Ecological dynamics

From http://explorer.natureserve.org/servlet/NatureServe?searchSystemUid=ELEMENT_GLOBAL.2.723013

The vegetation system coincides with the Appalachian (Hemlock)-Northern Hardwood Forest (CES202.593) (NatureServe 2007).

This forested system of the eastern U.S. ranges from central New England west to Lake Erie and south to the higher elevations of Virginia and West Virginia. It is one of the matrix forest types in the northern part of the Central Interior and Appalachian Division. Northern hardwoods such as Acer saccharum, Betula alleghaniensis, and Fagus grandifolia are characteristic, either forming a deciduous canopy or mixed with Tsuga canadensis (or in some cases Pinus strobus). Other common and sometimes dominant trees include Quercus spp. (most commonly Quercus rubra), Liriodendron tulipifera, Prunus serotina, Acer rubrum, and Betula lenta. It is of more limited extent and more ecologically constrained in the southern part of its range in northern parts of Virginia and West Virginia.

From Landfire http://www.landfire.gov/index.php:
Vegetation Description:
In the northern part of the range, dominant overstory species include eastern hemlock (Tsuga canadensis), American beech (Fagus grandifolia), sugar maple (Acer saccharum) and yellow birch (Betula allegheniensis). While this community as a whole occurs across a wide range of topographic conditions, the species mix can vary considerably. Hemlock will dominate the overstory on cool/moist sites at higher elevations and in shaded coves, valley bottoms and riparian areas. Moist bottomlands and footslopes may also contain a larger component of yellow birch, white ash (Fraxinus americana) and sycamore (Platanus occidentalis) (Whitney 1990). Locally, on slopes, sugar maple becomes more abundant, resulting in a beech-hemlock-sugar maple complex (Braun 2001). Other common associates include red maple (Acer rubrum), black cherry (Prunus serotina), black birch (Betula nigra), basswood (Tilia americana) and cucumber magnolia (Magnolia acuminata). The understory and mid-story are usually well developed and include hobblebush (Viburnum alnifolium), mapleleaf viburnum (Viburnum acerifolium), witch hazel (Hamamelis virginiana) , serviceberry (Amelanchier alnifolia), pin cherry (Prunus pensylvanica), large-leaved holly (Ilex monticola), and alternative-leaved dogwood (Cornus alternifolia). Common herbaceous species include wild lily of the valley (Maianthemum canadense), sensitive fern (Onoclea sensibilis), shining clubmoss (Lycopodium lucidulum), Dryopteris spinulosa (Dryopteris spinulosa), mountain woodsorrel (Oxalis montana) and partridgeberry (Mitchella repens) (Lutz 1930, Braun 2001).

In the southern part of the range, dominant vegetation is generally in two to three layers. The canopy in well developed late seral conditions is composed of eastern hemlock (Tsuga canadensis) (most common) and or white pine (Pinus strobus) mixed with various hardwoods including tulip poplar (Liriodendron tulipifera), American beech (Fagus grandifolia), black and white oaks (Quercus velutina, Q. alba), black birch (Betula lenta), bigleaf and umbrella magnolias (Magnolia macrophylla, M. tripetala). In the southern Appalachians, Fraser magnolia (M. fraseri) and silverbell (Halesia carolina) may also be found. There may be gaps with a younger cohort of the same set of species. A dense, low to high shrub layer of great laurel (Rhododendron maxima) and sometimes mountain laurel (Kalmia latifolia) is often present. Yellowroot (Xanthorhiza simplissima) may occur immediately adjacent to streams in sandy/silty alluvial deposits in gaps. Few if any herbs are found and bryophyte and hepatophyte cover is generally restricted to downed wood, tree/shrub boles, and rocks/boulders.

BpS Dominant and Indicator Species
Symbol Scientific Name Common Name
FAGR Fagus grandifolia American beech
TSCA Tsuga canadensis Eastern hemlock
ACSA3 Acer saccharum Sugar maple
BEAL2 Betula alleghaniensis Yellow birch
TIAM Tilia americana American basswood
LITU Liriodendron tulipifera Tuliptree
PIST Pinus strobus Eastern white pine
QUVE Quercus velutina Black oak

Disturbance Description
Non-Fire Disturbance: This system is dominated by long-lived, mesic species that form multi-layered uneven-aged forests over time. Canopy dynamics are dominated by single and multiple disturbances encouraging gap phase regeneration (Abrams and Orwig 1996). Larger disturbances include windthrow, insect attack and ice storms. Although stand-replacing wind events are rare, small to medium blowdown events are more common and occur at greater frequency on the plateau and exposed side slopes (Ruffner and Abrams 2003). Localized insect and disease outbreaks can create small to medium canopy gaps.

Running the VDDT model resulted in 0.9% disturbance (fire and/or wind, weather, stress) annually, consistent with disturbance rates documented by Runkle (1981, 1985) and others. Wind, weather, stress alone resulted in 0.7% disturbance annually.

Fire Regime Description: Historically, this system was probably only subject to occasional fires. Fires that did occur may have been catastrophic and may have lead to even-aged stands of pine and hemlock (NatureServe 2007).
Due to the predominance of cool, moist site conditions, surface and replacement fires are extremely rare, occurring at 700-1000yr intervals. Most protected sites are essentially fire free. The principal cause of fuel formation leading to fire in northern hardwood ecosystems is broad-scale, storm-driven windthrow of catastrophic proportions (Hough 1963, Runkle 1982).