Interior Highlands

Physiography—The Interior Highlands refers to two elevated physiographic provinces in Arkansas, Missouri, and Oklahoma. The Ozark Plateaus, to the north, formed on a broad, domed upwarp mostly of limestone and dolomite. Some chert gives the soil a rocky texture. In the southern Ozark sector, also called the Boston Mountains, sandstones and shales predominate. Elevations rise to above 2200 feet. Drainage from this range, exhibiting an east-west orientation, is radial, the south-flowing streams being the more vigorous in their dissection of the plateau. Relatively flat lands between rivers are commonly called prairies.

The Ouachita province lies south of the Ozark Plateaus, the 25- to 35-mile-wide Arkansas River trough separating the two ranges. The Ouachita region exhibits linear folds in the mantle, like the

Figure 1.24 Treeless dome-shaped summits occur above 4000 feet in the more-northern reaches of the Southern Appalachian Mountains. These "balds" support grass and an assortment of broadleaf heather-like shrubs (rhododendron and mountain laurel). Deciduous trees along with spruce and fir surround the balds.

Figure 1.24 Treeless dome-shaped summits occur above 4000 feet in the more-northern reaches of the Southern Appalachian Mountains. These "balds" support grass and an assortment of broadleaf heather-like shrubs (rhododendron and mountain laurel). Deciduous trees along with spruce and fir surround the balds.

Ridge and Valley province of the Appalachian Mountains. While most of these hills lie less than 1000 feet above sea level, they rise to 2600 feet to the west near the Oklahoma boundary. The soils, formed mainly on sandstones and shales, are classed as red-yellow podzolics. Ridge surface horizons are shallow and stony and of low fertility. Valleys have more productive, finer-textured soils.

Climate—In these provinces, precipitation ranges from 40 to 50 inches annually, with serious summer droughts taking a toll on the forest in survival and growth. Growing seasons average about 200 days. Because of the prevailing east-west orientation of these mountains, increased isolation on south-facing slopes affects more of the forested land than in other mountainous regions of North America. This, combined with erratic rainfall and high temperature effectiveness (700 units), limits much of the area to tree species adapted to drier sites.

Forests—Forests of the Interior Highlands are mostly (68%) oak-hickory. The pines, principally shortleaf and some loblolly, make up 15% of the forested area, while mixtures of pines and hardwoods compose another 7%. Greatest concentrations of shortleaf pine appear on the drier south- and west-facing slopes in the Ouachita Mountains, where both a national forest and industries maintain extensive pure stands. The virgin forest was rich in species variety. White oak, black walnut, black cherry, sugar maple, and eastern redcedar attained large diameter and excellent form. Quality hickory grew on the drier slopes. Some trees still find use by local craftsmen; riding the back roads, one may come upon a whittler, his back against a tree, carving a custom ax handle from a green hickory bough. Or, using eastern redcedar, he may shape a rolling pin so perfectly round it appears to have been turned on a cabinetmaker's lathe.

Eastern redcedar growing on the relatively chert-free limestone-derived soils seems to be maintaining its place in the biome, in spite of severe over-cutting for posts and for lumber for products requiring the aroma of the oil exuded from the wood. Yet, in spite of this demand, markets are inadequate for encouraging landowners to manage for this species. The Junipers do invade overgrazed grasslands of the glades of the zone.

As the prairie to the west is approached, the forest becomes more open, allowing bunch grasses to invade. Attempts to convert large tracts to pastureland have been only partially successful; drought-hardy deciduous scrubby trees take over the land.

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