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Quiz yourself on Ecosystems OverviewGet your flashcardsBuild my revision planTrack my progress🗺️ Global Biomes: Distribution and Climate
A biome is a large-scale ecosystem defined by its climate and characterised by a distinctive type of vegetation and the animals that depend on it. Biomes are the biggest ecosystems on Earth — they span continents and contain millions of species. Six major terrestrial (land) biomes are essential for your GCSE course.
The Six Major Terrestrial Biomes
| Biome | Climate | Location (latitude) | Characteristic vegetation |
|---|---|---|---|
| Tropical rainforest | Hot all year (25–27°C); very wet (>2,000 mm); no dry season | 0°–5° N and S of the equator | Dense multi-layered canopy; epiphytes; lianas; very high species diversity |
| Tropical savanna (grassland) | Hot (20–30°C); seasonal — distinct wet and dry season; 500–1,500 mm rain in wet season | 5°–15° N and S | Tall grasses with scattered, fire-resistant trees; baobabs; acacias |
| Hot desert | Extreme temperature range (day >40°C, night <10°C); very dry (<250 mm/yr) | 20°–30° N and S (high pressure belt) | Sparse; cacti; succulents; ephemeral plants after rare rain; adapted shrubs |
| Temperate deciduous forest | Four distinct seasons; moderate (6–17°C annual average); 600–1,500 mm distributed throughout year | 40°–60° N (and some S) | Oak, ash, beech, maple; undergrowth of bluebells, ferns; fungi-rich leaf litter |
| Coniferous forest (boreal / taiga) | Cold; -10 to +15°C; 300–900 mm; long winters, short warm summers | 60°–70° N | Pine, spruce, fir; needle leaves; conical shape to shed snow; acidic soils |
| Tundra | Very cold; average below 0°C most of year; <250 mm; permafrost below surface | >70° N (Arctic) | Mosses, lichens, dwarf shrubs, sedges; no trees; growing season 6–10 weeks |
Why Biomes Are Where They Are: The Five Drivers
Biomes are not randomly distributed — they follow predictable patterns controlled by five key factors. Understanding these factors allows you to explain any biome's location, and to predict what an area's vegetation would be like from its position on a globe.
1. Latitude → Temperature. The angle at which sunlight strikes the Earth determines how much energy reaches the surface per unit area. At the equator, the sun is near overhead: solar energy is concentrated, temperatures are high, and the growing season is year-round. At the poles, the sun strikes at a very low angle, spreading the same energy over a much larger area — temperatures are low and growing seasons minimal. This is the primary driver of the tropical-to-tundra sequence as you move from equator to poles.
2. Atmospheric pressure belts → Rainfall. At the equator, intense solar heating causes air to rise, cool, and release its moisture as heavy, reliable rain — producing the tropical rainforest's >2,000 mm. That same air, now dry, descends at around 20°–30° N and S, creating high-pressure belts where rainfall is suppressed — producing hot deserts. This is not a coincidence; the location of the Sahara, Arabian, and Australian deserts at these exact latitudes is a direct result of global atmospheric circulation.
3. Distance from the sea → Continentality. Oceans have a moderating effect on climate — they warm slowly and cool slowly, dampening temperature extremes. Coastal locations have mild, wet climates. Continental interiors (far from the sea) experience extreme seasonal temperature ranges and lower rainfall. The boreal forest of Siberia experiences -50°C winters partly because it is thousands of kilometres from any ocean.
4. Ocean currents → Modified coastal climates. Warm ocean currents transport tropical heat toward higher latitudes. The Gulf Stream carries warm water from the Gulf of Mexico northward across the Atlantic, keeping north-west Europe — including the UK — significantly warmer than its latitude would otherwise allow. Cold currents do the reverse: the cold Benguela Current off the Namibian coast contributes to the Namib Desert by cooling and stabilising the air above it, preventing rainfall.
5. Altitude → Temperature decreases. Temperature falls by approximately 6.5°C for every 1,000 m gained in altitude. Mountain ranges create vertical zonation: tropical forest at the base gives way to cloud forest, then alpine grassland, then bare rock and snow at the summit — even on the equator. The Andes, Himalayas, and East African mountains all show this pattern clearly.
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