Coastal Plain / Piedmont Basic Seepage Swamps
This group includes saturated deciduous forests occurring on moderately to highly base-rich substrates of the Coastal Plain and outer Piedmont. Stands in the former province occur in the bottoms of ravines that have downcut into Tertiary shell deposits or limesands. These are naturally rare, small-patch communities known from the dissected inner Coastal Plain of Surry, Isle of Wight, York, and James City Counties. Habitats consist of mucky, braided ravine bottoms saturated by constant groundwater seepage, and soils with high base status. Hummock-and-hollow microtopography is prevalent, and exposed shells are common in springs and rills. Green ash (Fraxinus pennsylvanica), red maple (Acer rubrum), and tulip-tree (Liriodendron tulipifera) are common overstory trees in most occurrences, but a subset of ravines on the south side of the James River features the unusual co-dominance of bald cypress (Taxodium distichum) or swamp tupelo (Nyssa biflora). Small trees and shrubs include stiff dogwood (Cornus stricta ), spicebush (Lindera benzoin var. benzoin and var. pubescens), and wax myrtle (Morella cerifera). A number of noteworthy mountain disjuncts have been documented in the herbaceous flora of these communities, including marsh marigold (Caltha palustris), rigid sedge (Carex tetanica), bog twayblade (Liparis loeselii; state-rare), swamp lousewort (Pedicularis lanceolata), and American false-hellebore (Veratrum viride). Reaching their northern limits are the southern species Florida adder's-mouth (Malaxis spicata), shadow witch orchid (Ponthieva racemosa), and drooping bulrush (Scirpus lineatus). Other characteristic herbs include lizard's-tail (Saururus cernuus), golden ragwort (Packera aurea = Senecio aureus), blackfruit clearweed (Pilea fontana), smooth bur-marigold (Bidens laevis), Carolina buttercup (Ranunculus carolinianus), common brome sedge (Carex bromoides spp. bromoides), and common wood reedgrass (Cinna arundinacea). The damp, fertile habitats are particularly susceptible to invasion by the introduced Japanese stiltgrass (Microstegium vimineum). The globally rare Tidewater interstitial amphipod (Stygobromus araeus) appears to be closely associated with groundwater in shell marl deposits.
Somewhat similar communities have been documented in the Piedmont and northern Coastal Plain of both Maryland and Virginia, and appear to represent a type that occurs north to southern New England. Piedmont / Northern Coastal Plain basic seepage swamps often occur in edge-zones or abandoned oxbows of floodplains, where groundwater is discharged from the base of an adjoining slope. Soils of these habitats are intermediate in chemistry - strongly acidic but with moderately high calcium , magnesium , and total base saturation levels. The most characteristic species of this type appear to be red maple, green ash, white ash (Fraxinus americana), tulip-tree, spicebush, skunk cabbage (Symplocarpus foetidus), cinnamon fern (Osmundastrum cinnamomeum var. cinnamomeum), orange jewelweed (Impatiens capensis), and clearweed (Pilea pumila). The rare Kentucky lady's-slipper (Cypripedium kentuckiense) occurs in a Coastal Plain stand of this type in Lancaster County .Reference: Fleming (2002a), Fleming (2007).
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Coastal Plain Calcareous Seepage Swamp in a shell-rich ravine bottom of the Grove Creek drainage southeast of Williamsburg, James City County. The abundant, large graminoid in the foreground is drooping bulrush (Scirpus lineatus). Photo: Gary P. Fleming.
Skunk cabbage (Symplocarpus foetidus) dominates a stand of Piedmont / Northern Coastal Plain Basic Seepage Swamp along Dead Run in Fairfax County (Turkey Run Park). Photo: Gary P. Fleming.