Chapter 20
Ecological Subregions of the United States

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Southeastern Mixed Forest

Seven Sections have been delineated in this Province:

These Sections are located in the southeastern conterminous States, including parts of Virginia, North and South Carolina, Georgia, Alabama, Mississippi, Arkansas, Louisiana, and Texas. The area of these Sections is about 193,000 mi2 (499,900 km2).

Section 231A--Southern Appalachian Piedmont

Geomorphology. This Section is in the Appalachian Piedmont geomorphic province. It consists of an intensely metamorphosed, moderately dissected plain consisting of thick saprolite, continental sediments, and accreted terranes. Differential erosion has produced some isolated mountains (monadnocks) which rise above the general land surface. Landforms on about 70 percent of the Section are irregular plains. Landforms on the remaining area are about equally divided; plains with high hills; open low hills; and tablelands of moderate relief. Elevation ranges from 330 to 1,300 ft (100 to 400 m). Local relief ranges from 100 to 300 ft (30 to 90 m).

Lithology and Stratigraphy. Rock units formed during the Precambrian (60 percent), Paleozoic (30 percent), and Mesozoic (10 percent) Eras. Precambrian strata consist of metamorphic complexes with compositions of schist and phylite, and mafic paragneiss. Paleozoic strata consist of about equal amounts of Cambrian eugeosynclinal and volcanic rocks. Mesozoic strata consists of Triassic marine deposits (sandstone, siltstone, and shale).

Soil Taxa. Udults are the predominant soils. Paleudults and Hapludults are on gently sloping uplands. Steeper slopes are dominated by Hapludults, Rhodudults, Dystrochrepts, and Hapludalfs. Dystrochrepts, Udifluvents, and Fluvaquests are on alluvium. Soils have a thermic temperature regime, and kaolinitic, mixed, or oxidic mineralogy. Soils are generally deep, with a clayey or loamy subsoil. In many areas soils are severely eroded as a result of past intensive agricultural practices, especially for cotton production.

Potential Natural Vegetation. K\"uchler mapped this area as oak-hickory-pine forest and southern mixed forest. Predominant vegetation form is evergreen forest with rounded crowns, and about equal areas of cold-deciduous broad-leaved forest with evergreen needle-leaved trees. The oak-hickory forest cover type consists of white, post, and southern red oaks, and hickories of pignut and mockernut. The loblolly-shortleaf pine cover type is common on disturbed areas and usually has an understory component of dogwood and sourwood.

Fauna. Among the fauna in this Section are white-tailed deer, black bear, bobcat, gray fox, raccoon, cottontail rabbit, gray squirrel, fox squirrel, eastern chipmunk, white-footed mouse, pine vole, short-tailed shrew and cotton mouse. The turkey, 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.

Climate. Average annual precipitation ranges from 45 to 55 in (1120 to 1400 mm). Temperature averages 58 to 64 oF (14 to 18 oC). The growing season lasts about 205 to 235 days.

Surface Water Characteristics. There is moderate density of small to medium size perennial streams and associated rivers, mostly with low to moderate rates of flow and moderate velocity. A dendritic drainage pattern has developed on moderately dissected surface, with some influence from the underlying bedrock. Many rivers drain this Section, including the Chattahoochee, Ocmulgee, Savannah, Saluda, and Yadkin.

Disturbance Regimes. Fire has probably been the principal historical disturbance, previously burning over small to moderate-size areas between natural barriers with low frequency and low intensity. Climatic influences include occasional summer droughts and winter ice storms, and infrequent tornadoes. Insect-related disturbances are often caused by southern pine beetles.

Land Use. Natural vegetation has been cleared for agriculture on most of the area, especially for cotton production in the 1800's.

Cultural Ecology. Reserved.

Compiled by Southeastern Forest Experiment Station and Southern Region.

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Section 231B--Coastal Plains, Middle

Geomorphology. This Section is in the Coastal plains geomorphic province. The predominant landform on about 80 percent of the area consists of moderately dissected, irregular plains of marine origin formed by deposition of continental sediments onto submerged, shallow continental shelf, which was later exposed by sea level subsidence. Elevation ranges from 80 to 650 ft (25 to 200 m). Local relief ranges from 100 to 300 ft (30 to 90 m).

Lithology and Stratigraphy. Rock units formed during the Mesozoic (40 percent) and Cenozoic (60 percent) Eras. Mesozoic strata consist of Cretaceous marine sediments (sands and clays). Cenozoic strata consists of Tertiary marine deposits (siliceous strata with lignitic, sandy, and argillaceous deposits).

Soil Taxa. Soils are mostly Udults. Paleudults and Hapludults are on level to strongly sloping uplands. Loamy Fragiudults and Paleudults are present on less sloping, moderately well drained areas. Small but significant areas of Quartzipsamments, Paleudalfs, and Glossaqualfs are present in localized areas. Albaquults and Paleaquults are found on low wetlands. Bottom land soils may be dominated by Fluvaquents and Dystrochrepts. The soils have a thermic temperature regime, an udic moisture regime, a loamy or sandy surface layer, and a loamy or clayey subsoil. Soils generally are deep, well to poorly drained, and have adequate moisture for use by vegetation during the growing season.

Potential Natural Vegetation. K\"uchler mapped vegetation as oak-hickory-pine forest, blackbelt, and oak-hickory forest. The predominate vegetation form is evergreen, needle-leaved forest with cold-deciduous, broad-leaved trees. The principal forest cover type consists of loblolly and shortleaf pine with hardwoods, including sweetgum, flowering dogwood, elm, red cedar, southern red oak, and hickories. In central Mississippi and Alabama the hardwood component may be dominant, depending on soil moisture regime and past disturbance. A narrow band of oak-hickory forest type occurs along the extreme western edge of the Section, adjacent to flood plains of the Mississippi River and along major river bottoms.

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.

Climate. Precipitation averages 40 to 60 in (1,020 to 1,520 mm). Temperature averages 60 to 68 oF (16 to 20 oC). The growing season lasts about 200 to 280 days.

Surface Water Characteristics. There is a moderate density of small to medium perennial streams and associated rivers, most with moderate volume of water at low velocity. Dendritic drainage pattern has developed on this moderately dissected plain, largely without bedrock structural control.

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

Land Use. Natural vegetation has been cleared for agriculture on about 30 percent of the area.

Cultural Ecology. Reserved.

Compiled by Southern Region and the Southeastern Forest Experimental Station.

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Section 231C--Southern Cumberland Plateau

Geomorphology. This Section is in the Appalachian Plateaus geomorphic province. It was formed by the broad uplift of gently-dipping strata to a level-bedded plateau, followed by fluvial erosion and mass wasting. The result of these geomorphic processes is a strongly dissected region of dendritic drainages. About 60 percent of this Section consists of open hills. Other landforms consist of tablelands of considerable relief and open high hills. Elevation ranges from 330 to 1,300 ft (100 to 400 m). Local relief ranges from 300 to 500 ft (90 to 150 m).

Lithology and Stratigraphy. Rock units formed during the Paleozoic Era. Strata consist of 5 percent Mississippian marine deposits (shales, limestone, and chert); 90 percent Pennsylvanian marine deposits (sandstone, shale, coal, and limestone); and 5 percent other Paleozoic marine deposits.

Soil Taxa. Soils are mainly Udults and Ochrepts. Hapludults are on plateaus and upper slopes. Deep Hapludults are present on level sites. Hapludults and Fragiudults are found on level uplands. Upper valley slopes and ridgetops are dominated by Dystrochrepts. Hapludults and Paleudults are found on lower side slopes and terraces. Rock outcrops are common, but not extensive. Soils have a udic moisture regime, a thermic temperature regime, and mixed mineralogy. Most soils are fine textured, deep, and moist during the growing season.

Potential Natural Vegetation. K\"uchler mapped vegetation as oak-hickory-pine forest and southern mixed forest. The predominant vegetation form consists of needle-leaved, evergreen trees with cold-deciduous, broad-leaved forest. Principal species include loblolly pine, sweetgum, water oak, red maple, southern red oak, and white oak.

Fauna. Among the fauna in this Section are white-tailed deer, black bear, bobcat, gray fox, raccoon, cottontail rabbit, gray squirrel, fox squirrel, eastern chipmunk, white-footed mouse, pine vole, short-tailed shrew, and cotton mouse. The turkey, 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.

Climate. Mean annual precipitation is 50 to 55 in (1,270 to 1,400 mm). Temperature averages 60 to 62 oF (16 to 17 oC). The growing season lasts for 200 to 210 days.

Surface Water Characteristics. There is a moderate density of small to medium size perennial streams and associated rivers, mostly with low to moderate rates of flow and moderate velocity. Dendritic drainage pattern has developed, with influence from the underlying bedrock.

Disturbance Regimes. Fire has probably been the principal historical disturbance. Climatic influences include occasional summer droughts, winter ice storms, and occasional tornadoes.

Land Use. Natural vegetation has been cleared for agriculture on about 30 percent of the area.

Cultural Ecology. Reserved.

Compiled by Southeastern Forest Experiment Station and Southern Region.

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Section 231D--Southern Ridge and Valley

Geomorphology. This Section is in the Ridge and Valley geomorphic province. The area is a folded, faulted, and uplifted belt of parallel valleys and ridges, strongly dissected by differential erosion, mass wasting, fluvial erosion, and transport and deposition. About 60 percent of this Section consists of plains with hills and 40 percent consists of open high hills. Elevation ranges from 650 to 2,000 ft (200 to 600 m). Local relief ranges from 300 to 500 ft (90 to 150 m) in areas of plains, with elevation ranging from 500 to 1,000 ft (150 to 300 m) in areas of high hills.

Lithology and Stratigraphy. Rock units formed during the Paleozoic Era. Strata consists of a mosaic of marine deposits of Lower Cambrian clastic rocks (granites), and a mixture of marine deposits of Cambrian (carbonates and shales), Lower Ordovician (carbonates), and Mississippian (shales, limestone, and chert) ages.

Soil Taxa. Soils are mostly Udults with some Ochrepts. Paleudults dominate upland areas underlain by limestone. Hapludults are in valleys underlain by shale. Dystrochrepts are common on side slopes of ridges. Hapludolls and Eutrochrepts are on bottom lands. Soils have an udic moisture regime and thermic or mesic temperature regime. Almost all soils are well drained. Soils range from shallow on sandstone and shales to very deep on limestone formations.

Potential Natural Vegetation. K\"uchler mapped vegetation as oak-hickory-pine forest and southern mixed forest. The predominant vegetation form is needle-leaved, evergreen trees with cold deciduous, broad-leaved forest. The principal cover type is oak-hickory, which includes southern red oak, white oak, post oak, red maple, winged elm, flowering dogwood, pignut hickory, and loblolly pine. In some areas, loblolly and shortleaf pines are dominant.

Fauna. Among the fauna in this Section are white-tailed deer, black bear, bobcat, gray fox, raccoon, cottontail rabbit, gray squirrel, fox squirrel, eastern chipmunk, white-footed mouse, pine vole, short-tailed shrew, and cotton mouse. The turkey, 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.

Climate. Precipitation averages 36 to 55 in (900 to 1,400 mm) annually. Mean annual temperature is from 55 to 61 oF (13 to 16 oC). The growing season lasts about 170 to 210 days.

Surface Water Characteristics. This Section has a moderate density of small to medium size perennial streams and associated rivers, mostly with low to moderate rates of flow and moderate velocity. Trellis drainage pattern has developed with bedrock structural control. One of the major rivers draining this Section is the Coosa.

Disturbance Regimes. Fire has probably been the principal historical disturbance, previously burning over small areas between natural barriers with moderate frequency and low intensity. Insect related disturbances have resulted from southern pine beetles. Climatic related influences include occasional droughts and ice storms.

Land Use. Natural vegetation has been cleared for agriculture on over 60 percent of the area.

Cultural Ecology. Reserved.

Compiled by Southern Region and Southeastern Forest Experiment Station.

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Section 231E--Mid Coastal Plains, Western

Geomorphology. This Section is in the Coastal Plains geomorphic province. The predominant landform occupying about 80 percent of the Section consists of moderately dissected irregular plains of marine origin. The plains were formed by deposition of continental sediments onto submerged, shallow continental shelf, which was later exposed by sea level subsidence. Other landforms consist of plains with hills and smooth plains. Elevations range from 80 to 650 ft (25 to 200 m). Local relief ranges from 100 to 300 ft (30 to 90 m).

Lithology and Stratigraphy. Rock units formed during the Cenozoic Era. Strata consist of Tertiary marine deposits (glauconitic sands and clays with lenses of coquinid limestone; clay and silty clay).

Soil Taxa. Soils are predominantly Udults. Paleudults, Hapludults, Hapludalfs, Paleudalfs, and Albaqualfs are on uplands. Fluvaquents, Udifluvents, Eutrochrepts, and Glossaqualfs are on bottom lands along major streams. Soils have a thermic temperature regime, a udic moisture regime, and siliceous or mixed mineralogy. Most soils have formed from sandstone and shale parent materials. Soils are generally coarse textured, deep, and have adequate moisture for plant growth during the growing season.

Potential Natural Vegetation. K\"uchler mapped this area as oak-hickory-pine forest, southern mixed forest, and southern floodplain forest. The predominant vegetation form consists of needle-leaved evergreen trees. Belts of cold deciduous, broad-leaved hardwoods are prevalent along rivers. The principal forest cover type is loblolly and longleaf pines. Where hardwoods are prevalent, species consist of post, white, blackjack, and southern red oaks. Species of bottom lands are red maple, green ash, Nuttall oak, sweetgum, and swamp hickory.

Fauna. The elk, mountain lion, wolf, Carolina parakeet, and ivory-billed woodpecker once inhabited this Section. Presently, the fauna include white-tailed deer, black bear, bobcat, gray fox, raccoon, cottontail rabbit, gray squirrel, fox squirrel, striped skunk, swamp rabbit, and many small rodents and shrews. The turkey, bobwhite, and mourning dove are game birds in various parts of this Section. In flooded areas, ibises, cormorants, herons, egrets, and kingfishers are common. 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.

Climate. Annual precipitation averages 40 to 54 in (1,000 to 1,300 mm). Temperature averages 61 to 68 oF (16 to 20 oC). The growing season lasts about 200 to 270 days.

Surface Water Characteristics. There is a moderate density of small to medium size perennial streams and associated rivers, most with moderate volume of water flowing at low velocity. Dendritic drainage pattern has developed. Major rivers draining this Section include the Red and Ouachita.

Disturbance Regimes. Fire has probably been the principal historical disturbance. Climatic influences include occasional summer droughts and winter ice storms, and infrequent hurricanes. 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. Much of the non-cleared land is managed for forestry.

Cultural Ecology. Reserved.

Compiled by Southern Region and Southern Research Station.

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Section 231F--Eastern Gulf Prairies and Marshes

Geomorphology. This Section is in the Coastal Plains geomorphic province. The predominant landform is a flat, weakly dissected alluvial plain formed by deposition of continental sediments onto submerged, shallow continental shelf, which was later exposed by sea level subsidence. Along the coast, fluvial deposition and shore zone processes are active in developing and maintaining beaches, swamps, and mud flats. Elevation ranges from 10 to 330 ft (3 to 100 m). Local relief ranges from 0 to 100 ft (0 to 30 m).

Lithology and Stratigraphy. Rock units formed during the Cenozoic Era. Strata consist of Quaternary marine deposits (non-glacial sand, silt, and clay deposits of upland origin).

Soil Taxa. Aquolls, Saprists, Aquents, and Hemists are the principal soils along the coast. Also along the coast are Aquolls, Haplaquolls, Medisaprists, Hydraquents, and Medihemists, all of which are poorly drained and subject to flooding and high water tables. These soils have a thermic temperature regime and an aquic moisture regime. Farther inland, Uderts and Aqualfs are the main soils, especially where saline prairie vegetation is present. Soils farther inland on low lands are Pelluderts, Pellusterts, Albaqualfs, Ochraqualfs, and Glossaqualfs. Situated on flood plains are Argiaquolls, Haplaquolls, and Haplaquepts. Soils have a thermic to hyperthermic moisture regime, and an aquic moisture regime. These soils are deep, clayey, poorly drained, and have subsoils that are slowly permeable.

Potential Natural Vegetation. K\"uchler classified vegetation as bluestem-sacahuista prairie and southern cordgrass prairie. Predominant vegetation is mid to tall grass grasslands. Species consist of little bluestem, indiangrass, switchgrass, and big bluestem. Occasional areas of live oak are present. Poorly drained areas along the coast support freshwater and saltwater marsh vegetation of sedges, rushes, saltgrass, and cordgrass.

Fauna. Typical large herbivores and carnivores include manatee, coyote, red wolf, ringtail, ocelots, and river otter. Smaller herbivores include swamp rabbit, fulvous harvest mouse, eastern wood rat, and nutria. Common birds of freshwater marshes, lakes, ponds, and rivers include reddish egret, white-faced ibis, white-fronted goose, and olivaceous cormorant. Attwater's prairie chicken was once common in the grasslands. Reptiles and amphibians include American alligator, Gulf coast salt marsh snake, Gulf coast toad and pig frog, diamondback terrapin, Mediterranean gecko, and the Texas horned lizard.

Climate. Average annual precipitation is from 30 to 55 in (750 to 1,400 mm). Temperature averages 66 to 74 oF (19 to 23 oC). The growing season lasts 250 to 330 days.

Surface Water Characteristics. There is a moderate density of small to medium size perennial streams and very low density of associated rivers; most have a moderate volume of water at very low velocity. Water table is high in many areas, resulting in poor natural drainage and abundance of wetlands. Poorly defined drainage pattern has developed on this very young, weakly dissected plain. Abundance of palustrine systems having seasonally high water level. This Section adjoins the Louisianian Marine and Estuarine Province delineated by the USDI Fish and Wildlife Service.

Disturbance Regimes. Fire and ocean tides have likely been the principal historical disturbance. Climatic influences include occasional hurricanes.

Land Use. Natural vegetation has been cleared for agricultural crops on about 40 percent of the area.

Cultural Ecology. Reserved.

Compiled by Southeastern Forest Experiment Station and Southern Region.

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Section 231G--Arkansas Valley

Geomorphology. This Section is in the Ouachita geomorphic province. The area consists of a folded, faulted, and uplifted belt of parallel valleys and ridges, moderately dissected by differential erosion, mass wasting, fluvial erosion and transport and deposition. About 80 percent of this land consists of plains with hills and 20 percent includes open low mountains. Elevation ranges from 330 to 3,000 ft (100 to 900 m). Local relief ranges from 300 to 500 ft (90 to 150 m) in areas with hills. Relief is 500 to 1,000 ft (150 to 300 m) in areas with low mountains.

Lithology and Stratigraphy. Rocks units formed during the Paleozoic Era. Strata consist of Pennsylvanian marine deposits (sandstone, shale, coal, and limestone).

Soil Taxa. Soils are predominately Udults. Hapludults and Paleudults are on ridgetops and upper slopes, and are also on mid to lower slopes in concave positions. Fragiudults are in valleys. Soils along the Arkansas River include Udifluvents, Udipsamments, Haplaquolls, and Hapludalfs. Soils have a thermic temperature regime, a udic moisture regime, and siliceous or mixed mineralogy. Soils are variable in characteristics, ranging from shallow to deep, but most are well drained. Soil moisture is adequate for plant growth during most of the growing season.

Potential Natural Vegetation. K\"uchler mapped vegetation as oak-hickory forest, oak-hickory-pine forest, cross timbers ({\it Quercus-Andropogon}), and southern floodplains forest. The predominant vegetation form is about equal areas of cold-deciduous, broad-leaved forest and needle-leaved evergreen trees. Principal forest cover types are oak-hickory and loblolly-shortleaf pine. Species include white, black, bur, post, and blackjack oaks; pignut and mockernut hickories; and loblolly and shortleaf pines. Oak-gum-cypress forest type is dominant along major river bottoms and includes cottonwood, sugarberry, river birch, and green ash.
Fauna. Historically, the elk, Florida panther, bison, passenger pigeon, ivory -billed woodpecker, Carolina parakeet, and Bachman's warbler inhabited this Section. Presently the fauna include white-tailed deer, black bear, bobcat, gray fox, raccoon, cottontail rabbit, gray squirrel, fox squirrel, striped skunk, swamp rabbit, and many small rodents and shrews. In flooded areas, beavers, ibises, cormorants, herons, egrets, and kingfishers are common. Endemics include the Magazine Mountain shagreen, longnose darter, and Arkansas darter. 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.

Climate. Annual average precipitation is 44 to 50 in (1,120 to 1,270 mm). Average temperature is 61 to 63 oF (16 to 17 oC). The growing season lasts 200 to 240 days.

Surface Water Characteristics. This Section has 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. One of the large rivers draining this Section is the Arkansas.

Disturbance Regimes. Reserved.

Land Use. Reserved.

Cultural Ecology. Reserved. Compiled by Southern Region and Southern Research Station.

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