The outline of the Cross Timbers as defined by the EPA
|Biome||Central forest-grasslands transition|
|States||Texas, Oklahoma and Kansas|
The term Cross Timbers, also known as Ecoregion 29, Central Oklahoma/Texas Plains, is used to describe a strip of land in the United States that runs from southeastern Kansas across Central Oklahoma to Central Texas.Made up of a mix of prairie, savanna, and woodland, it forms part of the boundary between the more heavily forested eastern country and the almost treeless Great Plains, and also marks the western habitat limit of many mammals and insects.
An ecoregion is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than an ecozone. All three of these are either less or greater than an ecosystem. Ecoregions cover relatively large areas of land or water, and contain characteristic, geographically distinct assemblages of natural communities and species. The biodiversity of flora, fauna and ecosystems that characterise an ecoregion tends to be distinct from that of other ecoregions. In theory, biodiversity or conservation ecoregions are relatively large areas of land or water where the probability of encountering different species and communities at any given point remains relatively constant, within an acceptable range of variation.
The United States of America (USA), commonly known as the United States or America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico. The State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.
Kansas is a U.S. state in the Midwestern United States. Its capital is Topeka and its largest city is Wichita, with its most populated county being Johnson County. Kansas is bordered by Nebraska on the north; Missouri on the east; Oklahoma on the south; and Colorado on the west. Kansas is named after the Kansas River, which in turn was named after the Kansa Native Americans who lived along it banks. The tribe's name is often said to mean "people of the (south) wind" although this was probably not the term's original meaning. For thousands of years, what is now Kansas was home to numerous and diverse Native American tribes. Tribes in the eastern part of the state generally lived in villages along the river valleys. Tribes in the western part of the state were semi-nomadic and hunted large herds of bison.
No major metropolitan areas lie wholly within the Cross Timbers, although roughly the western half of the Dallas-Fort Worth Metroplex does, including the cities of Fort Worth, Denton, Arlington, and Weatherford.The western suburbs of the Tulsa metropolitan area and the northeastern suburbs of the Oklahoma City metropolitan area also lie within this area. The main highways that cross the region are I-35 and I-35W going north to south (although they tend to skirt the Cross Timbers' eastern fringe south of Fort Worth) and I-40 going east to west. Numerous U.S. Highways also cross the area.
Fort Worth is a city in the U.S. state of Texas. It is the 15th-largest city in the United States and fifth-largest city in Texas. It is the county seat of Tarrant County, covering nearly 350 square miles (910 km2) into four other counties: Denton, Johnson, Parker, and Wise. According to the 2017 census estimates, Fort Worth's population is 874,168. Fort Worth is the second-largest city in the Dallas–Fort Worth–Arlington metropolitan area, which is the 4th most populous metropolitan area in the United States.
Denton is a city in and the county seat of Denton County, Texas, United States. As of the 2010 United States Census, its population was 113,383, making it the 27th-most populous city in Texas, the 200th-most populous city in the United States, and the 12th-most populous city in the Dallas–Fort Worth metroplex.
Arlington is a city in the U.S. state of Texas, located in Tarrant County. It is part of the Mid-Cities region of the Dallas–Fort Worth–Arlington metropolitan area, approximately 12 miles (19 km) east of downtown Fort Worth and 20 miles (32 km) west of downtown Dallas.
The Cross Timbers are defined by the United States Environmental Protection Agency as Ecoregion 29, a Level III ecoregion. Some organizations and maps refer to the Cross Timbers ecoregion as the Central Oklahoma/Texas Plains.The Cross Timbers are contained within the WWF Central forest-grasslands transition ecoregion.
The Environmental Protection Agency (EPA) is an independent agency of the United States federal government for environmental protection. President Richard Nixon proposed the establishment of EPA on July 9, 1970 and it began operation on December 2, 1970, after Nixon signed an executive order. The order establishing the EPA was ratified by committee hearings in the House and Senate. The agency is led by its Administrator, who is appointed by the President and approved by Congress. The current Administrator is former Deputy Administrator Andrew R. Wheeler, who had been acting administrator since July 2018. The EPA is not a Cabinet department, but the Administrator is normally given cabinet rank.
The Central forest-grasslands transition is a prairie ecoregion of the central United States, an ecotone between eastern forests and the North American Great Plains. It is a classification defined by the World Wildlife Fund.
The woodland and savanna portions of the Cross Timbers are mainly post oak and blackjack oak on coarse, sandy soils; 890,000 acres (3,600 km2) of old-growth forest scattered throughout the region. These old-growth forests contain millions of post oak from 200 to 400 years old and red cedar over 500 years old. The prairie portions are chiefly tallgrass on finer, dry soils; overall, the Cross Timbers are not as arable as the surrounding ecoregions. Today, land use is a mixture of rangeland, pastures, and farmland. The area has also been an important site of oil extraction for over 80 years.fire suppression in recent years has increased forest density and allowed eastern redcedar to invade as well. The short, stout oaks that grow in the Cross Timbers were not usable as timber and those that were not cleared for farmland constitute one of the least disturbed forest types in the eastern United States (MADISON), with some
Juniperus virginiana, known as red cedar, eastern redcedar, Virginian juniper, eastern juniper, red juniper, pencil cedar, and aromatic cedar, is a species of juniper native to eastern North America from southeastern Canada to the Gulf of Mexico and east of the Great Plains. Further west it is replaced by the related Juniperus scopulorum and to the southwest by Juniperus ashei.
An old-growth forest — also termed primary forest or late seral forest — is a forest that has attained great age without significant disturbance and thereby exhibits unique ecological features and might be classified as a climax community. Old-growth features include diverse tree-related structures that provide diverse wildlife habitat that increases the biodiversity of the forested ecosystem. The concept of diverse tree structure includes multi-layered canopies and canopy gaps, greatly varying tree heights and diameters, and diverse tree species and classes and sizes of woody debris.
The Tallgrass prairie is an ecosystem native to central North America. Natural and anthropogenic fire, as well as grazing by large mammals, were historically agents of periodic disturbance, which regulates tree encroachment, recycles nutrients to the soil, and catalyzes some seed dispersal and germination processes. Prior to widespread use of the steel plow, which enabled conversion to agricultural land use, tallgrass prairies expanded throughout the American Midwest and smaller portions of southern central Canada, from the transitional ecotones out of eastern North American forests, west to a climatic threshold based on precipitation and soils, to the southern reaches of the Flint Hills in Oklahoma, to a transition into forest in Manitoba.
Geologically speaking, the Cross Timbers are underlain by Pennsylvanian and Cretaceous-era sandstone and limestone that has been moderately dissected, giving the region a gently to moderately rolling topography,including some cuestas. Although local relief is relatively low, it is generally greater than that in the surrounding ecoregions, although this is not the case with the Flint Hills in Kansas.
Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can also include the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology significantly overlaps all other earth sciences, including hydrology and the atmospheric sciences, and so is treated as one major aspect of integrated earth system science and planetary science.
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughlyto Ma. As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain by a few hundred thousand years. The Pennsylvanian is named after the U.S. state of Pennsylvania, where the coal-productive beds of this age are widespread.
The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago (mya) to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, and the longest period of the Phanerozoic Eon. The Cretaceous Period is usually abbreviated K, for its German translation Kreide.
Ecologically, the EPA includes the Cross Timbers as part of the vast Great Plains, which comprise Level I Ecoregion 9.0, stretching from central Alberta in Canada to northern Mexico.More specifically, the Cross Timbers fall into Level II Ecoregion 9.4, the smaller South Central Semi-Arid Plains. In southern Oklahoma, the Cross Timbers are literally located on the very edge of the Great Plains, as they border directly onto parts of Level I Ecoregion 8.0, the Eastern Temperate Forests; elsewhere, the Cross Timbers are separated slightly from the Eastern Temperate Forests. In turn, the Cross Timbers are themselves subdivided into nine Level IV Ecoregions:
Ecology is the branch of biology which studies the interactions among organisms and their environment. Objects of study include interactions of organisms that include biotic and abiotic components of their environment. Topics of interest include the biodiversity, distribution, biomass, and populations of organisms, as well as cooperation and competition within and between species. Ecosystems are dynamically interacting systems of organisms, the communities they make up, and the non-living components of their environment. Ecosystem processes, such as primary production, pedogenesis, nutrient cycling, and niche construction, regulate the flux of energy and matter through an environment. These processes are sustained by organisms with specific life history traits. Biodiversity means the varieties of species, genes, and ecosystems, enhances certain ecosystem services.
The Great Plains is the broad expanse of flat land, much of it covered in prairie, steppe, and grassland, that lies west of the Mississippi River tallgrass prairie in the United States and east of the Rocky Mountains in the U.S. and Canada. It embraces:
Central Alberta is a region located in the Canadian province of Alberta.
A wide belt of land stretching from south-central Oklahoma into southeastern Kansas, this is the only part of the Cross Timbers that extends into Kansas. In that state, it covers eastern Chautauqua and Elk counties and smaller portions of Greenwood, Woodson, Wilson, and Montgomery counties, while in Oklahoma, this region covers all of Seminole, Pottawatomie, and Okfuskee counties, large parts of Osage, Lincoln, Creek, Oklahoma, Cleveland, Pontotoc, Hughes, McIntosh, and Okmulgee counties, and smaller parts of Logan, Garvin, Murray, Pawnee, Tulsa, Wagoner, and Washington counties. The towns of Sand Springs, Sapulpa, Ada, and Shawnee, Oklahoma fall within this large area; Bartlesville and Okmulgee lie on the eastern edge.
In Oklahoma, this belt of woodland covers all of Marshall County and parts of Love, Carter, Johnston, and Bryan counties, but in Texas, this region exists as a long, very narrow strip of dense forest stretching from the Red River to just north of Waco, Texas. It passes through northwestern Grayson County, eastern Cooke, Denton and Tarrant counties, central Johnson County, western Hill County, and northern McClennan County. The city of Arlington, Texas lies within this zone, and Denton and Cleburne are on its western edge.
A much wider band than the Eastern Cross Timbers, the Western Cross Timbers band extends from far southern Oklahoma, including parts of Love and Carter counties, into central Texas, where it covers large parts of Montague, Young, Jack, Wise, Stephens, Palo Pinto, Parker, Eastland, Erath, Brown, San Saba, and Mills counties, as well as smaller parts of Clay, Cooke, Callahan, Hood, Coleman, and McCulloch counties. In Texas, this area includes the towns of Weatherford and Mineral Wells; Stephenville lies on the eastern fringe, while Brownwood is on the western edge.
The part of this region north of I-20 is sometimes colloquially referred to as the Palo Pinto Mountains;the hills are isolated, rugged, and scenic, with spectacular bluffs along the Brazos River as it flows through the region.
Coal mining has historically been an important activity, as bituminous coal deposits are found throughout the region;indeed, the town of Newcastle in Young County was named after the English city of the same name due to the coal connection.
In the mid-to-late 19th century, Comanche Indians occupied this area, and it became a flash point for conflict between various groups of white settlers, the Comanche, and the U.S. Cavalry; Forts Belknap and Richardson were built in the area to protect this part of the frontier.
Numerous roads cross this region, including US 70 in Oklahoma and I-20, I-30, US 67, US 81, US 82, US 180, US 183, US 281, US 287, and US 380 in Texas.
A fairly narrow strip dividing the Eastern and Western Cross Timbers, the Grand Prairie differs in physiography, topography, and land use from both of these, as it is much more nearly level and better suited to agriculture.It includes a small part of Love County, Oklahoma (the only part of this region outside of Texas) and passes south through western Cooke County, eastern Wise County, and western Denton, Tarrant, and Johnson counties, and also includes parts of Parker, Erath, Hood, Somervell, Hill, and McClennan counties. This region contains the cities of Fort Worth, Granbury and Denton, although Denton lies on the border with the Eastern Cross Timbers. I-35 and I-35W cross north to south, while US 82, US 380, I-30, I-20, US 377, and US 67 cross east to west; US 81 and US 287 also cross southwest to northeast.
A broader, southern extension of the Grand Prairie, found only in Texas; it is underlain by limestone rather than sandstone, and serves as a physiological and vegetational transition to the Edwards Plateau, which it borders to the south. All of Hamilton and Coryell counties, large parts of Bell, Lampasas, Mills, Erath, and Bosque counties, and smaller parts of Williamson, Burnet, Brown, Comanche, Hood, Somervell, and McClennan counties, including the towns of Killeen, Copperas Cove, and Lampasas as well as the Fort Hood Army base, fall within this region.Among the few major roads that cross the Limestone Cut Plains are US 281 north to south and US 84 east to west.
This ecoregion exists as an enclave within the Western Cross Timbers, stretching from southern Jack County, Texas across northwestern Palo Pinto County into eastern Stephens County, as well as tiny parts of Young and Eastland counties. The region features a limestone substrate as opposed to sandstone, and has greater topographical relief and denser and different vegetation than other parts of the Cross Timbers. No towns of any size lie within this area, although Possum Kingdom Lake and State Park do;the region is crossed by US 180 and Texas State Highway 16.
Covering a fairly small area in south-central Oklahoma and underlain by a unique mosaic of several different minerals, this region includes the town of Ardmore.
An extension in two branches of the Cross Timbers into southwestern Oklahoma, this area features reduced tree density and height, but also small forests dominated by sugar maple, bur oak, and live oak in deeper river canyons. The towns of Duncan, Oklahoma and Walters, Oklahoma, lie in this region.
The Arbuckle Mountains are located in a small area nestled in between regions 29g and h; it is made of folded, rather than dissected, limestone, sandstone, and dolomite, and features the greatest topographical relief of the entire Cross Timbers, though not the highest elevations. The landscape includes many caves, sinkholes, springs, and streams.I-35 crosses this region north to south.
Part of the difference in the Cross Timbers region and the surrounding regions west (drier) and east (wetter) has to do with the Dry line which separates humid air from the Gulf of Mexico from the dry air of the Llano Estacado, the Texas Panhandle, and the High Plains.
The thick growth formed an almost impenetrable barrier for early American explorers and travelers. Washington Irving, in 1835, described it as "like struggling through forests of cast iron."Rachel Plummer, while a captive of the Comanche in 1836, described it as "a range of timber-land from the waters of Arkansas, bearing a southwest direction, crossing the False Ouachita, Red River, the heads of Sabine, Angelina, Natchitoches, Trinity, Brazos, Colorado...the range of timber is of an irregular width, say 5 to 35 miles wide...abounding with small prairies, skirted with timber of various kinds - oak, of every description, ash, elm, hickory, walnut and mulberry...the purest atmosphere I ever breathed was that of these regions." Josiah Gregg described the Cross Timbers in 1845 as varying in width from five to thirty miles and attributed their denseness to the continual burning of the prairies.
The Cross Timbers vary in width from five to thirty miles, and entirely cut off the communication betwixt the interior prairies and those of the great plains. They may be considered as the "fringe" of the great prairies, being a continuous brushy strip, composed of various kinds of undergrowth; such as black-jack, post-oaks, and in some places hickory, elm, etc., intermixed with a very diminutive dwarf oak, called by the hunters, "shin-oak." Most of the timber appears to be kept small by the continual inroads of the "burning prairies;" for, being killed almost annually, it is constantly replaced by scions of undergrowth; so that it becomes more and more dense every reproduction. In some places, however, the oaks are of considerable size, and able to withstand the conflagrations. The Underwood is so matted in many places with grapevines, green-briars, etc., as to form almost impenetrable "roughs," which serve as hiding-places for wild beasts, as well as wild Indians; and would, in savage warfare, prove almost as formidable as the hammocks of Florida.— Josiah Gregg
Robert Neighbors and Rip Ford reached the "Cross Timbers, two parallel strips of timber region that ran down the middle of Texas", in 1849 while blazing an emigrant trail from Austin to El Paso. 116:
In physical geography, a steppe is an ecoregion, in the montane grasslands and shrublands and temperate grasslands, savannas and shrublands biomes, characterized by grassland plains without trees apart from those near rivers and lakes. In South Africa, they are referred to as veld. The prairie of North America is an example of a steppe, though it is not usually called such. A steppe may be semi-arid or covered with grass or shrubs or both, depending on the season and latitude. The term is also used to denote the climate encountered in regions too dry to support a forest but not dry enough to be a desert. The soil is typically of chernozem type.
Quercus marilandica, the blackjack oak, is a small oak, one of the red oak group Quercus sect. Lobatae. It is native to the eastern and central United States, from Long Island to Florida, west as far as Texas, Oklahoma, and Nebraska. There are reports of a few isolated populations in southern Michigan, but these appear to represent introductions.
The Piney Woods is a temperate coniferous forest terrestrial ecoregion in the Southern United States covering 54,400 square miles (141,000 km2) of East Texas, southern Arkansas, western Louisiana, and southeastern Oklahoma. These coniferous forests are dominated by several species of pine as well as hardwoods including hickory and oak. Historically the most dense part of this forest region was the Big Thicket though the lumber industry dramatically reduced the forest concentration in this area and throughout the Piney Woods during the 19th and 20th centuries. The World Wide Fund for Nature considers the Piney Woods to be one of the critically endangered ecoregions of the United States. The United States Environmental Protection Agency (EPA) defines most of this ecoregion as the South Central Plains.
The Texas Blackland Prairies are a temperate grassland ecoregion located in Texas that runs roughly 300 miles (480 km) from the Red River in North Texas to San Antonio in the south. The prairie was named after its rich, dark soil.
The geography of Texas is diverse and large. Occupying about 7% of the total water and land area of the U.S., it is the second largest state after Alaska, and is the southernmost part of the Great Plains, which end in the south against the folded Sierra Madre Oriental of Mexico. Texas is in the south-central part of the United States of America, and is considered to form part of the U.S. South and also part of the U.S. Southwest.
The Osage Plains are a physiographic section of the larger Central Lowland province, which in turn is part of the larger Interior Plains physiographic division. The area is sometimes called the Lower Plains, North Central Plains,or Rolling Plains. The Osage Plains, covering west-central Missouri, the southeastern third of Kansas, most of central Oklahoma, and extending into north-central Texas, is the southernmost of three tallgrass prairie physiographic areas. It grades into savanna and woodland to the east and south, and into shorter, mixed-grass prairie to the west. The Osage Plains consist of three subregions. The Osage Plains proper occupy the northeast segment. Although sharply demarcated from the Ozark uplift, the plains are nonetheless a transitional area across which the boundary between prairie and woodland has shifted over time. In the central portion of the physiographic area lies the second subregion, the Flint Hills, commonly called "the Osage" in Oklahoma. This large remnant core of native tallgrass prairie is a rocky rolling terrain that runs from north to south across Kansas and extends into Oklahoma. To the west and south of these hills are the Blackland Prairies and Cross Timbers. This vegetatively complex region of intermixed prairie and scrubby juniper-mesquite woodland extends into north-central Texas. Bluestem prairies and oak-dominated savannas and woodlands characterize the natural vegetation in the Cross Timbers. Much of the area has been converted to agriculture, although expanses of oak forest and woodland are still scattered throughout the eastern portion of the subregion.
The Willamette Valley ecoregion is a Level III ecoregion designated by the United States Environmental Protection Agency in the U.S. states of Oregon and Washington. Slightly larger than the Willamette Valley for which it is named, the ecoregion contains fluvial terraces and floodplains of the Willamette River system, scattered hills, buttes, and adjacent foothills. It is distinguished from the neighboring Coast Range, Cascades, and Klamath Mountains ecoregions by lower precipitation, lower elevation, less relief, and a different mosaic of vegetation. Mean annual rainfall is 37 to 60 inches, and summers are generally dry. Historically, the region was covered by rolling prairies, oak savanna, coniferous forests, extensive wetlands, and deciduous riparian forests. Today, it contains the bulk of Oregon's population, industry, commerce, and agriculture. Productive soils and a temperate climate make it one of the most important agricultural areas in Oregon.
The term Palo Pinto Mountains properly refers to a specific cuesta-like range of hills in western Palo Pinto County, Texas. The name Palo Pinto roughly translates to "painted stick" in reference to the juniper trees of the area. Isolated, rugged, and scenic, the ridge extends some 15 miles, from near the intersection of Texas State Highway 16 and Farm to Market Road 207 in the southwest, to Crawford Mountain just south of the Fortune Bend on the Brazos River in the northeast.
The Ozark Highlands is a Level III ecoregion designated by the Environmental Protection Agency (EPA) in four U.S. states. Most of the region is within Missouri, with a part in Arkansas and small sections in Oklahoma and Kansas. It is the largest subdivision of the region known as the Ozark Mountains, flatter in comparison to the Boston Mountains in Arkansas, the steepest part of the Ozarks.
The East Central Texas forests (33) is a small temperate broadleaf and mixed forests ecoregion almost entirely within the state of Texas, United States. The northern forests perimeter is partially within the southeast Oklahoma border.
The Interior Low Plateaus are a physiographic region in eastern United States. It consists of a diverse landscape that extends from north Alabama across central Tennessee and Kentucky into southern Illinois, Indiana, and Ohio. Its natural communities are a matrix of temperate forests, woodlands, and prairies.
The Central Great Plains are a semi-arid prairie ecoregion of the central United States, part of North American Great Plains. The region runs from west-central Texas through west-central Oklahoma, central Kansas, and south-central Nebraska.
The southwestern tablelands is an ecoregion running from east-central to south-east Colorado, east-central and a small portion of east New Mexico, some eastern portions of the Oklahoma Panhandle, far south-central Kansas and portions of northwest Texas. This ecoregion has a "cold semi-arid" climate. Some years, a National Weather Service warning is issued in parts of Texas due to a dust storm originating from the lower part of the Southwestern Tablelands ecological region or from the southern end of the Western High Plains ecological region.
The Arkansas Valley is a Level III ecoregion designated by the Environmental Protection Agency (EPA) in the U.S. states of Arkansas and Oklahoma. It parallels the Arkansas River between the flat plains of western Oklahoma and the Arkansas Delta, dividing the Ozarks and the Ouachita Mountains with the broad valleys created by the river's floodplain, occasionally interrupted by low hills, scattered ridges, and mountains. In Arkansas, the region is often known as the Arkansas River Valley, especially when describing the history and culture of the region.