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Three level I areas were not subdivided for level 2. [2] Level III subdivides the continent into 182 smaller ecoregions; of these, 104 lie partly or wholly with the United States. [1] [3] Level IV is a further subdivision of Level III ecoregions. Level IV mapping is still underway but is complete across most of the United States.
The Springfield Plateau is the only Ozark Highland Level IV ecoregion within all four states. [1] The nearly level to rolling Springfield Plateau is underlain by cherty limestone of the Mississippian Boone Formation and Burlington Limestone; it is less rugged and wooded than Ecoregions 38, 39b, and 39c, and lacks the Ordovician dolomite and limestone of Ecoregions 39c and 39d.
[2] [7] Its highest and lowest points follow this trend, with its highest peak, Black Mesa, at 4,368 feet (1,516 m) above sea level, situated near the far northwest corner of the Oklahoma Panhandle. The state's lowest point is on the Little River near its far southeastern boundary, which dips to 289 feet (88 m) above sea level. [8]
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 ...
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. [4] The Cross Timbers are contained within the WWF central forest-grasslands transition ecoregion.
Ecoregions of North America, featuring the 50 United States, the District of Columbia and the five inhabited territories. The following is a list of ecoregions in the United States as identified by the World Wide Fund for Nature (WWF). The United States is a megadiverse country with a high level of endemism across a wide variety of ecosystems.
"Level I" divides North America into 15 broad ecoregions. "Level II" subdivides the continent into 52 smaller ecoregions. "Level III" subdivides those regions again into 182 ecoregions. [1] [2] "Level IV" is a further subdivision of Level III ecoregions. Level IV mapping is still underway but is complete across most of the United States.
The Boston Mountains is a Level III ecoregion designated by the Environmental Protection Agency (EPA) in the U.S. states of Arkansas and Oklahoma. Part of the Ozarks, the Boston Mountains are a deeply dissected plateau. The ecoregion is steeper than the adjacent Springfield Plateau to the north, and bordered on the south by the Arkansas Valley.