Biomes and Ecosystems: KS3 Geography Guide

Earth's surface is divided into distinct zones called biomes — large-scale regions shaped by climate, vegetation and wildlife. Within each biome, living organisms and their non-living surroundings interact to form an ecosystem. Understanding biomes means thinking spatially: from a tropical rainforest in Borneo to frozen tundra in northern Canada, location determines life.

Biome vs ecosystem: what is the difference?

A biome operates at the grandest geographical scale — it is a large region defined by its characteristic climate, dominant plant types and associated wildlife. The tropical rainforest is a biome; so is the hot desert. A biome typically spans multiple countries or even continents.

An ecosystem is a more flexible concept. It describes the living (biotic) components — plants, animals, bacteria and fungi — together with the non-living (abiotic) components — temperature, rainfall, sunlight, soil and water — and, crucially, the interactions between them. An ecosystem can be as small as a garden pond or as vast as the entire Amazon Basin. Every biome contains many ecosystems nested within it.

What controls biome distribution?

Biomes are not randomly scattered across the map. Their locations follow predictable patterns driven by several interlocking factors.

Climate is the primary control. Temperature and precipitation together determine what vegetation can survive where. A simple climate diagram — plotting monthly temperature against monthly rainfall — captures this relationship powerfully: where it is hot and wet year-round, tropical rainforest thrives; where it is hot and dry, desert dominates.

Latitude controls temperature because the tropics (0°–23.5° N/S) receive intense solar radiation year-round, while polar regions (above ~66°) receive weak, angled sunlight and far less heat energy. Altitude mimics latitude — climb Mount Kenya and you ascend through biome zones that mirror the progression from equator to pole.

Ocean currents and continentality (distance from the sea) fine-tune the picture. The cold Benguela Current off south-west Africa creates the Namib Desert at the same latitude as the tropical forest of central Africa. Inland areas far from the sea experience more extreme temperatures and drier conditions — hence the vast temperate grasslands of central Asia.

The major terrestrial biomes

Nine major terrestrial (land) biomes are recognised in KS3 geography. The table below summarises their key characteristics.

Biome | Location examples | Annual rainfall (approx) | Temperature range | Key vegetation
Tropical rainforest | Amazon Basin; Congo; Borneo | >2,000 mm | 20–30°C year-round | Tall evergreen broadleaved trees, epiphytes
Tropical savanna | East Africa; northern Australia | 500–1,500 mm | 20–35°C; distinct wet/dry seasons | Grasses, scattered acacia and baobab
Hot desert | Sahara; Arabian Desert; Atacama | <250 mm | −5 to 45°C (extreme range) | Cacti, succulents, sparse xerophytes
Mediterranean | Southern Europe; California; SW Australia | 300–700 mm (mostly winter) | 10–30°C | Drought-resistant shrubs, cork oak, olive
Temperate grassland | Pampas (Argentina); North American prairies | 250–750 mm | −20 to 30°C | Grasses; very few trees
Temperate deciduous forest | Western Europe; north-east USA; eastern China | 600–1,500 mm | −5 to 25°C | Oak, beech, ash; shed leaves in autumn
Boreal forest (taiga) | Siberia; Canada; Scandinavia | 200–600 mm | −40 to 20°C | Coniferous trees: pine, spruce, fir
Tundra | Northern Canada; Alaska; northern Russia | <250 mm | −40 to 10°C | Mosses, lichens, dwarf shrubs
Polar | Antarctica; Arctic Ocean fringe | <100 mm | −60 to 0°C | Ice and bare rock; no vascular plants

Biodiversity and nutrient cycling

Biodiversity — the variety of species present in an area — varies dramatically between biomes. Tropical rainforests cover roughly 6% of Earth's land area yet harbour approximately 50% of all known species. High temperatures and reliable moisture allow continuous photosynthesis, creating a complex, multi-layered canopy structure that supports extraordinary variety. Polar regions, by contrast, support the fewest species because extreme cold limits viable survival strategies.

Nutrient cycling follows a similarly dramatic pattern. In tropical rainforests, warmth and moisture drive rapid decomposition — dead leaves can break down within weeks, cycling nutrients back into the soil almost immediately. The soil itself is often surprisingly nutrient-poor: trees absorb nutrients so quickly that little accumulates in the ground.

In the tundra, cold temperatures slow decomposition to a near halt. Organic material and carbon accumulate in permafrost — permanently frozen ground — for thousands of years. Climate change is beginning to thaw this permafrost, releasing stored carbon dioxide and methane and potentially accelerating warming in a dangerous feedback loop.

SEEP analysis: what happens when biomes are lost?

The SEEP lens (Social, Economic, Environmental, Political) reveals the full consequences of biome change.

Social: Indigenous communities across the Amazon and Congo Basin depend directly on forest biomes for food, shelter, medicine and cultural identity. The Yanomami people of the Amazon and the Baka people of central Africa are just two examples of communities whose wellbeing is inseparable from biome health. When biomes are cleared, these communities face displacement and the destruction of irreplaceable knowledge about plants and ecosystems.

Economic: Biomes provide ecosystem services — benefits delivered to humanity free of charge. Carbon storage, water purification, soil formation, crop pollination and raw materials for medicines together represent trillions of pounds in economic value annually. Short-term profit from clearing land typically falls far short of this long-term value.

Environmental: Habitat loss is driving species towards extinction at a rate estimated at 1,000–10,000 times the natural background level. Biome degradation also releases stored carbon, accelerating climate change — which in turn stresses remaining biomes, creating a self-reinforcing cycle.

Political: International agreements attempt to slow these losses. The Paris Agreement (2015) sets global temperature targets that require forests to remain standing. The Kunming-Montreal Global Biodiversity Framework (2022) aims to protect 30% of Earth's land and ocean by 2030. Tension persists, however, between wealthy nations that industrialised by exploiting their own biomes and developing nations seeking the same economic development pathway.

Frequently asked questions

What is the difference between a biome and an ecosystem?

A biome is a large-scale geographical region with characteristic climate, vegetation and wildlife — such as the tropical rainforest or the hot desert. An ecosystem is any community of living organisms interacting with their non-living environment; it can be tiny (a rock pool) or enormous (the whole Amazon). Every biome contains many ecosystems.

Why do tropical rainforests have far higher biodiversity than other biomes?

High temperatures and heavy rainfall occur year-round in tropical rainforests, allowing continuous photosynthesis and plant growth. This produces a complex, multi-layered canopy structure — from the dark forest floor to emergent trees 50 m above — creating thousands of distinct microhabitats and ecological niches. More niches means more species can coexist without competing directly.

How does altitude affect which biome you find on a mountain?

Climbing a mountain causes temperature to fall at roughly 6.5°C per 1,000 m of ascent, replicating the effect of moving towards higher latitudes. A mountain near the equator may therefore pass through tropical forest, cloud forest, alpine meadow (resembling tundra) and finally bare rock and ice at the summit — a vertical journey through multiple biomes in the space of a few kilometres.

Why is nutrient cycling so much slower in tundra than in tropical rainforest?

Decomposition requires warmth and moisture. Tundra temperatures remain below freezing for most of the year, which drastically slows bacterial and fungal activity. Organic material — including enormous stores of carbon — therefore accumulates in permafrost rather than being broken down and recycled through plants, as happens rapidly in the warm, moist conditions of a tropical rainforest.

What do international agreements actually do to protect biomes?

Agreements like the Paris Agreement and the Kunming-Montreal Global Biodiversity Framework set binding or aspirational targets — for example, limiting warming to 1.5°C, or protecting 30% of land and ocean by 2030. They can unlock funding such as REDD+ payments to forest nations, set national commitments and create diplomatic pressure. However, enforcement remains limited, as countries largely retain sovereignty over how they manage their own land.

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