Nearctic realm

Nearctic realm
carol · CC BY-SA 3.0 · source
Name	Nearctic realm
Countries	United States, Canada, Mexico, Greenland, Bermuda
Biogeographic class	Terrestrial realm

Nearctic realm The Nearctic realm is a major biogeographic region that comprises much of North America, including United States, Canada, Greenland, and parts of Mexico and associated islands such as Bermuda. It is defined by distinctive assemblages of mammals, birds, reptiles, amphibians, invertebrates, and plants shaped by geological, climatic, and evolutionary processes. The realm features contrasts from Arctic tundra to temperate forests and deserts, and it interfaces with the Neotropical realm and Palearctic realm along complex transition zones.

Geography and boundaries

The Nearctic realm spans from the high Arctic islands of Greenland and the Canadian Arctic Archipelago through the boreal belt of Canada and the conterminous United States to the central Mexican highlands and the lowlands of Baja California. Northern boundaries meet the Arctic Ocean and the North Atlantic Ocean around Labrador Sea and Baffin Bay, while western coasts face the North Pacific Ocean and eastern shores border the Atlantic Ocean. Southern connections to the Neotropical realm occur across montane corridors in central and southern Mexico including the Sierra Madre Oriental, Sierra Madre Occidental, and the Trans-Mexican Volcanic Belt. Insular extensions include the Aleutian Islands, Hawaii is excluded, and transitional floras occur on islands such as Bermuda and parts of the Caribbean Sea margin.

Climate and major biomes

Climates range from polar climates along Greenland and the Arctic Archipelago to subarctic climate across Yukon and Northwest Territories, continental climates throughout the Great Plains and Interior Plateau, maritime climates on the Pacific Coast and Gulf Coast, and arid climates in the Mojave Desert, Sonoran Desert, and Chihuahuan Desert. Major biomes include Arctic tundra across Nunavut and Nunavik, boreal forest (taiga) across Saskatchewan, Manitoba, and Alberta, temperate coniferous forests along the Pacific Northwest in Washington and British Columbia, temperate broadleaf and mixed forests in the Northeastern United States and Quebec, grasslands across the Great Plains and Pampas? (note: Pampas is South American), and xeric shrublands in regions such as Sonora and New Mexico. Montane ecosystems in the Rocky Mountains and the Sierra Nevada add alpine tundra and subalpine forests.

Flora and fauna

Vegetation reflects glacial legacies and biogeographic exchanges with the Palearctic realm and Neotropics: boreal forests dominated by Picea abies is European; in North America native genera include Picea glauca, Abies balsamea, Pinus contorta, Tsuga heterophylla, and Sequoiadendron giganteum in the Sierra Nevada. Deciduous forests feature Acer saccharum, Quercus rubra, Fagus grandifolia, and understories with Cornus florida and Rhododendron maximum. Grassland flora include Bouteloua gracilis and Andropogon gerardii on the Great Plains; desert flora include Carnegiea gigantea in Arizona and Agave deserti in California. Faunal assemblages include iconic mammals such as Bison bison, Ursus americanus, Canis lupus, Odocoileus virginianus, Lynx rufus, and remnant populations of Gulo gulo; avifauna includes Corvus brachyrhynchos, Cardinalis cardinalis, Branta canadensis, Falco peregrinus, and migratory species that link to Central America flyways. Freshwater ichthyofauna include Salmo salar (introduced), native Oncorhynchus mykiss, and Micropterus salmoides in lentic systems. Invertebrate diversity features taxa such as Danaus plexippus, Helicoverpa zea, and diverse ground beetles; plant-animal interactions are shaped by pollinators like Apis mellifera (introduced) and native bees in genera including Bombus.

Biogeographic provinces and ecoregions

Biogeographic subdivisions recognized by conservation frameworks include provinces and ecoregions such as the Canadian Shield, Eastern Temperate Forests, Western Cordillera, Great Plains, Mojave Desert, Chihuahuan Desert, Baja California Mediterranean zones, and coastal systems like the Gulf Coastal Plain. Other important ecoregions comprise the Laurentian Mixed Forest Province, Appalachian mixed mesophytic forests, California Floristic Province, Madrean Pine-Oak Woodlands, Sonoran-Sinaloan transition subtropical dry forest, and the Mackenzie River Delta wetlands. These units are used by international organizations such as the World Wildlife Fund and regional agencies including Environment and Climate Change Canada and the United States Fish and Wildlife Service for planning and assessment.

Geological history and paleobiogeography

Tectonic history involves interactions among the North American Plate, fragments of the former Farallon Plate, and terranes accreted along the Cordilleran orogeny to form the Rocky Mountains and Sierra Nevada. Pleistocene glaciations sculpted landscapes across the Laurentide Ice Sheet extent, producing refugia in areas like Beringia across the Bering Land Bridge that connected to the Palearctic realm and permitted faunal exchange including megafauna migrations involving genera such as Mammuthus and Equus. Fossil records from formations such as the Hell Creek Formation and La Brea Tar Pits document extinction events and faunal turnover including Smilodon and Megalonyx. Postglacial colonization shaped modern distributions of Pinus, Populus tremuloides, and vertebrates; vicariance and dispersal during the Miocene and Pliocene fostered endemism in montane regions and peninsulas like Florida and Baja California.

Conservation and threats

Conservation challenges include habitat loss from agriculture and urbanization across regions including California, the Midwest and Yucatan adjacency, invasive species such as Dreissena polymorpha and Rhododendron ponticum (where introduced), climate change impacts on Arctic systems including Greenland ice melt, and fragmentation of corridors in the Southern Appalachians and Great Plains. Conservation actions are led by agencies and organizations including the National Park Service, Parks Canada, Mexican National Commission of Natural Protected Areas, World Wildlife Fund, and NGOs like The Nature Conservancy; strategies emphasize protected areas such as Yellowstone National Park, Banff National Park, Saguaro National Park, and transboundary initiatives like the Waterton-Glacier International Peace Park. Restoration, species recovery plans for taxa such as Bison bison and Ursus arctos horribilis populations, and landscape-scale planning aim to address threats posed by wildfire regimes, altered hydrology in basins like the Colorado River and Mississippi River, and pressures from extractive industries in regions including the Alaska North Slope.

Category:Biogeographic realms