Name:
Fraxinus americana / Andropogon gerardii - Sorghastrum nutans - Schizachyrium scoparium - Pycnanthemum tenuifolium Riverscour Wet Meadow
Reference:
NatureServe Biotics 2019
Description:
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. <i>Andropogon gerardii</i> is the most abundant species, with <i>Sorghastrum nutans, Schizachyrium scoparium</i>, and <i>Panicum virgatum</i> each occurring constantly and achieving codominance in a subset of stands. Other characteristic, but less constant, graminoid associates include <i>Sporobolus clandestinus, Aristida purpurascens, Dichanthelium depauperatum, Dichanthelium dichotomum, Chasmanthium latifolium, Danthonia spicata, Eragrostis spectabilis, Tripsacum dactyloides, Scleria triglomerata</i>, and <i>Muhlenbergia capillaris</i>. The type also contains a number of characteristic xerophytic forbs, the most constant of which are <i>Pycnanthemum tenuifolium, Solidago simplex var. racemosa, Symphyotrichum patens var. patens, Euphorbia corollata, Allium cernuum, Cerastium arvense, Phlox subulata, Coreopsis tripteris, Ionactis linariifolius, Lespedeza virginica, Potentilla canadensis, Veronicastrum virginicum, Lathyrus venosus</i>, and <i>Helianthus divaricatus</i>. Other noteworthy herbs occurring less frequently include <i>Asclepias verticillata, Cheilanthes lanosa, Dichanthelium laxiflorum, Eupatorium hyssopifolium</i> (two vars.), <i>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</i>, and <i>Tridens flavus</i>. Scattered, stunted, flood-damaged trees and shrubs occasionally achieve 25% aggregate cover in an individual 400-m2 plot. Species richness of this community is typically high to exceptional, averaging 88 taxa per 400 m2 (range 51 to 138 taxa) in 16 plots.
Accession Code:
urn:lsid:vegbank.org:commConcept:35116-{023C7705-6A0E-4727-B09F-7502BF437DFE}
Plot-observations of this Community Concept:
10
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