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INTRODUCTION Southwestern Arkansas, as the term is used here, includes all or parts of seven counties recognized as a distinctive region of the state, the Southwestern Arkansas Section of the West Gulf Coastal Plain Natural Division (Foti 1974). This section is underlain by geological deposits from the Cretaceous period, in contrast to the Tertiary-period deposits that underlie the rest of the West Gulf Coastal Plain of southern Arkansas , with which it nonetheless shares many characteristics. An important difference is that the geological substrate of southwestern Arkansas sometimes includes calcareous materials such as limestone, chalk, and marl. Areas within southwestern Arkansas underlain by these deposits are here referred to as the blackland prairie region. This term does not denote one contiguous area, but rather several discrete areas shown on the General Soil Map of Arkansas as blackland prairie or Oktibbeha-Sumter soil association (USDA Soil Conservation Service 1982; Figure 7.1). Within these areas, calcareous soils supporting blackland prairies and related communities are interspersed with areas of acidic soils covered with pine-hardwood forests like those of the rest of the coastal plain. Roberts (1979) estimated the total area of the blackland prairie region of southwestern Arkansas at about 130,000 ha. Although the landscape is generally made up of rolling hills, slopes of over 50 percent gradient occur, along with at least one nearly vertical cliff (White Cliffs in Little River County). Severe erosion is common, with gullies up to 10 m deep. Level areas are characterized by black soils with high levels of organic matter that give the region its name, but soils abused by 7 Blackland Prairie Landscapes of Southwestern Arkansas Historical Perspective, Present Status, and Restoration Potential Thomas L. Foti, Scott Simon, Douglas Zollner, and Meryl Hattenbach poor management practices (such as overgrazing land) and other eroded soils over chalk are olive to white in color. The presence of calcareous geologic materials has had profound effects on the vegetation, soil, and land use of the region. A distinctive landcover type, the blackland prairie , and related savanna, woodland, and forest communities occurred on these calcareous substrates. Owing to a lack of systematic inventories , descriptions, and studies, however, the nature of these communities has been poorly understood. As recently as 1974, no contemporary examples were recognized (Foti 1974). As used here, a prairie is an area dominated by characteristic herbaceous plants (typically over a hundred species). Blackland prairies are those that occur on these distinctive calcareous substrates; they differ in both dominant vegetation and characteristic species from other tallgrass prairies of the Midwest and Midsouth. On calcareous soils within the blackland prairie region of southwestern Arkansas, four prairie communities, six woodland communities, and two forest communities were de¤ned by Hattenbach et al. (2000). The dominant grasses include little bluestem (Schizachyrium scoparium) and Indiangrass (Sorghastrum nutans), with big bluestem (Andropogon gerardii) and gamma grass (Tripsacum dactyloides) on moister areas. Compassplant (SilFig . 7.1. Blackland soil associations of southwestern Arkansas as mapped by NRCS. Landscapes of Southwestern Arkansas 95 phium laciniatum) and prairie clover (Dalea purpurea) are typical forbs. These prairies usually occur on shallow soils over chalk ridges or marl (calcareous clay) slopes, often on the steep faces of asymmetrical ridges known as cuestas, which have a shallow slope and a steep slope. On the steep slopes are chalk or marl outcrops mantled with only a thin layer of soil that may be black but is more commonly olive. According to the original land-survey notes, it appears that the prairies occurred primarily on the steep slopes but extended for a distance onto the gentle slopes at the foot of the ridge. However, they were usually replaced by forest within a short distance of the toes of the slopes (Figure 7.2). Woodlands have few enough trees that herbaceous prairie vegetation dominates the ground level (typically 25–60 percent tree cover). Savannas are mostly prairie but with scattered trees. Trees of savannas and woodlands include chinkquapin oak (Quercus muhlenbergii), bois d’arc (Maclura pomifera), eastern redcedar (Juniperus virginiana), and nutmeg hickory (Carya myristicaeformis). Interestingly, ¤eld notes from both the ¤rst land survey and current research show that pecan (Carya illinoensis) makes up about 10 percent of the trees within savannas and woodlands in the blackland prairie region. In other regions it is usually associated with sandy riverfronts along large rivers, in contrast to the calcareous clays of the blackland prairies. Fig. 7.2. A generalized model of the geology, soil, vegetation, and topography of a cuesta in southwestern...

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