Department of Conservation and Recreation
Conserve. Protect. Enjoy.
Department of Conservation and Recreation
Table of ContentsRocky Bars and Shores
This group contains seasonally flooded to intermittently exposed woodland, shrub, and herbaceous vegetation of bouldery and cobbly depositional bars, or less frequently bedrock exposures, on the shores and islands of high-gradient streams. Communities in this group are scattered throughout the Virginia mountains and Piedmont, primarily along major rivers and their largest tributaries but also along some smaller streams. Habitats are influenced by a frequent regime of powerful flood scouring, including occasional scouring by ice flows during the winter months. Substrates vary from bedrock outcrops to deeply piled cobbles and boulders, with soils consisting of fine to coarse alluvial materials deposited among the rocks.
Vegetation varies from woodlands to entirely herbaceous or sparse. Common water-willow (Justicia americana) is one of the most widespread and characteristic herbs of rocky bars and shores in Virginia, often forming extensive, nearly monospecific beds. Another well-marked herbaceous type of this group, known from bouldery banks and bars along a number of mountain streams, is dominated by twisted sedge (Carex torta). The typical overstory on wooded depositional bars consists of moderately to widely spaced, often battered or flood-trained specimens of sycamore (Platanus occidentalis), river birch (Betula nigra), and willows (primarily black willow [Salix nigra] and Carolina willow [Salix caroliniana]). Stands located on broader, bedrock floodplains that are scoured by frequent powerful floods and ice flows have more diverse overstories of green ash (Fraxinus pennsylvanica), swamp white oak (Quercus bicolor), eastern boxelder (Acer negundo var. negundo), American elm (Ulmus americana), sycamore, river birch, and other trees. Shrubs include silky dogwood (Cornus amomum and Cornus obliqua), American hornbeam (Carpinus caroliniana), and common ninebark (Physocarpus opulifolius var. opulifolius).
The herbaceous flora of rocky bars and shores is highly variable and includes species common to both ephemeral fine-textured sand, gravel, or mud bars (e.g., halberd-leaf rose-mallow [Hibiscus laevis]) and somewhat more stable, bedrock habitats (e.g., big bluestem [Andropogon gerardii]). The clasping-leaved dogbane (Apocynum sibiricum) is also particularly characteristic. These communities are threatened by rampantly invasive weeds such as purple loosestrife (Lythrum salicaria) and Johnson-grass (Sorghum halepense), which are readily dispersed and established in high-energy alluvial environments.
References: Hupp (1983b), Hupp (1986), Fleming (2007), Fleming and Moorhead (1996), Lea (2000), Vanderhorst (2000).
Click here for more photos of this ecological community group.
© DCR-DNH, Gary P. Fleming.
Download a spreadsheet of compositional summary statistics for each of the community types listed below.
