Mountain / Piedmont Cliffs
Cliff communities consist of woodland, scrub, and herbaceous vegetation (often sparse) of very steep to precipitous bedrock faces. Calcareous cliffs develop on outcrops of limestone, dolostone, shale, mudstone, and metabasalt in the mountains (most frequently in the Ridge and Valley province), and occasionally on Triassic-age siltstone in Mesozoic basins of the Piedmont. Habitats are usually formed by incision of high-order streams and feature rugged and complex microtopography, with very high cover of exposed bedrock. Acidic cliffs of sandstone, quartzite, shale, and other felsic rocks occur under several geomorphic conditions, especially on slopes undercut by large streams or rivers and on resistant mountain-ridge caprock exposed by differential weathering of weaker underlying strata. Habitats vary with aspect and other environmental conditions. Local zones of ephemeral seepage may be present.
On south- and west-facing cliffs of carbonate formations, the surficial bedrock, hot microclimates, and associated edaphic stresses limit overall vegetation cover, woody growth, and species richness. Scattered scrub growth of eastern red cedar (Juniperus virginiana), chinquapin oak (Quercus muehlenbergii), hairy mock orange (Philadelphus hirsutus), poison ivy (Toxicodendron radicans var. radicans), and other shrubs is typical. Prevalent among herbaceous species are lithophytic calciphiles such as blackstem spleenwort (Asplenium resiliens), wall-rue (Asplenium ruta-muraria var. cryptolepis), ebony sedge (Carex eburnea), rocktwist (Draba ramosissima), three-flowered melic (Melica nitens), rock sandwort (Minuartia michauxii var. michauxii), plains muhly (Muhlenbergia cuspidata), cliff-brakes (Pellaea atropurpurea and Pellaea glabella ssp. glabella), moss phlox (Phlox subulata), and aromatic aster (Symphyotrichum oblongifolium).
On north-facing limestone or dolostone cliffs, habitats are open but sheltered, with limited direct solar exposure. Local zones of ephemeral seepage are frequent. Woody vegetation of these more mesic calcareous cliffs is comparatively diverse and often achieves larger size than on similar xeric sites. Typical woody plants include northern white-cedar (Thuja occidentalis), basswoods (Tilia americana var. americana and var. heterophylla), slippery elm (Ulmus rubra), and wild hydrangea (Hydrangea arborescens). Characteristic herbs include ebony sedge (Carex eburnea), bulblet fern (Cystopteris bulbifera), cliff stonecrop (Sedum glaucophyllum), northern bedstraw (Galium boreale), white-flowered leafcup (Polymnia canadensis), walking fern (Asplenium rhizophyllum), smooth rock cress (Boechera laevigata), lyre-leaf rock cress (Arabidopsis lyrata), fernleaf phacelia (Phacelia bipinnatifida), and Carolina saxifrage (Micranthes caroliniana). This is the principal habitat in Virginia for the globally rare, evergreen sub-shrub Canby's mountain-lover (Paxistima canbyi).
Cliffs on metamorphic and non-carbonate sedimentary rocks are poorly documented and known from relatively few siltstone, metasiltstone, and metabasaltic (greenstone) cliffs in the western Piedmont and Blue Ridge. Ordovician red mudstone/shale cliffs of the Ridge and Valley Province also support communities of this group. All require additional investigation. Habitats probably vary with aspect and other microhabitat conditions. Vegetation is generally dominated by umbilicate, foliose, and/or crustose lichens, with relatively sparse representation of vascular plants. Stunted trees and shrubs, e.g., white ash (Fraxinus americana), eastern red cedar (Juniperus virginiana), chestnut oak (Quercus montana), wild hydrangea (Hydrangea arborescens), and common ninebark (Physocarpus opulifolius var. opulifolius), occur in crevices or on cliff shelves. Herbaceous lithophytes such as wild columbine (Aquilegia canadensis), rock cresses (Boechera spp.), Allegheny stonecrop (Hylotelephium telephioides), field chickweed (Cerastium velutinum var. velutinum), maidenhair spleenwort (Asplenium trichomanes ssp. trichomanes), and blunt-lobed woodsia (Woodsia obtusa ssp. obtusa) also find scattered footholds.
The vegetation of acidic cliffs is generally dominated by lichens, with the umbilicate "rock tripe" species of Umbilicaria and Lasallia especially prominent (see the Lichen / Bryophyte Nonvascular Cliffs and Boulderfields ecological group for cliffs entirely lacking vascular plants). Vascular plants are confined to crevices and humus-covered shelves. On drier, south- to west-facing cliffs, vascular species may be very sparse and consist of stunted pines (Pinus virginiana, Pinus pungens, and/or Pinus rigida) ericaceous shrubs, and occasional herbaceous lithophytes such as mountain spleenwort (Asplenium montanum), silverling (Paronychia argyrocoma), and wild bleeding heart (Dicentra eximia). Sheltered, north- to east-facing cliffs often support more diverse shrub and herbaceous flora. Characteristic species include stunted eastern hemlock (Tsuga canadensis), evergreen rhododendrons (Rhododendron maximum and Rhododendron catawbiense), rock polypodies (Polypodium appalachianum and Polypodium virginianum), cliff saxifrage (Hydatica petiolaris), rock alumroot (Heuchera villosa), and wavy hairgrass (Avenella flexuosa). Shaded grottoes and "rock houses" on cliffs of the Cumberland Mountains in southwestern Virginia support colonies of small-flowered alumroot (Heuchera parviflora var. parviflora) and round-leaf catchfly (Silene rotundifolia).
Cliff communities are generally considered state-rare, but their conservation status needs further investigation. Because of inaccessible locations, stands seem immune from many types of anthropogenic disturbance. Scattered individuals of non-native weeds sometimes find footholds on xeric cliffs but are largely excluded by the hot, rocky substrates. On more mesic calcareous cliffs, Japanese honeysuckle (Lonicera japonica), Japanese stiltgrass (Microstegium vimineum), and other non-native plants find more favorable growing conditions and pose a serious threat to the sparse indigenous flora of these habitats.
Reference: Fleming (1999), Fleming and Coulling (2001).Click here for more photos of this ecological community group.
© DCR-DNH, Gary P. Fleming.Calcareous/mafic cliff vegetation is poorly inventoried and represented by only eight plots in Virginia (Fig. 1). The four classified types are conceptually broad and subject to modification if more data become available. The two acidic cliff community types listed below are USNVC associations defined using data collected in other states. Based on qualitative observations, it is apparent that similar or identical vegetation occurs in Virginia. However, these types most likely do not represent the full range of compositional variation on acidic cliffs in Virginia. Because of dangerous, mostly inaccessible habitats, it may not be possible to acquire many more quantitative samples of this group. Click on any highlighted CEGL code below to view the global USNVC description provided by NatureServe Explorer.
Download a spreadsheet of compositional summary statistics for each of the community types listed below.