Department of Conservation and Recreation
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Department of Conservation and Recreation
Table of ContentsRiverside Prairies
Communities in this group are globally and state-rare, consisting of temporarily flooded, sparse shrub and dense grassland vegetation of stabilized outcrop or boulder bars along the shores of major mountain and Piedmont rivers. In Virginia, most of the few known occurrences are located in the Potomac River gorge west of Washington, D.C. and along the James River near the Blue Ridge. Habitats supporting Riverside Prairies are elevated above mean water levels and are flood-scoured at return intervals ranging from greater than annually to about 15 years. Because of rockiness and limited alluvial deposition, soils are relatively shallow and site moisture conditions range from mesic to quite xeric.
The vegetation is a lush assemblage of warm-season grasses and forbs, with scattered, small trees almost always present. In the Potomac gorge, where the greatest environmental and floristic variation is found, prairies occurring on and just above the channel shelf often have a savanna-like growth of stunted green ash (Fraxinus pennsylvanica), swamp white oak (Quercus bicolor), silky dogwood (Cornus amomum and Cornus obliqua), and other floodplain trees. Prairies occurring on a higher, less frequently flooded bedrock terrace contain stunted upland trees such as white ash (Fraxinus americana), post oak (Quercus stellata), and pignut hickory (Carya glabra). Dominant grasses in both variants are usually big bluestem (Andropogon gerardii), indian grass (Sorghastrum nutans), and switchgrass (Panicum virgatum var. virgatum), with little bluestem (Schizachyrium scoparium var. scoparium) also abundant on higher, drier terrace outcrops. Other generally characteristic plants include blue wild indigo (Baptisia australis ), violet bush-clover (Lespedeza frutescens), whorled rosin weed (Silphium asteriscus var. trifoliatum), Culver's-root (Veronicastrum virginicum), freshwater cordgrass (Spartina pectinata), narrow-leaf mountain-mint (Pycnanthemum tenuifolium), flattened spikerush (Eleocharis compressa var. compressa), veiny pea (Lathyrus venosus), and common golden-alexanders (Zizia aurea). Species characteristic of the Potomac River prairies include western sunflower (Helianthus occidentalis ssp. occidentalis), dense blazing star (Liatris spicata var. spicata), tall coreopsis (Coreopsis tripteris), and rough dropseed (Sporobolus clandestinus). Species characteristic of the James River prairies include Sampson's snakeroot (Orbexilum psoralioides), northern obedient-plant (Physostegia virginiana ssp. virginiana), and American vetch (Vicia americana var. americana).
Riverside Prairies often occur in patch-mosaics with Riverside Outcrop Barrens, but are readily distinguished by their dense grassland vegetation (vs. sparse vegetation on the outcrops).
References: Fleming (2007), Fleming and Coulling (2001), Lea (2000), Rawinski et al . (1996).Click here for more photos of this ecological community group.
© DCR-DNH, Gary P. Fleming.
Download a spreadsheet of compositional summary statistics for each of the community types listed below.
