Southern Appalachian Dry Limestone Forest

This system includes dry to dry-mesic calcareous forests of the Southern Ridge and Valley region of Alabama and Georgia, extending north into Tennessee, Kentucky, Virginia and adjacent West Virginia. It includes calcareous forests on lower escarpments of the Cumberland Plateau and other related areas. Examples occur on a variety of different landscape positions and occur on generally deeper soils than glade systems of the same regions. This system is distinguished from those farther north in the Ridge and Valley by its relatively southern location in the region, in an area which is transitional to the "Oak-Pine-Hickory" region. High-quality and historic examples are typically dominated by combinations of Quercus species and Carya species, sometimes with Pinus species and/or Juniperus virginiana as a significant component in certain landscape positions and with particular successional histories. These forests occur in a variety of habitats and are the matrix vegetation type that covers portions of the landscape under natural conditions. Examples can occur on a variety of topographic and landscape positions including valley floors, sideslopes, and lower to midslopes. Fire frequency and intensity are factors determining the relative mixture of deciduous hardwood versus evergreen trees in this system. Much of this system is currently composed of successional forests that have arisen after repeated cutting, clearing, and cultivation of the original forests. The range of this system is primarily composed of circumneutral substrates, which exert an expected influence on the composition of the vegetation.

Natural vegetation consists of forests (or woodlands) dominated most typically by Quercus alba, Quercus muehlenbergii, Quercus stellata, and Quercus shumardii, with varying amounts of Carya spp., Acer saccharum, Acer floridanum (= Acer barbatum), Acer leucoderme, Acer rubrum, and other species. This system concept also includes successional communities that have been impacted by logging or agriculture, including upland forest types dominated by Liriodendron tulipifera, Pinus spp., Juniperus virginiana, and Robinia pseudoacacia.

Examples of this forest and woodland system occur usually on dry sites, on a variety of topographic and landscape positions, including sideslopes (particularly south- and west-facing ones), ridges, and knobs, as well as valley floors, depending on where the base-rich rock is present or crops out, and where the soils are influenced by calcareous/circumneutral geology. Elevation is generally between 200 and 500 m. In some landscapes, the ridges and ridgetops will more likely be composed of sandstones and other more weather-resistant and acidic materials.

Fire frequency and intensity are factors determining the relative mixture of deciduous hardwood versus evergreen trees in this system. Presettlement fire-return intervals are believed to have ranged from 3 to 14 years from both lightning and Native American ignitions. These frequent surface fires maintained the grassy understory and kept hardwoods and shrubs from dominating the understory and forming a midstory layer. These fires occurred in the dormant season with occasional growing-season mosaic fires (most likely occurring infrequently once or twice every 20 to 25 years) (Landfire 2007a). Occasionally, during extensive droughts, mixed-severity or stand-replacement fires could occur, especially in drier stands or those containing Juniperus virginiana. In addition, local thunderstorm-caused blowdowns and windthrow created gaps on a small but continual basis. More extensive regional disturbances included winter ice storms. Dense stands of middle to older aged pines (where present) were susceptible to periodic mortality from bark beetle epidemics, and younger Juniperus virginiana trees were killed by periodic droughts.

The most critical anthropogenic threats include removal of the characteristic dominant hardwoods and a lack of fire. Removal of the characteristic dominant hardwoods (primarily Quercus species and Carya species) through logging may result in a stand dominated by wind-blown or bird-dispersed tree species, including Acer rubrum, Celtis spp., Fraxinus americana, Juglans nigra, Juniperus virginiana, Liquidambar styraciflua, Liriodendron tulipifera, Prunus serotina, Robinia pseudoacacia, Sassafras albidum, Ulmus americana, and the exotic Ailanthus altissima. Lack of fire in the system leads to a closing of the subcanopy, and consequent loss of ground layer diversity. Patches dominated by Juniperus virginiana (or rarely with Pinus taeda and/or Pinus echinata) are artifacts of past disturbance and succession in the absence of fire. These are likely to eventually succumb to drought, fire or insect damage (in the case of Pinus species, which are generally atypical due to the high base status in the soils). Another major threat is conversion to human-created land uses, including residential development, quarries, industrial development, and infrastructure development (TNC 1996c).

This system is endemic to the Southern Ridge and Valley and the Cumberland Plateau escarpment in Alabama, Georgia, Tennessee, Kentucky, and southwestern Virginia.