Biomes are the major types of terrestrial ecosystems

34.3

What is a Biome???

The major types of terrestrial ecosystems that cover large regions of Earth are called biomes.

Each biome is characterized by communities of plants and other organisms that are adapted to its climate and other abiotic factors.

Biomes But while the landscapes may appear

similar across a biome, the specific organisms vary in different parts of the world.

For example, bison and pronghorns graze in North American grasslands, while the grazing mammals in Asian grasslands include saiga (also called "antelope goats") and yaks.

Biomes

Figure 34-9 shows the natural distribution of eight major biomes, plus large areas of ice found near both poles.

Notice that there are some latitudinal patterns—certain biomes appear at similar latitudes on several different continents.

Tropical Forest

Tropical forests occur near the equator where temperatures are warm year-round.

One major type of tropical forest, the tropical rain forest, can receive as much as 350 centimeters of rainfall yearly.

These ideal growing conditions result in a lush diversity of plants growing in vertical layers.

Tropical Forests

Of all biomes, tropical rain forests have the greatest diversity of life, with an estimated 50 percent of all known species on Earth.

Rain forests on the island of Madagascar, off the coast of Africa, are home to some 8,000 species of flowering plants, 80 percent of which occur only there.

Many of the unique species provide food, medicine, and other valuable products.

Tropical Forests

Rain forests in Madagascar and many other parts of the world are shrinking.

Clearing forests for mining, lumber, and farmland has affected many rainforest species.

Tropical Rainforests of the world

Savannas

Found in tropical regions of Africa, Australia, and South America, savannas are grasslands with scattered trees.

Savanna grasses grow rapidly, providing food for many grazing animals, such as zebras, wildebeest, antelope, and, in Australia, kangaroos, as well as numerous insects.

Savannas

Savannas typically have a warm climate with alternating wet and dry seasons.

The dry seasons may include long periods of drought, when no rain falls.

Organisms in the savanna must be able to cope with drought.

For example, some animals wander until they find greener pastures or scattered watering holes.

Deserts

Land areas receiving less than 30 centimeters of rain per year are typically classified as deserts.

Deserts

Some deserts have surface soil temperatures above 60°C during the day and then cool off at night.

Other deserts, such as those in central Asia, are relatively cold, especially during winter nights.

The driest deserts, such as those in central Australia and Africa, have little or no plant life.

Chaparral

The chaparral (shap uh RAL) is a temperate coastal biome dominated by dense evergreen shrubs.

The climate consists of mild, rainy winters and hot, dry summers.

Chaparral

The chaparral's dry, woody shrubs are frequently ignited by lightning and are adapted to survive periodic brushfires.

In fact, some of the plant species produce seeds that will germinate only after a hot fire.

Animals of the chaparral include deer, birds, and rodents that feed on the shrubs and their seeds, as well as lizards and snakes.

Temperate Grassland

The temperate grassland biome is characterized by deep, nutrient-rich soil that supports a variety of grass species and other plants.

The winters are colder than in the tropical savannas

Temperate Grasslands

Grassland soils contain a great diversity of microorganisms and animals, including worms, arthropods, and burrowing rodents.

Above ground, the North American grasslands (also known as prairies) include grazing mammals such as bison and pronghorns, as well as coyotes, snakes, lizards, and insects.

Temperate Deciduous Forests

Dense stands of deciduous trees—trees that drop their leaves each year—characterize temperate deciduous forests.

These forests occur throughout the temperate zone where there is enough precipitation to support the growth of large trees.

Temperate Deciduous Forests

In this region winters tend to be very cold, while summers can be quite hot.

Common deciduous trees such as maples, oaks, beeches, and hickory shed their leaves in autumn, which helps reduce evaporation during the winter when water is not easily replaced from frozen soil.

Temperate Deciduous Forests Mammals found in the temperate

deciduous forests of eastern North America include deer, squirrels, chipmunks, foxes, and bears.

During the cold winter, many of these animals conserve energy by greatly reducing their activity levels.

Some bird species migrate to warmer climates.

Coniferous Forest

Towering cone-bearing evergreen trees such as pine, spruce, fir, and hemlock characterize the coniferous forest.

The northern regions of the biome, also called the taiga, have long, cold winters with heavy snowfall.

Coniferous Forests

In coastal Oregon, Washington, and British Columbia, Canada, conditions are warmer and wetter than in most other coniferous forest areas.

These forests are actually considered temperate rain forests because of the amount of precipitation they receive.

Tundra Bitterly cold

temperatures and high winds characterize the tundra.

Tundra communities are found within the Arctic Circle and on high mountaintops at all latitudes due to the similar conditions there (Figure 34-17).

The permanently frozen subsoil, called permafrost, ranges in depth from a few meters to 1,500 meters.

Tundra

During the brief Arctic growing season, clouds of mosquitoes fill the air. Lemmings, caribou, and reindeer eat the tundra ground cover.

Some tundra animals, including the arctic hare and snowy owl, turn white in the winter, allowing them to blend in with the snow.

During the summer they turn brown, better enabling them to hide in their rock-strewn environment.