1911 Encyclopædia Britannica/United States, The/Fauna and Flora

IV.—Fauna and Flora

Fauna.—Differences of temperature have produced in North America seven transcontinental life-zones or areas characterized by relative uniformity of both fauna and flora; they are the Arctic, Hudsonian and Canadian, which are divisions of the Boreal Region; the Transition, Upper Austral and Lower Austral, which are divisions of the Austral Region, and the Tropical. The Arctic, Hudsonian and Canadian enter the United States from the north and the Tropical from the south; but the greater part of the United States is occupied by the Transition, Upper Austral and Lower Austral, and each of these is divided into eastern and western subzones by differences in the amount of moisture. The Arctic or Arctic-Alpine zone covers in the United States only the tops of a few mountains which extend above the limit of trees, such as Mt Katahdin in Maine, Mt Washington and neighbouring peaks in the White Mountains of New Hampshire, and the loftier peaks of the Rocky, Cascade and Sierra Nevada Mountains. The larger animals are rare on these mountain-tops and the areas are too small for a distinct fauna. The Hudsonian zone covers the upper slopes of the higher mountains of New England, New York and North Carolina and larger areas on the elevated slopes of the Rocky and Cascade Mountains; and on the western mountains it is the home of the mountain goat, mountain sheep, Alpine flying-squirrel, nutcracker, evening grosbeak and Townsend's solitaire. The Canadian zone crosses from Canada into northern and north-western Maine, northern and central New Hampshire, northern Michigan, and north-eastern Minnesota and North Dakota, covers the Green Mountains, most of the Adirondacks and Catskills, the higher slopes of the mountains in Pennsylvania, West Virginia, Virginia, western North Carolina and eastern Tennessee, the lower slopes of the northern Rocky and Cascade Mountains, the upper slopes of the southern Rocky and Sierra Nevada Mountains, and a strip along the Pacific coast as far south as Cape Mendocino, interrupted, however, by the Columbia Valley. Among its characteristic mammals and birds are the lynx, marten, porcupine, northern red squirrel, Belding's and Kennicott's ground squirrels, varying and snowshoe rabbits, northern jumping mouse, white-throated sparrow, Blackburnian Warbler, Audubon Warbler, olive-backed thrush, three-toed woodpecker, spruce grouse, and Canada jay; within this zone in the North-eastern states are a few moose and caribou, but farther north these animals are more characteristic of the Hudsonian zone. The Transition zone, in which the extreme southern limit of several boreal species overlaps the extreme northern limit of numerous austral species, is divided into an eastern humid or Alleghanian area, a western arid area, and a Pacific coast humid area. The Alleghanian area comprises most of the lowlands of New England. New York and Pennsylvania, the north-east corner of Ohio, most of the lower peninsula of Michigan, nearly all of Wisconsin, more than half of Minnesota, eastern North Dakota, north-eastern South Dakota, and the greater part of the Appalachian Mountains from Pennsylvania to Georgia. It has few distinctive species, but within its borders the southern mole and cotton-tail rabbit of the South meet the northern star-nosed and Brewer's moles and the varying hare of the North, and the southern bobwhite, Baltimore oriole, bluebird, catbird, chewink, thrasher and wood thrush are neighbours of the bobolink, solitary vireo and the hermit and Wilson's thrushes. The Arid Transition life-zone comprises the western part of the Dakotas, north-eastern Montana, and irregular areas in Washington, Oregon, Idaho, Wyoming, California, Nevada, Utah, Colorado, Arizona, New Mexico and western Texas, covering for the most part the eastern base of the Cascade and Sierra Nevada Mountains and the higher parts of the Great Basin and the plateaus. Its most characteristic animals and birds are the white-tailed jack-rabbit, pallid vole, sage hen, sharp-tailed grouse and green-tailed towhee; the large Columbia ground-squirrel (Spermophilus columbianus) is common in that part of the zone which is west of the Rocky Mountains, but east of the Rockies it is replaced by another species (Cynomys) which closely resembles a small prairie dog. The Pacific Coast Transition life-zone comprises the region between the Cascade and Coast ranges in Washington and Oregon, parts of northern California, and most of the California coast region from Cape Mendocino to Santa Barbara. It is the home of the Columbia black-tail deer, western raccoon, Oregon spotted skunk, Douglas red squirrel, Townsend's chipmunk, tailless sewellel (Haplodon rufus), peculiar species of pocket gophers and voles, Pacific coast forms of the great-horned, spotted, screech and pigmy owls, sooty grouse, Oregon ruffed grouse, Steller's jay, chestnut-backed chickadee and Pacific winter wren. The Upper Austral zone is divided into an eastern humid (or Carolinian) area and a western arid (or Upper Sonoran) area. The Carolinian area extends from southern Michigan to northern Georgia and from the Atlantic coast to western Kansas, comprising Delaware, all of Maryland except the mountainous western portion, all of Ohio except the north-east corner, nearly the whole of Indiana, Illinois, Iowa and Missouri, eastern Nebraska and Kansas, south-eastern South Dakota, western central Oklahoma, northern Arkansas, middle and eastern Kentucky, middle Tennessee and the Tennessee valley in eastern Tennessee, middle Virginia and North Carolina, western West Virginia, north-eastern Alabama, northern Georgia, western South Carolina, the Connecticut Valley in Connecticut, the lower Hudson Valley and the Erie basin in New York, and narrow belts along the southern and western borders of the lower peninsula of Michigan. It is the northernmost home of the opossum, grey fox, fox squirrel, cardinal bird, Carolina wren, tufted tit, gnat catcher, summer tanager and yellow-breasted chat. The Upper Sonoran life-zone comprises south-eastern Montana, central, eastern and north-eastern Wyoming, a portion of south-western South Dakota, western Nebraska and Kansas, the western extremity of Oklahoma, north-western Texas, eastern Colorado, south-eastern New Mexico, the Snake plains in Idaho, the Columbia plains in Washington, the Malheur and Harney plains in Oregon, the Great Salt Lake and Sevier deserts in Utah, and narrow belts in California, Nevada and Arizona. Among its characteristic mammals and birds are the sage cotton-tail, black-tailed jack-rabbit, Idaho rabbit, Oregon, Utah and Townsend’s ground squirrels, sage chipmunk, five-toed kangaroo rats, pocket mice, grasshopper mice, burrowing owl, Brewer’s sparrow, Nevada sage sparrow, lazuli finch, sage thrasher, Nuttall’s poor-will, Bullock’s oriole and rough-winged swallow. The Lower Austral zone occupies the greater part of the Southern states, and is divided near the 98th meridian into an eastern humid or Austroriparian area and a western arid or Lower Sonoran area. The Austroriparian zone comprises nearly all the Gulf States as far west as the mouth of the Rio Grande, the greater part of Georgia, eastern South Carolina, North Carolina and Virginia, and extends up the lowlands of the Mississippi Valley across western Tennessee and Kentucky into southern Illinois and Indiana and across eastern and southern Arkansas and eastern Oklahoma into south-eastern Missouri and Kansas. It is the home of the southern fox-squirrel, cotton rat, rice field rat, wood rat, free-tailed bat, mocking bird, painted bunting, prothonotary Warbler, red-cockaded woodpecker, chuck will’s-widow, and the swallow-tailed and Mississippi kites. A southern portion of this zone, comprising a narrow strip along the Gulf Coast from Texas to Florida and up the Atlantic coast to South Carolina, is semi-tropical, and is the northernmost habitation of several small mammals, the alligator (Alligator mississippiensis), the ground dove, white-tailed kite, Florida screech owl and Chapman’s night-hawk. The Lower Sonoran zone comprises the most arid parts of the United States: south-western Texas, south-western Arizona and a portion of northern Arizona, southern Nevada and a large part of southern California. Some of its characteristic mammals and birds are the long-eared desert fox, four-toed kangaroo rats, Sonoran pocket mice, big-eared and tiny white-haired bats, road runner, cactus Wren, canyon wren, desert thrashers, hooded oriole, black-throated desert sparrow, Texas night-hawk and Gambel’s quail. It is the northernmost home of the armadillo, ocelot, jaguar, red and grey cats, and the spiny pocket mouse, and in southern Texas especially it is visited by several species of tropical birds. There is some resemblance to the Tropical life-zone at the south-eastern extremity of Texas, but this zone in the United States is properly restricted to southern Florida and the lower valley of the Colorado along the border of California and Arizona, and the knowledge of the latter is very imperfect. The area in Florida is too small for characteristic tropical mammals, but it has the true crocodile (Crocodilus americanus) and is the home of a few tropical birds. Most of the larger American mammals are not restricted to any one faunal zone. The bison, although now nearly extinct, formerly roamed over nearly the entire region between the Appalachian and the Rocky Mountains. The black bear and beaver were also widely distributed. The Virginia deer still ranges from Maine to the Gulf states and from the Atlantic coast to the Rocky Mountains. The grizzly bear, cougar, coyote, prairie dog and antelope are still found in several of the Western states, and the grey wolf is common in the West and in northern Minnesota, Wisconsin and Michigan.

Flora.—The Alpine flora, which is found in the United States only on the tops of those mountains which rise above the limit of trees, consists principally of a variety of plants which bloom as soon as the snow melts and for a short season make a brilliant display of colours. The flora of the Hudsonian and the Canadian zone consists largely of white and black spruce, tamarack, canoe-birch, balsam-poplar, balsam-fir, aspen and grey pine. In the Alleghanian Transition zone the chestnut, walnut, oaks and hickories of the South are interspersed among the beech, birch, hemlock and sugar maple of the North. In the Western Arid Transition zone the flora consists largely of the true sage brush (Artemisia tridentata), but some tracts are covered with forests of yellow or bull pine (Pinus ponderosa). The Pacific coast Transition zone is noted for its forests of giant conifers, principally Douglas fir, Sitka spruce, Pacific cedar and Western hemlock. Here, too, mosses and ferns grow in profusion, and the sadal (Gaultheria shallon), thimble berry (Rubus nootkamus), salmon berry (Rubus spectabilis) and devil’s club (Fatsia horrida) are characteristic shrubs. In the Carolinian zone the tulip tree, sycamore, sweet gum, rose magnolia, short-leaf pine and sassafras find their northernmost limit. Sage brush is common to both the western arid Transition zone and the Upper Sonoran zone, but in suitable soils of the latter several grease woods (Artiplex confertifolia, A. canescens, A. nuttalli, Tetradymia canescens, Sarcobatus vermicuiatus and Grayia spinosa) are characteristic species, and on the mountain slopes are some nut pines (piñon) and junipers. The Austroriparian zone has the long-leaf and loblolly pines, magnolia and live oak on the uplands, and the bald cypress, tupelo and cane in the swamps; and in the semi-tropical Gulf strip are the cabbage palmetto and Cuban pine; here, too, Sea Island cotton and tropical fruits are successfully cultivated. The Lower Sonoran zone is noted for its cactuses, of which there is a great variety, and some of them grow to the height of trees; the mesquite is also very large, and the creosote bush, acacias, yuccas and agaves are common. The Tropical belt of southern Florida has the royal palm, coco-nut palm, banana, Jamaica dogwood, manchineel and mangrove; the Tropical belt in the lower valley of the Colorado has giant cactuses, desert acacias, palo-verdes and the Washington or fan-leaf palm. Almost all of the United States east of the 98th meridian is naturally a forest region, and forests cover the greater part of the Rocky Mountains, the Cascades, the Sierra Nevadas and the Coast Range, but throughout the belt of plains, basins and deserts west of the Rocky Mountains and on the Great Plains east of the Rocky Mountains there are few trees except along the watercourses, and the prevailing type of vegetation ranges from bunch grass to sage brush and cactuses according to the degree of aridity and the temperature. In the eastern forest region the number of species decreases somewhat from south to north, but the entire region differs from the densely forested region of the Pacific Coast Transition zone in that it is essentially a region of deciduous or hardwood forests, while the latter is essentially one of coniferous trees; it differs from the forested region of the Rocky Mountains in that the latter is not only essentially a region of coniferous trees, but one where the forests do not by any means occupy the whole area, neither do they approach in density or economic importance those of the eastern division of the country. Again, the forests of most of the eastern region embrace a variety of species, which, as a rule, are very much intermingled, and do not, unless quite exceptionally, occupy areas chiefly devoted to one species; while, on the other hand, the forests of the west—including both Rocky Mountain and Pacific coast divisions—exhibit a small number of species, considering the vast area embraced in the region; and these species, in a number of instances, are extraordinarily limited in their range, although there are cases in which one or two species have almost exclusive possession of extensive areas.

Bibliography.—C. H. Merriam, Life Zones and Crop Zones of the United States, Bulletin No. 10 of the United States Department of Agriculture, Division of Biological Survey (Washington, 1898); I. C. Russell, North America (New York, 1904); W. T. Hornaday, American Natural History (New York, 1904); W. Stone and W. E. Cram, American Animals (New York, 1902); E. Coues, Key to North American Birds (Boston, 1896); Florence M. Bailey, Handbook of Birds of the Western United States (Boston, 1902); E. D. Cope, “The Crocodilians, Lizards and Snakes of North America,” in the Report of the United States National Museum for the year 1898 (Washington, 1900); L. Stejneger, “The Poisonous Snakes of North America,” ibid., 1893 (Washington, 1895). (N. D. M.)