What is an ecosystem?

An ecosystem is the way living things (plants, animals) and non-living things (climate, soil, water) are linked and depend on each other — their interdependence.

Large-scale ecosystems are called biomes. Their global distribution follows climate:

• Tropical rainforests — around the Equator (hot, wet all year).
• Hot deserts — ~30° N/S (sinking air, dry).
• Grasslands — tropical (savanna) and temperate.
• Temperate forests — mid-latitudes (e.g. UK).
• Polar regions — high latitudes (very cold).

Key term — interdependence: if one part changes (e.g. trees removed), the others are affected (soil erodes, animals lose habitat).

Inside a tropical rainforest

Tropical rainforests are the most biodiverse land ecosystem. Their key features:

• Climate: hot (~27 °C) and wet (over 2,000 mm rain) all year.
• Structure: layered — emergents, canopy, under-canopy, shrub layer.
• Nutrient cycle: fast — dead leaves decompose quickly in the heat, so most nutrients are stored in the biomass (living things), not the soil.
• Soil: thin and infertile once trees are removed; heavy rain leaches nutrients.
• Adaptations: tall trunks, drip-tip leaves, buttress roots, lianas.

Misconception: rainforest soils are not very fertile. The nutrients are locked in the plants, so when the forest is cleared the soil quickly loses fertility.

Where are the nutrients?

Why are rainforests exploited?

Rainforests provide goods (timber, foods, medicines) and services (storing carbon, regulating climate, biodiversity). But human activity threatens them:

• Logging — for hardwood timber.
• Agriculture — clearing for cattle ranching and crops (e.g. soy, palm oil).
• Mineral extraction — mining for gold, iron ore, oil.
• Tourism — can damage habitats if poorly managed.

Deforestation reduces biodiversity, releases stored carbon and degrades soil.

Managing rainforests sustainably

OCR wants a case study of sustainable rainforest management (local/regional). Widely-taught: Amazonia (Brazil). Strategies include:

• Ecotourism — small-scale, low-impact tourism that funds conservation and gives locals income.
• Selective logging and sustainable forestry — only some trees felled; replanting.
• Community programmes and biosphere reserves — protected zones managed with local people.

Sustainable means meeting today's needs without stopping future generations meeting theirs — using the forest while conserving it.

Match the strategy to its meaning

Tap a strategy on the left, then tap its correct description on the right.

Polar and tundra environments

OCR contrasts rainforests with cold polar environments (Antarctica and the Arctic):

• Climate: extremely cold, dry, with long dark winters and 24-hour daylight in summer.
• Antarctica: a frozen continent, no permanent human population, home to penguins, seals and krill.
• Arctic: a frozen ocean surrounded by land; polar bears, and indigenous peoples (e.g. the Inuit).
• Fragile & interdependent: short food chains mean damage spreads quickly; slow growth means slow recovery.

Threats to polar environments

Human activity threatens polar regions:

• Climate change — melting sea ice threatens polar bears; the Arctic is warming fast.
• Fishing, whaling, mineral & oil exploitation — disturb wildlife and habitats.
• Tourism and scientific research — can cause pollution and disturbance.

Management includes sustainable tourism, conservation, and global agreements — the Antarctic Treaty (1959) reserves Antarctica for peaceful science and bans mining, and Earth Summits coordinate global action.

Protecting Antarctica

Your turn — ecotourism

Rainforest or polar feature?

Tap a feature, then tap the box it belongs in.

Sustainable or not?

Is each action a sustainable way to use an ecosystem?

Rainforest climate

Interdependence

The key ideas to know

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