Piedmont Oak - Hickory Woodlands, Savannas, and Grasslands
Piedmont military base training areas ("impact areas") that have been subject to frequent incendiary fires for about 80 years support the deciduous woodlands and savanna-like grasslands that constitute this group. As currently defined, these communities are endemic to Virginia and are now found only at Quantico Marine Base in the northern Piedmont (Fauquier, Prince William, and Stafford Counties) and Fort Pickett in the southern Piedmont (Dinwiddie and Nottoway Counties), where they cover hundreds of hectares. Habitats at both sites are rolling uplands underlain by granitic rocks. Soils are generally sandy and range from extremely to strongly acidic, with relatively low base cation levels. However, in a small (20-25 ha) area of Fort Pickett that is underlain by a sill of intrusive Triassic diabase, soils are dark, slightly acidic to circumneutral loams with relatively high calcium and magnesium levels. A few similar stands also occur at Fort A.P. Hill in the inner Coastal Plain of Caroline County.
Although communities of this group are strongly influenced by an artificial disturbance regime, they are Virginia's only extant examples of vegetation that is shaped by random burns of a size, frequency, and intensity comparable to those of putative pre-settlement fire regimes. Thus, they may provide important clues about the probable composition and environmental dynamics of woodlands that burned under a regime of natural fires and fires intentionally set by Native Americans beginning in the early Holocene.
Stand physiognomy encompasses semi-closed woodlands with little understory; graminoid-rich savannas with widely spaced trees; and dense thickets of small, sprout-origin trees. Field experience has demonstrated that physiognomy can be temporally and spatially dynamic, with vegetation structure in a given stand frequently changing in response to fire or a lengthy interval without fire. Variable mixtures of white oak (Quercus alba), black oak (Quercus velutina), southern red oak (Quercus falcata), scarlet oak (Quercus coccinea), post oak (Quercus stellata), and mockernut hickory (Carya tomentosa), along with scattered loblolly and shortleaf pines (Pinus taeda and (Pinus echinata), form the woodland overstories. Understories are highly variable in both density and composition. Dense herb layers are rich in both grasses and legumes. Abundant species include little bluestem (Schizachyrium scoparium var. scoparium), indian grasses (Sorghastrum nutans and Sorghastrum elliottii), broomsedges (Andropogon virginicus var. virginicus, Andropogon ternarius, and Andropogon gyrans), poverty oatgrass (Danthonia spicata), silver plumegrass (Erianthus alopecuroides), tick-trefoils (Desmodium spp.), and bush-clovers (Lespedeza spp.). Goldenrods (Solidago spp., especially Solidago nemoralis var. nemoralis and Solidago juncea), thoroughworts (Eupatorium spp.), and other composites are characteristic of the diverse late-flowering flora of the woodlands. Additional species that are important in some stands include purple false-foxglove (Agalinis purpurea), purple three-awn grass (Aristida purpurascens), scaly blazing star (Liatris squarrosa var. squarrosa), narrow-leaf mountain-mint (Pycnanthemum tenuifolium), orange coneflower (Rudbeckia fulgida), and papillose nutrush (Scleria pauciflora var. pauciflora).
Stands on basic soil have a more species-rich herbaceous flora characterized by forbs, including nettle-leaf sage (Salvia urticifolia), glade wild quinine (Parthenium auriculatum), naked-flowered tick-trefoil (Hylodesmum nudiflorum), green-and-gold (Chrysogonum virginianum var. virginianum), perfoliate bellwort (Uvularia perfoliata), sunflowers (Helianthus strumosus and Helianthus divaricatus), small white snakeroot (Ageratina aromatica), skunk meadow-rue (Thalictrum revolutum), and hog-peanut (Amphicarpaea bracteata).
Although most pre-settlement grasslands were likely to have been part of woodland patch-mosaics, there may have been patches of larger, mostly treeless grasslands that constituted the Piedmont analogue to Midwestern prairies. There are no remnants of such prairies in the contemporary landscape, and it is now impossible to determine their original extent; but the grassland component of military-base savannas, as well as patches of native herbaceous vegetation in some old fields and powerline clearings, probably have plant species compositions similar to pre-settlement grasslands. Open woodlands, savannas, and grasslands provide habitat for many of the Piedmont's light-loving, state-rare plants, including stiff goldenrod (Solidago rigida var. rigida), Torrey's mountain-mint (Pycnanthemum torreyi), earleaf false foxglove (Agalinis auriculata), and American bluehearts (Buchnera americana).The largest known population in the world of the globally rare, federally listed shrub Michaux's sumac (Rhus michauxii) is associated with the fire-influenced woodlands at Fort Pickett.
References: Fleming (2002a), Fleming et al. (2001), Maxwell (1910).
Click here for more photos of this ecological community group.
© DCR-DNH, Gary P. Fleming.