Biomes

Imagine you could fly all around the world.

You would see thick, green forests. You would see wide, grassy plains and dry, sandy deserts. You would see cold, flat lands near the North Pole, and the big blue sea. Each one is a biome.

If you flew around the world, you would pass over very different landscapes: steamy rainforests, rolling grasslands, dry deserts, snowy forests, frozen tundra and wide oceans. Scientists call each of these big areas a biome.

A biome is a large area with its own climate, soil, plants and animals. National Geographic describes five major types: aquatic biomes in water, grasslands, forests, deserts and tundra. Many of these split into smaller groups. For example, forests can be tropical rainforests, temperate forests or the snowy northern forests called taiga. The same biome can appear on different continents, far apart, wherever the climate is similar.

National Geographic defines a biome as a large area characterized by its vegetation, soil, climate and wildlife: a large community of plants and animals adapted to a particular climate. It recognizes five major types, aquatic, grassland, forest, desert and tundra, each divided further, into freshwater and marine, savanna and temperate grassland, tropical rainforest, temperate rainforest, taiga and so on.

Biome boundaries are drawn at a large scale and are often gradual: NSIDC describes Arctic tundra slowly giving way to forest as you move south. Because a biome reflects climate, the same type can recur on several continents. Temperate grasslands, for example, are found in North America, Argentina and Uruguay, South Africa, Hungary and Russia.

Why is one place a forest and another a desert? It is about rain and warmth.

Places with lots of rain grow forests. Places with very little rain become deserts. Very cold places are tundra.

The biggest thing that decides a biome is climate: how warm it is and how much rain or snow falls. Plants need water and warmth to grow, and animals need the plants. National Geographic explains that places with more rain and higher temperatures grow more forests, and places with less rain tend to be deserts.

NASA gives typical yearly rainfall for each biome. Rainforests get the most: about 2,000 to 10,000 millimeters a year. Temperate forests get about 750 to 1,500 millimeters, grasslands about 500 to 900, and deserts only about 250. The cold tundra gets just 150 to 250 millimeters.

Vegetation is shaped first by water and temperature. National Geographic notes that the plants that grow in a region depend on its temperature and precipitation, so wetter and warmer regions support more forest while drier regions tend toward desert; Köppen built his climate classification on that link. NASA's typical annual precipitation figures make the gradient concrete: rainforest about 2,000 to 10,000 mm, temperate deciduous forest about 750 to 1,500 mm, coniferous forest about 300 to 900 mm, grassland about 500 to 900 mm, desert about 250 mm and tundra about 150 to 250 mm.

Temperature works alongside. Rainforests stay frost-free, with average daily temperatures of about 20 to 25 °C (NASA), while tundra combines low precipitation with the lowest temperatures of the five major biomes. Because both factors change with latitude and altitude, biomes form rough belts from the Equator to the poles and up mountainsides: tropical forests near the Equator, temperate forests at higher latitudes, boreal forests higher still, and tundra beyond the tree line.

Forests are full of trees. Near the Equator, rainforests are warm and wet all year.

Farther north, many forest trees lose their leaves in autumn. In the cold north are forests of pine trees with needles.

Forests are biomes where trees rule. The UN's Food and Agriculture Organization (FAO) reported in 2025 that forests cover about one-third of the world's land, and nearly half of them are in the tropics. Forests are home to many of the world's land insects, birds and mammals.

There are three main kinds. Tropical forests, near the Equator, are warm and humid. Temperate forests, farther from the Equator, have four seasons; in many of them, the leaves change color in autumn, fall in winter and grow back in spring. Boreal forests, also called taiga, grow even farther north. They have the coldest, driest climate of the forests, with snowy winters and evergreen trees that bear cones and needles.

Forests are dominated by trees and hold much of the world's terrestrial biodiversity. The FAO's Global Forest Resources Assessment 2025 puts global forest area at 4.14 billion hectares, about 32 percent of the land area, with nearly half in the tropics. It reports that deforestation slowed to 10.9 million hectares a year in 2015–2025, down from 17.6 million in 1990–2000, though the FAO still calls the current rate too high; about 20 percent of forests are in legally protected areas.

National Geographic distinguishes three forest biomes by latitude. Tropical forests near the Equator are warm and humid. Temperate forests at higher latitudes experience four seasons; NASA notes that deciduous trees there shed leaves in autumn, an adaptation to survive cold winters, and receive about 750 to 1,500 mm of precipitation a year. Boreal forests, or taiga, at higher latitudes still, have the coldest and driest forest climate, with precipitation mostly as snow; NASA describes their conifers as evergreen trees with cones and needles.

Grasslands are wide, open places covered with grass. There are few trees.

Some grasslands are warm all year, with a few trees. Zebras and giraffes live in places like these. Other grasslands have hot summers and cold winters.

Grasslands are wide, open lands where grasses grow instead of forests. They usually have a warm, dry climate. NASA says grasslands get about 500 to 900 millimeters of rain a year.

There are two kinds. Tropical grasslands, called savannas, are nearer the Equator and can have a few scattered trees. They cover almost half of Africa, as well as parts of Australia, India and South America. Temperate grasslands are farther from the Equator and have no trees or shrubs. They have different names in different places: the prairies of North America, the pampas of South America, the veldt of South Africa and the steppes of Central Eurasia. Prairies have taller grasses; steppes have shorter ones.

Grasslands are open regions dominated by grasses, generally with a warm, dry climate. National Geographic divides them into tropical grasslands, or savannas, close to the Equator with scattered trees, covering almost half of Africa and parts of Australia, India and South America; and temperate grasslands, farther from the Equator, without trees or shrubs and with less precipitation than savannas. Prairies, with taller grasses, and steppes, with shorter grasses, are two types of temperate grassland.

NASA gives grasslands about 500 to 900 mm of precipitation a year and an annual temperature range, depending on latitude, of roughly −20 to 30 °C. It lists the prairies of the Great Plains, the pampas of South America, the veldt of South Africa and the steppes of Central Eurasia among them. Its list of typical grassland plants includes prairie clover, salvia, coneflowers and grasses such as oats, wheat and barley.

Deserts are very dry. Some are hot, and some are cold. Plants and animals there can live with very little water.

Tundra is cold, flat land near the North Pole and high on mountains. The ground under it stays frozen. Only small plants grow there.

Deserts are the driest biomes. NASA says a typical desert gets about 250 millimeters of rain a year. Deserts can be hot or cold. In a hot desert, NASA says, days average about 38 °C, but nights average about −4 °C. Desert plants and animals have special ways to survive with little water; many desert animals are reptiles and small mammals.

Tundra is the coldest biome on land. It gets little rain or snow, and just under the surface the ground stays frozen all year. This frozen layer is called permafrost. Trees cannot grow, so the tundra has shrubs, grasses, mosses and lichens. Arctic tundra lies north of the great northern forests, and alpine tundra lies high on mountains, above where trees can grow.

Deserts are defined by dryness, though definitions differ: National Geographic's biome article uses less than 50 cm (20 inches) of rain a year, its glossary 25 cm, and NASA says deserts get about 250 mm a year and most receive less than 300 mm. Deserts can be hot or cold; most lie in subtropical areas, and they divide into hot and dry, semiarid, coastal and cold types. NASA gives typical hot-desert averages of about 38 °C by day and −3.9 °C at night. Desert life, mostly reptiles and small mammals, is less diverse than in other biomes and depends on special adaptations; NASA notes that some desert annuals complete their whole life cycle in weeks.

Tundra has the lowest temperatures of the five major biomes: National Geographic gives average yearly temperatures from −34 to 12 °C, 15 to 25 cm of precipitation, poor soils and short summers. Permafrost, a permanently frozen layer beneath the surface, limits vegetation to shrubs, grasses, mosses and lichens. Arctic tundra lies north of the boreal forests; alpine tundra lies on mountains above the altitude where trees can survive.

Biomes are not only on land. Oceans, lakes and rivers are biomes too.

The salty sea is the biggest biome of all. Coral reefs are part of it.

Water biomes are called aquatic biomes. There are two kinds. Freshwater biomes are ponds, rivers and lakes surrounded by land, where the water has less than 1 percent salt. Marine biomes are salty: the ocean, coral reefs and estuaries, where rivers meet the sea.

Marine biomes cover close to three-quarters of Earth's surface, far more than all the land biomes put together. The ocean zones page explores how life changes from sunny coral reefs to the dark deep sea.

Aquatic biomes divide into freshwater and marine. National Geographic defines freshwater biomes as bodies of water surrounded by land, such as ponds, rivers and lakes, with a salt content of less than 1 percent; marine biomes include the ocean, coral reefs and estuaries and cover close to three-quarters of Earth's surface.

Estuaries, where rivers meet the sea, bridge the two kinds. The ocean zones, coasts and river pages explore these watery environments in more detail, from sunlit reefs to the deep sea.