The Piney Woods cover a 54,400-square-mile (141,000 km2) area of eastern Texas, northwestern Louisiana, southwestern Arkansas and the southeastern corner of Oklahoma.

Rodents found in the Piney Woods include the southern flying squirrel (Glaucomys volans), common muskrat (Ondatra zibethicus), Baird's pocket gopher (Geomys breviceps), woodland vole (Microtus pinetorum), and about 10 additional native rats and mice.

[8][9] Several of the larger carnivores that once occurred in the Piney Woods are entirely extirpated, including the hog-nosed skunk (Conepatus leuconotus), red wolf (Canis rufus), jaguar (Panthera onca), and ocelot (Leopardus pardalis).

The mountain lion (Puma concolor) and black bear (Ursus americanus) have also been extirpated from most areas; however, very rare sightings or remains are occasionally documented, likely representing wandering individuals rather than breeding populations.

[10][11] Stable populations of black bears occur in adjacent areas north and east of the Piney Woods and they appear to be slowly increasing in numbers and dispersing.

[12][13] With the clearing of forest and decline of the native predators (or competitors), the nine-banded armadillo (Dasypus novemcinctus), coyotes (Canis latrans), and black-tailed jackrabbit (Lepus californicus) have expanded their ranges eastward into the region.

A few of the many year round residents include the wood duck (Aix sponsa), black vulture (Coragyps atratus), red-shouldered hawk (Buteo lineatus), American kestrel (Falco sparverius), wild turkey (Meleagris gallopavo), northern bobwhite (Colinus virginianus), American woodcock (Scolopax minor), greater roadrunner (Geococcyx californianus), red-cockaded woodpecker (Picoides borealis), loggerhead shrike (Lanius ludovicianus), northern mockingbird (Mimus polyglottos), brown thrasher (Toxostoma rufum), Carolina chickadee (Poecile carolinensis), brown-headed nuthatch (Sitta pusilla), pine warbler (Dendroica pinus), Bachman's sparrow (Aimophila aestivalis), and fish crow (Corvus ossifragus).

Conversely, a different assemblage of birds migrate from the north to spend the winters months in the region, including the Canada goose (Branta canadensis), ring-necked duck (Aythya collaris), hooded merganser (Lophodytes cucullatus), blue-headed vireo (Vireo solitarius), Henslow's sparrow (Ammodramus henslowii), Le Conte's Sparrow (Ammodramus leconteii), and Smith's longspur (Calcarius pictus).

A few species that once occurred in the region are now extinct like the passenger pigeon (Ectopistes migratorius), Carolina parakeet (Conuropsis carolinensis), ivory-billed woodpecker (Campephilus principalis), and Bachman's warbler (Vermivora bachmanii).

Some of the non-venomous snakes include the rough greensnake (Opheodrys aestivus), Dekay's brownsnake (Storeria dekayi), eastern hog-nosed snake (Heterodon platirhinos), western ribbonsnake (Thamnophis proximus), glossy swampsnake (Liodytes rigida), southern watersnake (Nerodia fasciata), diamond-back watersnake (Nerodia rhombifer), red-bellied mudsnake (Farancia abacura), North American racer (Coluber constrictor), coachwhip (Masticophis flagellum), scarletsnake (Cemophora coccinea), prairie kingsnake (Lampropeltis calligaster), speckled kingsnake (Lampropeltis holbrooki), western ratsnake (Pantherophis obsoletus).

The western mosquitofish (Gambusia affinis), a species that has been widely introduced around the world and considered a pest in many areas, is a native in the Piney Woods.

[25][26][27] Some endemic flora and fauna of the Piney Woods (threatened species: Federal++; State +: historical isolated Illinois population now extirpated = *).

The rolling Tertiary Uplands, gently to moderately sloping, cover a large area in eastern Texas, southern Arkansas, and northern Louisiana.

[32] Major settlements in the region include much of Little Rock; El Dorado, Arkansas; Texarkana; Ruston, Louisiana; and Longview, Tyler, and Nacogdoches in Texas.

The Floodplains and Low Terraces of Ecoregion 35 comprise the western margin of the southern bottomland hardwood communities that extend along the Gulf and Atlantic coastal plains from Texas to Virginia.

[33] Region 35b is nearly level, veneered by Holocene alluvium, and contains natural levees, swales, oxbow lakes, and meander scars.

[32] Active, meandering alluvial river channels are dynamic systems, with erosion and deposition reworking the topography of levees, ridges, and swales.

Overbank flooding, subsurface groundwater, and local precipitation recharge water levels in backswamps, pools, sloughs, oxbows, and depressions of this floodplain region.

[32] Understory flora include holly, grape genus, poison ivy, crossvine, greenbriar, and a variety of ferns and mosses.

[34] Settlements of the Floodplains and Low Terraces include parts of Beaumont and Lake Charles; typically these narrow and wet regions are less developed.

[31] The southernmost piece of 35c, around Marksville, Louisiana, is a Pleistocene terrace with some similarities in soils and historical natural vegetation to that of the Lafayette Loess Plains (34j).

Streams lying in the Muddy Boggy Creek and Blue River watersheds often originate in, and share many aquatic species with, the Arbuckle Uplift (29g); alkalinity, hardness, and conductivity values are influenced by local springs, and increase westward.

[32] Some sandstone outcrops of the Catahoula Formation have distinctive barrens or glades in Texas and Louisiana that contain several rare species.

Forested seeps in sand hills support acid bog species including southern sweetbay, hollies, wax-myrtles, fetterbush, insectivorous plants, orchids, and wild azalea; this vegetation becomes more extensive in the Flatwoods (35f).

Currently, the ecoregion in Texas and Louisiana has more pine forest than the oak–pine and pasture land cover more typical to the north in the Tertiary Uplands (35a).

In the eastern part of the region near the boundary with the Red River Bottomlands (35g), more loess occurs, the landscape becomes more dissected, and it supports a mixed hardwood–pine forest.

[33] The area has a long history of modification, particularly by the lumber, railroad, and oil and gas industries that contributed to boom and bust cycles of development and occupance.

[34] The Holocene alluvium associated with Red River deposition developed well to somewhat poorly drained Vertisols and Entisols with clayey and loamy, reddish-brown, neutral to calcareous surfaces.

The Louisiana portion of the Red River Bottomlands shares similarities in natural vegetation and other biota, hydrology, and land uses with parts of the Mississippi Alluvial Plain (ecoregion 73).

The level to rolling Blackland Prairie characteristically has dark soils derived from underlying Cretaceous marl, chalk, and limestone.