Low-Elevation Boulderfield Forests and Woodlands
This group contains open forests and woodlands occupying relatively unweathered boulderfields at elevations mostly below 975 m (3,200 ft). Low-Elevation Boulderfield Forests and Woodlands are known from the northern and central Appalachian regions, extending from Vermont and New Hampshire south to Virginia and West Virginia. In Virginia, these communities are widely scattered throughout the mountains on steep side slopes of ridges, often in zones below cliffs and large outcrops. They are also common along the Virginia side of the Potomac River Gorge between Washington, D.C., and Great Falls, and locally upstream. Stand composition varies greatly with substrate, aspect, and slope position. Sweet birch (Betula lenta var. lenta) is usually the sole woody invader of large-block sandstone and quartzite boulderfields, forming pure stands of gnarled, spreading trees. Here, Virginia-creeper (Parthenocissus quinquefolia) is sometimes the only low-growing plant able to become established in the deep interstices between boulders. On somewhat more weathered or less blocky boulderfields, chestnut oak (Quercus montana, =Quercus prinus) or mixtures of chestnut oak, northern red oak (Quercus rubra), blackgum (Nyssa sylvatica), and sweet birch, along with a greater diversity of shrubs and herbs, may prevail. Cool, north-facing, sandstone/quartzite boulderfields frequently support some eastern hemlock (Tsuga canadensis) and, locally, disjunct populations of mountain paper birch (Betula cordifolia, = Betula papyrifera var. cordifolia).
On base-rich metabasalt boulderfields of the northern Blue Ridge, basswood (Tilia americana var. americana and var. heterophylla), white ash (Fraxinus americana), and red oak (Quercus rubra) are characteristic trees. Characteristic shrubs and herbs on basic boulderfields include eastern hop-hornbeam (Ostrya virginiana), red elderberry (Sambucus racemosa var. pubens, = Sambucus pubens), wild hydrangea (Hydrangea arborescens), flowering raspberry (Rubus odoratus), Virginia-creeper (Parthenocissus quinquefolia), yellow jewelweed (Impatiens pallida), marginal wood fern (Dryopteris marginalis), wood nettle (Laportea canadensis), white-flowered leafcup (Polymnia canadensis) and the state-rare herb robert (Geranium robertianum). Rich boulderfields on calcareous slopes along rivers of the northern Piedmont and Ridge and Valley support open stands of basswood, sugar maple (Acer saccharum), and white ash, with bladdernut (Staphylea trifolia) abundant in the shrub layer and a variety of mosses, bulblet fern (Cystopteris bulbifera), yellow jewelweed, and other calciphilic herbs forming dense mats on rock surfaces.
Communities in this group are uncommon in Virginia; their classification and distributional status need further assessment. They are floristically distinguished from communities of the High-Elevation Boulderfield Forests and Woodlands group by the preponderance of widely distributed plants and the near-absence of elevation-limited northern and Southern Appalachian species.References: Fleming (1999), Fleming (2002a), Fleming (2007), Fleming et al. (2007), Fleming and Coulling (2001), Fleming and Moorhead (2000), Harrison et al . (1989), Hupp (1983a), Rawinski et al . (1994), Rawinski et al . (1996).
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Mesic quartzite rubble supports a relatively diverse assemblage of low-cover herbs under large oaks (Quercus montana and Q. rubra) and tulip-tree (Liriodendron tulipifera). Jackson Hollow, Bull Run Mountains Natural Area Preserve, Prince William County. Gary P. Fleming / © DCR Natural Heritage.
Thin woodland of sweet birch (Betula lenta var. lenta) occupies a relatively fine quartzite talus deposit on Trayfoot Mountain (Shenandoah National Park). Gary P. Fleming / © DCR Natural Heritage.
Sugar maple (Acer saccharum)-dominated boulderfield on basic, intrusive rocks along the Potomac River Gorge, Fairfax County (Turkey Run Park). Gary P. Fleming / © DCR Natural Heritage.
Gnarled sweet birch (Betula lenta var. lenta) trees on deeply piled quartzite talus on the northern Blue Ridge. Near Blackrock, Rockingham County (Shenandoah National Park). Gary P. Fleming / © DCR Natural Heritage. Central Appalachian Basic Boulderfield Forest on metabasalt (greenstone) talus on Saddleback Mountain, Greene County (Shenandoah National Park). White-flowered leafcup (Polymnia canadensis) and wood nettle (Laportea canadensis) dominate a sparse herb layer under an overstory of white ash (Fraxinus americana) and basswood (Tilia americana var. americana). Gary P. Fleming / © DCR Natural Heritage.