Circumboreal Subregion

a subregion of the Holarctic zoogeographic region. The Circumboreal subregion is located south of the Arctic subregion and includes the asiatic taiga, the conifer, mixed, and broad-leaved forests of Europe, the taiga of North America, a large part of the Caucasus, and the Elburz Mountains. Many zoogeographers do not include the last two mountain regions in the Circumboreal subregion. Instead of a Circumboreal subregion, some zoogeographers recognize two subregions, the European-Siberian and Canadian subregions.

The faunas of the taiga and broad-leaved forests in Eurasia share many common species, for example, such mammals as the pine squirrel, Asiatic chipmunk, and Russian flying squirrel and numerous birds, including many species of thrushes, woodpeckers, and tits. In North America, however, the taiga fauna is more clearly distinguished from the fauna of the broad-leaved forests.

The similarity between the fauna of the American and Eurasian parts of the Circumboreal subregion is shown by the existence of widespread Holarctic forms such as the wolf, fox, and ermine and tundra-taiga animals such as the reindeer (called the caribou in North America), blue hare, and willow ptarmigan, as well as such widespread forest animals as the beaver and lynx. The wolverine, moose (elk), three-toed woodpecker, crossbills, Tengmalm’s owl (boreal owl), and waxwings are found in both parts of the subregion but not outside it. The number of common genera is much greater, including redbacked mice and bears.

A few species are typical only of the Eurasian part of the subregion, for example, the wood lemming, sable (whose ecological niche in North America is inhabited by the American pine marten), capercaillie, hazel hen, and nutcracker. Many more forms are found only in the American part, for example, the tree porcupine, red squirrel, greater flying squirrel, jumping squirrel, several genera of hamsters that inhabit the same ecological niche as mice, star-nosed mole, American badger, skunk, warblers, cardinal, and blue jay. Even hummingbirds sometimes occur.

The American part of the Circumboreal subregion is so much richer in fauna than the Eurasian part because less of its area underwent glaciation and because it maintained an almost uninterrupted link with the more southern parts of America, including Central and South America.

The few reptiles in the Circumboreal subregion include some viviparous forms of snakes, such as vipers, and lizards. Amphibians are represented by the frogs, toads, and newts. The predominant fish are salmon, whitefish, pike, and perch. Vicarious species occur widely; some Eurasian species are so similar to the North American species that it has not yet been decided whether they are in fact independent species.