Piedmont / Mountain Floodplain Forests and Swamps
These temporarily to seasonally flooded forests encompass most river floodplain habitats of the northern and western Piedmont and major mountain valleys, except those that are cleared.
From the James River north, sandy river banks and first-bottom terraces that are frequently (but shortly) flooded support forests dominated by silver maple (Acer saccharinum) and boxelder (Acer negundo var. negundo), with herb layers containing many broad-leaved forbs such as wood-nettle (Laportea canadensis), clear-weed (Pilea pumila), and white snakeroot (Ageratina altissima var. altissima). Higher, better drained, sandy or silty river floodplains support mixed forests of sycamore (Platanus occidentalis), black walnut (Juglans nigra), hackberry (Celtis occidentalis), American elm (Ulmus americana), and boxelder, with understories of paw-paw (Asimina triloba) and spicebush (Lindera benzoin var. benzoin). Herb layers in the mixed floodplains are usually very lush with nutrient-demanding, early-season species such as Virginia bluebells (Mertensia virginica), Canada waterleaf (Hydrophyllum canadense), wild ginger (Asarum canadense), yellow trout-lily (Erythronium americanum ssp. americanum), white trout-lily (Erythronium albidum), Potomac River only), wild blue phlox (Phlox divaricata), miami-mist (Phacelia purshii), large solomon's-seal (Polygonatum biflorum var. commutatum), striped violet (Viola striata), and many others. Eastern cottonwood (Populus deltoides ssp. deltoides) is a frequent, early-successional pioneer of these habitats, while sycamore and river birch (Betula nigra) are pioneering invaders of stabilized depositional river bars.
Forested swamps are scattered in backswamps and sloughs 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 northern 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). 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, Carex typhina, Carex squarrosa, Carex grayi).
Most Piedmont/Mountain Floodplain Forests have been severely impacted by clearing, grazing, agricultural run-off, and invasive introduced weeds. Many of these forests have been destroyed and few, if any, of the remaining stands are in excellent or pristine condition. Large, well-developed swamp forests are uncommon in the Piedmont and rare in the mountains. Some of them have been destroyed or hydrologically altered by dams and reservoirs.
References: Fleming (2002a), Fleming (2007), Fleming and Coulling (2001), Fleming and Patterson (2004), Lea (2000), Rawinski et al . (1996), Vanderhorst (2000).Click here for more photos of this ecological community group.
© DCR-DNH, Gary P. Fleming.