Ultramafic Woodlands and Barrens
Vegetation of this group is confined to xeric uplands underlain by serpentinite, soapstone, talc-tremolite schist, and other ultramafic rocks. These naturally rare woodlands and barrens are only known from scattered locations in the mountains and Piedmont of Georgia, North Carolina , Virginia , Maryland , and Pennsylvania . Only five occurrences of ultramafic woodlands are documented in Virginia : three in the Piedmont (Amherst , Franklin , and Nelson Counties) and two in The Glades region of the southern Blue Ridge plateau (Grayson County). Ultramafic barrens are endemic to Virginia and occur in only two of the above sites as patch-mosaics with ultramafic woodlands (Franklin County and Grayson County). Habitats are relatively gentle, rocky uplands with very dry, shallow, magnesium- and iron-rich soil. Ultramafic woodlands and barrens are the only terrestrial communities documented in Virginia that grow in soils with Ca:Mg ratios < 1.
The original vegetation of the Piedmont examples was probably open, stunted savanna of post oak (Quercus stellata), blackjack oak (Quercus marilandica), and Virginia pine (Pinus virginiana) over little bluestem (Schizachyrium scoparium). The present-day stands are semi-closed and more heavily dominated by Virginia pine as the result of disturbances such as cutting and fire exclusion. The Blue Ridge occurrences are open woodlands dominated by post oak, pitch pine (Pinus rigida), and eastern white pine (Pinus strobus), with a relatively dense herb layer containing little bluestem, big bluestem (Andropogon gerardii), balsam ragwort (Packera paupercula, = Senecio pauperculus), skunk meadowrue (Thalictrum revolutum) and other xerophytes. Also present are anomalous populations of several species more typical of wetland habitats, e.g ., Canada burnet (Sanguisorba canadensis) and pine-barren death-camas (Zigadenus leimanthoides).
Vegetation of the two ultramafic barrens sites differs considerably. The dry, rocky Piedmont habitat is dominated by little bluestem (Schizachyrium scoparium), prairie ragwort (Packera plattensis = Senecio plattensis), and glade wild quinine (Parthenium auriculatum). Noteworthy associates include northern dropseed (Sporobolus heterolepis), Menge's fame-flower (Talinum mengesii), Pitcher's stichwort (Minuartia patula var. patula), and Kate's Mountain clover (Trifolium virginicum). The southern Blue Ridge barren features considerable seasonal wetness and a peculiar mixture of upland and wetland species, but is treated here as a community of the Terrestrial System. Little bluestem and indian grass (Sorghastrum nutans) are the dominant grasses, while white colicroot (Aletris farinosa), narrowleaf whitetop aster (Sericocarpus linifolius), narrow-leaved mountain-mint (Pycnanthemum tenuifolium), and balsam ragwort (Packera paupercula, = Senecio pauperculus) are characteristic forbs. Coastal plain disjuncts such as crossleaf milkwort (Polygala cruciata), twisted yellow-eyed-grass (Xyris torta), pitted nutrush (Scleria muhlenbergii), yellow screwstem (Bartonia virginica), and Virginia meadow-beauty (Rhexia virginica) are numerous in seasonally wet gravel.Along with unusual edaphic conditions, fire probably played a key role in maintaining natural ultramafic woodlands and barrens in the pre-settlement landscape. Today, following decades of fire exclusion and other disturbances, these communities are extremely rare in Virginia and globally. Quarrying has partly or wholly destroyed occurrences of ultramafic woodlands at two sites and poses a serious threat at another site. Other threats include fire exclusion, woody species encroachment, grazing, agriculture, and development.
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|A remnant ultramafic woodland on talc-chlorite-tremolite schist in Franklin County.Photo: Irvine Wilson / © DCR Natural Heritage.|
|A remnant ultramafic barren on talc-tremolite-chlorite schist in Franklin County. Photo: Tom Rawinski.|
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