Ozark Dry Acidic Glade and Barrens

This ecological system is primarily found in the Interior Highlands of the Ozark, Ouachita, and Interior Low Plateau regions with small occurrences in northern Missouri. It occurs on flatrock outcrops and along moderate to steep slopes or valley walls of rivers along most aspects. Parent material includes chert, igneous and/or sedimentary (sandstone, shale, siltstone) bedrock with well- to excessively well-drained, shallow soils interspersed with rock and boulders. These soils are typically dry during the summer and autumn, becoming saturated during the spring and winter. Grasses such as Schizachyrium scoparium and Sorghastrum nutans dominate this system with stunted oak species (Quercus stellata, Quercus marilandica) and shrub species such as Vaccinium spp. occurring on variable depth soils. Juniperus virginiana can be present and often increases in the absence of fire. In Kentucky, this system includes both sandstone glades found in the Shawnee Hills, as well as shale and siltstone glades and barrens found in the Knobs region, both in the Kentucky Interior Low Plateau. It also includes dry Quercus stellata-dominated barrens on Cretaceous-aged gravel substrates on the northern fringes of the Upper East Gulf Coastal Plain Ecoregion in southern Illinois and western Kentucky. This system is influenced by drought and infrequent to occasional fires. Prescribed fires help manage this system by maintaining an open glade structure.

Grasses such as Schizachyrium scoparium and Sorghastrum nutans dominate this system with stunted oak species (Quercus stellata, Quercus marilandica) and shrub species such as Vaccinium spp. occurring on variable depth soils. In the Shawnee Hills (EPA Ecoregions 71a, 72h of Woods et al. (2002)) of the Kentucky Interior Low Plateau, Quercus marilandica, Quercus stellata, and Juniperus virginiana are the dominant trees. Ulmus alata may be an understory component. Scattered shrubs, such as Vaccinium arboreum and Chionanthus virginicus, occur on the margins in patches of deeper soil. Quercus montana (= Quercus prinus) may be present in the eastern part of the range. Some other plants that may be associated with these glades include Andropogon ternarius, Danthonia spicata, Symphyotrichum patens var. patentissimum, Silene rotundifolia, Pityopsis graminifolia var. latifolia, Coreopsis grandiflora, Silene regia, Coreopsis lanceolata, Croton michauxii var. ellipticus (= Croton willdenowii), Sedum nuttallianum, Selaginella rupestris, and Portulaca pilosa.

This system occurs on flat rock outcrops and along moderate to steep slopes or valley walls of rivers along most aspects. Parent material includes chert, shale, igneous and/or sedimentary (sandstone, shale, siltstone) bedrock with well- to excessively well-drained, shallow soils interspersed with rock and boulders. These soils are typically dry during the summer and autumn, becoming saturated during the spring and winter.

Ericaceous shrubs found here are different from calcareous glades. 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 ericaceous shrubs can be frequent, too, or woodlands dominated by Quercus stellata, Quercus marilandica, or Quercus prinus. 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 lead to increased erosion and loss of soil as the roots of the formerly dominant herbaceous vegetation no longer hold the soil.

The most significant potential climate change effects over the next 50 years include shifts to dramatically drier or moister climate regimes. A cooler and wetter regime would most likely accelerate the trend toward woody plant encroachment, removing drought as a factor in its inhibition. A moderately drier regime during the growing season could favor the characteristic native grasses and forbs, which are adapted to these conditions better than the generalists. An extremely drier regime for an extended period of time could ultimately have negative effects.

This system is found in the Interior Highlands of the Ozark, Ouachita, and Interior Low Plateau regions, with rare and limited occurrences in the Upper East Gulf Coastal Plain of Kentucky and Illinois. That includes the Shawnee Hills (EPA Ecoregions 71a, 72h of Woods et al. (2002)) and Knobs region (EPA Ecoregions 70d, 71c of Woods et al. (2002)).