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.

Vegetation consists primarily of forests dominated by Picea rubens, Abies fraseri, or occasionally by Sorbus americana. Betula alleghaniensis, Tsuga canadensis, and Quercus rubra are the only other locally common canopy species. Acer rubrum, Betula lenta, Magnolia acuminata, and Magnolia fraseri may occur. Lower strata are most typically dominated by mosses, ferns or forbs, but a few associations have dense shrub layers of Rhododendron catawbiense, Rhododendron maximum, or Vaccinium erythrocarpum.

This system occurs at elevations typically above about 1300 m (4300 feet), up to the highest peaks. Species distribution follows an elevational gradient, with Picea rubens-dominated stands occurring between 1370 and 1675 m, mixed stands between 1675 and 1890 m, and Abies fraseri stands above 1890 m (Whittaker 1956 cited in Nicholas and Zedaker 1989). Examples occur on most of the landforms that are present in this elevational range; most sites are strongly exposed and convex in shape. 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 factors in the structure and dynamics of this vegetation. Concentration of air pollutants has been implicated as an important anthropogenic stress in recent years. In recent decades, the balsam woolly adelgid (Adelges piceae), an introduced insect, has killed almost all of the mature Abies fraseri. The saplings are not susceptible, resulting in many dense stands of young trees. Soils are generally very rocky, with the matrix ranging from well-weathered parent material to organic deposits over boulders. Soils may be saturated for long periods from a combination of precipitation and seepage. Any kind of bedrock may be present, but most sites have erosion-resistant felsic igneous or metamorphic rocks (White et al. 1993).

This system is naturally dominated by stable, uneven-aged forests, with canopy dynamics dominated by gap-phase regeneration on a fine scale, as well as larger disturbances resulting primarily from ice storms (Nicholas and Zedaker 1989). Despite the extreme climate, Picea rubens is long-lived (300-400 or more years) (White et al. 1993). Both Picea and Abies seedlings are shade-tolerant, and advanced regeneration is important in stand dynamics. Natural disturbances are primarily wind and ice storms, but may include debris avalanches or very rarely lightning fires (White 1984b, Nicholas and Zedaker 1989, White et al. 1993). Occasional extreme wind events disturb larger patches on the most exposed slopes. Fire is a very rare event under natural conditions, due to the wetness and limited flammability of the undergrowth (Korstian 1937 cited in White et al. 1993), and return intervals have been estimated between 500 and 1000 years or more. If fires do occur, they are likely to be catastrophic, because few of the species are at all fire-tolerant. Anthropogenic fires fueled by logging slash were extremely destructive, turning large expanses of this system into grass-shrub-hardwood scrub (e.g., Dolly Sods, Graveyard Fields) that has not recovered to conifer dominance after 100 years.

Estimates of the loss in extent of the Southern Appalachian spruce-fir forest range from 50% (White 1984c) to 90% (Korstian 1937 cited in Nicholas and Zedaker 1989). The primary disturbances are weather-related, including ice storms and windthrow, occurring at intervals of 100 to 200 years. There have been multiple events of wind and ice damage in single- and multiple-tree patches that have cumulatively damaged a lot of the canopy in spruce forests (M. Schafale pers. comm. 2013). Rare extreme weather events are also important large-scale disturbances. In contrast to northern stands of Picea-Abies vegetation, insect outbreaks are not important disturbances (M. Schafale pers. comm. 2013). Windthrow produces dense Abies seedlings if overstory is mature (Eyre 1980). In general, fire is extremely rare in Southern Appalachian Picea-Abies vegetation, and fire is not a primary factor in its successional dynamics.

Anthropogenic disturbances and stresses, beyond the effects of logging, have had major effects on dynamics in these systems in recent decades. Anthropogenic fires fueled by logging slash were extremely destructive, turning large expanses of this system into grass-shrub-hardwood scrub (e.g., Dolly Sods, Graveyard Fields) that has not recovered to conifer dominance after 100 years. An introduced insect, the balsam woolly adelgid (Adelges piceae), has killed almost all of the mature Abies fraseri. Saplings are not susceptible, and dense stands have established from advanced regeneration in some areas. Other areas were converted to long-term successional vegetation dominated by deciduous trees such as Sorbus americana, Betula alleghaniensis, and Prunus pensylvanica (White and Cogbill 1992), as well as Rubus and/or shrubs. It is unclear if the young fir stands will establish seedlings before they too are killed. Stress caused by concentrated air pollutants on the mountaintops has been suggested as an important anthropogenic stress and as a cause of observed growth declines in Picea rubens. Climate changes may severely affect this system. Global warming can be expected to raise the lower elevational limit and greatly reduce the land area available to this system.

This system ranges from the Balsam Mountains and Great Smoky Mountains of North Carolina and Tennessee northward to the mountains of western Virginia and eastern West Virginia.