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The Major Biomes
Earth's surfaces are classified as mountains or ice caps.
Each biome has a characteristic climate and community of organisms.
Ecologists recognize at least ten different biomes.
The world’s major land biomes include
- Tropical rain forest
- Tropical dry forest
- Tropical savanna
- Desert
- Temperate grassland
- Temperate woodland and shrubland
- Temperate forest,
- Northwestern coniferous forest
- Boreal forest
- Tundra.
Each of these biomes is defined by a unique set of abiotic factors – particularly climate – and has a characteristic ecological community.
Structure of a particular biome will differ slightly, depending on location and elevation above sea level.
Tropical Rain Forest
Tropical rain forests are home to more species than all other land biomes combined.
The leafy tops of tall trees – extending up to 70 meters above the forest floor – form a dense covering called a canopy. In the shade below the canopy, the second layer of shorter trees and vines forms an understory.
Organic matter that falls to the forest floor quickly decomposes and the nutrients are recycled.
- Abiotic factors: hot and wet year-round; thin, nutrient-poor soils
- Dominant plants: broad-leaved evergreen trees; ferns; large woody vines and climbing plants; orchids and bromeliads
- Dominant wildlife: herbivores such as sloths, tapirs, and capybaras; predators such as jaguars; anteaters; monkeys; birds such as toucans, parrots, and parakeets; insects such as butterflies, ants, and beetles; piranhas and other freshwater fishes; reptiles such as frogs, Caymans, boa constrictors, and anacondas
- Geographic distribution: parts of South and Central America, Southeast Asia, parts of Africa, southern India, and northeastern Australia
Tropical Dry Forest
Tropical dry forests 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.
- Abiotic factors: generally warm year-round; alternating wet and dry seasons; rich soils subject to erosion
- Dominant plants: tall, deciduous trees that form a dense canopy during the wet season; drought-tolerant orchids and bromeliads; aloes and other succulents
- Dominant wildlife: tigers; monkeys; herbivores such as elephants, Indian rhinoceros, hog deer; birds such as great pied hornbill, pied harrier, and spot-billed pelican; insects such as termites; reptiles such as snakes and monitor lizards
- Geographic distribution: parts of Africa, South and Central America, Mexico, India, Australia, and tropical islands
Tropical Savanna
Receiving more seasonal rainfall than deserts but less than tropical dry forests, tropical savannas, or grasslands, are characterized by a cover of grasses.
Savannas 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 rhinoceros prevent some savanna areas from turning into dry forests.
- Abiotic factors: warm temperatures; seasonal rainfall; compact soil; frequent fires set by lightning
- Dominant plants: tall, perennial grasses; sometimes drought-tolerant and fire-resistant trees or shrubs
- Dominant wildlife: predators such as lions, leopards, cheetahs, hyenas, and jackals; aardvarks; herbivores such as elephants, giraffes, antelopes, and zebras; baboons; birds such as eagles, ostriches, weaver birds, and storks; insects such as termites
- Geographic distribution: large parts of eastern Africa, southern Brazil, northern Australia
Desert
All deserts are dry –a desert biome is defined as having annual precipitation of fewer than 25 centimeters. Beyond that, deserts 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 extreme conditions.
- Abiotic factors: low precipitation, variable temperatures; soils rich in minerals but poor in organic material
- Dominant plants: cacti and other succulents; creosote bush and other plants with short growth cycles
- Dominant wildlife: predators such as mountain lions, gray foxes, and bobcats; herbivores such as mule deer, pronghorn antelope, desert bighorn sheep, and kangaroo rats; bats; birds such as owls, hawks, and roadrunners; insects such as ants, beetles, butterflies, flies, and wasps; reptiles such as tortoises, rattlesnakes, and lizards
- Geographic distribution: Africa, Asia, the Middle East, United States, Mexico, South America, and Australia
Temperate Grassland
Characterized by a rich mix of grasses and underlaid by some of the world's most fertile soils, temperate grasslands – such as plains and prairies – once covered vast areas of the Midwestern 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. 6
- Abiotic factors: warm to hot summers; cold winters; moderate, seasonal precipitation; fertile soils; occasional fires
- Dominant plants: lush, perennial grasses and herbs; most are resistant to drought, fire, and cold
- Dominant wildlife: predators such as coyotes and badgers -- historically included wolves and grizzly bears; herbivores such as mule deer, pronghorn antelope, rabbits, prairie dogs, and introduced cattle -- historically included bison; birds such as hawks, owls, bobwhite, prairie chicken, mountain plover; reptiles such as snakes; insects such as ants and grasshoppers
- Geographic distribution: central Asia, North America, Australia, central Europe, and upland plateaus of South America
Temperate Woodland
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.
- Abiotic factors: hot, dry summers; cool, moist winters; thin, nutrient-poor soils; periodic fires
- Dominant plants: woody evergreen shrubs with small, leathery leaves; fragrant, oily herbs that grow during winter and die in summer
- Dominant wildlife: predators such as coyotes, foxes, bobcats, and mountain lions; herbivores such as black-tailed deer, rabbits, squirrels, and mice; birds such as hawks, California quail, western scrub-jay, warblers, and other songbirds; reptiles such as lizards and snakes; butterflies; spiders
- Geographic distribution: western coasts of North and South America, areas around the Mediterranean Sea, South Africa, and Australia
Temperate Forest
Temperate forests contain a mixture of deciduous and coniferous (Koh-NIF-ur-us) 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 temperate forests are often rich in humus (HYOO-mus), a material formed from decaying leaves and other organic matter that makes the soil fertile.
- Abiotic factors: cold to moderate winters; warm summers; year-round precipitation; fertile soils
- Dominant plants: broadleaf deciduous trees; some conifers; flowering shrubs; herbs; a ground layer of mosses and ferns
- Dominant wildlife: Deer; black bears; bobcats; nut and acorn feeders, such as squirrels; omnivores such as raccoons and skunks; numerous songbirds; turkeys
- Geographic distribution: the eastern United States; southeastern Canada; most of Europe; and parts of Japan, China, and Australia
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, the northwestern coniferous forest is sometimes called a "temperate rain forest"
- Abiotic factors: mild temperatures; abundant precipitation during fall, winter, and spring; relatively cool, dry summer; rocky, acidic soils
- Dominant plants: Douglas fir, Sitka spruce, western hemlock, redwood
- Dominant wildlife: bears; large herbivores such as elk and deer; beavers; predators such as owls, bobcats, and members of the weasel family
- Geographic distribution: Pacific coast of the northwestern United States and Canada, from northern California to Alaska Boreal
Forest Boreal
Forest Along the northern edge of the temperate zone are dense evergreen forests of coniferous trees. These biomes are called boreal forests, or taiga (TY-guh).
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 boreal forests occur mostly in the Northern Hemisphere.
- Abiotic factors: long, cold winters; short, mild summers; moderate precipitation; high humidity; acidic, nutrient-poor soils
- Dominant plants: needle leaf coniferous trees such as spruce and fir; some broadleaf deciduous trees; small, berry-bearing shrubs
- Dominant wildlife: predators like lynx and Timberwolves and members of the weasel family; small herbivorous mammals; moose and other large herbivores; beavers; songbirds and migratory birds
- Geographic distribution: North America, Asia, and northern Europe
Tundra
The tundra 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 tundra plants are small and stunted. Cold temperatures, high winds; the short growing season, and humus-poor soils also limit plant height
- Abiotic factors: strong winds; low precipitation; short and soggy summers; long, cold, and dark winters;. poorly developed soils; permafrost
- Dominant plants: ground-hugging plants such as mosses, lichens, sedges, and short grasses
- Dominant wildlife: a few resident birds and mammals that can withstand the harsh conditions; migratory waterfowl, shorebirds, musk ox, Arctic foxes, and caribou; lemmings and other small rodents
- Geographic distribution: northern North America, Asia, and Europe
