Chapter 23
Ecological Subregions of the United States



Ouachita Mixed Forest - Meadow

One Section has been delineated in this Province:

This Section is located in Arkansas and Oklahoma. The area is about 8,800 mi2 (22,800 km2).

Section M231A--Ouachita Mountains

Geomorphology. This section is in the Ouachita geomorphic province. It was formed by tectonic faulting and uplift of resistant bedrock into a narrow band of metamorphosed, parallel (east-west trending) mountain ranges. This was followed by mass wasting and steep and gentle stream valley erosion with fluvial transport. About 75 percent of the area consists of open high hills. Also included are open low mountains. Elevation ranges from 330 to 2,600 ft (100 to 800 m). Local relief in much of the section ranges from 500 to 800 ft, but it can range from 1,000 to 2,000 ft in areas with low mountains.

Lithology and Stratigraphy. Rocks formed during the Paleozoic (50 percent), Mesozoic (40 percent), and Cenozoic (10 percent) Eras. Paleozoic strata consist of: Cambrian marine deposits (carbonates and shales); Ordovician marine deposits (carbonates, shales, and limestones); Mississippian marine deposits (sandstone); and Pennsylvanian marine deposits (sandstone). Mesozoic strata consist of Lower and Upper Cretaceous marine deposits (limestone). Cenozoic stata consist of Quaternary marine deposits.

Soil Taxa. Soils are mainly Udults. Hapludults are at higher elevations on steep slopes, gentle slopes of ridgetops, and foot slopes. Dystrochrepts and Ochraquults are on flood plains. Some localized areas of Hapludults are on terraces in the valleys. These soils have a thermic temperature regime, a udic moisture regime, and siliceous or mixed mineralogy. Soils are generally deep, often stony, and have adequate moisture for use by vegetation during the growing season.

Potential Natural Vegetation. K\"uchler classified vegetation as oak-hickory-pine forest. Existing forest types are mainly loblolly-shortleaf pine. The predominant vegetation form is evergreen needle-leaved forest and a small area of cold deciduous, broad-leaved forest. Loblolly pine and shortleaf pine cover types occur widely. Lesser areas of a shortleaf-oak type (southern red, scarlet, black, post, and blackjack oaks) and oak-hickory (black, scarlet, post, and white oaks and pignut and mockernut hickories) occur in Oklahoma.

Fauna. Among the fauna in this Section are white-tailed deer, black bear, bobcat, gray fox, raccoon, gray squirrel, fox squirrel, eastern chipmunk, white-footed mouse, pine vole, short-tailed shrew, and cotton mouse. The turkey, ruffed grouse, bobwhite, and mourning dove are game birds in various parts of this Section. Songbirds include the red-eyed vireo, cardinal, tufted titmouse, wood thrush, summer tanager, blue-gray gnatcatcher, hooded warbler, and Carolina wren. The herpetofauna include the box turtle, common garter snake, and timber rattlesnake. Endemics are Fourche Mountain salamander, Caddo Mountain salamander, Rich Mountain salamander, Ouachita madtom, Ouachita Mountain shiner, Kiamichi shiner, Ouachita darter, peppered shiner, and Rich Mountain slitmouth snail. Threatened and endangered species include the red-cockaded woodpecker, bald eagle, American burying beetle, Arkansas fatmucket, and rock pocketbook mussel. Other characteristic species include the Western diamondback rattlesnake and eastern collared lizard.

Climate. Average precipitation is 48 to 56 in (1,220 to 1,420 mm). Mean annual temperature is 61 to 63 oF (16 to 17 oC). The growing season lasts 200 to 240 days

Surface Water Characteristics. There is a high density of small to medium size perennial streams and associated rivers; those in intermountain basins have moderate rates of flow, and some on mountain sides are characterized by high rates of flow and velocity. A trellis drainage pattern has developed, largely with bedrock structural control. Major rivers include the Fourche and Dutch Creek, which flow into the Arkansas River.

Disturbance Regimes. Fire has probably been the principal historical disturbance. Climatic influences include occasional summer droughts, winter ice storms, and infrequent tornados. Insect disturbances are often caused by southern pine beetles.

Land Use. Natural vegetation has been cleared for agriculture on about 25 percent of the area.

Cultural Ecology. Reserved.

Compiled by Southern Region and Southeastern Forest Experiment Station.