By Drew Chaney, Center for Urban Habitats
The Acidic Piedmont Prairie/Savanna is one of the most frequent types of grassland still occurring on the uplands of the Virginia Piedmont.
Acidic Piedmont Prairies/Savannas occupy soils that are less fertile than those where Basic Piedmont Prairies/Savannas occur. They typically occur on gentle, flat or rolling uplands underlain by metasedimentary or felsic granitic rocks and have nutrient-poor, shallow, sandy or clay soils unsuitable for agricultural production. The name “acidic” refers to the relatively low pH of these soils, though it is somewhat misleading since the Basic grassland types can overlap Acidic grasslands in soil chemistry. The main difference in the soils is that Basic grasslands have high levels of soluble base cations, while Acidic grasslands have nutrient-poor soils with few soluble base cations.
Most remaining examples occur in utility corridors, in large unplowed fields, and along roadsides. A few more sizable patches occur in Quantico Marine Corps Base (Fauquier Co.) and Fort Barfoot (Nottoway, Dinwiddie, and Brunswick Cos.). The graminoid-dominated structure of these is maintained by random incendiary fires that mimic those set by Indigenous peoples as well as ones caused by lightning strikes. Most other examples are now maintained by periodic mowing. Though these grasslands typically have an open structure free of trees or large shrubs, we hypothesize that they represent remnants of the herbaceous layers of woodlands and savannas now long extirpated. Due to the hillier terrain of much of the Virginia Piedmont, it is likely that natural fire intervals would have been between 5 and 8 years in most areas, allowing for woody vegetation to develop further. True prairie structure would only have occurred in patches on land forms that experienced more frequent fires.
Unlike many other grassland ecosystems, such as the Midwestern tallgrass prairies, the primary threats to Acidic Piedmont Prairies/Savannas are herbicide spraying along roadsides and utility corridors, and impacts of heavy machinery used for logging.
Vegetation is characterized by warm-season grasses such as little bluestem (Schizachyrium scoparium), yellow prairie grass (Sorghastrum nutans), Elliott’s (Andropogon gyrans) and splitbeard (A. ternarius) bluestems, broomsedge (Andropogon virginicus), poverty and silky oatgrasses (Danthonia spicata, D. sericea), small-fruited and Ashe’s panic grasses (Dichanthelium dichotomum var. dichotomum and D. commutatum var. ashei), purple lovegrass (Eragrostis spectabilis), beaked panic grass (Coleataenia anceps), and silver plumegrass (Erianthus alopecuroides).
Forbs associated with this vegetation type include a wide variety of generalist and acidophilic conservative heliophytes including goldenrods (especially Solidago bicolor, S. nemoralis, S. rugosa, S. juncea, S. odora, S. pinetorum, S. puberula), thoroughworts (especially Eupatorium hyssopifolium, E. pubescens, E. pilosum, and E. rotundifolium), flat-topped white aster (Sericocarpus asteroides), Maryland golden-aster (Chrysopsis mariana), grass-leaved blazing star (Liatris pilosa), Small’s ragwort (Packera anonyma), purple-disc sunflower (Helianthus atrorubens), yellow wild indigo (Baptisia tinctoria), clasping milkweed (Asclepias amplexicaulis), narrow-leaf mountain-mint (Pycnanthemum tenuifolium), pussytoes (Antennaria parlinii, A. plantaginifolia), whorled loosestrife (Lysimachia quadrifolia), pinweeds (Lechea spp.), yellow flax (Linum medium var. texanum), bracken fern (Pteridium aquilinum), low St. Andrew’s cross (Hypericum stragulum), native bush-clovers (Lespedeza hirta, L. procumbens, L. repens, L. violacea, L. virginica) goat’s-rue (Tephrosia virginiana) and bird’s foot violet (Viola pedata).
Woody species are present in Acidic Piedmont Prairies/Savannas, and mainly consist of seedlings of tree species such as oaks (Quercus alba, Q. coccinea, Q. falcata, Q. phellos, Q. velutina), pines (Pinus echinata, taeda, virginiana), and hickories (Carya spp), as well as blackberries (Rubus cuneifolius, R. pensilvanicus), and dewberries (Rubus flagellaris). Common greenbrier (Smilax rotundifolia) is a frequent component of the shrub layer, as is winged sumac (Rhus copallinum). Ericaceous species such as blueberries (Vaccinium pallidum, V. x marianum), deerberry (Vaccinium stamineum), black huckleberry (Gaylussacia baccata), and maleberry (Lyonia ligustrina) are usually present. Woody vegetation in these ecosystems is typically maintained by mowing nowadays, while historically, fire would have been the primary factor in keeping these prairies open.
Rare species present in Acidic Piedmont Prairies/Savannas include rattlesnake-master (Eryngium yuccifolium), Elliott’s prairie grass (Sorghastrum elliottii), Torrey’s mountain-mint (Pycnanthemum torreyi), and Michaux’s sumac (Rhus michauxii). The VA/NC/SC endemic large-flowered aster (Symphyotrichum grandiflorum) can also be found in these ecosystems.
Heliophyte: a plant species requiring high levels of sunlight.
Acidophile: a plant species that requires or prefers growing in soils with a low pH (below 6.5).
Conservative: a species that is restricted to high-quality, relatively undisturbed natural ecosystems.
Felsic – a rock with a high percentage of light colored minerals, such as quartz and feldspar.
Graminoid – a member of the grass (Poaceae), sedge (Cyperaceae), or rush (Juncaceae) families.
Base cations – the soil-borne elements calcium, magnesium, potassium, and sodium, most of which are essential for plant growth. Heavily weathered soils will tend to have fewer of these nutrients and to be more acidic.