Piedmont / Mountain Swamp Forests
This group contains seasonally flooded deciduous forests of backswamps and sloughs in the floodplains of northern and western Piedmont and mountain-region rivers and large streams. Communities of this group are most common in the broad, clay-rich floodplain deposits of Piedmont Mesozoic basins, but occur locally throughout the northernl and western parts of Virginia. Habitats generally have some hummock-and-hollow microtopography, with maximum flooding depths in hollows of 50 to 70 cm (20 to 28 in). Soils are usually white- or orange-mottled clay loams and loamy clays, with moderately low to moderately high base status.
Characteristic trees of these swamps include pin oak (Quercus palustris), swamp white oak (Quercus bicolor), willow oak (Quercus phellos), green ash (Fraxinus pennsylvanica), red maple (Acer rubrum), American elm (Ulmus americana) and sweetgum (Liquidambar styraciflua). In the larger river backswamps, where flooding depths may exclude oaks, stands are usually dominated by combinations of silver maple (Acer saccharinum), red maple, and green ash. Small trees and shrubs include winterberry (Ilex verticillata), common elderberry (Sambucus canadensis), silky dogwood (Cornus amomum), and American hornbeam (Carpinus caroliniana ssp. caroliniana and ssp. virginiana). High-climbing woody vines, including poison ivy (Toxicodendron radicans var. radicans), grapes (Vitis spp.), and trumpet-creeper (Campsis radicans), are also typical. The herb layers of these communities are quite species-rich because of microtopographic diversity, but species tolerant of seasonal inundation are prevalent, including lizard's-tail (Saururus cernuus), false nettle (Boehmeria cylindrica), common wood reedgrass (Cinna arundinacea), winged monkeyflower (Mimulus alatus), and various sedges (e.g., Carex tribuloides var. tribuloides, Carex typhina, Carex squarrosa, Carex grayi). Large, well-developed swamp forests are somewhat uncommon in the Piedmont and rare in the mountains. Some of them have been destroyed or hydrologically altered by dams and reservoirs.Reference: Fleming (2002a), Fleming and Patterson (2004).
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Southern water-plantain (Alisma subcordatum) in a recently drawn down, seasonally flooded slough along Cub Run in Fairfax County (Cub Run Stream Valley Park). The overstory here consists primarily of pin oak (Quercus palustris) and green ash (Fraxinus pennsylvanica). Photo: Gary P. Fleming / © DCR Natural Heritage. Large colonies of common wood reedgrass (Cinna arundinacea), growing under swamp white oak (Quercus bicolor) and American elm (Ulmus americana), characterize the drier, late-season aspect of this swamp along Elklick Run in Fairfax County (Fairfax County Park Authority lands). Photo: Gary P. Fleming / © DCR Natural Heritage. Seasonally flooded backswamp along South Fork Quantico Creek at Prince William Forest Park, Prince William County. The overstory is primarily pin oak (Quercus palustris) while the dominant herbs are false nettle (Boehmeria cylindrica) and blunt broom sedge (Carex tribuloides var. tribuloides). Photo: Gary P. Fleming / © DCR Natural Heritage.