World biomes in depth

In Grade 5 you met the three broad climate zones — tropical, temperate, and polar — that wrap around the Earth like belts. This year we go one level deeper. A biome is a large region of the world defined not just by climate but by the whole community of plants and animals that live there. Biomes are how ecologists carve up the planet. Two biomes can sit inside the same climate zone, and a third can stretch across two climate zones. Climate sets the stage; life fills it in.

Tropical rainforest

Tropical rainforests sit in a belt near the equator — the Amazon in South America, the Congo in central Africa, and much of South-East Asia. Temperatures stay warm year-round (around 25 °C / 77 °F), and rainfall is enormous: 2,000 to 4,000 mm a year, with no real dry season. The result is dense, layered forest with the world's highest biodiversity. Jaguars, sloths, orangutans, toucans, poison-dart frogs, and tens of thousands of insect species live here.

Savanna (tropical grassland)

Savannas sit on the edges of the tropics — across much of sub-Saharan Africa, parts of South America, and northern Australia. They are warm year-round, but rain falls in a single wet season and the long dry season turns the land golden brown. Vegetation is mainly tall grass, dotted with scattered trees like acacias and baobabs. Famous animals include lions, elephants, giraffes, zebras, and wildebeest, whose huge herds migrate to follow the rains.

Desert

Deserts get less than 250 mm of rain a year. Hot deserts (Sahara, Arabian, Sonoran, Australian Outback) bake by day and cool by night. Cold deserts also exist — the Gobi, parts of central Asia, even Antarctica is technically a desert because it gets so little precipitation. Plants are adapted to store water (cacti, succulents) or to live as seeds underground for years between rains. Animals like camels, fennec foxes, and kangaroo rats can go long stretches without drinking.

Temperate forest

Temperate forests cover much of eastern North America, western and central Europe, and parts of East Asia. Four distinct seasons mark this biome: snowy winters, mild springs, warm summers, and crisp autumns when broadleaf trees (oak, maple, beech, birch) lose their leaves. Rainfall is moderate. Deer, foxes, squirrels, bears, songbirds, and many insects live here. Most of the world's big cities sit in or near temperate forest country.

Taiga (boreal forest)

The taiga is the largest land biome on Earth — a vast belt of evergreen forest sweeping across Canada, Alaska, Scandinavia, and Russia. Winters are long and bitterly cold (-30 °C or colder); summers are short and cool. Pines, firs, and spruces dominate because their needle-shaped leaves and waxy coating survive freezing. Moose, wolves, lynx, bears, and beavers live here. The taiga locks up huge amounts of carbon in its soil.

Tundra

The tundra rings the Arctic and covers high mountaintops. Below the surface lies permafrost — soil that stays frozen all year. Temperatures rarely rise above 10 °C even in summer; winters plunge to -50 °C. Trees cannot survive, so the vegetation is low and tough: mosses, lichens, hardy grasses, and dwarf shrubs. Caribou (reindeer), Arctic foxes, snowy owls, lemmings, and musk oxen live here. The growing season is only a few weeks long.

Why biomes matter

Biomes set the rules for everything that lives inside them — including humans. People in the savanna build differently and farm differently from people in the taiga. Climate change is now shifting biome boundaries: tundra is thawing, deserts are expanding, and tropical rainforests are being cleared. Understanding biomes helps us protect the rich web of life that depends on each one.