Chapter 35
Ecological Subregions of the United States



Great Plains Steppe and Shrub

One Section has been delineated in this Province:
most of which is located in Oklahoma. The area of this Section is about 17,600 mi2 (45,600 km2).

Section 311A--Redbed Plains

Geomorphology. This Section is in the Central Lowlands geomorphic province. Platform uplift of continental sediments deposited previously into a shallow inland sea, followed by a long period of erosion; these processes resulted in a moderately to strongly dissected region. About 70 percent of this Section consists of irregular plains. Other landforms include about equal areas of plains with low mountains, smooth plains, and tablelands. Elevation ranges from 1,600 to 3,000 ft (500 to 900 m). Local relief in much of the Section ranges from 100 to 300 ft (30 to 90 m). Smaller areas are present where relief ranges from 30 to 60 ft (10 to 20 m) in tablelands and up to 1,000 ft (300 m) in low mountains.

Lithology and Stratigraphy. Rocks formed during the Paleozoic Era. About 80 percent of the geologic strata consist of Permian marine deposits (sandstone, shale, and limestone). Other strata include Quaternary marine deposits and small isolated areas of Lower Cretaceous marine deposits (limestone).

Soil Taxa. Soils are Ustolls, Ustalfs, and Ochrepts. Most soils are on uplands and include Argiustolls, Paleustolls, Natrustolls, Haplustalfs, Paleustalfs, and Ustochrepts. Localized areas of Ustifluvents are on flood plains. These soils have a thermic temperature regime, a ustic moisture regime, and mixed mineralogy. Most soils are deep, well drained, variable in texture, and have limited moisture supplies for use by vegetation during part of the growing season.

Potential Natural Vegetation. K\"uchler classified vegetation as bluestem-grama prairie, and cross timbers ({\it Quercus-Andropogon}); shinnery ({\it Quercus-Andropogon}); and sandsage-bluestem prairie. The predominant vegetation form is medium-tall grasslands with sparse tree cover. Grasses consist mainly of sand bluestem, little bluestem, and sand saltbrush.

Fauna. Representative large to medium size herbivores and carnivores include coyote, ringtail, and ocelot. Small herbivores include eastern cottontail, desert shrew, plains pocket mouse, Texas kangaroo rat, and prairie vole. Bison and black-footed ferret are historically associated with this Section. Common birds of thickets and grasslands include the roadrunner, bobwhite, barn owl, scissor-tailed flycatcher, and common crow. The golden-fronted woodpecker has a more restricted range. Amphibians common to this environment include Plains spadefoot toad, Great Plains narrow-mouthed frog, green toad, spotted chorus frog, and yellow-mud turtle. Typical reptiles include lesser earless lizard, Texas horned lizard, Prairie skink, and Texas blind snake.

Climate. Precipitation averages 20 to 30 in (500 to 750 mm); snow averages 20 to 30 in (500 to 750 mm) annually. Temperature averages 57 to 64 oF (14 to 18 oC). The growing season lasts 185 to 230 days.

Surface Water Characteristics. The area has a low density of small to medium intermittent streams and associated rivers, most with a low volume of water flowing at low velocity. Dendritic drainage pattern has developed without bedrock structural control. Major rivers include the Washita, Canadian, and Red.

Disturbance Regimes. Fire and drought have probably been the principal historical disturbances.

Land Use. Natural vegetation has been converted to agricultural crops or pasture on about 90 percent of the area.

Cultural Ecology. Reserved.

Compiled by Southern Region and Southeastern Forest Experiment Station.