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The Natural Communities of Virginia Classification of Ecological Community Groups second approximation (Version 2)

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The Natural Communities of Virginia
Classification of Ecological Community Groups

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. There is at least one outlying occurrence in Lancaster County. 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-poplar (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). Small trees and shrubs include stiff dogwood (Cornus foemina), spicebush (Lindera benzoin var. benzoin and var. pubescens), and southern bayberry (Myrica cerifera var. 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), Kentucky lady-slipper (Cypripedium kentuckiense); state-rare), 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 hispidus var. nitidus), brome sedge (Carex bromoides ssp. bromoides), and 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 of both Maryland and Virginia, and appear to represent a type that occurs north to southern New England. Piedmont basic seepage swamps often occur in edge-zones or abandoned oxbows of floodplains, where groundwater is discharged from the base of an adjoining slope. The most characteristic species of this type appear to be red maple, green ash, white ash (Fraxinus americana), tulip-poplar, spicebush, skunk-cabbage (Symplocarpus foetidus), cinnamon fern (Osmunda cinnamomea var. cinnamomea), spotted jewelweed (Impatiens capensis), and greenfruit clearweed (Pilea pumila).

Reference: Fleming (2002a).

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

Coastal Plain Basic Seepage Swamp in a calcareous 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 Northern Piedmont / Lower New England Basic Seepage Swamp along Dead Run in Fairfax County (Turkey Run Park). Photo: Gary P. Fleming.

Communities in this group are not well documented or protected in Virginia and should be high priorities for future inventory and conservation. Two community types have been classified to date. The endemic Coastal Plain Basic Seepage Swamp is supported by seven plot samples but needs additional inventory and sampling to determine the full extent of its distribution and compositional variation. The Northern Piedmont / Lower New England type, based on plot samples from both Maryland and Virginia, is more problematic, as examples further north are considered to be “acidic,” according to the USNVC. Environmental data are not available for the Maryland samples of this unit, but data from recently sampled Virginia plots indicate that soils are moderately base-rich. This type appears to be intermediate between strongly basic and strongly acidic seepage swamps in floristic composition and environmental affiliations. Click on any highlighted CEGL code below to view the global USNVC description provided by NatureServe Explorer.

  • Acer rubrum – Fraxinus pennsylvanica / Lindera benzoin / Symplocarpus foetidus Forest
    Northern Piedmont / Lower New England Basic Seepage Swamp
    USNVC: = CEGL006406
    Global/State Ranks: G4G5/S2?

  • Acer rubrum – Fraxinus pennsylvanica / Pilea fontana Packera aurea – (Scirpus lineatus) Forest
    Coastal Plain Basic Seepage Swamp
    USNVC: = CEGL006413
    Global/State Ranks: GNR/S1S2

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