Ecological dynamics

A PROVISIONAL ECOLOGICAL SITE is a conceptual grouping of soil map unit components within a major land resource area (MLRA) based on the similarities in response to management. Although there may be wide variability in the productivity of the soils grouped into a provisional site, the soil vegetation interactions as expressed in the state and transition model are similar and the management actions required to achieve objectives, whether maintaining the existing ecological state or managing for an alternative state, are similar. Provisional sites are likely to be refined into more precise group during the process of meeting the APPROVED ECOLOGICAL SITE DESCRIPTION criteria.

This PROVISIONAL ECOLOGICAL SITE has been developed to meet the standards established in the National Ecological Site Handbook. The information associated with this ecological site does not meet the approved ecological site description standard, but it has been through a quality control and quality assurance processes to ensure consistency and completeness. Further investigations, reviews and correlations are necessary before it becomes an approved ecological site description.

The vegetation groupings described in this section are based on the terrestrial ecological system classification developed by NatureServe (Comer et al. 2003). Ecological systems represent recurring groups of biological communities that are found in similar physical environments and are influenced by similar dynamic ecological processes, such as fire or flooding. They are intended to provide a classification unit that is readily mappable, often from remote imagery, and readily identifiable by conservation and resource managers in the field.

Provisional Ecological Sites are intended to be very broad and should be considered first approximations based on existing available data. This PES covers multiple ecological systems. The systems included display gradual intergradation with elevation and so were initially grouped together. The ecological systems defined by NatureServe that occur within the reference community of this PES include:

1. Southern Appalachian Northern Hardwood Forest
2. Central and Southern Appalachian Spruce-Fir Forest
3. Central and Southern Appalachian Montane Oak Forest

Southern Appalachian Grass and Shrub balds also occur in small acreages on this PES. However, they are ecologically significant and so will be included in the narrative.

The following descriptions were taken directly from NatureServe:

Central and Southern Appalachian Northern Hardwood Forest: "This ecological system consists of hardwood forests of the higher elevation zones of the Southern Appalachians, generally above 1372 m (4500 feet) elevation within its primary range. Included are classic northern hardwood forests, dominated by various combinations of mesophytic hardwoods, which interfinger with high-elevation oak forests downslope or on more exposed aspects. The combination of elevation and aspect provides habitat for this system. Included in this system are limited areas locally known as "beech gaps" and "boulderfields." Stands are dominated by various combinations of Appalachian mesophytic trees, including Acer saccharum, Aesculus flava, Betula alleghaniensis, Fagus grandifolia, and Tsuga canadensis. Prunus serotina and Tilia americana var. heterophylla are occasionally abundant. Quercus rubra may be present but is not dominant."

Central and Southern Appalachian Spruce-Fir Forest: "This system consists of forests in the highest elevation zone of the Blue Ridge and parts of the Central Appalachians,
generally dominated by Picea rubens, Abies fraseri, or by a mixture of spruce and fir. Abies fraseri is the constituent fir from Mount
Rogers in Virginia southward. Examples occur above 1676 m (5500 feet) in the Southern Blue Ridge, but as low as 975 m (3200 feet)
at the northern range in West Virginia, and may range up to the highest peaks. Elevation and orographic effects make the climate cool
and wet, with heavy moisture input from fog as well as high rainfall. Strong winds, extreme cold, rime ice, and other extreme weather
are periodically important. The border of this system with adjacent systems is often gradational. The non-forested systems that occur in the same elevational zone may have transition zones of open woody vegetation, though some have sharp borders. The transition to Southern Appalachian Northern Hardwood Forest (CES202.029) or other systems that adjoin at lower elevations is marked by a
gradual shift in canopy dominance from conifers to hardwoods. In relatively undisturbed stands, the canopy composition and structure are the best way to determine the boundary of this system."

Central and Southern Appalachian Montane Oak Forest (may occur): "This system is found in the central and southern Appalachian Mountains. These high-elevation deciduous forests occur on exposed sites mostly between 915 and 1372 m (3000-4500 feet) elevation. The weathered soils are thin, nutrient-poor, low in organic matter, and acidic. The forests are dominated by Quercus spp. (most commonly Quercus rubra and Quercus alba ), with the individuals often stunted or wind-flagged. Castanea dentate sprouts are also common, but the importance of chestnut in these forests has been dramatically altered by chestnut blight. Ilex montana and Rhododendron prinophyllum are characteristic shrubs. Above 1372 m (4500 feet) elevation and below spruce-fir communities, this system tends to be replaced by the Southern Appalachian Northern Hardwood Forest (CES202.029)."

Southern Appalachian Grass and Shrub Balds: "This ecological system consists of dense herbaceous and shrubland communities in the highest elevational zone of the
southern Appalachians, generally above 1524 m (5000 feet) but occasionally to 1220 m (4000 feet), and at slightly lower elevations at
its northern limit in Virginia and West Virginia, and in the Cumberland Mountains along the Virginia-Kentucky border. Vegetation
consists either of dense shrub-dominated areas (heath balds) or dense herbaceous cover dominated by grasses or sedges (grassy balds).
The combination of high-elevation, non-wetland sites and dense herbaceous or shrub vegetation without appreciable rock outcrop conceptually distinguishes this system from all others in the southern Appalachians. However, the widespread areas of degraded spruce-fir with grass and shrub cover and the invasion of grassy balds by trees blur the distinction somewhat."

It is worthwhile to note and describe the beech gaps that occur in this ecological site. While there has been some debate about their origin, they are most likely a result of wind events (Russell 1953). Beech gaps occur on south-facing concave slopes, near the tops of major ridges (Fuller 1977) so it's likely that they receive more force from the wind. They persist in nearly uniform stands, reproducing primarily from sprouts. Russell (1953) documented that soils could be different in beech gaps (only weakly acid, no accumulation of peat, excessive depth of litter, and no podsolization) but whether that is due to the presence of beech or not is unclear. Fuller (1977) documented a combination of "interference mechanisms" that progressively increase spruce seed and seedling mortality in the beech gaps, thereby maintaining a nearly uniform stand of beech. Beech gaps have been negatively impacted by beech bark disease, an exotic insect-fungal pathogen complex that can result in mortality (Jenkins 2007). When queried, staff of the Great Smoky Mountains National Park (GRSM) report that many impacted sites still have beech present as young clones with only minor loading of beech bark disease. Where beech has been lost, the sites are either existing as a High Elevation Pin Cherry - Mountain Ash - Blackberry Thicket, or as a very young version of the northern hardwood forest (Troy Evans, personal communication).

This PES largely falls under public ownership and is primarily forested. It is mostly managed for recreation, watershed protection, and wildlife habitat. There are some small pastures and Christmas tree farms. Potentially the greatest threat to this PES is invasive, exotic species. In particular, numerous forest pests have been introduced that have had serious negative impacts.