biomes

desert

All are dry—in fact, this biome is defined as having annual precipitation of less than 25 centimeters. Beyond that, the biome vary greatly, depending on elevation and latitude. Many undergo extreme temperature changes during the course of a day, alternating between hot and cold. The organisms in this biome can tolerate the extreme conditions.

boreal forest

Along the northern edge of the temperate zone are dense evergreen forests of coniferous trees. These biomes are also called taiga. Winters are bitterly cold, but summers are mild and long enough to allow the ground to thaw. The word boreal comes from the Greek word for "north," reflecting the fact that this biome occur mostly in the Northern Hemisphere.

temperate grassland

Characterized by a rich mix of grasses and underlaid by some of the world's most fertile soils, this biome—such as plains and prairies—once covered vast areas of the midwestern and central United States. Since the development of the steel plow, however, most have been converted to agricultural fields. Periodic fires and heavy grazing by large herbivores maintain the characteristic plant community.

northwestern coniferous forest

Mild, moist air from the Pacific Ocean provides abundant rainfall to this biome. The forest is made up of a variety of conifers, ranging from giant redwoods along the coast of northern California to spruce, fir, and hemlock farther north. Moss often covers tree trunks and the forest floor. Flowering trees and shrubs such as dogwood and rhododendron are also abundant. Because of its lush vegetation, this biome is sometimes called a "temperate rain forest."

tropical savanna

Receiving more seasonal rainfall than deserts but less than tropical dry forests or grasslands, are characterized by a cover of grasses. they are spotted with isolated trees and small groves of trees and shrubs. Compact soils, fairly frequent fires, and the action of large animals such as rhinoceroses prevent some these areas from turning into dry areas

tropical rain forest

The leafy tops of tall trees—extending from 50 to 80 meters above the forest floor—form a dense covering called a canopy. In the shade below the canopy, a second layer of shorter trees and vines forms an understory. Organic matter that falls to the forest floor quickly decomposes, and the nutrients are recycle

temperate woodland and shrubland

This biome is characterized by a semiarid climate and a mix of shrub communities and open woodlands. In the open woodlands, large areas of grasses and wildflowers such as poppies are interspersed with oak trees. Communities that are dominated by shrubs are also known as chaparral. The growth of dense, low plants that contain flammable oils makes fires a constant threat.

tundra

This biome is characterized by permafrost, a layer of permanently frozen subsoil. During the short, cool summer, the ground thaws to a depth of a few centimeters and becomes soggy and wet. In winter, the topsoil freezes again. This cycle of thawing and freezing, which rips and crushes plant roots, is one reason that the plants in this biome are small and stunted. Cold temperatures, high winds, the short growing season, and humus-poor soils also limit plant height.

tropical dry forest

grow in places where rainfall is highly seasonal rather than year-round. During the dry season, nearly all the trees drop their leaves to conserve water. A tree that sheds its leaves during a particular season each year is called deciduous.

temperate forest

this boime contain a mixture of deciduous and coniferous trees. Coniferous trees, or conifers, produce seed-bearing cones and most have leaves shaped like needles. These forests have cold winters that halt plant growth for several months. In autumn, the deciduous trees shed their leaves. In the spring, small plants burst out of the ground and flower. Soils of this biome are often rich in humus, a material formed from decaying leaves and other organic matter that makes soil fertile.