Upper Beaches and Overwash Flats
The Marine System is represented by a single group containing vascular plants, which are associated with sparsely vegetated ocean shores and flats behind breached foredunes. Similar vegetation occurs from Maine south to South Carolina. Upper-beach habitats are situated just above the mean high tide limit, but are flooded by high spring tides and storm surges. Constant salt spray maintains generally moist conditions. Substrates consist of unconsolidated sand and shell sediments that are constantly shifted by winds and floods. Dynamic disturbance regimes largely limit vegetation to pioneering, salt-tolerant, succulent annuals. American sea rocket (Cakile edentula) and/or saltwort (Salsola kali) are usually most numerous and characteristic. Other scattered associates include small sea-purslane (Sesuvium maritimum), sea-beach knotweed (Polygonum glaucum), bushy knotweed (Polygonum ramosissimum var. prolificum), sea-blites (Suaeda linearis and Suaeda maritima), and sea-beach orach (Atriplex mucronata). In Virginia, these communities are distributed along the barrier islands of the Eastern Shore (Accomack and Northampton Counties) and on Cape Henry and False Cape (City of Virginia Beach).
Upper beach / overwash flat habitats are critical to several globally rare, federally listed species, including the northeastern beach tiger beetle (Cicindela dorsalis dorsalis). The threatened plant sea-beach amaranth (Amaranthus pumilus) occurred historically on overwash flats in both Eastern Shore counties. The loggerhead sea turtle (Caretta caretta) and the piping plover (Charadrius melodus melodus) utilize beaches and overwash flats for nesting. Extensive construction of high, artificial dunes along the Atlantic coast has reduced the extent of these habitats by increasing oceanside beach erosion and eliminating the disturbance regime that creates and maintains overwash flats.
References: Clampitt (1991), The Nature Conservancy (1997).
Click on the images below to open a larger image in a separate window.
Succulent, annual, upper-beach vegetation on Parramore Island, a maritime barrier island in Accomack County. Saltwort (Salsola kali) is the dominant species in this stand. Photo: Tom Rawinski / © DCR Natural Heritage.
Clumps of saltwort (Salsola kali) on an extensive overwash flat at the southern tip of the Eastern Shore in Northampton County (Fisherman's Island National Wildlife Refuge). Photo: Irvine Wilson / © DCR Natural Heritage.
Quantitative data have been collected from just 11 plots of Upper Beach / Overwash Flat vegetation in Virginia (map). While sampled and observed Virginia stands unquestionably match the USNVC association listed below in general concept, they exhibit apparently significant compositional variation from one locality to another. More data collection and analysis are therefore needed to capture the range of this variation over the state's coastline, firm up classification at the community-type level, and assess the conservation status of this group. Click on any highlighted CEGL code below to view the global USNVC description provided by NatureServe Explorer.