Global Biomes & The Biosphere
A Patchwork of Living Worlds
Look at any global map of vegetation and you can see Earth’s major biomes arranged in roughly horizontal bands. Hot and wet equatorial belts hold tropical rainforests. Hot and dry zones at 30° latitude are deserts. Mid-latitudes hold temperate forests and grasslands. Cold high-latitude bands carry boreal forest (taiga) and tundra. The pattern is not coincidence: it is the product of global atmospheric circulation, ocean currents and altitude.
The Major Biomes
Edexcel asks you to know the global distribution and characteristics of seven major biomes. Tropical rainforest straddles the equator (Amazon, Congo, Indonesia) — year-round warmth, 2,000+ mm of rainfall, very high biodiversity. Temperate deciduous forest covers western Europe, eastern North America and East Asia — four seasons, 600–1,500 mm rainfall, oak/beech/maple trees. Boreal (taiga) forest circles the northern hemisphere (Siberia, Canada, Scandinavia) — cold, low rainfall, conifers like spruce and pine. Tropical grasslands (savanna) sit between rainforest and desert — wet/dry seasons, scattered trees. Temperate grasslands include the prairies and steppes — cold winters, hot summers, treeless. Hot deserts at 30° latitude (Sahara, Atacama) get under 250 mm rainfall a year. Tundra ringing the Arctic has frozen ground (permafrost) and very short summers.
Biomes form latitudinal bands because temperature and rainfall depend on global atmospheric circulation. Hadley-cell rising air at the equator gives rainforest; sinking air at 30° gives desert; rising Ferrel-cell air at 60° gives temperate forest; sinking Polar air gives tundra.
Why Climate Drives Distribution
Three climate factors shape biome distribution: temperature, precipitation and sunshine hours. Tropical regions are hot because the Sun’s rays strike near vertically; polar regions are cold because rays are slanted. Rainfall depends on the rising arms of circulation cells (equator, 60°) where air cools, condenses and dumps moisture. Sunshine hours influence growing seasons — Arctic summers have 24-hour daylight that lets tundra plants flower briefly.
Local Factors
Climate isn’t the only thing that matters. Altitude can recreate latitudinal patterns vertically — Mount Kilimanjaro near the equator has tropical forest at the base, alpine grassland higher up, and an icecap at the summit. Soil type: rainforest grows on poor soils because nutrients cycle quickly through living matter; deserts often have alkaline crust soils that limit plant choice. Drainage: poor drainage creates wetlands and bogs even in dry regions. Rock type: granite uplands hold acidic moorland; chalk supports calcium-loving species.
Biotic components are the living parts of a biome — plants, animals, fungi, bacteria. Abiotic components are the non-living physical parts — soil, rock, water, air, temperature, sunlight. The two are interdependent: plants need abiotic water and sunlight to grow; their decay enriches abiotic soils. Disrupt one and the other suffers — cutting tropical rainforest reduces transpiration, which reduces local rainfall, which slows regrowth.
The Biosphere as a Life-Support System
The biosphere provides goods and services to people. Goods are direct outputs: food (crops, fish, livestock), timber and fibre, medicines (a quarter of modern drugs come from rainforest plants), and fuels (firewood, biofuels). Services are less visible but vital: regulating the atmosphere’s composition (forests absorb CO₂ and release O₂), filtering water as it moves through soils and wetlands, recycling nutrients, pollinating crops, providing fresh-water storage. Without these services, modern civilisation could not function.
The biosphere provides goods (food, timber, medicines, fuel) and services (atmospheric regulation, water purification, pollination, nutrient cycling). A 1997 study in the journal Nature valued these services at about $33 trillion a year — nearly double the size of the world economy at the time.
Indigenous and Local People
For Indigenous peoples and rural communities, the biosphere is daily life. The Yanomami of the Amazon harvest hundreds of plant species for food, medicine, building material and ritual use. The Sami of northern Scandinavia herd reindeer through the taiga. Maasai pastoralists graze cattle on East African savanna. These livelihoods depend on intact biomes and on traditional knowledge built up over centuries. Pressure on biomes — from logging, mining, climate change — threatens these communities first and most directly.
Compare three biome climate graphs side by side and the differences leap out. Equatorial rainforest: a flat, high temperature line at 25–28°C; high rainfall (200+ mm) every month. Hot desert: a wide temperature swing (5°C nights to 45°C days), almost no rainfall in any month. Tundra: temperatures below freezing for most of the year, with a brief summer above zero; very low rainfall, mostly as snow. Identifying biomes from climate graphs is a regular exam task — practise pattern recognition.