Non-Riverine Flatwoods and Swamps
Most of the seasonally saturated to seasonally flooded forests in this ecological group occupy nearly flat, broad, outer Coastal Plain terraces and poorly drained peatlands, as well as old, very broad stream terraces that are no longer subject to overland flooding. A small subset also occurs in swampy streamheads and toe-slope depressions in sandhill areas of the inner Coastal Plain, where hydrology is influenced by seepage inputs in addition to fluctuating groundwater. Similar communities have been well documented in North Carolina , and may extend north on terraces of the Chesapeake Bay region to Maryland and Delaware . In Virginia , these communities range locally from inland portions of the Eastern Shore through most low-relief portions of the Coastal Plain. The group contains two saturated community types and two with a seasonally flooded hydrologic regime.
Non-riverine saturated forests are frequently referred to as wet flatwoods. Most remaining examples of this vegetation occur on the outer Coastal Plain from the Eastern Shore to the Embayed Region, but scattered stands are also present in the inner and northern parts of the region. Habitats are nearly flat, with seasonally perched water tables. Some sites experience periodic sheet flows of anastomosing seepage from adjacent slope-base springs. Shallow, braided channels and depressions which pond water intermittently are frequent habitat features. Soils are silt, sand, and clay loams, sometimes with a thin (< 30 cm [12 in]) mantle of coarse, fibric peat. Late-successional stands of non-riverine saturated forests contain mixtures of hydrophytic oaks ( Quercus spp.). Dominants, varying regionally, include swamp chestnut oak (Quercus michauxii), cherrybark oak (Quercus pagoda), willow oak (Quercus phellos), laurel oak (Quercus laurifolia), water oak (Quercus nigra), pin oak (Quercus palustris), and white oak (Quercus alba). Cutting and other disturbances result in higher proportions of sweetgum (Liquidambar styraciflua), red maple (Acer rubrum), and other intolerant trees. Small trees and shrubs include American hornbeam (Carpinus caroliniana), switch cane (Arundinaria tecta), American holly (Ilex opaca var. opaca), sweet pepperbush (Clethra alnifolia), sweetbay magnolia(Magnolia virginiana), coastal dog-hobble (Leucothoe axillaris), and highbush blueberries (Vaccinium spp.). Herb layers tend to be depauperate, but usually contain netted chain fern (Woodwardia areolata) and a variety of sedges, (e.g., Carex abscondita, Carex debilis, Carex intumescens). Large, rhizomatous colonies of Virginia chain fern (Woodwardia virginica) and/or the sedges Carex striata var. brevis, Carex bullata, and Carex barrattii occasionally dominate. Late-successional non-riverine saturated forests have been greatly reduced in extent or modified by extensive agricultural clearing, logging, conversion to pine silvicultures, and hydrologic alterations such as ditching and draining. Both oak-dominated community types in this group (see below) are now globally uncommon to rare. Associated rare species in southeastern Virginia include the globally rare Virginia least trillium (Trillium pusillum var. virginianum), the federally listed Dismal Swamp southeastern shrew (Sorex longirostris fisheri), and the state-listed canebrake rattlesnake (Crotalus horridus atricaudatus).
More prevalent are early-successional flatwoods dominated by mixtures of loblolly pine (Pinus taeda), red maple (Acer rubrum), and sweetgum (Liquidambar styraciflua), frequently with scattered pond pine (Pinus serotina). Small trees and shrubs of these non-riverine pine-hardwood forests include sweetbay magnolia (Magnolia virginiana), blackgum (Nyssa sylvatica), red bay (Persea palustris), and coastal dog-hobble (Leucothoe axillaris). South of the James River, switch cane (Arundinaria tecta) typically dominates the shrub layer in patchy to very dense colonies. Herbaceous species are sparse. In southeastern Virginia, many forests of this composition appear to be successional stands that have replaced once-extensive "canebrakes" (i.e., switch cane savannas with scattered pond pine) following the virtual elimination of fire in the region. Similar occurrences appear to have replaced oak-dominated non-riverine saturated forests and Atlantic white-cedar forests following heavy cutting or catastrophic fires. Although modified communities in this group are not conservation priorities, they provide opportunities for ecological restoration of now-extirpated canebrake vegetation. In addition, large populations of the state-rare bird Swainson's warbler (Limnothlypis swainsonii) are associated with non-riverine pine-hardwood forests. Switch cane is believed to be the host plant for several state and globally rare insects.
Seasonally flooded non-riverine swamp forests that are somewhat similar to alluvial bald cypress - tupelo forests occur on poorly drained peatlands of the Coastal Plain. These communities are most abundant on terraces of the Embayed Region of extreme southeastern Virginia and northeastern North Carolina, but occasionally occur further inland. Habitats are non-riverine wetland flats with deep or shallow organic soils and seasonal flooding to depths of approximately 30 cm (12 in) by elevated water tables. Hummock-and-hollow microtopography is typical. Dominant trees are bald cypress (Taxodium distichum), swamp tupelo (Nyssa biflora), and red maple (Acer rubrum). Red maple now greatly dominates most stands because of extensive past logging, catastrophic fires, and ditching. Red bay (Persea palustris) and sweet pepperbush (Clethra alnifolia) are abundant in the lower woody layers. Also abundant are high-climbing vines of greenbriers (Smilax rotundifolia and Smilax laurifolia), poison ivy (Toxicodendron radicans var. radicans), climbing hydrangea (Decumaria barbara), supplejack (Berchemia scandens), cross-vine (Bignonia capreolata), Virginia-creeper (Parthenocissus quinquefolia), and muscadine grape (Vitis rotundifolia var. rotundifolia). Netted chain fern (Woodwardia areolata) and Virginia chain fern (Woodwardia virginica) are among the few herbs that occur regularly. Non-riverine swamp forest is the characteristic vegetation in and near the Great Dismal Swamp in Virginia. Its dense, vine-rich aspect gave the Swamp much of its historical reputation as a dark, mysterious, or dreadful place. Although most stands are now much altered, The Nature Conservancy has protected an impressive old-growth occurrence at Gum Swamp (City of Chesapeake) that contains bald cypress up to 1.75 m (5 ft 9 in) in diameter.
The few representatives of this group occurring in the inner Coastal Plain sandhills have vegetation somewhat reminiscent of Peatland Atlantic White-Cedar Forests and Pond Pine Woodlands and Pocosins. Atlantic white-cedar (Chamaecyparis thyoides), loblolly pine (Pinus taeda), pond pine (Pinus serotina), red maple (Acer rubrum), swamp tupelo (Nyssa biflora), and sweetbay magnolia (Magnolia virginiana) comprise an open canopy over an extremely thick shrub complex of shining fetterbush (Lyonia lucida), swamp cyrilla (Cyrilla racemiflora), sweet pepperbush (Clethra alnifolia), Carolina laurel (Kalmia carolina), dusty zenobia (Zenobia pulverulenta), inkberry (Ilex glabra), smooth winterberry (Ilex laevigata), evergreen bayberry (Morella heterophylla), greenbriers (Smilax spp.), and several deciduous heaths. Cinnamon fern (Osmundastrum cinnamomeum var. cinnamomeum), Virginia chain fern (Woodwardia virginica), and netted chain fern (Woodwardia areolata) may dominate the herb layer. Because they are generally wet and do not carry fire well, streamhead pocosins probably experience infrequent but intense burns when fires on adjacent uplands spread into them during dry periods.
Non-Riverine Swamp Forests differ from Bald Cypress - Tupelo Swamps by their occurrence on non-alluvial, more shallowly flooded, organic soils (vs. deeply flooded alluvial sloughs and bottoms), as well as by lower-strata floristics. Communities in this group are globally uncommon to rare and provide habitat for the federally listed Dismal Swamp southeastern shrew (Sorex longirostris fisheri) and two rare bats.
References: Dabel and Day (1977), Day (1985), Dean (1969), Fleming and Moorhead (1998), Frost (1995), Frost and Musselman (1987), Levy and Walker (1979), Train and Day (1982).
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Shallow surface ponding during wet periods is characteristic of non-riverine wet hardwood forests. Powhatan Creek watershed, James City County (Colonial National Historical Park). Photo: Gary P. Fleming / © DCR Natural Heritage.
Swamp white oaks (Quercus michauxii) and Virginia chain fern (Woodwardia virginica) in a non-riverine wet hardwood forest near Massaponax, Spotsylvania County (Fredericksburg-Spotsylvania National Military Park). Photo: Gary P. Fleming / © DCR Natural Heritage. Non-riverine wet hardwood forest near the western edge of the Great Dismal Swamp, City of Suffolk. Overstory dominants are laurel oak (Quercus laurifolia), swamp chestnut oak (Quercus michauxii), and cherrybark oak (Quercus pagoda), with switch cane (Arundinaria tecta) and coastal dog-hobble (Leucothoe axillaris) prominent in the understory (Great Dismal Swamp National Wildlife Refuge). Photo: Gary P. Fleming / © DCR Natural Heritage.
Dense understories of switch cane (Arundinaria tecta) are typical of non-riverine pine-hardwood forests of large outer Coastal Plain terraces in southeastern Virginia. Northwest River drainage near Indian Creek, City of Chesapeake. Photo: Gary P. Fleming / © DCR Natural Heritage. An 80-year old non-riverine swamp forest in the eastern part of the Great Dismal Swamp, near the headwaters of the Northwest River, City of Chesapeake. Red maple (Acer rubrum), sweetgum (Liquidambar styraciflua), bald cypress (Taxodium distichum), and water tupelo (Nyssa aquatica) share overstory dominance, while ferns and common greenbrier (Smilax rotundifolia) are abundant in the lower strata. Photo: William H. Moorhead III / © DCR Natural Heritage.
Late-season, exsiccated aspect of a seasonally flooded, non-riverine swamp forest dominated by young bald cypress (Taxodium distichum). Near Washington Ditch in the Great Dismal Swamp, City of Suffolk (Great Dismal Swamp National Wildlife Refuge). Photo: Gary P. Fleming / © DCR Natural Heritage. Non-Riverine Swamp Forest characterized by an extremely thick shrub layer dominated by shining fetterbush (Lyonia lucida) and a mixed overstory of loblolly and pond pines (Pinus taeda and P. serotina), Atlantic white-cedar (Chamaecyparis thyoides), and red maple (Acer rubrum). The site is a peat-filled, sandhill slough near the Blackwater River in Southampton County. Photo: Tom Rawinski / © DCR Natural Heritage.
Thick understory of cinnamon fern (Osmundastrum cinnamomeum var. cinnamomeum), Virginia chain fern (Woodwardia virginica), switch cane (Arundinaria tecta), and several ericaceous shrubs in a Non-Riverine Swamp Forest near South Quay, City of Suffolk . Photo: Gary P. Fleming / © DCR Natural Heritage.