THE NATURAL COMMUNITIES OF VIRGINIA
CLASSIFICATION OF ECOLOGICAL COMMUNITY GROUPS
Second Approximation (Version 2.5)
Information current as of February, 2012
Eastern Hemlock - Hardwood Forests
Forests of this group are characterized by the dominance or co-dominance of eastern hemlock (Tsuga canadensis
) in nearly every vertical stratum. Similar forests are known from the Great Lakes region and the northeastern United States and range as far south as the southern Blue Ridge of North Carolina and Tennessee. In Virginia, stands occupy mesic, sheltered habitats throughout the mountains and isolated, north-facing river bluffs and ravines of the Piedmont. A number of tree associates, especially sweet and yellow birches (Betula lenta
and Betula alleghaniensis
), northern red and chestnut oaks (Quercus rubra
) and (Quercus montana
), and eastern white pine (Pinus strobus
), usually contribute to mixed overstories, but the total cover of overstory and understory hemlock in these forests usually exceeds that of any other species. In the Piedmont, where hemlock forests may intergrade with Mesic Mixed Hardwood forests, American beech (Fagus grandifolia
) and white oak (Quercus alba
) are frequent associates. Understories vary from sparse to moderately dense; some stands have ericaceous shrub layers dominated by mountain-laurel (Kalmia latifolia
) or Catawba rhododendron (Rhododendron catawbiense
). Herbs are typically very sparse, but rare stands on basic or calcareous substrates have more diverse lower strata.
Eastern Hemlock - Hardwood Forests are closely related to Acidic Cove Forests but generally have a less diverse composition of woody species, a greater dominance of hemlock in all strata, and considerably lower species richness. Several notable old-growth hemlock forests occur in Virginia, including a stand in the Skidmore Fork drainage on Shenandoah Mountain (Rockingham County) and The Limberlost in Shenandoah National Park (Madison County). All eastern hemlock forests in Virginia are now highly threatened by the hemlock woolly adelgid (Adelges tsugae), an introduced insect that has caused extensive mortality in many stands.
References: Coulling (1999), Fleming (2002a), Fleming (2002b), Fleming et al. (2007), Harrison et al. (1989), Nemeth (1973), Rawinski et al. (1994), Rawinski et al. (1996).
Click on the images below to open a larger image in a separate window.
||Eastern hemlock (Tsuga canadensis)-dominated forest on a rocky, north-facing bluff in the northern Piedmont (Loudoun County). Photo Gary P. Fleming
||Eastern hemlock - Hardwood Forests prefer mesic, sheltered, montane habitats. Lewis Spring Falls, Page County (Shenandoah National Park).Photo: © Gary P. Fleming.
||An eastern hemlock - northern hardwood
forest on a high-elevation slope of Flagpole Knob above Skidmore Fork, Rockingham County (George Washington and Jefferson National Forests). Evergreen wood-fern (Dryopteris intermedia) dominates the herb layer.Gary P. Fleming / © DCR Natural Heritage.
||Nearly pure stand of eastern hemlock (Tsuga canadensis) on a steep, north-facing slope along North Branch Chopawamsic Creek,
Prince William Forest Park, Prince William County.
Gary P. Fleming / © DCR Natural Heritage.
REPRESENTATIVE COMMUNITY TYPES:
Three community types have been classified through analysis of data from 38 plots (map)
that were included in several large-scale regional classification projects. However, more plot data is needed from a wider geographic sample of this group. Additionally, there is considerable urgency to complete the needed data collection as intact stands of this group become fewer each year because of the hemlock woolly adelgid. Click on any highlighted CEGL code below to view the global USNVC description provided by NatureServe Explorer.
- Tsuga canadensis - Betula alleghaniensis / Maianthemum canadense Forest
Appalachian Hemlock - Northern Hardwood Forest
USNVC: = CEGL006109
Global/State Ranks: G4?/S2
- Tsuga canadensis - Fagus grandifolia - Quercus (montana, alba) Forest
Piedmont / Coastal Plain Hemlock - Hardwood Forest
USNVC: = CEGL006474
Global/State Ranks: G2G3/S1S2
- Tsuga canadensis - (Betula alleghaniensis, Quercus rubra) / Ilex montana - Rhododendron catawbiense Forest
Appalachian Hemlock / Catawba Rhododendron Forest
USNVC: = CEGL008513
Global/State Ranks: G1?/S1