Kentucky Karst Prairie and Barrens

This system consists of open, prairielike vegetation of the northwestern Highland Rim (Pennyroyal Plateau) of Tennessee and adjacent Kentucky (EPA Ecoregion 71e; part of Subsection 223Eh; also possibly 71g, 223Ea in Kentucky). Stands are dominated by grasses and forbs with scattered shrubby vegetation and, occasionally, trees. The scattered trees are mainly Quercus falcata and Quercus imbricaria. In addition, Quercus alba and Quercus marilandica would also be expected. The primary dominant grass is Schizachyrium scoparium, with some Sorghastrum nutans present. Other more mesic to wet grasses, including Andropogon gerardii and Tripsacum dactyloides are restricted to ditches. The largest extant examples are presently found on Fort Campbell Military Reservation, Tennessee, where ecological burning and fires from live munitions use result in open herbaceous-dominated landscapes. This vegetation was the predominant type here in the early 1800s and probably originated from burning by Native Americans.

Stands of this system are dominated by grasses and forbs with scattered shrubby vegetation trees. The scattered trees are mainly Quercus falcata and Quercus imbricaria. The primary dominant grass is Schizachyrium scoparium, with some Sorghastrum nutans present. Other more mesic grasses (Andropogon gerardii, Tripsacum dactyloides) are restricted to ditches. Other herbaceous components may include Andropogon gyrans, Andropogon ternarius, Lespedeza capitata, Lespedeza virginica, Symphyotrichum novae-angliae (= Aster novae-angliae), Sericocarpus linifolius (= Aster solidagineus), Coreopsis major, Coreopsis tripteris, Helianthus angustifolius, Helianthus hirsutus, Helianthus mollis, Helianthus occidentalis, Silphium trifoliatum, Solidago juncea, Pycnanthemum tenuifolium, Pycnanthemum verticillatum var. pilosum (= Pycnanthemum pilosum), and Lobelia puberula. In addition, rare plants found in some examples include Agalinis auriculata (= Tomanthera auriculata), Prenanthes barbata, and Rudbeckia subtomentosa (rare east and south of the Mississippi and Ohio rivers). Other typical woody species include Cercis canadensis, Cornus florida, Ilex decidua, Prunus angustifolia, Rhus copallinum, Rosa carolina, and Symphoricarpos orbiculatus.

This system occurs in an open rolling Karst Plain landscape which easily carries fire if maintained in a grassy condition. Bedrocks are the St. Louis or Ste. Genevieve, Upper Milan limestones of the Meramecian Series including some of the area which forms the base of the Dripping Springs Escarpment. Sinkholes mostly range up to 200 m wide and 10 m deep, with some areas nearly sinkhole-free while other areas have sinkholes up to 1600 m wide and 60 m deep with some sinkhole ponds and lakes. One sinkhole covers 1261 ha (3114 acres). Some sinkhole ponds were created by sinkhole plugging via agricultural erosion or human disturbance. The area exhibits well-developed underground drainage, low stream density, and soils that become dry very rapidly. Most upland streams have limited discharge with intermittent or ephemeral flow.

The barrens of this area exhibit two types of uncharacteristic conditions. Agricultural changes converted much of the landscape for use as fields and for grazing. With fire suppression they grew up with woody vegetation. Today in many areas, old pastures or agricultural fields have succeeded into areas dominated by Juniperus virginiana. It is not likely this would have been common in presettlement times. However, with fencerow habitats that encourage Juniperus survival being created in recent history, this has become the most common successional pathway (Landfire 2007a).

Most of the area historically occupied by these barrens has been significantly disturbed and it is now mostly in agricultural uses, with drainage of upland wet soils and fracturing of hardpans with deep-running plows (Chester et al. 1997). Soils develop over limestones of upper Mississippian age, and are fertile, deep, well-drained, flat to gently sloping and rarely steep upland soils formed in loess, cherty residuum weathered from limestone, old alluvium, or some combination of these (Chester et al. 1997). Soil series include Crider, Dickson, Hammack-Baxter, Mountview, Nicholson, Pembroke, and Pickwick.

This vegetation was the predominant type here in the early 1800s and probably originated from burning by Native Americans. The largest extant examples are presently found on Fort Campbell Military Reservation, Tennessee, where ecological burning and fires from live munitions use result in open herbaceous-dominated landscapes. Much of the area supports crops and livestock production. Very few "original" presettlement barrens exist. These barrens originated by burning of forests by Native Americans. If not grazed or farmed, these barrens quickly grew into oak-dominated forests after settlement by Europeans and occur on soil that developed under forest vegetation (Landfire 2007a).

The most critical anthropogenic threat to native grasslands, savannas and barrens is their conversion to human-created land uses, including residential development, quarries, industrial development, infrastructure development, and others (TNC 1996c). Rocky glade areas, if present, 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 (e.g., fire, grazing) 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. Without it, 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). In landscapes where open grassland or savanna vegetation is part of the matrix, and where woody plants have taken over areas once occupied by open grassland and savanna vegetation, the light-dependent species may only persist on the open edges (roadsides, powerlines) of forested patches (Taft 1997). In southeastern grasslands, complete transition to forest dominated vegetation can occur in one or two decades (Wiens and Dyer 1975). More information is needed about the particular appropriate ranges of fire-return times and intensities in the various systems, along with factors other than fire (e.g., soil/substrate, aspect, herbivory, hydroperiod and flooding) that help maintain grasslands and related communities. Occasional surface fire will retard woody plant encroachment and help maintain herbaceous diversity, as will, to an extent, grazing or mowing. Too intensive or frequent application of these disturbances will have deleterious effects on stand structure and species diversity. In general, mosaics of scrub and grassland, produced by light to moderate grazing (or occasional fire) will support the greatest diversity (Duffey et al. 1974). Cutting or mowing is not as favorable to plant diversity as is grazing because it is nonselective and does not result in the same kind of soil disturbance and compaction as do the hooves of grazing animals (DeSelm and Murdock 1993). Fire is a critical disturbance factor for southeastern native grasslands, but the intensity, duration, and timing of the fires are all important in their effect on the vegetation (DeSelm and Murdock 1993). In addition to occasional fire, periodic drought may also be important in regulating woody plant encroachment in native grasslands. It is believed that native grasslands have evolved under a combined system of grazing, drought, and periodic fire (Duffey et al. 1974, Estes et al. 1979, Noss 2013).

Fragmentation of 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. A small isolated patch has a low probability of receiving a lightning strike frequently enough to maintain a grassland condition. In many cases, 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 or glade system naturally occurs in small isolated patches occurring within an otherwise forested matrix.

Many native grassland sites, particularly the more productive ones, have been converted to plantations of exotic grasses and legumes (DeSelm and Murdock 1993). Even if not completely converted, the extirpation of native species and the concomitant spread of invasive exotic plants (particularly Ligustrum species and Lonicera species shrubs, as well as Ailanthus altissima, Albizia julibrissin, Alliaria petiolata, Lespedeza cuneata, Microstegium vimineum, and Miscanthus sinensis) will fundamentally alter the character of native grasslands, barrens, savannas, and glades. 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 system is found in the northern Highland Rim (Pennyroyal Plateau) of Tennessee and adjacent Kentucky (EPA Ecoregion 71e [Western Pennyroyal Karst Plain] of Griffith et al. (1998) and Woods et al. (2002); part of Subsection 222Eh of Keys et al. (1995); also possibly in 71g (northwestern portion), 223Ea in Kentucky).