Common (Translated Scientific) Name: Switchgrass - Big Bluestem Gravel Riverscour Wet Meadow

Colloquial Name: Ridge & Valley Gravel Riverscour Prairie

Hierarchy Level:  Association

Type Concept: This association is known from several rivers and their major river tributaries (e.g., Potomac, James, Shenandoah, Monongahela, and Cheat rivers) in Maryland, Virginia, and West Virginia. It occurs primarily in the upper river sections on cobbly and gravelly depositional bars, primarily in river reaches that are underlain by shale bedrock. The substrate is sand, gravel, and cobble, with patches of gravelly sand or sandy loam soils. Flooding appears to occur several times a year, and stands may be inundated for long periods during the dormant season and occasionally during the growing season, but are generally somewhat well-drained and seasonally dry. Hydrologic regime is best characterized as temporarily flooded. This association occurs in small patches, with some stands exceeding 500 m2 in area. The vegetation is strongly dominated by Panicum virgatum and Andropogon gerardii with relatively low species richness (Virginia samples: 38 taxa/plot in five 100-m2 and 200-m2 plots). Scattered, stunted, floodplain shrubs or small trees may be present, but the vegetation structure is a grassland. The only completely constant woody associate is Platanus occidentalis. Other shrubs or small trees may include Salix caroliniana, Physocarpus opulifolius, and the exotic Rosa multiflora. Associated herbaceous species are weedy annuals or short-lived perennials that rarely attain as much as 2% cover in a given stand. Dichanthelium clandestinum and Verbesina alternifolia are the most frequent associates (>75%); other common associates include Oxalis stricta, Verbena urticifolia, Cyperus strigosus, Acalypha rhomboidea, Viola sororia, Plantago lanceolata, and the exotics Microstegium vimineum, Ambrosia artemisiifolia, Daucus carota, Centaurea stoebe ssp. micranthos, and Solanum carolinense.

Diagnostic Characteristics: No Data Available

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: The classification is supported by analysis of plot data from riverside prairie vegetation during the National Capital Region Parks project and Camp Dawson and other projects in West Virginia. Consideration was given to whether this might be considered an extremely depauperate form of ~Andropogon gerardii - Panicum virgatum - Baptisia australis Riverscour Wet Meadow (CEGL006283)$$, which is considerably more species-rich and has many perennial forbs of relatively stable habitats, compared to the depauperate, weedy herbaceous flora of this association (CEGL006477). However, the latter performed convincingly in analysis, arguing for its recognition as a USNVC type. The two types occur sympatrically in topographically adjacent zones near the west end of the Paw Paw Tunnel in the Ridge and Valley and in a small area of the Mather Gorge in the Piedmont. In these cases, CEGL006283 occupies a higher topographic position and is often a community of stable bedrock outcrops on the channel shelf or walls, as opposed to this association (CEGL006477), which occurs on less stable sand/cobble depositional bars. However, examples of ~Andropogon gerardii - Panicum virgatum - Baptisia australis Riverscour Wet Meadow (CEGL006283)$$ along the New and Greenbrier rivers in West Virginia occur on ephemeral cobble bars (J. Vanderhorst pers. comm. 2006), suggesting that the differences between this community and related types may have more to do with flooding frequency/intensity and/or substrate chemistry than to topography (i.e., outcrop vs. cobble bar).

Similar NVC Types: No Data Available

note: No Data Available