Southern Coastal Plain Blackland Prairie

This system includes natural grassland vegetation and associated wooded vegetation found primarily in two relatively small natural regions in the southeastern Coastal Plains, primarily in Alabama and Mississippi (with one of these extending barely into southern Tennessee), and a related area of southern Georgia. The larger of these, the so-called Black Belt, is approximately 480 km (300 miles) long and 40-50 km (25-30 miles) wide, and is delineated as the Black Belt Subsection 231Ba and the Blackland Prairie EPA Ecoregion 65a. The smaller and more southerly one of the two is known as the Jackson Prairie region, is found on younger geologic strata and is delineated as the Jackson Hills Subsection (231Bj) and as the Jackson Prairie EPA Ecoregion (65r). The vegetation of this system is comproed of natural grasslands and associated wooded vegetation (woodlands and savannas). The Black Belt region derives its name from the nearly black, rich topsoil that developed over Selma Chalk, and has long been noted as a distinct topographic region in the state of Mississippi. In Alabama, the formations on which this system primarily occurs are Demopolis Chalk and Mooreville Chalk (members of the Selma Group). In Tennessee, only Demopolis Chalk is mapped. Examples occur over relatively deep soils (as opposed to "glades and barrens" on or adjacent to rock outcrops), with circumneutral surface soil pH. Vegetation of this ecological system includes evergreen Juniperus virginiana-dominated forests and deciduous Quercus-dominated woodlands of varying densities, interspersed with native prairielike grasslands. Much of the natural vegetation of the region has been converted to pasture and agricultural uses, but even old-field vegetation reflects the distinctive composition of the flora and ecological dynamics. In most cases individual prairie openings are small and isolated from one another, but were formerly more extensive prior to European settlement, forming a mosaic of grasslands and woodlands under frequent fire regimes. The flora has much in common with other prairies of the East Gulf Coastal Plains, as well as the classic Midwestern prairies. Within this natural region, there are pockets of acidic soils which produce more typical pine-oak woodland or forest vegetation. The Jackson Prairie component of the system includes natural grassland vegetation and associated wooded vegetation in the Jackson Hills Subsection (231Bj), also called the Jackson Prairie EPA Ecoregion (65r), a relatively small natural region of Mississippi and adjacent Alabama. This system occurs on montmorillonitic Vertisols, which are deep, slowly permeable soils formed in residuum weathered from marl or chalk. Examples occur in a larger matrix of primarily acidic soils and of generally Pinus taeda-dominated forest vegetation. In most cases individual prairie openings are small and isolated from one another but were formerly more extensive prior to European settlement, forming a mosaic of grassland and woodland under frequent fire regimes. Much of the natural vegetation of the region has been converted to pasture and agricultural uses, with concomitant destruction of most prairie remnants.

Vegetation of this ecological system includes evergreen Juniperus virginiana-dominated forests and deciduous Quercus-dominated woodlands of varying densities, interspersed with native prairie-like grasslands. Much of the natural vegetation of the region has been converted to pasture and agricultural uses, but even old-field vegetation reflects the distinctive composition of the flora and ecological dynamics. The oak woodlands of the Black Belt component typically contain Quercus stellata, Quercus muehlenbergii, and Quercus marilandica. Other woody components include Quercus falcata, Carya tomentosa (= Carya alba), Carya glabra, Fraxinus americana, Celtis laevigata, Cercis canadensis var. canadensis, Crataegus engelmannii, Diospyros virginiana, Ilex decidua, Prunus angustifolia, Frangula caroliniana, Sideroxylon lycioides, and Ulmus alata. Prairie forbs and grasses may persist in small openings and in edge situations in the more heavily forested areas of the Black Belt. The presence of Juniperus virginiana-dominated zones may represent invasion by this species in the absence of sufficiently frequent or intense fire (DeSelm and Murdock 1993). Pines are generally absent, being inhibited by the higher surface soil pH. In the grass-dominated areas of the Black Belt, Schizachyrium scoparium and Sorghastrum nutans are the principal herbs. Other herbaceous taxa include Andropogon glomeratus, Andropogon virginicus, Bouteloua curtipendula, Panicum virgatum, and Schizachyrium scoparium, with lesser amounts of Paspalum floridanum, Setaria parviflora, and Sporobolus indicus (exotic). Other common species include Arnoglossum plantagineum, Symphyotrichum dumosum (= Aster dumosus), Symphyotrichum patens (= Aster patens), Crotalaria sagittalis, Dalea candida, Dalea purpurea, Desmanthus illinoensis, Desmodium ciliare, Dracopis amplexicaulis, Liatris aspera, Liatris squarrosa, Liatris squarrulosa, Neptunia lutea, Ratibida pinnata, Ruellia humilis, Silphium terebinthinaceum, Silphium trifoliatum var. latifolium, and Solidago nemoralis. In depressions and drainages, Andropogon gerardii and/or Panicum virgatum will have greater importance (DeSelm and Murdock 1993). At this more mesic end of the continuum, invasion by woody plants is a more serious threat to the system. Moist, seepy inclusions within this system are often dominated by Rhynchospora colorata and Scleria verticillata; Rhynchospora divergens, Lythrum alatum var. lanceolatum, Mitreola petiolata, and Mecardonia acuminata also occur but much less frequently (A. Schotz pers. comm.). The most prominent tall grasses of the Jackson Prairie component are Andropogon gerardii, Schizachyrium scoparium, Sorghastrum nutans, and Panicum virgatum. Additional tall grasses include Tripsacum dactyloides, Andropogon glomeratus, and Paspalum floridanum. Along with Schizachyrium scoparium, two other species provide over 50% cover in prairie openings: Carex cherokeensis and Helenium autumnale. Other plants closely affiliated with less disturbed prairie openings include Dalea purpurea, Dalea candida, Sporobolus compositus var. macer, Muhlenbergia capillaris, Penstemon laxiflorus (= Penstemon australis ssp. laxiflorus), Symphyotrichum novae-angliae (= Aster novae-angliae), Echinacea purpurea, Manfreda virginica, Ruellia purshiana, Desmanthus illinoensis, and Spiranthes magnicamporum (Wieland 1995).

The Black Belt component of this system generally occurs on Cretaceous age chalk, marl and calcareous clay. This includes calcareous soils of the Sumter, Binnsville, and Demopolis series, described as beds of marly clay over Selma Chalk (including the Demopolis and Mooreville formations). The area has an average annual precipitation of 130-140 cm and a frost-free period of 200-250 days. The soils of the Jackson Prairie openings are presently mapped as the Maytag Series, a fine montmorillonitic, thermic Entic Chromudert. This deep slowly permeable soil has formed in residuum weathered from marl of chalk of the Blackland Prairies (Wieland 1995). Examples occur in a larger matrix of primarily acidic soils and of generally Pinus taeda-dominated forest vegetation (Jones 1971).

In the presettlement landscape and throughout the nineteenth century, a combination of fire and grazing (first by native ungulates and then by free-ranging cattle) kept these sites open and grass-dominated (DeSelm and Murdock 1993).

Blackland prairie and woodland occurs on eponymous rich, black, circumneutral topsoils formed over clayey, heavy, usually calcareous subsoils with carbonatic or montmorillonitic mineralogy. The system occurs in association with formations of the Tertiary Jackson (Yazoo Clay), Claiborne (Cook Mountain) and Fleming groups, and the Cretaceous Selma group (Selma, Mooreville or Demopolis chalks). The matrix around the blackland prairies is pine-oak forests growing in acidic, sandier soils with less clay (recent STATSGO soils maps).

Floristic similarity among sites across this geographic range generally appears to be 50% or greater, although a number of different alliances within this type have been recognized according to dominant, codominant, and diagnostic species. Extant prairies occur in single patches as well as mosaics less than one acre to over several hundred acres in response to soil depth, slope and fire. Mosaics may include virtually treeless patches associated with other patches of widely scattered trees, open deciduous woodlands and evergreen thickets (eastern red-cedar "balds"). This vegetation is a mosaic of Juniperus virginiana woodland, Quercus stellata - Quercus marilandica woodland, and Schizachyrium scoparium - Sorghastrum nutans herbaceous alliances. It is a rare and imperiled vegetation type consisting of scattered remnants. Most of the original cover has been destroyed or altered by conversion to agriculture and the exclusion of fire (Landfire 2007a).

For the last 500-1000 years, fires were probably annual in most of the system, many if not most set by Native Americans. Fires were probably used to clear prairies for agricultural planting, to eliminate woody growth, and to aid in hunting. The modern landscape shows a tendency toward erosion, creating shallow-soil areas known as "cedar balds" where soil erosion, presumably from historic agriculture or overgrazing, has reduced topsoil. These areas often show exposures of underlying chalk. Such areas may have resulted (albeit at much lower frequencies) from aboriginal agriculture or overgrazing by native herbivores (Landfire 2007a).

The Black Belt was one of the South's most important agricultural areas before the American Civil War, and has long been noted as a distinct topographic region in the state of Mississippi (Lowe 1921). A long history of cultivation and disturbance has left few large, intact prairies remaining. With range enclosure and fire suppression increasing during the twentieth century, the dynamics of the landscape changed, and the coverage of fire-intolerant woody species increased. The formerly extensive system is now reduced to patches or its flora persists in pastures which are under more continuous grazing pressure than the former processes would have allowed. This has probably led to more uniformity of the vegetation and would favor some taxa over others. More study is needed. Invasive exotic plants include Ligustrum sinense, Maclura pomifera, and Sorghum halepense; many of these are bird-dispersed and were deliberately or accidentally introduced to the region. The increase in eastern red-cedar (also bird-dispersed) has also been pronounced. Pasture improvement, replacement of native warm-season grasses with exotic forage grasses, is also a threat. Black Belt prairie sites characterized as having good to exceptional integrity are very limited in number. Those that were extant as of 2009 were characterized at that time as being represented by a diverse natural landscape context (i.e., a mosaic of native prairies and forests), diversity of native prairie taxa, and a minimal incursion of exotic and native weedy species (e.g., eastern red-cedar) (Schotz and Barbour 2009). In contrast to native prairies, abandoned pastures may be dominated by Bermuda grass, Johnson grass and eastern red-cedar, but may appear similar in remote sensing to native prairies.

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 Lespedeza cuneata, Miscanthus sinensis, Microstegium vimineum, Alliaria petiolata, Ailanthus altissima, and Albizia julibrissin) 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 has several distinct components. The Black Belt Prairie component is primarily restricted to the Black Belt (Subsection 231Ba of Keys et al. 1995) or Blackland Prairie area (EPA Ecoregion 65a) and Flatwoods/Blackland Prairie Margins area (EPA Ecoregion 65b) of Griffith et al. (2001). This region is primarily in Alabama and Mississippi, ranging north in a depauperate form to southern Tennessee (McNairy County) (DeSelm 1989b). The Jackson Prairie component of this system is found in a relatively small natural region of Mississippi, known as the Jackson Hills Subsection 231Bj of Keys et al. (1995) and the Jackson Prairie Ecoregion 65r of EPA (EPA 2004). There is also a recently recognized component found in limited parts of Georgia (e.g., on both sides of the Ocmulgee River on the Fort Valley Plateau of Bleckley, Houston, Peach, and Twiggs counties). There are also outlying occurrences southward in the Chunnenuggee Hills and Red Hills (both of these parts of the Southern Hilly Coastal Plain -EPA Ecoregion 65d), and Buhrstone/Lime Hills (EPA Ecoregion 65q) of southern Alabama (in Washington, Wilcox, Monroe, and Clark counties). There are some limited examples in EPA Ecoregion 65i (Fall Line Hills; e.g., Jones Bluff in Alabama).