Boundaries

This ecoregion covers southeastern Oklahoma, northeastern Texas, southern Arkansas, and northwestern Louisiana, and is largely defined by the Red River and the Ouachita River drainages. The Ouachita Highlands ecoregion is separated from the Ozark Highland ecoregion [147] by the Arkansas River. Like the Ozark Highlands, this ecoregion is distinguished by its relative biogeographic isolation.

Topography

The Ouachita Mountains lie south of the Ozark Plateau and together form the U.S. Interior Highlands. The area is characterized by east-west trending ridges and valleys, and share affinities with the Blue Ridge province, which was formed at the same time. Elevations range between 150 to 790 m, with Magazine Mountain rising 839 m (Robison 1986).

Freshwater habitats

The ecoregion is a source area for several larger streams and is an area of high-gradient and spring-fed springs, and can almost be considered an island surrounded by the Great Plains, coastal plains, and prairie.

Terrestrial habitats

The ecoregion is characterized by oak-hickory-pine forests, which are some of the best developed in the United States.  Dominant species include white oak (Q. alba), red oak (Quercus rubra), blackjack oak (Quercus marilandica), hickory (Carya texana), shortleaf yellow pine (Pinus echinata), and loblolly pine (Pinus taeda) (Ricketts et al. 1999).

Description of endemic fishes

The ecoregion contains a number of endemic species, including two madtoms (Noturus lachneri and N. taylori) and a darter (Etheostoma pallididorsum) that occur in the headwaters of the Ouachita, and a darter (Percina pantherina), which is endemic to the Little River. Other species that are primarily found in the Ouachita Mountains and Red and Ouachita drainages include the peppered shiner (Notropis perpallidus), rocky shiner (N. suttkusi), and Ouachita shiner (Lythrurus snelsoni) (Cross et al. 1986).