Coastal Plain / Piedmont Seepage Bogs
The saturated shrub and herbaceous vegetation of this group occupies oligotrophic spring-heads, seepage slopes, and less frequently small, headwater stream bottoms. Sites are scattered throughout the Coastal Plain (except the maritime zone) and outer Piedmont, typically on lower or toe slopes, where groundwater is forced to the surface by impermeable clay layers. Surficial soils are usually peaty or sandy, very acidic, infertile, and covered by dense mats of Sphagnum mosses. The term "bog," as applied to these wetlands, is a technical misnomer, since most of these habitats are not true peatlands and none is an ombrotrophic system. This term, however, is now so widely used in the southeastern United States as a descriptor for open, acidic seepage wetlands that we have adopted it here for consistency (see Weakley and Schafale 1994 for additional discussion). Although early botanical explorers of Virginia frequently reported open boggy habitats, natural examples of these communities have nearly been extirpated by decades of fire exclusion, hydrologic alterations (ditching, draining, and impoundments), or outright destruction. The elimination of fire as an ecological process has allowed many former bogs to become overgrown with shrubs and trees. Good examples remain in military base training ("impact") areas at Quantico Marine Base (Fauquier and Prince William Counties), Fort A.P. Hill (Caroline County), and Fort Pickett (Nottoway County), where habitats have been subject to frequent incendiary burning for at least 50 years. Artificially maintained bog habitats are frequent in powerline clearings.
The vegetation of seepage bogs is usually a mosaic of scattered trees, shrub patches, and graminoid-dominated herbaceous patches. Typical woody species include sweetbay (Magnolia virginiana), poison sumac (Toxicodendron vernix), highbush blueberries (Vaccinium corymbosum, Vaccinium fuscatum, and Vaccinium formosum), possum-haw (Viburnum nudum), and smooth alder (Alnus serrulata). Among the most abundant herbaceous species, are twisted spikerush (Eleocharis tortilis), beakrushes (Rhynchospora spp.), narrow-leaved bluestem (Andropogon perangustatus), panic grasses (Dichanthelium dichotomum var. dichotomum and var. ensifolium), hairy umbrella-sedge (Fuirena squarrosa), meadow-beauties (Rhexia mariana var. mariana, Rhexia nashii, and Rhexia petiolata), clubmosses (Lycopodiella alopecuroides and Lycopodiella appressa), sundews (Drosera brevifolia, (Drosera capillaris), and Drosera rotundifolia var. rotundifolia), tawny cotton-grass (Eriophorum virginicum), bushy bluestem (Andropogon glomeratus var. glomeratus), Nuttall's reed-grass (Calamagrostis coarctata), yellow-eyed-grasses (Xyris spp.), yellow milkwort (Polygala lutea), and vervain thoroughwort (Eupatorium pilosum). Widely scattered, but nevertheless diagnostic, species of these bogs include red milkweed (Asclepias rubra), Rafinesque's seedbox (Ludwigia hirtella), large white fringed orchid (Platanthera blephariglottis var. conspicua), crossleaf milkwort (Polygala cruciata), purple pitcher-plant (Sarracenia purpurea ssp. venosa and ssp. purpurea), and large-flowered camas (Zigadenus glaberrimus). A large number of state-rare plants and several state-rare odonates (dragonflies and damselflies) are associated with seepage bogs.
In the Fall Line zone of the greater Washington, D.C. area, distinctive bogs which occurred on large terrace gravel deposits were well documented by McAtee (1918) nearly a century ago. Although most of these bogs were in Maryland and the District of Columbia and were subsequently destroyed by development, at least two remnants still occur in the northern Virginia suburbs.
References: Fleming (2002a), Fleming et al. (2001), McAtee (1918).
Click on the images below to open a larger image in a separate window.
|Giant plumegrass (Saccharum giganteum) and sweetbay (Magnolia virginiana) in a frequently burned seepage bog at Fort Pickett Military Reservation, Nottoway County. Photo: Gary P. Fleming.|
|A low, partly shrubby, hillside seepage bog in the frequently burned impact area at Fort Pickett Military Reservation, Nottoway County. Photo: Gary P. Fleming.|
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