii - Sorghastrum nutans - Schizachyrium scoparium - Pycnanthemum tenuifolium Herbaceous Vegetation Equivalent Certain Harrison 2011


Other Related Concepts
Related Concept Name: Fraxinus americana / Andropogon gerardii - Sorghastrum nutans - Schizachyrium scoparium - Pycnanthemum tenuifolium Herbaceous Vegetation
Relationship: = - Equivalent
Reference: Fleming, G. P. 2007. Ecological communities of the Potomac Gorge in Virginia: Composition, floristics, and environmental dynamics. Natural Heritage Technical Report 07-12. Unpublished report submitted to the National Park Service. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond. 341 pp. plus appendices.
Relationship: = - Equivalent
Reference: Fleming, G. P., and K. Taverna. 2006. Vegetation classification for the National Capitol Region parks, western region. Regional (VA-WVA-MD-DC) analysis prepared for NatureServe and USGS-NPS Vegetation Mapping Program, March 2006. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond.
Related Concept Name: Quercus stellata / Andropogon gerardii - Schizachyrium scoparium - Aristida purpurascens Wooded Herbaceous Vegetation
Relationship: = - Equivalent
Reference: Lea, C. 2000. Plant communities of the Potomac Gorge and their relationship to fluvial factors. M.S. thesis, George Mason University. Fairfax, VA. 219 pp.
Related Concept Name: Quercus stellata / Andropogon gerardii - Sorghastrum nutans - Schizachyrium scoparium - Aristida purpurascens Wooded Herbaceous Vegetation
Relationship: = - Equivalent
Reference: Lea, C. 2004. Draft vegetation types in National Capital Region Parks. Edited by S.C. Gawler and J. Teague. Working draft for review by NatureServe, Virginia Natural Heritage, West Virginia Natural Heritage, Maryland Natural Heritage, and National Park Service. July 2004. 157 pp.
Related Concept Name: Riverside Prairie
Relationship: B - Broader
Reference: Fleming, G. P., P. P. Coulling, K. D. Patterson, and K. Taverna. 2006. The natural communities of Virginia: Classification of ecological community groups. Second approximation. Version 2.2. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond. [http://www.dcr.virginia.gov/natural_heritage/ncTIV.shtml]
Relationship: B - Broader
Reference: Harrison, J. W., compiler. 2004. Classification of vegetation communities of Maryland: First iteration. A subset of the International Classification of Ecological Communities: Terrestrial Vegetation of the United States, NatureServe. Maryland Natural Heritage Program, Maryland Department of Natural Resources, Annapolis. 243 pp.

Ecological Systems Placement

Ecological Systems Placement
Ecological System Unique ID Ecological System Name
CES202.608 Central Appalachian River Floodplain
CES202.609 Central Appalachian Stream and Riparian


NatureServe Conservation Status
Global Status: G1 (30May2007)
Rounded Global Status: G1 - Critically Imperiled
Reasons: There are probably fewer than ten occurrences of this community rangewide, all associated with a specific set of rare habitat conditions. Patch size is very small and the aggregate size of all known occurrences is probably <5 ha. The potential for additional occurrences in the Potomac or other watersheds is good, but new occurrences would probably not significantly increase the acreage of the type.

Distribution
Color legend for Distribution Map
United States Distribution: MD, VA
Global Distribution: United States
Global Range: This association is known only from scattered riverside outcrops and bedrock terraces along the Potomac River in Maryland and Virginia. An additional dolomite outcrop along the Shenandoah River in Clarke County, Virginia, may also represent this type. Occurrences are concentrated in the high-gradient fall-line section (Potomac Gorge) of the river near Great Falls, with at least one occurrence along the upper Potomac in the Ridge and Valley province.

Vegetation

Vegetation Summary: The composition is dominated by warm-season grasses, with moderate to locally dense total herbaceous cover. Andropogon gerardii is the most abundant species, with Sorghastrum nutans, Schizachyrium scoparium, and Panicum virgatum each occurring constantly and achieving codominance in a subset of stands. Other characteristic, but less constant, graminoid associates include Sporobolus clandestinus, Aristida purpurascens, Dichanthelium depauperatum, Dichanthelium dichotomum, Chasmanthium latifolium, Danthonia spicata, Eragrostis spectabilis, Tripsacum dactyloides, Scleria triglomerata, and Muhlenbergia capillaris var. capillaris. The type also contains a number of characteristic xerophytic forbs, the most constant of which are Pycnanthemum tenuifolium, Solidago simplex var. racemosa, Symphyotrichum patens var. patens (= Aster patens var. patens), Euphorbia corollata, Allium cernuum, Cerastium arvense, Phlox subulata, Coreopsis tripteris, Ionactis linariifolius, Lespedeza virginica, Potentilla canadensis, Veronicastrum virginicum, Lathyrus venosus, and Helianthus divaricatus. Other noteworthy herbs occurring less frequently include Asclepias verticillata, Cheilanthes lanosa, Dichanthelium laxiflorum, Eupatorium hyssopifolium (two vars.), Galactia volubilis, Helianthus occidentalis ssp. occidentalis, Lespedeza capitata, Lespedeza violacea, Liatris spicata var. spicata, Onosmodium virginianum, Paronychia virginica, Physostegia virginiana, Selaginella rupestris, Solidago nemoralis, Stylosanthes biflora, and Tridens flavus. Scattered, stunted, flood-damaged trees and shrubs occasionally achieve 25% aggregate cover in an individual 400-square-meter plot. The most frequent (>50% constancy) and abundant (>1% mean cover) of these woody species are Fraxinus americana, Robinia pseudoacacia, Fraxinus pennsylvanica, Hypericum prolificum, Viburnum prunifolium, Rubus flagellaris, Carpinus caroliniana, Quercus rubra, Diospyros virginiana, Quercus stellata, and Carya glabra. Small wet depressions contain localized populations of wetland species such as Carex straminea, Eleocharis compressa, Juncus dichotomus, Juncus scirpoides, Ludwigia alternifolia, Mecardonia acuminata, Rhynchospora capitellata, Scirpus pendulus, and Trautvetteria caroliniensis. Species richness of this community is typically high to exceptional, averaging 88 taxa per 400 square meters (range 51 to 138 taxa) in 16 plots.

Vegetation Composition (incomplete)
Species Name Rounded Global Status Growth Form Stratum Charact-
eristic
Dominant Constant
Cover Class %
Con-
stancy
%
Fraxinus americana G1 Broad-leaved deciduous tree Tree canopy  
 
 
Baptisia australis var. australis G1 Flowering forb Herb (field)      
 
 
Cerastium arvense G1 Flowering forb Herb (field)      
 
 
Helianthus occidentalis ssp. occidentalis G1 Flowering forb Herb (field)      
 
 
Onosmodium virginianum G1 Flowering forb Herb (field)      
 
 
Paronychia virginica G1 Flowering forb Herb (field)      
 
 
Pycnanthemum tenuifolium G1 Flowering forb Herb (field)    
 
 
Solidago simplex var. racemosa G1 Flowering forb Herb (field)      
 
 
Andropogon gerardii G1 Graminoid Herb (field)  
 
 
Carex straminea G1 Graminoid Herb (field)      
 
 
Eleocharis compressa G1 Graminoid Herb (field)      
 
 
Schizachyrium scoparium G1 Graminoid Herb (field)  
 
 
Sorghastrum nutans G1 Graminoid Herb (field)  
 
 


At-Risk Species Reported for this Association
Scientific Name
  (Common Name)
NatureServe Global Status U.S. Endangered Species Act Status
Baptisia australis var. australis
  (Blue Wild Indigo)
G5T3T4  
Solidago simplex var. racemosa
  (Racemose Goldenrod)
G5T3?  


Environmental Setting

Wetland Indicator: Y
Environmental Summary: The type occupies steeply sloping riverside outcrops and eroded bedrock terraces along high-gradient, rocky river reaches where depositional features are very poorly developed. These habitats are exposed to considerable scouring during major floods, and are seasonally xeric. Bedrock parent material of sites in the fall-line gorge of the Potomac River includes metagraywacke and schist, with local mafic and ultramafic intrusive bodies. An additional site on the upper Potomac (Allegany Co., MD) is on shale, and another potential site on the Shenandoah River is located on an exposure of dolomite. Lea (2000) estimated that sites on the Maryland side of the Potomac Gorge had a mean flood-return interval of 2.5 to 7 years, with 15 to 40% (up to 85%) of ground cover consisting of exposed rock and soils consisting of shallow (usually <10 cm), sandy loams or loamy sands. On the Virginia side of the Potomac Gorge, this vegetation occupies sites ranging from about 2 to 15 m above mean water level, with 15 to 90% of the substrate consisting of bedrock, and soils with moderately high pH and calcium levels. Some sites have very small, wet inclusions developed in bedrock depressions with impeded drainage.


Dynamic Processes


Plot Sampling & Classification Analysis

Plots stored in VegBank


Authors/Contributors
Concept Author(s): C. Lea
Element Description Edition Date: 30May2007
Element Description Author(s): G.P. Fleming and C. Lea
NatureServe Conservation Status Factors Edition Date: 30May2007
NatureServe Conservation Status Factors Author(s): G.P. Fleming

Ecological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).


References
  • Eastern Ecology Working Group of NatureServe. No date. International Ecological Classification Standard: International Vegetation Classification. Terrestrial Vegetation. NatureServe, Boston, MA.

  • Fleming, G. P. 2007. Ecological communities of the Potomac Gorge in Virginia: Composition, floristics, and environmental dynamics. Natural Heritage Technical Report 07-12. Unpublished report submitted to the National Park Service. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond. 341 pp. plus appendices.

  • Fleming, G. P., K. Taverna, and P. P. Coulling. 2007b. Vegetation classification for the National Capitol Region parks, eastern region. Regional (VA-MD-DC) analysis prepared for NatureServe and USGS-NPS Vegetation Mapping Program, March 2007. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond.

  • Fleming, G. P., P. P. Coulling, K. D. Patterson, and K. Taverna. 2006. The natural communities of Virginia: Classification of ecological community groups. Second approximation. Version 2.2. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond. [http://www.dcr.virginia.gov/natural_heritage/ncTIV.shtml]

  • Fleming, G. P., and K. D. Patterson. 2011a. Natural communities of Virginia: Ecological groups and community types. Natural Heritage Technical Report 11-07. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond. 34 pp.

  • Fleming, G. P., and K. Taverna. 2006. Vegetation classification for the National Capitol Region parks, western region. Regional (VA-WVA-MD-DC) analysis prepared for NatureServe and USGS-NPS Vegetation Mapping Program, March 2006. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond.

  • Harrison, J. W. 2011. The natural communities of Maryland: 2011 working list of ecological community groups and community types. Unpublished report. Maryland Department of Natural Resources, Wildlife and Heritage Service, Natural Heritage Program, Annapolis. 33 pp.

  • Harrison, J. W., compiler. 2004. Classification of vegetation communities of Maryland: First iteration. A subset of the International Classification of Ecological Communities: Terrestrial Vegetation of the United States, NatureServe. Maryland Natural Heritage Program, Maryland Department of Natural Resources, Annapolis. 243 pp.

  • Lea, C. 2000. Plant communities of the Potomac Gorge and their relationship to fluvial factors. M.S. thesis, George Mason University. Fairfax, VA. 219 pp.

  • Lea, C. 2004. Draft vegetation types in National Capital Region Parks. Edited by S.C. Gawler and J. Teague. Working draft for review by NatureServe, Virginia Natural Heritage, West Virginia Natural Heritage, Maryland Natural Heritage, and National Park Service. July 2004. 157 pp.


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