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The Natural Communities of Virginia
Classification of Ecological Community Groups

Second Approximation (Version 2.7)
Information current as of February, 2016

Table of Contents Table of Contents

Calcareous Fens

This group includes both calcareous hillside or foot-slope spring seeps and prairie-like wetlands on stream or river floodplain terraces constantly saturated by perched groundwater or seepage from adjacent slopes. These small-patch wetlands are widely scattered in carbonate rock districts of western Virginia, primarily in valleys of the Ridge and Valley province. Graminoid-dominated "prairie fens" examples are limited in Virginia to a few sites in the west-central Ridge and Valley region, most notably along the South River in Augusta County.

The vegetation of hillside/foot-slope fens is often a patch-mosaic of shrubs and herbaceous openings. Habitats typically have irregular or hummock-and-hollow microtopography, with areas of muck and abundant gravel or travertine marl deposits in the seepage rills. Soils, which are typically derived from underlying limestone or dolomite, are slightly to moderately alkaline with high calcium levels. Strictly defined, fens are minerotrophic wetlands with organic soils > 40 cm deep. Because they usually have only superficial organic soil layers, most of the Virginia communities in this group are technically "seeps," although we retain the term "fen" due to its wide application to various base-rich seepage wetlands in the southeastern United States; see Weakley and Schafale (1994) for additional discussion. Common shrubs include willows (Salix spp.), smooth alder (Alnus serrulata), swamp rose (Rosa palustris), alder-leaved buckthorn (Rhamnus alnifolia), and chokeberries (Aronia arbutifolia and Aronia prunifolia). Herbaceous species that are more or less diagnostic of calcareous fens or seeps include several sedges (e.g ., Carex flava, Carex hystericina, Carex interior, Carex schweinitzii, Carex suberecta, Carex tetanica), showy lady's-slipper (Cypripedium reginae), small-headed rush (Juncus brachycephalus), bog twayblade (Liparis loeselii), large-leaved grass-of-parnassus (Parnassia grandifolia), swamp lousewort (Pedicularis lanceolata), shining ladies'-tresses (Spiranthes lucida), and needle beaksedge (Rhynchospora capillacea). Other common herbs include bristly-stalk sedge (Carex leptalea var. leptalea), royal fern (Osmunda spectabilis), and golden ragwort (Packera aurea = Senecio aureus).

Vegetation of prairie fens is diverse and generally graminoid-dominated; patch-dominance of sedges (e.g., Carex stricta, Carex tetanica, Carex interior, Carex buxbaumii, Carex prairea, Carex trichocarpa, Carex emoryi), baltic rush (Juncus balticus var. littoralis), bald spikerush (Eleocharis erythropoda), freshwater cordgrass (Spartina pectinata), switchgrass (Panicum virgatum var. virgatum) and, at a single known Virginia site, holy grass (Anthoxanthum hirtum) is typical. Many low-cover forbs are also components, including several state-rare and unusual species, such as queen-of-the-prairie (Filipendula rubra), prairie loosestrife (Lysimachia quadriflora), spotted joe-pye weed (Eutrochium maculatum var. maculatum), northern winged loosestrife (Lythrum alatum), hooded skullcap (Scutellaria galericulata), rough avens (Geum laciniatum), purple fringeless orchid (Platanthera peramoena), and marsh pea (Lathyrus palustris). Reed canary grass (Phalaris arundinacea) is a native perennial grass that frequently becomes invasive in disturbed wet prairies.

The ecological factors that keep these communities open are not well understood, and many examples appear to be threatened by shrub and tree invasion. Ditching, grazing, and introduced weeds are additional threats to these naturally rare wetlands, most of which are unprotected and are high priorities for conservation.

References: Artz and Krouse (1967), Carr (1939), Fleming (1999), Fleming and Coulling (2001), Fleming and Van Alstine (1999), Ogle (1989).

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Central Appalachian Calcareous Shrub Fen / Seep along Peters Mill Run in the Massanutten Mountains, where calcareous shales provide the requisite soil chemistry. Characteristic plants at this site include smooth alder (Alnus serrulata), royal fern (Osmunda spectabilis), and rigid sedge (Carex tetanica). Photo © Gary P. Fleming.
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Eastern indian paintbrush (Castilleja coccinea), golden ragwort (Packera aurea), and field horsetail (Equisetum arvense) dominate a Ridge and Valley calcareous seep in Montgomery County. Photo: Irvine Wilson / © DCR Natural Heritage
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Wet, prairie-like grassland in the Mill Creek valley of Bath County. Emory's sedge (Carex emoryi) is the prominent graminoid in the foreground. Gary P. Fleming / © DCR Natural Heritage.
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Baltic rush (Juncus balticus var. littoralis) and marsh fern (Thelypteris palustris) form dominance patches in a wet prairie along a tributary of the South River in Augusta County (Warehouse Marsh Natural Area). Photo: Gary P. Fleming.
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Dense growth of tussock sedge (Carex stricta), freshwater cordgrass (Spartina pectinata), and woolgrass (Scirpus cyperinus) in a wet prairie along the South River in Augusta County. Gary P. Fleming / © DCR Natural Heritage.

About half of the known occurrences in Virginia have been documented with data from 16 plots (map), resulting in the classification of three community types. The second of these (Ridge and Valley Calcareous Fen / Seep) is supported by only two plots and must be considered provisional pending data collection from a wider sample of related vegetation. A single community type of Shenandoah Valley prairie fen has been classified, based on five plots from two sites in Augusta County, and one site in Bath County. The likelihood of finding additional examples of this group in Virginia is small. Click on any highlighted CEGL code below to view the global USNVC description provided by NatureServe Explorer.
  • Alnus serrulata / Osmunda spectabilis - Carex tetanica - Carex leptalea Shrubland
    Central Appalachian Calcareous Shrub Fen / Seep
    USNVC: = CEGL008408
    Global/State Ranks: G1?/S1

  • Packera aurea - Carex interior - Carex hystericina - Parnassia grandifolia Herbaceous Vegetation (PROVISIONAL)
    Ridge and Valley Calcareous Sedge Fen / Seep
    USNVC: no equivalent
    Global/State Ranks: -/S1

  • Carex (tetanica, prairea) - Eleocharis erythropoda - Lysimachia quadriflora Herbaceous Vegetation
    Shenandoah Valley Prairie Fen
    USNVC: = CEGL006170
    Global/State Ranks: G1Q/S1

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