BIOMES
Coniferous Forest
Young spruces and first begin to crowd out deciduous aspens in the coniferous forest biome. Evergreens domÃnate this broad belt, some 400 to 800 miles wide, which stretches across Canada, Alaska and Eurasia and, farther south, covers high mountains. Moose are found in the northern area, mule deer in the western mountains. One bird, the red crossbill, has a beak so specialized for picking seeds from cones that it can live only here.
Temperate Deciduous Forest
In temperate areas, where seasons change from summer heat to winter cold and where there is sufficient precipitation, the natural ground cover is forest—and forest of a particular kind. These are conditions that favor the growth, above all other plants, of deciduous trees. Named for their habit of shedding their leaves in the fall, they include such varieties as oaks, maples and beeches. The canopies they form affect all life in their shade, and the deciduous forest biome of eastern North America, temperate Europe and eastern Asia harbors many of the familiar plants and animals of the North Temperate Zone.
Tropical Forest
The rampant green growth of a Brazilian mountainside, nurtured by abundant rains and simmering warmth, is characteristic of but one kind of tropical forest. The diverse forests which make up this ancient biome, whether South American, Asian or African, are stratified into conspicuous stories—some having as many as eight levels. Each story is formed by the crowns of trees and shrubs of many different species growing closely together. And each story may shelter plants—from low-lying ferns to aerial epiphytes—and animals different in habits and adaptations from those living directly above or below.
The Reef
A watery Eden of clear blue, blue-green and green, the reef is a flourishing marine biome. Like this section of Australia's Great Barrier Reef, it occurs where waters are warm and shallow, and builds up slowly from the calcareous remains of organisms like the polyps below. Self-sufficient worlds, reefs support a variety of plants and animals, from algae to clouds of brightly colored fishes—which in turn attract both fish-eating birds and larger fishes from the deep ocean waters just beyond.
The Desert
In contrast to the watery reef is the arid desert biome: hummocks of vegetation rising from sun-singed sands. Deserts cover about one fifth of the Earth's surface. Controlled by climate, desert plants develop tough skins and reduced foliage to prevent evaporation and withstand heat. Large mammals are scarce, but birds and rodents like the mourning doves and desert rat above abound. Many are nocturnal in habit: night offers concealing darkness, coolness—and often dew.
The Tundra
Caribou are among the largest mammals of the Canadian tundra, adapted for life in this far northern region. The tundra biome begins where the coniferous forest ends and runs to the barrier of permanent snows and ice in Eurasia and North America. It also occurs in modified form on high mountains. Its principal vegetation of lichens, mosses and grasses makes the most of a brief growing season in which the subsoil never thaws completely, and provides food for the caribou, whose trails are marked by the grim mementoes of wolves.
The Rocky Shore
Beyond the carpet of flowers opposite lies the rocky shore, a rigorous biome. Pounded by waves, exposed by lides to sun and air. this is yet an area in which lile abounds. Extending from high to below tide levels, it is divided into three major zones. Snails prevail in the upper zone, acorn barnacles and masses of brown algae in the middle or intertidal region, and kelps with long stalks and ribbonlike branches at the bottom—each reflecting a tolerance to varying degrees of exposure.
Grassland
A sea of grass rolling toward distant mountains typifies the grassland biome often found in the interiors of continents. Climate is a controlling factor: rainfall is insufficient to support trees but high enough to keep deserts from forming. The result is a variety of tall, medium and short grasses which reflect the gradient of rainfall—as in the United States, with its zones of progressively shorter growth westward to the Rockies. Grassland soil is rich in humus in areas of taller grass, since leaves die at the end of each growing season and decay quickly. Man with his agriculture and livestock ha destroyed much of the world's grassland biome, and few large patches survive. In earlier days they supported big herds of grazing mammal and colonies of rodents like the prairie dog.
The Ocean
Vast and in many places seemingly thinly populated, the sea is actually a reservoir of life—filled in different regions and at different times with billions of animals and plants so small that they cannot be seen by the human eye. These tiny, passively floating and weak-swimming organisms, the plankton. constitute one of the lowest links on the food chain. Together with the nekton, or actively moving organisms—the fishes, squids, whales, seals and porpoises and fish-eating birds—they make up the oceanic plankton-nekton biome. Here such factors as light, pressure, temperature, salinity and oxygen content of the water determine the make-up of the various plant and animal communities. With its potential as a source of food for mankind relatively unexplored, this biome, perhaps more than any other, is receiving the concentrated attention of ecologists seeking ways to develop—while conserving—its rich abundance.
