Alabama Ketona Dolomite Glade

This system consists of open glades and related vegetation on Ketona dolomite slopes found in Bibb County, Alabama, in the vicinity of the Little Cahaba River. The vegetation includes herbaceous, shrubland, and open woodlands, which occur on thin soils or outcrops of Ketona dolomite. Juniperus virginiana, Quercus muehlenbergii, Pinus palustris, Croton alabamensis, Sabal minor, and Phyllanthopsis phyllanthoides are the dominant woody plants of the woodlands. The system supports eight endemic and numerous disjunct plant taxa and has very high conservation value based on rare plants.

The vegetation of the system includes a mixture of herbaceous, shrubland, and open woodlands, which occur on thin soils surrounding outcrops of Ketona dolomite. Juniperus virginiana, Quercus muehlenbergii, Pinus palustris, Croton alabamensis, Sabal minor, and Phyllanthopsis phyllanthoides (= Leptopus phyllanthoides) are the dominant woody plants of the woodlands. Schizachyrium scoparium is a frequent grass in this system and is commonly associated with Andropogon gerardii and other calcium-loving, drought-tolerant plant species. Stunted woodlands are primarily dominated by Quercus muehlenbergii interspersed with Juniperus virginiana and occur on variable-depth-to-bedrock soils. The trees may 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 or fissures in the bedrock). Small-scale stands of annual Sporobolus spp. may be prominent in some examples. More than 60 plant taxa of conservation concern occur on or near these glades, marking them as one of the most significant reservoirs of botanical diversity in the eastern United States. Eight endemic taxa were recently found and newly described: Castilleja kraliana, Coreopsis grandiflora var. inclinata, Dalea cahaba, Erigeron strigosus var. dolomiticola, Liatris oligocephala, Onosmodium decipiens, Silphium glutinosum, and Spigelia alabamensis (= Spigelia gentianoides var. alabamensis). Seven Alabama state records were discovered: Solanum pumilum (last collected in 1837 and presumed extinct), Astrolepis integerrima (disjunct from Texas), Paronychia virginica (bridging a gap between Arkansas and Virginia), Baptisia australis var. australis, Rhynchospora capillacea, Rhynchospora thornei, and Spiranthes lucida.

This system consists of open glades and related vegetation on Ketona dolomite slopes found in Bibb County, Alabama, in the vicinity of the Little Cahaba River (Allison and Stevens 2001).

Fire and periodic drought both play a role in the natural dynamics of this system. Fires help manage this system by restricting woody growth and maintaining the more open glade structure. Historically, grazing by wild and domestic ungulate species represented a significant disturbance regime. Regionally significant drought cycles affect severity of other disturbance regimes. Some portions of sites for this system are so droughty and rocky that woody succession is severely retarded, and fuels are either sparse of composed of low annual grasses and scattered forbs (Landfire 2007a). Severe droughts kill tree saplings growing in cracks and potholes, helping to retain the open character of the glades (Quarterman et al. 1993).

The most critical anthropogenic threat to native glade and rock outcrop vegetation is their conversion to human-created land uses, including residential development, quarries, industrial development, infrastructure development, and others (TNC 1996c). Rocky glades and outcrops may be the last areas to be converted to development and housing due to the unsuitability of the soil to septic tanks. Other common threats and stressors include both the removal of disturbance and the effects of inappropriate or too intensive or constant disturbance. These areas often attract off-road-vehicle use.

Fire plays a critical role in the maintenance of most native grasslands, which may surround or interfinger with rocky glades. 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). More information is needed about the particular appropriate ranges of fire-return times and intensities in the various systems. The actual rocky or gravelly glades may not support sufficient fuel to consistently carry fire, but in the adjacent or interpenetrating perennial grasslands, occasional surface fire will retard woody plant encroachment and help maintain herbaceous diversity, as will, to an extent, grazing or mowing (Duffey et al. 1974). In addition to occasional fire, periodic drought may also be important in regulating woody plant encroachment into native grasslands. It is believed that these native glade-grassland systems have evolved under a combined system of grazing, drought, and periodic fire (Duffey et al. 1974, Estes et al. 1979, Noss 2013).

Fragmentation of glades and their accompanying native grasslands, barrens, and savannas occurs with the development of housing and industrial sites, as well as the construction of roads, which not only function as firebreaks, limiting the areas that can be burned with one ignition event, but which make it more difficult to mitigate the effects of smoke on human populations and their activities. In many cases, these glade-grassland systems were once extensive on the landscape, but have now been reduced to scattered and isolated remnant patches, presenting conservation and management challenges. These disturbances have had damaging effects on fragile soil profiles and plant and animal species. These combined impacts also foster a trend toward biotic homogenization, which results in the gradual replacement of ecologically distinct natural communities by those dominated by weedy generalists (McKinney and Lockwood 1999). In other cases, the grassland and/or glade system naturally occurs in small isolated patches occurring within an otherwise forested matrix.

Many glade sites, have been used as pastures, or as dumping grounds for trash (Quarterman et al. 1993). The spread of invasive exotic plants (particularly Ligustrum species and Lonicera species shrubs, as well as Lespedeza cuneata, Ailanthus altissima, and Albizia julibrissin) will fundamentally alter the character of glades and their accompanying native grasslands. Some of these exotics are allelopathic, thereby presenting a greater threat to native species (N. Murdock pers. comm.). Opportunistic native increaser plant species (e.g., Juniperus virginiana) can also shade out light-requiring herbaceous plants (TNC 1996c).

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 small-patch system is restricted to Ketona dolomite slopes found in Bibb County, Alabama, in the vicinity of the Little Cahaba River.