Tropical rainforests

The rainforest climate

Tropical rainforests grow near the equator, where the sun is high in the sky all year and air rises (the low-pressure belt).

A typical rainforest climate (data written for this app).

Hot all year: about 26–28 °C, with a very small range.
Wet: usually over 2,000 mm of rain a year, often in afternoon thunderstorms.
No real seasons, though some months are drier than others.

The constant warmth and rain let plants grow all year round.

Layers of the forest

The forest grows in layers as plants compete for light:

the tallest trees, up to about 50 m, poking above the rest.
a dense layer of treetops, about 30 m up, home to most of the animals.
Under-canopy: younger trees and tall shrubs, in shade.
Shrub layer and forest floor: dark and damp. Few plants grow; dead leaves rot quickly.

Remember

From the top: emergents, canopy, under-canopy, shrub layer and forest floor.

Key terms

Soils and the nutrient cycle

Rainforest is very fast:

In the heat and damp, dead leaves are broken down by decomposers in weeks.
Plants take up the nutrients almost at once, so most nutrients are stored in the plants, not the soil.

The soil, a , is deep but infertile, apart from a thin fertile layer at the top. Heavy rain washes nutrients down through it (), and iron left behind makes it red.

This is why cleared rainforest land quickly loses its fertility: with the trees gone, there's nothing to keep nutrients cycling, and rain washes the thin top layer away.

Key terms

Interdependence and adaptations

Climate, soil, water, plants, animals and people are all : trees shelter animals; animals spread seeds; dead matter feeds the soil; trees return water to the air, which falls again as rain.

support tall trees in thin soil.
on leaves let heavy rain run off.
Lianas, woody climbers, root in the ground and climb to the light.
Epiphytes grow on branches, high up in the light.

Animal adaptations:

Orangutans have long, strong arms for swinging through the canopy.
Camouflage: leaf insects look like leaves.
Some animals glide between trees, such as flying squirrels.

Key terms

Biodiversity

Tropical rainforests have the highest , the variety of plant and animal species, of any land ecosystem. Many species haven't yet been discovered or named.

This biodiversity is under threat. As forests are cleared, species lose their habitats: the Bornean orangutan is now classed as critically endangered. Losing one species can affect many others that depend on it, for food, pollination or spreading seeds.

Key terms

Exam practice

Plan your own answer first, then open the model answers to see what each level looks like.

6 marks · about 6 minutes

Explain how plants and animals are adapted to the physical conditions of the tropical rainforest.

Explain means: Give the reasons why something happens, developing each point with "because" or "so".

Level 1 (Basic)· 2/6 marks (band 1–2)

Trees have drip tips. Monkeys live in the trees. Some plants grow on other plants.

Why this level: Correct adaptations named, but none is linked to the condition it helps with. To reach Level 2: explain why each adaptation helps survival in the rainforest's conditions.

Level 2 (Clear)· 4/6 marks (band 3–4)

The rainforest is very wet, so many leaves have drip tips that let the rain run off quickly. The forest floor is dark, so lianas climb up trees to reach the light. Tall trees have buttress roots to support them, because the soil is thin. Orangutans have long arms for moving through the canopy.

Why this level: Clear adaptations linked to conditions, for plants and an animal. To reach Level 3: develop each further and cover more of the conditions (heat, competition for light, thin soil) and more animal adaptations, such as camouflage.

Level 3 (Detailed)· 6/6 marks (band 5–6)

The rainforest is hot and wet all year, and plants compete fiercely for light. Lianas root in the ground and climb up tree trunks to reach the sunlight in the canopy, while epiphytes grow high on branches, taking water from the humid air. Heavy daily rain could damage leaves and encourage fungi, so many leaves have drip tips that let water run off quickly. The soil is thin because nutrients are quickly recycled, so tall emergent trees have wide buttress roots to support them. Animals are adapted too: orangutans have long, strong arms for swinging through the canopy, where most food is found, and leaf insects are camouflaged to look like leaves, hiding them from predators.

Why this level: Detailed adaptations of plants and animals, each linked to a specific physical condition, with correct terms. This is Level 3.

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