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NATURAL HERITAGE

THE NATURAL COMMUNITIES OF VIRGINIA
CLASSIFICATION OF ECOLOGICAL COMMUNITY GROUPS


Second Approximation (Version 2.6)
Information current as of July, 2013



Maritime Swamps

This group includes all seasonally flooded woody vegetation, as well as saturated forests, of sheltered and near-estuarine maritime wetlands. In maritime habitats, vegetation physiognomy of a single vegetation type can be highly variable depending on stage of successional development and the extent to which it is exposed to pruning by wind and salt spray. As a result, the same vegetation type may be expressed as a shrubland, woodland, or forest at various sites under different conditions. A good example is the black willow (Salix nigra) type of maritime swamp forest, which may initially become established as a shrubland but quickly attains a woodland or forest stature as the trees mature. Nevertheless, this group can generally be subdivided into maritime shrub swamps and maritime swamp forests, not only by their mature physiognomy, but also by floristic composition.

Maritime shrub swamps are seasonally flooded, often dense shrublands of sheltered, back-dune hollows and inlet heads, where surface water is present throughout most of the year. Perched water tables and intermittent to seasonal flooding characterize the hydrology. Both groundwater and surface water are typically fresh (< 0.5 ppt), although salt water may pool in these areas after episodic storm surges during events such as hurricanes. Soils are stratified, with a thin layer of muck up to 30 cm (12 in) thick over wet sand. Species composition of these communities is highly variable and changes somewhat from the southeastern coast (City of Virginia Beach) to the Eastern Shore (Accomack and Northampton Counties). Throughout the region, wax myrtle (Morella cerifera) is the characteristic dominant, Southern areas characteristically contain inkberry (Ilex glabra), and highbush blueberries (Vaccinium spp.). These species are less important in this group northward on the Eastern Shore. Climbing vines of poison ivy (Toxicodendron radicans var. radicans) are abundantly intertwined with the shrubs in most occurrences of these swamps. Herb layers may be rich in ferns, including royal fern (Osmunda spectabilis), marsh fern (Thelypteris palustris var. pubescens), netted chain fern (Woodwardia areolata) and Virginia chain fern (Woodwardia virginica), but also include a variety of forbs such as whorled marsh-pennywort (Hydrocotyle verticillata). The classification, geographic distribution and conservation status of maritime shrub swamps are currently somewhat uncertain and need intensive study.

Maritime swamp forests are seasonally flooded and saturated forests occupying large, protected, interdune swales, flats immediately behind tidal marshes, and the bottoms of streams just inland from estuarine zones. These communities definitely occur from southern New Jersey to North Carolina, but may range further south. In Virginia, stands are scattered along the outer Coastal Plain from the Eastern Shore (Accomack and Northampton Counties) to Cape Henry and False Cape (City of Virginia Beach). The status of these communities on the western shore of the Chesapeake Bay is less clear. Habitats are generally characterized by hummock-and-hollow microtopography, with mucky to sandy, mottled soils and sizeable areas of seasonally standing water. The apparent nutrient status and flooding regimes of soils are highly variable and probably relate to the wide compositional variation in documented stands. Dominant overstory trees in the seasonally flooded forests of the group include red maple (Acer rubrum), sweetgum (Liquidambar styraciflua), swamp tupelo (Nyssa biflora), blackgum (Nyssa sylvatica), black willow (Salix nigra), sweetbay magnolia (Magnolia virginiana) and, less frequently, bald cypress (Taxodium distichum) and Atlantic white-cedar (Chamaecyparis thyoides). Shrubs are diverse but usually include highbush blueberries (Vaccinium corymbosum, Vaccinium fuscatum, Vaccinium formosum), wax myrtle (Morella cerifera), red bay (Persea palustris), and greenbriers (Smilax spp.). Herb layers range from floristically depauperate, with dominance by Virginia chain fern (Woodwardia virginica) or low shrubs, to species-rich with a diversity of marsh and swamp species.

Saturated pine forests in this group occur in back-dune depressions of barrier islands and on terrace flats bordering estuaries further inland. In Virginia, these communities are locally scattered along the Chesapeake Bay (both shores) and its major estuarine tributaries, as well as around Back Bay and estuarine tributaries of Currituck Sound in the southeastern corner of the state. Occasionally, stands occupy slightly elevated "islands" within the upper portions of salt marshes. Habitats are level flats with shallow water tables and hummock-and-hollow microtopography. Areas of seasonally ponded water and organic muck are present; elsewhere, soils are heavily mottled sands. Loblolly pine (Pinus taeda) is the usual dominant overstory tree, sometimes with hardwood associates. Wax myrtle (Morella cerifera) and vines of common greenbrier (Smilax rotundifolia) and poison ivy (Toxicodendron radicans var. radicans) are usually abundant. In southern areas (e.g., on False Cape), pond pine (Pinus serotina) and inkberry (Ilex glabra) are characteristic woody associates. Wetland species such as cinnamon fern (Osmundastrum cinnamomeum var. cinnamomeum), royal fern (Osmunda spectabilis), switchgrass (Panicum virgatum var. virgatum and var. cubense), and smartweeds (Persicaria spp.) dominate species-poor herb layers. A distinctive variant occurring in southeastern Virginia and North Carolina has a dense understory of switch cane (Arundinaria tecta). Some of the maritime wet pine forests appear to represent formerly open, bog-like maritime grasslands that have been invaded by loblolly pines. There is a well documented example of this variant from the Eastern Shore (Assateague Island, Accomack County) and at least one poorly documented occurrence on False Cape (City of Virginia Beach). These stands occupy swales in sheltered back dunes that are protected from salt spray except during major storm surges. A thin organic layer, frequently covered by dense mats of Sphagnum mosses, is usually present at the soil surface. On Assateague Island the vegetation is an open stand of young, salt-spray-stunted loblolly pine, with a very sparse shrub layer. Cranberry (Vaccinium macrocarpon) forms dense mats locally beneath the pines. Elsewhere, scattered herbs include saltmeadow cordgrass (Spartina patens), tall flat panic grass (Coleataenia rigidula ssp. rigidula), and switchgrass (Panicum virgatum var. virgatum) in shallow pools and depressions, and bushy bluestem (Andropogon glomeratus var. glomeratus), Virginia marsh St. John's-wort (Hypericum virginicum), beaksedges (Rhynchospora spp.), twisted yellow-eyed grass (Xyris torta), white-bracted thoroughwort (Eupatorium leucolepis), and water sundew (Drosera intermedia) in wet sand and Sphagnum mats. Maritime Wet Pine Forests are similar to and often intergrade with non-wetland maritime loblolly pine forests and maritime evergreen forests.

The ecological dynamics of maritime swamps, as well as their distinction from inland swamp forests, are poorly understood. Like other communities of the maritime zone, they are subject to potential disturbance by storm surges, salt spray, and shifting dunes. Maritime Swamp Forests are uncommon to rare in Virginia and are subject to encroaching development, logging, and agricultural pollutants.

References: Harvill (1967), Fleming and Moorhead (1998), The Nature Conservancy (1997).



Click on the images below to open a larger image in a separate window.

This link opens a new browser window to display a larger photo Open swamp forest dominated by swamp tupelo (Nyssa biflora) and common spatterdock (Nuphar advena) at First Landing / Seashore State Park, City of Virginia Beach. Photo: Gary P. Fleming / © DCR Natural Heritage.
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Maritime Swamp Forest with an overstory of sweetgum (Liquidambar styraciflua) and red maple (Acer rubrum), and an herb layer consisting mostly of Virginia chain fern (Woodwardia virginica). The habitat is a seasonally flooded swale between dune ridges on the bay side of Assateague Island, Accomack County (Chincoteague National Wildlife Refuge). Photo: Gary P. Fleming / © DCR Natural Heritage.
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Spanish-moss (Tillandsia usneoides)-draped bald cypress (Taxodium distichum) swamp forest in a dune swale behind Cape Henry, City of Virginia Beach (First Landing / Seashore State Park). Photo © Gary P. Fleming.
This link opens a new browser window to display a larger photo Flooded pine forest in dune swales near Ragged Point on Assateague Island, Accomack County (Chincoteague National Wildlife Refuge). Gary P. Fleming / © DCR Natural Heritage.
This link opens a new browser window to display a larger photo Maritime Wet Pine Forest in undulating dunes at False Cape State Park , City of Virginia Beach . Photo © Gary P. Fleming.
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Seasonally flooded dune hollow supporting a maritime shrub swamp dominated by wax myrtle (Morella cerifera ) and saltmeadow cordgrass (Spartina patens). Southern part of Assateague Island, Accomack County (Chincoteague National Wildlife Refuge).Gary P. Fleming / © DCR Natural Heritage.

REPRESENTATIVE COMMUNITY TYPES:
Data have been collected from 33 plots of Maritime Swamps located in three outer Coastal Plain counties (map). Most of these samples are of forested swamps, and additional data from shrub swamps is badly needed. Analysis of Virginia maritime vegetation data, while somewhat limited, seems adequate to describe the composition of Virginia types and their relationship to the USNVC. Documentation of communities in this group from the western shore of the Chesapeake Bay remains a priority. Click on any highlighted CEGL code below to view the global USNVC description provided by NatureServe Explorer.

  • Acer rubrum - Nyssa (biflora, sylvatica) / Morella cerifera / Leersia (oryzoides, virginica) Forest
    Maritime Swamp Forest (Red Maple - Tupelo Type)
    USNVC: = CEGL004082
    Global/State Ranks: G2/S2

  • Morella cerifera - Toxicodendron radicans / Hydrocotyle verticillata Shrubland
    Wax Myrtle Maritime Shrub Swamp
    USNVC: = CEGL003840
    Global/State Ranks: G2G3/S2
  • Pinus taeda / Morella cerifera / Osmunda spectabilis Forest
    Maritime Wet Loblolly Pine Forest
    USNVC: = CEGL006137
    Global/State Ranks: G3/S2?

  • Salix nigra Forest
    Maritime Swamp Forest (Black Willow Type)
    USNVC: = CEGL006348
    Global/State Ranks: G2G3/SU

  • Taxodium distichum / Cephalanthus occidentalis / Boehmeria cylindrica - Ceratophyllum echinatum Forest
    Maritime Swamp Forest (Bald Cypress Type)
    USNVC: = CEGL004079
    Global/State Ranks: G1/S1


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