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A biome is a large-scale ecosystem defined by its dominant vegetation, climate and wildlife. Biomes cover vast areas of the Earth's surface and are shaped primarily by temperature and precipitation patterns. Understanding the global distribution of biomes is the starting point for the Edexcel B Paper 3 topics on People and the Biosphere, because it explains why different parts of the world support different types of life and provide different resources for human populations.
Three main factors control the global distribution of biomes:
Latitude is the single most important factor controlling biome distribution. As you move from the equator (0°) towards the poles (90°N and 90°S), average temperatures fall because the Sun's rays strike the surface at an increasingly low angle, spreading energy over a larger area.
Exam Tip: When explaining biome distribution, always link back to latitude as the primary factor. Examiners reward answers that clearly connect latitude to solar energy input and therefore temperature.
Altitude refers to height above sea level. For every 1,000 metres of altitude gained, temperature drops by approximately 6.5°C (the environmental lapse rate). This means that mountains can support tundra-like conditions even at tropical latitudes. For example, Mount Kilimanjaro in Tanzania (3°S) has glaciers at its summit despite being near the equator, and its slopes pass through several distinct biome zones as altitude increases.
The sea has a moderating effect on temperatures because water heats up and cools down more slowly than land. Coastal areas therefore tend to have milder winters and cooler summers (a maritime climate), while areas deep in the interior of continents experience extreme temperature ranges — very hot summers and bitterly cold winters (a continental climate). This is why the vast interior of Russia and Canada is dominated by taiga and tundra, whereas coastal western Europe at similar latitudes has temperate deciduous woodland.
The Earth's land surface can be divided into several major biomes. Each has distinctive characteristics shaped by its climate.
| Feature | Detail |
|---|---|
| Location | Within 10° of the equator — Amazon Basin, Congo Basin, South-East Asia |
| Climate | Hot (25–28°C year-round), wet (over 2,000 mm rainfall/year), no distinct seasons |
| Vegetation | Dense, multi-layered forest; broadleaf evergreen trees reaching 40–50 m; enormous biodiversity |
| Soils | Thin, nutrient-poor latosols; nutrients locked in biomass rather than soil |
| Biodiversity | Highest of any biome — the Amazon alone contains an estimated 10% of all species on Earth |
| Feature | Detail |
|---|---|
| Location | 10°–25° N/S — East Africa (Serengeti), Brazil (Cerrado), northern Australia |
| Climate | Warm (20–30°C), distinct wet and dry seasons; 500–1,500 mm rainfall, mostly in the wet season |
| Vegetation | Tall grasses (up to 2 m) with scattered drought-resistant trees like baobab and acacia |
| Soils | Moderately fertile; can be red laterite soils, often leached during the wet season |
| Biodiversity | Supports large herds of herbivores (wildebeest, zebra, elephant) and their predators |
| Feature | Detail |
|---|---|
| Location | Around 30° N/S — Sahara, Arabian, Kalahari, Atacama, Australian deserts |
| Climate | Very hot days (up to 50°C), cold nights (below 0°C possible); less than 250 mm rainfall/year |
| Vegetation | Sparse; cacti, succulents, thorny bushes; plants have deep roots or water-storing adaptations |
| Soils | Sandy or rocky; very thin and low in organic matter; often saline |
| Biodiversity | Low but highly specialised; nocturnal animals, drought-adapted reptiles and insects |
| Feature | Detail |
|---|---|
| Location | 40°–60° N — Western Europe, eastern USA, eastern China, Japan |
| Climate | Moderate temperatures (5–20°C through the year); 500–1,500 mm rainfall spread evenly |
| Vegetation | Broadleaf trees (oak, beech, ash, birch) that shed leaves in autumn; distinct seasons |
| Soils | Brown earths — fertile, with a thick layer of leaf litter that decomposes each year |
| Biodiversity | Moderate; deer, foxes, badgers, woodland birds, invertebrates |
| Feature | Detail |
|---|---|
| Location | 50°–70° N — Russia (Siberia), Canada, Scandinavia, Alaska |
| Climate | Long, bitterly cold winters (down to −40°C); short, cool summers (10–20°C); low precipitation (300–600 mm), often as snow |
| Vegetation | Dense coniferous forest — spruce, pine, fir, larch; needle leaves and conical shapes |
| Soils | Thin, acidic podzols; slow decomposition due to cold temperatures |
| Biodiversity | Relatively low species diversity; wolves, bears, moose, lynx, migratory birds |
| Feature | Detail |
|---|---|
| Location | Above 65° N — Arctic fringes of Russia, Canada, Alaska, Greenland, Scandinavia |
| Climate | Extremely cold (−30°C to 10°C); very short growing season (6–10 weeks); less than 250 mm precipitation |
| Vegetation | Low-growing mosses, lichens, grasses, dwarf shrubs; no trees (too cold and windy) |
| Soils | Thin and waterlogged in summer; underlain by permafrost (permanently frozen ground) |
| Biodiversity | Very low; Arctic fox, caribou/reindeer, snowy owl, lemmings |
The global distribution of biomes forms a broadly zonal pattern — that is, biomes tend to occur in east-west belts that follow lines of latitude. This is because latitude is the dominant factor controlling temperature.
graph LR
A["Equator<br/>0°"] -->|"Hot & wet"| B["Tropical<br/>Rainforest"]
A -->|"Wet/dry seasons"| C["Tropical<br/>Grassland"]
C -->|"Drier, 30° lat"| D["Hot Desert"]
D -->|"Cooler, 40–60°"| E["Temperate<br/>Deciduous Forest"]
E -->|"Colder, 50–70°"| F["Taiga<br/>(Boreal Forest)"]
F -->|"Coldest, 65°+"| G["Tundra"]
G -->|"Polar ice"| H["Ice Cap"]
However, this zonal pattern is disrupted by several factors:
Exam Tip: If asked to explain anomalies in biome distribution (e.g. why a desert exists at an unexpected latitude), discuss ocean currents, altitude or rain shadow as the disrupting factor. Always start with the expected zonal pattern and then explain what has changed it.
The distribution of biomes has a profound impact on human activity:
| Biome | Key Human Uses | Approximate Global Population |
|---|---|---|
| Tropical rainforest | Logging, mining, farming, medicines | ~500 million |
| Tropical grassland | Pastoralism, tourism (safaris), arable farming | ~1 billion |
| Hot desert | Oil/gas extraction, solar energy, irrigation farming | ~200 million |
| Temperate deciduous | Agriculture, industry, urbanisation | ~3 billion |
| Taiga | Logging, mining, oil/gas extraction | ~200 million |
| Tundra | Indigenous subsistence, oil/gas extraction | ~4 million |
| Term | Definition |
|---|---|
| Biome | A large-scale ecosystem defined by climate, vegetation and wildlife |
| Latitude | Distance north or south of the equator, measured in degrees |
| Altitude | Height above sea level |
| Continentality | The effect of distance from the sea on climate |
| Zonal pattern | The tendency of biomes to occur in east-west belts following latitude |
| Lapse rate | The rate at which temperature falls with altitude (approx. 6.5°C per 1,000 m) |
| Rain shadow | A dry area on the leeward side of a mountain range |
Exam Tip: Learn the latitude ranges for each biome. In Paper 3, you may be asked to identify a biome from a map or describe its global distribution. Being able to give specific latitude ranges (e.g. "tropical rainforest is found within 10° of the equator") shows precise knowledge and will earn you marks.
Understanding biome distribution is essential because the rest of this course examines how humans interact with two specific biomes — the tropical rainforest and the taiga — and how our demand for energy resources affects environments around the world.