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GRASSLANDS IN THE SOUTHEASTERN UNITED STATES Grass-dominated communities occur in a variety of edaphic and climatic conditions in the southeastern United States, as reviewed and characterized by DeSelm and Murdock (1993). A diversity of upland grasslands are present in the upper Coastal Plain and interior areas of the region, including serpentine barrens in the Piedmont (Radford 1948), barrens and cedar glades on limestone in Kentucky, Tennessee, and elsewhere (Dicken 1935; Quarterman 1950, 1986; Somers 1986; Baskin et al. 1994; Chester et al. 1997), the Grand Prairie on alluvial soils in Arkansas (Foti et al., this volume; Zollner et al., this volume; Irving et al. 1980), and the blackland prairies, which occur in Texas, Arkansas, Mississippi, and Alabama (Foti 1989; DeSelm and Murdock 1993; Schauwecker 1996; Leidolf and McDaniel 1998). THE BLACK BELT OF MISSISSIPPI AND ALABAMA The largest of the blackland prairies, as well the most southeastern grassland of the tall prairie type, is the Black Belt of Mississippi and Alabama (Figure 2.1). This crescent-shaped region has a width up to 40 km and extends more than 500 km from McNairy County, Tennessee , south across east-central Mississippi and east to Russell County, Alabama; it covers more than 14,141 square km (Brent 1973; Harper 1943; Schauwecker 1996; Schiefer 1998). The Black Belt is situated near the northeastern and northern border of the Gulf Coastal Plain in Mississippi and Alabama, respectively, and underlies the eastern border of the Mississippi embayment. The Black Belt was formed on soils that 2 Paleoenvironment and Biogeography of the Mississippi Black Belt Evidence from Insects Richard L. Brown originated from Demopolis chalk of the Selma group, which dates to the Upper Cretaceous (Stephenson and Monroe 1940; Kaye 1974). Much of the Black Belt includes a mosaic of three plant communities : open prairie, chalk outcrops, and forest (Leidolf and McDaniel 1998) (Figure 2.2). The open prairie and chalk outcrops include many species widely occurring in the eastern United States, but which in Mississippi are restricted to the Black Belt or also to the Jackson Prairie in the central area of the state, for example, Agalinus auriculata (Michx.), Silphium terebinthinaceum, S. laciniatum L., and Rhamnus lanceolata Pursh. The Black Belt also includes species that occur primarily in the Great Plains, for example, Bouteloua curtipendula (Michx.), Agalinus oligophylla Pennell, Heliotropium tenellum (Nutt.), Neptunia lutea (Leavenw.), Dalea candida Michx., D. purpurea Vent., Arnoglossum plantagineum Raf., Galium virgatum Nutt., Aster sericeus Vent., Evax prolifera Nutt., Crataegus engelmanni Sarg., and Spiranthes magnicamporum Sheviak. Six forest communities have been identi¤ed in the Black Belt: xeric post-oak ridges, mesic oak-hickory forests, bottomland hardwood forFig . 2.1. Black Belt (solid gray) and Jackson Prairie (hatched) in Mississippi and Alabama. Dots indicate sampling sites for insect survey. 12 Richard L. Brown ests, water tupelo swamps, mixed hardwood gallery forests, and prairie cedar woodlands, the latter appearing to be a recent feature resulting from the absence of ¤re and grazing (Leidolf and McDaniel 1998). Quercus durandii Buckl. and Carya myristiciformis (Michx.) are relatively common in oak-hickory forests in the Black Belt, although these species are rare or localized elsewhere in their ranges. Lowe (1921) considered prairie to be historically more extensive than forest. Based on analysis of a land survey of Sumter County, Alabama, in 1832, Jones and Patton (1966) concluded that 23.4 percent of the 112,588 ha in the Black Belt of that county had few or no trees, 14.5 percent had relatively dense forest (296 trees/ha), and 62.1 percent had forest of intermediate density, with some of the latter having savanna vegetation. They further showed that open prairie was associated with alkaline soils, whereas dense forests were associated with acidic soils. Jones and Patton also reported that areas designated as prairie in the 1832 survey ranged in size from 7 to 2024 ha. Most of the Black Belt was converted to agriculture by the late 1800s, leaving only small remnants of prairies, forests, and chalk outcrops, with many of the latter being highly eroded. Fig. 2.2. Obsorn Prairie in Oktibbeha County, Mississippi, with Schizachyrium scoparium, little bluestem, in foreground bordered by Demopolis chalk exposed by erosion and Juniperus virginiana mixed with woodland in background. Paleoenvironment and Biogeography of the Mississippi 13 HISTORY OF GRASSLANDS IN THE SOUTHEASTERN UNITED STATES According to Axelrod (1985), extensive grasslands developed in midcontinental North America about 75 million years before present (b.p.) during the driest part of the Tertiary, which resulted in a restriction...

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