Name:
Rhynchospora spp. - Panicum (rigidulum, verrucosum) - Rhexia virginica Seasonally Flooded Herbaceous Alliance
Reference:
Eastern Ecology Working Group of...
Description:
This alliance accommodates a variety of seasonally flooded vegetation of pondshore and lakeshore environments. It occurs primarily along the Atlantic Coastal Plain from Nova Scotia, Canada, south to Georgia, with inland stations in the central Great Lakes area, the Great Valley of Virginia, and central Tennessee. Occurrences of this alliance are usually small and are dominated predominantly by herbaceous, mostly graminoid, species. Many species are annual or short-lived perennial plants. They persist for years in the seed bank until the hydrologic conditions are right for germination. Thus, species composition of particular stands may change from year to year. In interior stations of this alliance, many of these seedbank plants are species significantly disjunct from their main range on the Atlantic Coastal Plain. There are two major vegetation zones that occur in this environment: Zone 1 is a seasonally flooded zone of sparse cover by graminoids; and Zone 2 is a saturated zone of dense graminoid cover. Some associations may include a zone dominated by taller graminoids, including Saccharum spp. or Scirpus cyperinus. These zones remain largely intact, but a succession of wet or dry years can cause them to shift slightly in location. Pondshore examples of this alliance occupy a zone around a more open pond center with a longer hydroperiod. These ponds have a pronounced seasonal fluctuation in water level, filling in the winter and drying in the summer. Examples of this alliance from Lower New England and the North Atlantic Coast of Nova Scotia south to Delaware may be found on Coastal Plain pondshores with cobble substrates and little or no organic material accumulation; the broad margins and shorelines of shallow basins or deeper ponds on variable substrates; or on the shores of glacial outwash ponds or large lakes. In the Great Lakes, stands of this alliance are found on sandy pitted outwash plains and glacial lake plains. The level topography of these plains produces gently sloping, shallow basins with no outlets and sometimes no inlets. The water table fluctuates seasonally and yearly. It is highest in late winter and spring, and during years of high precipitation. The soils are derived mainly from sand. The sand is poor in nutrients and is acidic, with pH ranging from 4.4-7.0. These conditions inhibit microbial decomposition and considerable organic material accumulates as peat. The peat mixes with sand or forms more-or-less pure deposits. Basin shorelines typically have stretches of pure sand in areas where wave action is greatest, pure peat in protected areas, and a mixture of the two substrates in other areas. In some basins, an impermeable layer of clay develops 2-5 m below the surface. This layer may hold the local water table above the regional water table for long periods. In the South, this alliance is found in upland depression ponds of the Interior Low Plateau (Eastern Highland Rim) of Tennessee, seasonally flooded anthropogenic peatland depressions in the Great Dismal Swamp of Virginia (where it may occupy seasonally ponded depressions of anthropogenic origin, such as experimental marsh restoration clearings, burned-out peat areas, or depressional basins in powerlines), seasonally flooded upland depressions occurring on clays in the Inner Coastal Plain of southeastern Virginia, as well as Grady Ponds in Georgia and possibly some vegetation of Carolina bays. In central Tennessee examples, vegetation of this alliance may grade down into that of the Juncus repens - Eleocharis microcarpa Seasonally Flooded Herbaceous Alliance (A.1376).
Accession Code:
VB.CC.20997.RHYNCHOSPORASPP
Plot-observations of this Community Concept:
0
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