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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.
A comparative case study of the Amazon rainforest and the Siberian taiga illustrates how latitude, climate and continentality combine to create radically different ecosystems that nevertheless share one feature: enormous global importance for carbon storage and climate regulation.
The Amazon rainforest spans roughly 5.5 million km² centred on the equator between 5°N and 15°S, across nine countries (Brazil holds around 60%). Annual rainfall of 2,000–3,500 mm, temperatures of 26–28°C year-round and 80–90% humidity produce the most biodiverse biome on Earth — an estimated 10% of all known species (around 40,000 plant species, 1,300 bird species, 3,000 fish species). The Amazon stores around 150–200 gigatonnes of carbon in biomass and soils. Indigenous peoples include around 305 groups totalling around 900,000 people across 690 indigenous territories, with groups such as the Yanomami, Kayapó and Ashaninka.
The Siberian taiga covers around 12 million km² of Russia — almost twice the Amazon's area — stretching from Scandinavia across Russia to the Pacific, between roughly 50°N and 70°N. Winter temperatures regularly reach −40°C in Yakutia; summer highs around 15–20°C. Annual precipitation is a modest 400–600 mm, much of it snow. Vegetation is dominated by five coniferous species — spruce, pine, fir, larch and Siberian cedar — with slow growth and 80–120-year maturation. Biodiversity is modest (around 1,500 plant species) but carbon storage is vast: when soils and permafrost are included, Siberian taiga and peat hold an estimated 500+ gigatonnes of carbon — potentially more than the entire atmosphere.
Contrasting human use. The Amazon supports around 34 million people directly, including indigenous communities, mestizo riverine populations, and fast-growing cities like Manaus (2.2 million) and Belém. Siberia has only around 37 million people in its vast area, concentrated in cities like Novosibirsk (1.6 million) and Irkutsk. Both biomes face deforestation, though from different drivers: cattle and soya expansion in the Amazon (around 13,000 km² cleared in 2021), versus industrial logging, oil/gas extraction and wildfires in Siberia (18.8 million ha burned in 2021 alone). The two biomes show how latitude determines climate, which determines vegetation, which determines human use — and how both are now being reshaped by global climate change.
Why comparison matters for Paper 3. Edexcel B's decision-making examination often asks candidates to compare contrasting biomes. A strong answer uses the same sub-headings (climate, soils, vegetation, human use, threats) for each biome to structure a genuine comparison, rather than describing them in isolation.
Misconception: "Biomes are determined only by temperature — hotter places have more life."
This is wrong. Biomes are shaped by the combination of temperature and precipitation, and by secondary factors like altitude, ocean currents and continentality. Hot deserts are hotter on average than tropical grasslands, yet support far less life because rainfall is below 250 mm per year. Temperate deciduous forests are cooler than deserts but, with 500–1,500 mm of evenly spread rain, support abundant life. Biodiversity also depends on stability — the consistent equatorial climate of the tropical rainforest has allowed millions of years of speciation, whereas the taiga's harsh seasonality limits species number even though biomass and carbon storage are enormous. Always explain biomes with both temperature and precipitation, and with the idea of climate stability.
Question: "Explain how latitude and other factors shape the global distribution of biomes. Refer to named examples." (8 marks)
Grade 3–4 response: "Biomes are different because of latitude. Hot places near the equator have rainforests and cold places near the poles have tundra. The Amazon is a rainforest and Russia has taiga. Mountains and the sea also affect biomes."
Examiner comment: Very basic outline, no figures, minimal named detail. Level 1, 2 marks.
Grade 5–6 response: "Latitude is the main factor shaping biome distribution because the Sun's rays are most concentrated at the equator and spread out at the poles, so temperatures fall with latitude. Within 10° of the equator, tropical rainforests like the Amazon (5.5 million km²) form because of high temperatures (26–28°C) and rainfall over 2,000 mm. Between 50°N and 70°N, taiga like the Siberian boreal forest (12 million km²) forms because of long cold winters (down to −40°C). Altitude also matters — Mount Kilimanjaro has multiple biomes up its slopes. Ocean currents can warm (North Atlantic Drift keeping Britain temperate) or cool regions."
Examiner comment: Good figures, named examples, multiple factors. Could strengthen by explaining continentality. Level 2, 6 marks.
Grade 7–9 response: "Biome distribution follows a broadly zonal pattern driven primarily by latitude, because solar insolation at 0° is several times greater than at 70°N on an annual average, dictating temperature. Within 10° of the equator, high temperatures (26–28°C) and constant convectional rainfall of 2,000–3,500 mm produce tropical rainforests like the 5.5 million km² Amazon. Between around 50°N and 70°N, low solar input and continentality produce long, cold winters (−40°C in Yakutia) and the 12 million km² Siberian taiga. However, the zonal pattern is modified by three secondary factors. Altitude produces altitudinal zonation — Kilimanjaro (3°S) has glaciers because temperature drops around 6.5°C per 1,000 m. Ocean currents move the warm North Atlantic Drift north, keeping western Europe under temperate deciduous forest at latitudes where continental Canada has taiga. Continentality means the interior of Asia (Siberia) has taiga/tundra at latitudes where coastal Norway has milder forest, because seas moderate temperature. Biodiversity within a biome is further shaped by climate stability — the Amazon's millennia-long equatorial stability has driven rich speciation, while the taiga's seasonal extremes limit species number despite its vast carbon stores. My judgement is that latitude sets the broad pattern but the secondary factors explain most anomalies that students are asked to identify."
Examiner comment: Clear primary/secondary factor framework, figures, named examples, analytical judgement. Level 3, 8 marks.
This content is aligned with the Edexcel GCSE Geography B (1GB0) specification, Paper 3: People and environment issues — Making geographical decisions. For the most accurate and up-to-date information, please refer to the official Pearson Edexcel specification document.