332 Great Plains Steppe Province

High plains and central lowlands between the prairie parkland and the 104th meridian, from the Canadian border through Oklahoma, 134,000 mi2 (347,100 km2)

Land-surface form.--This region is characterized by flat and rolling plains with relief of less than 300 ft (90 m). Elevations range from 2,500 ft (760 m) near the western edge of the province to 1,000 ft (300 m) at the eastern edge. Except south of the Missouri River, most of the lands are young glacial drifts and dissected till plains. Water covers much of the surface. Loess and sand deposits cover the area south of the Missouri River. This flat-to-rolling hill land has well-developed drainage systems.

Mixed-grass steppe Mixed-grass steppe in the sandhills of central Nebraska.

Climate.--Average annual temperatures in this province range from 40F (4C) in the north to 55F (13C) in the east, 60F (15C) in the west, and 65F (18C) in the south. Along its eastern boundary from Oklahoma to Nebraska, annual precipitation approaches 30 in (770 mm), dropping to about 20 in (510 mm) in North Dakota. Along the western limit of the region, precipitation ranges from 20 in (510 mm) in Oklahoma to 25 in (640 mm) in Nebraska, dropping to 15 in (380 mm) in the extreme northwest. Drought periods are less frequent and severe near the prairie parkland than in the more westerly areas.

Vegetation.--This region, called mixed-grass steppe, reaches from the tallgrass prairie parkland to the shortgrass steppe at about long. 104 W. As its name suggests, it contains a mixture of shortgrass and tallgrass species. The tall grasses grow to a height of about 48 in (1,230 mm); the shorter grasses reach 18 in (460 mm). Shorter dominants include blue grama, hairy grama, and buffalo grass. Taller grasses include little bluestem and needle-and-thread grass. Woody vegetation is rare, except on the cottonwood floodplains.

In mixed-grass steppe, additional species include green needlegrass, sand dropseed, slender wheatgrass, galleta, and purple three-awn. There are numerous species of forbs throughout the region. Match weed or broomweed, scurf-pea, sunflowers, goldenrods, and ragweed occur from Oklahoma into Canada.

The eastern and western boundaries of this region continually shift with changes in precipitation. A series of dry years results in an increased dominance of short grasses (better adapted to a dry climate), moving the region's boundaries to the east. Westward shifts occur after periods of relatively high precipitation, which favor the taller grasses.

Soils.--The soils of the mixed-grass steppe are primarily Mollisols. There are smaller areas of Entisols, such as the sandhills of Nebraska, and one small area of Vertisols. Most soils have dark upper horizons.

Fauna.--Bison once grazed the western margin of the mixed-grass steppe. Pronghorn antelope and coyotes are still present. Jackrabbits are numerous on the steppe, and cottontails are present where there are streams and cover. Burrowing rodents include ground squirrels, prairie dogs, pocket gophers, and many smaller species. Burrowing predators include the badger and the blackfooted ferret, now classified as an endangered species.

The northern portion of this region is an important breeding area for migrating waterfowl. Mourning doves have become abundant in shelterbelt plantings. The sharp-tailed grouse, greater prairie chicken, and bobwhite are present in fair numbers; but the northern greater prairie chicken is classified as threatened.