Ozark Limestone Glade and Barrens

This system is found primarily in the Interior Highlands of the Ozark, Ouachita, and Interior Low Plateau regions with scattered occurrences in northern Missouri. It occurs along moderate to steep slopes and steep valleys on primarily southerly to westerly facing slopes. Limestone and/or dolomite bedrock typify this system with shallow, moderately to well-drained soils interspersed with rocks. These soils often dry out during the summer and autumn, and then become saturated during the winter and spring. Schizachyrium scoparium dominates this system and is commonly associated with Andropogon gerardii, Bouteloua curtipendula, and calcium-loving plant species. Stunted woodlands primarily dominated by Quercus muehlenbergii interspersed with Juniperus virginiana occur on variable-depth-to-bedrock soils. Fire is the primary natural dynamic, and prescribed fires help manage this system by restricting woody growth and maintaining the more open glade structure.

Schizachyrium scoparium dominates this system and is commonly associated with Andropogon gerardii, Bouteloua curtipendula, and calcium-loving plant species. Stunted woodlands primarily dominated by Quercus muehlenbergii interspersed with Juniperus virginiana occur on variable-depth-to-bedrock soils. The trees typically occur as islands in a wider herbaceous or rocky area. The islands are found in microenvironments where the soil depth and available water are sufficient to support trees (e.g., depressions in the bedrock). Other woody plants associated with this system (within their ranges) include Quercus shumardii, Cercis canadensis, Ulmus alata, Fraxinus quadrangulata, Juniperus ashei, Acer saccharum, and Frangula caroliniana. Other herbaceous taxa include Silphium trifoliatum, Silphium terebinthinaceum, Liatris spp., Symphyotrichum oblongifolium, Castilleja coccinea, Stenaria nigricans (= Hedyotis nigricans), Phemeranthus (= Talinum) spp., Sedum spp., and Panicum flexile. Small-scale stands of annual Sporobolus spp. may be prominent in some examples. In some examples, small-scale seepage areas may contain Eleocharis compressa, Nothoscordum bivalve, Isoetes butleri, and Hypoxis hirsuta.

This system is found primarily along moderate to steep slopes and steep valleys on primarily southerly to westerly facing slopes. Limestone and/or dolomite bedrock typify this system with shallow, moderately to well-drained soils interspersed with rocks. Soils are affected by the bedrock chemistry and tend to have high levels of calcium and potassium and a relatively high pH. Due to seasonal rainfall patterns and the extremely thin soils, these soils dry out during the summer and autumn and become saturated during the winter and spring. In northern Alabama (Moulton Valley), the stratum on which the system is found is a type of "marl." Seeps may occur where impervious rock strata meet relatively permeable limestone.

The thin, dry soil characteristic of this system dries out during the growing season and much of the vegetation dries, as well. This allows fires to spread easily and these fires restrict the abundance of woody species. In high-quality examples where the natural fire regime operates, small trees and shrubs are limited to the edges of stands or small "islands" of deeper soil that retain more moisture while grasses are the dominant vegetation. Sparsely vegetated areas between the dominant grassy zones contain most of the rare species found in this system (Ware 2002). In the absence of fire, from active suppression or a lack of fuel due to excessive grazing, woody species can increase greatly.

Disruption of the natural fire regime leads to conversion of this system to shrublands, typically dominated by Juniperus virginiana, though Rhus aromatica and Rhus copallinum can be frequent, too, or sometimes Quercus-dominated woodlands (Baskin and Baskin 2000). This disruption can occur as a result of active fire suppression in the glades or surrounding landscape or a lack of fuel due to removal of the herbaceous vegetation, usually due to prolonged overgrazing. In addition to removing fuel for fires, prolonged overgrazing reduces diversity and production of most native herbaceous species but does not reduce shrub invasion (Martin and Houf 1993) and reduces competition for weedy species that can tolerate the glade conditions. Excessive grazing can also lead to increased erosion as the soil is not held by the dominant herbaceous species. In the absence of fire and appropriate disturbance in the landscape matrix, the areas with the most shallow soils (e.g., the glades) may be the only open areas persisting in a series of woody shrub thickets. Without fire or other disturbance, Juniperus species, Quercus species and other hardwoods quickly regenerate, shading out the herbaceous plants, and leading to a shift in species diversity from the ground layer to the upper woody strata, resulting in a net loss of species diversity (Taft et al. 1995). At sites with intermediate levels of woody encroachment, a signal of restoration potential is an inverse relationship between woody stem density and ground layer species richness (Taft 2009).

This system is found primarily in the Interior Highlands of the Ozark, Ouachita, and the Interior Low Plateau regions ranging east to southern Ohio and including the Knobs region and Cliff section of Kentucky, the Cumberland Plateau escarpment of Tennessee, the Western Valley of the Tennessee River, and the Moulton Valley of northern Alabama.