Northern Hardwood Ecosystem Description

In the Southern Appalachians, northern hardwood forests occur at elevations between 4000 and 5500 ft (1200 – 1650 m), mostly in high elevation coves but also on upper slopes with relatively high precipitation. North of the Asheville Basin, northern hardwoods are also likely to occur on high base rock at higher elevations (Simon et al. 2004). Due to low temperatures and increased rainfall at high elevations, conditions on these sites are usually mesic. Soils comprise various upland series including umbric dystrochrepts and typic haplumbrepts (Schafale & Weakley 1990).

Mesophytic tree species dominate the canopy, particularly American beech (Fagus grandifolia), yellow birch (Betula alleghaniensis) and yellow buckeye (Aesculus flava).  Depending on geographic region and subtype, associated canopy species may include basswood (Tilia americana var. heterophylla), sugar maple (Acer saccharum), white ash (Fraxinus americana), black cherry (Prunus serotina), eastern hemlock (Tsuga canadensis), red spruce (Picea rubra) or northern red oak (Quercus rubra) (Schafale & Weakley 1990; Ulrey 1999; Pearson 2004). Yellow birch-spruce forests and high elevation red oak forests belong in the broader ecological group of high elevation hardwood forests. However, their fire ecology is different from the northern hardwoods.

Towards higher elevations, northern hardwoods grade into spruce-fir forests, grass or heath balds or high elevation rocky summits. As elevation decreases, they become rich cove forests on mesic sites or chestnut oak forests on drier sites. On drier, more exposed sites of equivalent elevation, northern hardwoods may grade into high elevation red oak forest (Schafale & Weakley 1990).

Typical northern hardwood forests and their subtypes (boulderfield forests and beech gaps/slopes) cover about 197,000 acres (= 3.5 %) in the Southern Appalachians (Simon et al. 2004). In addition to seedlings of canopy species like yellow birch, beech, buckeye and maple, understory species may include mountain ash (Sorbus americana), Allegheny serviceberry (Amelanchier laevis), striped maple (Acer pensylvanicum), and hophornbeam (Ostrya virginiana). The most common or abundant species in the usually dense and diverse herb layer are Pennsylvania sedge (Carex pensylvanica), wood nettle (Laportea canadensis), Roan snakeroot (Ageratina altissima var. roanensis) and wild leeks, also known as ramps (Allium tricoccum) (Schafale & Weakley 1990; Simon et al. 2004).

Boulderfields are relicts of periglacial activity in the Pleistocene and offer a variety of wet and dry microsites. They are dominated by yellow birch with gooseberry (Ribes glandulosum) as a characteristic shrub species. Beech gaps/slopes can occur in south-facing gaps or on ridge tops within the spruce-fir zone where spruce and fir are actually lacking. In well-developed beech gaps, beech is the typical canopy species over dense beds of Pennsylvania sedge (Schafale & Weakley 1990).

Northern hardwoods provide important habitat for various bird species like the Appalachian yellow-bellied sapsucker (Sphyrapicus varius appalachiensis), ruffed grouse (Bonasa umbellus), black-throated blue warbler (Dendroica caerulescens), veery (Catharus fuscescens), rose-breasted grosbeak (Pheucticus ludovicianus) and blue-headed vireo (Vireo solitarius). The sapsucker, a subspecies strictly endemic to the Southern Blue Ridge, prefers rather open high-elevation forests with dead trees for cavities, while ruffed grouse, warbler and vireo like dense brush and shrub understory. The grosbeak favors edge habitats with a mixture of dense shrubs and trees (Hunter et al. 1999; Chris Kelly, personal communication).

Other animals using the northern hardwood habitat are southern rock vole (Microtus chrotorrhinus), red squirrel (Tamiasciurus hudsonicus) and the Carolina northern flying squirrel (Glaucomys sabrinus coloratus). The flying squirrel is a federally endangered species that occurs in mature stands within the spruce-fir / northern hardwood ecotone. Long-tailed shrew (Sorex dispar) might inhabit rock outcrops within the northern hardwood zone and southern water shrew (Sorex palustris punctulatus) can be found along mountain streams above 3200 ft (975 m) (Chris Kelly, personal communication).