Nearctic ecozone

Nearctic ecozone

The Nearctic is one of the eight terrestrial ecozones dividing the Earth's land surface.

The Nearctic Ecozone

The Nearctic ecozone covers most of North America, including Greenland and the highlands of Mexico. Southern Mexico, southern Florida, Central America, and the Caribbean islands are part of the Neotropic ecozone, together with South America.

Contents

Major ecological regions

The World Wildlife Fund (WWF) divides the Nearctic into four Bioregions, defined as "geographic clusters of ecoregions that may span several habitat types, but have strong biogeographic affinities, particularly at taxonomic levels higher than the species level (genus, family)."

Canadian Shield

The Canadian Shield bioregion extends across the northern portion of the continent, from the Aleutian Islands to Newfoundland. It includes the Nearctic's Arctic Tundra and Boreal forest ecoregions.

In terms of floristic provinces, it is represented by part of the Canadian Province of the Circumboreal Region.

Eastern North America

The Eastern North America bioregion includes the Temperate broadleaf and mixed forests of the eastern United States and southeastern Canada, the Great Plains temperate grasslands of the central United States and south-central Canada, and the Temperate coniferous forests of the southeastern United States.

In terms of floristic provinces, it is represented by the North American Atlantic Region and part of the Canadian Province of the Circumboreal Region.

Western North America

The Western North America bioregion includes the Temperate coniferous forests of the coastal and mountain regions of southern Alaska, western Canada, and the western United States from the Pacific Coast and Northern California to the Rocky Mountains, as well as the cold-winter intermountain deserts and xeric shrublands and temperate grasslands and shrublands of the western United States.

In terms of floristic provinces, it is represented by the Rocky Mountain Region.

Northern Mexico and Southwestern North America

The Northern Mexico bioregion includes the mild-winter to cold-winter deserts and xeric shrublands of northern Mexico, Southern California, and the Southwestern United States, including the Chihuahuan, Sonoran, and Mojave deserts. The Mediterranean climate ecoregions of the Southern and Central Coast of California include the California chaparral and woodlands, California coastal sage and chaparral, California interior chaparral and woodlands, and California montane chaparral and woodlands.

The bioregion also includes the warm temperate and subtropical pine and pine-oak forests, including the Arizona Mountains forests and the Sierra Madre Occidental, Sierra Madre Oriental, and Sierra Juarez and San Pedro Martir pine-oak forests.

In terms of floristic provinces, it is represented by the Madrean Region.

History

Although North America and South America are presently joined by the Isthmus of Panama, these continents were separated for about 180 million years, and evolved very different plant and animal lineages. When the ancient supercontinent of Pangaea split into two about 180 million years ago, North America remained joined to Eurasia as part of the supercontinent of Laurasia, while South America was part of the supercontinent of Gondwana. North America later split from Eurasia. North America has been joined by land bridges to both Asia and South America since then, which allowed an exchange of plant and animal species between the continents, the Great American Interchange.

A former land bridge across the Bering Strait between Asia and North America allowed many plants and animals to move between these continents, and the Nearctic ecozone shares many plants and animals with the Palearctic. The two ecozones are sometimes included in a single Holarctic ecozone.

Many large animals, or megafauna, including horses, camels, mammoths, mastodonts, ground sloths, sabre-tooth cats (Smilodon), the giant short-faced bear (Arctodus simus), and the cheetah, became extinct in North America at the end of the Pleistocene epoch (ice ages), at the same time the first evidence of humans appeared, in what is called the Holocene extinction event. Previously, it was believed that the megafaunal extinctions were caused by the changing climate, but many scientists now believe that while the climate change contributed to these extinctions, the primary cause was hunting by newly-arrived humans or, in the case of some large predators, extinction resulting from prey becoming scarce. The American bison (Bison bison), brown bear or grizzly bear (Ursus arctos), and elk or wapiti (Cervus canadensis) entered North America around the same time as the first humans, and expanded rapidly, filling ecological niches left empty by the newly-extinct North American megafauna.

Flora and fauna

Flora and fauna that originated in the Nearctic

Animals originally unique to the Nearctic include:

Flora and fauna endemic to the Nearctic

One bird family, the wrentits (Timaliinae), is endemic to the Nearctic region. The Holarctic has four endemic families: divers (Gaviidae), grouse (Tetraoninae), auks (Alcidae), and the waxwings (Bombycillidae). The scarab beetle families Pleocomidae and Diphyllostomatidae (Coleoptera) are also endemic to the Nearctic. The fly species Cynomya cadaverina is also found in high numbers in this area.

Plants families endemic or nearly endemic to the Nearctic include Crossosomataceae, Simmondsiaceae, and Limnanthaceae.

Nearctic Terrestrial Ecoregions

Nearctic Tropical and subtropical dry broadleaf forestsv · Sonoran-Sinaloan transition subtropical dry forest
Mexico
Nearctic Tropical and subtropical coniferous forestsv · Bermuda subtropical conifer forests
Bermuda
Sierra Madre Occidental pine-oak forests Mexico, United States
Sierra Madre Oriental pine-oak forests Mexico, United States
Nearctic Temperate broadleaf and mixed forestsv · Allegheny Highlands forests
United States
Appalachian mixed mesophytic forests United States
Appalachian-Blue Ridge forests United States
California mixed evergreen forest United States
Central U.S. hardwood forests United States
East Central Texas forests United States
Eastern forest-boreal transition Canada, United States
Eastern Great Lakes lowland forests Canada, United States
Gulf of St. Lawrence lowland forests Canada
Lac Saint-Jean and Saguenay valley forests Canada
Mississippi lowland forests United States
New England-Acadian forests Canada, United States
Northeastern coastal forests United States
Ozark Mountain forests United States
Southeastern mixed forests United States
Southern Great Lakes forests United States
Upper Midwest forest-savanna transition United States
Western Great Lakes forests Canada, United States
Willamette Valley forests United States
Nearctic Temperate coniferous forestsv · Alberta Mountain forests
Canada
Alberta-British Columbia foothills forests Canada
Arizona Mountains forests United States
Atlantic coastal pine barrens United States
Blue Mountains forests United States
British Columbia mainland coastal forests Canada, United States
Cascade Mountains leeward forests Canada, United States
Central and Southern Cascades forests United States
Central British Columbia Mountain forests Canada
Central Mexican Volcanoes forests Mexico
Central Pacific coastal forests Canada, United States
Colorado Rockies forests United States
Eastern Cascades forests Canada, United States
Fraser Plateau and Basin complex Canada
Great Basin montane forests United States
Klamath-Siskiyou forests United States
Maritime Coast Range Ponderosa Pine forests United States
Middle Atlantic coastal forests United States
North Central Rockies forests Canada, United States
Northern California coastal forests United States
Northern Pacific coastal forests Canada, United States
Northern transitional alpine forests Canada
Okanogan dry forests Canada, United States
Piney Woods forests United States
Puget lowland forests Canada, United States
Queen Charlotte Islands Canada
Sierra Juarez and San Pedro Martir pine-oak forests Mexico
Sierra Nevada forests United States
South Central Rockies forests United States
Southeastern conifer forests United States
Wasatch and Uinta montane forests United States
Nearctic Boreal forests/taigav · Alaska Peninsula montane taiga
United States
Central Canadian Shield forests Canada, United States
Cook Inlet taiga United States
Copper Plateau taiga United States
Eastern Canadian forests Canada
Eastern Canadian Shield taiga Canada
Interior Alaska-Yukon lowland taiga Canada, United States
Mid-Continental Canadian forests Canada
Midwestern Canadian Shield forests Canada, United States
Muskwa-Slave Lake forests Canada
Newfoundland Highland forests Canada
Northern Canadian Shield taiga Canada
Northern Cordillera forests Canada
Northwest Territories taiga Canada
South Avalon-Burin oceanic barrens Canada
Southern Hudson Bay taiga Canada
Yukon Interior dry forests Canada
Nearctic Tropical and subtropical grasslands, savannas, and shrublandsv · Pre-Columbian savannas of North America (greatly declined)
Canada, United States
Eastern savannas of the United States (greatly declined) United States
Central Hardwood Region (greatly declined) United States
Western Gulf coastal grasslands Mexico, United States
Nearctic Temperate grasslands, savannas, and shrublandsv · California Central Valley grasslands
United States
Canadian aspen forests and parklands Canada, United States
Central and Southern mixed grasslands United States
Central forest-grasslands transition United States
Central tall grasslands United States
Columbia Plateau United States
Edwards Plateau savanna United States
Flint Hills tall grasslands United States
Montana valley and foothill grasslands United States
Nebraska Sand Hills mixed grasslands United States
Northern mixed grasslands Canada, United States
Northern short grasslands Canada, United States
Northern tall grasslands Canada, United States
Palouse grasslands United States
Texas blackland prairies United States
Western short grasslands United States
Nearctic Tundrav · Alaska-St. Elias Range tundra
Canada, United States
Aleutian Islands tundra United States
Arctic coastal tundra Canada, United States
Arctic foothills tundra Canada, United States
Baffin coastal tundra Canada
Beringia lowland tundra United States
Beringia upland tundra United States
Brooks-British Range tundra Canada, United States
Davis Highlands tundra Canada
High Arctic tundra Canada
Interior Yukon-Alaska alpine tundra Canada, United States
Kalaallit Nunaat high arctic tundra Greenland
Kalaallit Nunaat low arctic tundra Greenland
Low Arctic tundra Canada
Middle Arctic tundra Canada
Ogilvie-MacKenzie alpine tundra Canada, United States
Pacific Coastal Mountain icefields and tundra Canada, United States
Torngat Mountain tundra Canada
Nearctic Mediterranean forests, woodlands, and scrubv · California coastal sage and chaparral
Mexico, United States
California interior chaparral and woodlands United States
California montane chaparral and woodlands United States
Nearctic Deserts and xeric shrublandsv · Baja California desert
Mexico
Central Mexican matorral Mexico
Chihuahuan desert Mexico, United States
Colorado Plateau shrublands United States
Great Basin shrub steppe United States
Gulf of California xeric scrub Mexico
Meseta Central matorral Mexico
Mojave desert United States
Okanagan (South) shrub steppe Canada
Snake-Columbia shrub steppe United States
Sonoran desert Mexico, United States
Tamaulipan matorral Mexico
Tamaulipan mezquital Mexico
Wyoming Basin shrub steppe United States

External links

References

  • Flannery, Tim (2001). The Eternal Frontier: an Ecological History of North America and its Peoples. Grove Press, New York.
  • Ricketts, Taylor H., Eric Dinerstein, David M. Olson, Colby J. Loucks, et al. (1999). Terrestrial Ecoregions of North America: a Conservation Assessment. Island Press, Washington DC.

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