Earth’s richest biome
Tropical rainforests cover only about 6% of Earth’s land, but they’re home to more than half of all known plant and animal species. That makes them the biome with the highest biodiversity on land.
Where rainforests are
Tropical rainforests grow near the equator.
| Region | Notes |
|---|---|
| Amazon (South America) | The largest rainforest, about 5.5 million km², mostly in Brazil |
| Congo Basin (Central Africa) | The second largest |
| Southeast Asia | Borneo, Sumatra, Malaysia, Indonesia |
| Others | Central America, northern Australia, Madagascar |
Climate
| Feature | Tropical rainforest |
|---|---|
| Temperature | Warm all year, about 25–30 °C |
| Rainfall | 2000–10 000 mm per year |
| Humidity | Often 77–88% |
| Seasons | Little change; no cold season |
It often rains almost every day, usually in the afternoon.
The layers of the rainforest
| Layer | Height | Description | Life |
|---|---|---|---|
| Emergent layer | 40–70 m | Giant trees poking above the canopy | Eagles, butterflies, bats |
| Canopy | 20–40 m | Thick roof of leaves that blocks most sunlight | Most rainforest animals: monkeys, toucans, sloths, frogs |
| Understory | Up to 20 m | Dim and still; young trees, shrubs, large-leaved plants | Jaguars, snakes, insects |
| Forest floor | Ground | Dark; only about 2% of sunlight reaches it | Decomposers, insects, ants, tapirs |
Plants
Plants compete fiercely for sunlight.
| Plant feature | Purpose |
|---|---|
| Buttress roots | Huge wing-like roots support tall trees in shallow soil |
| Drip tips | Pointed leaf tips let rain run off quickly |
| Epiphytes | Orchids, bromeliads and ferns grow on tree branches to reach sunlight |
| Lianas | Woody vines climb trees to reach the canopy |
| Large leaves | Capture what little light reaches the understory |
Surprisingly, rainforest soil is poor. Heavy rain washes nutrients away, and dead material decomposes so quickly that most nutrients are stored in the plants themselves.
Animals
| Animal | Adaptation |
|---|---|
| Sloths | Move so slowly that algae grows on their fur, providing camouflage |
| Poison dart frogs | Bright colours warn predators they’re toxic |
| Toucans | Large bills reach fruit and help release heat |
| Spider monkeys | Grasping tails act like a fifth hand |
| Jaguars | Spotted coats for camouflage; strong swimmers |
| Leafcutter ants | "Farm" fungus on cut leaves |
| Orangutans (Borneo and Sumatra) | Long arms for swinging through trees |
Scientists estimate that millions of rainforest insect species haven’t even been named yet.
Why rainforests matter
| Benefit | Details |
|---|---|
| Biodiversity | Home to most of the world’s land species |
| Climate | Store huge amounts of carbon; help regulate rainfall |
| Water | Rainforests make much of their own rain through transpiration |
| Medicine | About a quarter of modern medicines come from rainforest plants, like quinine for malaria |
| Food | Bananas, cocoa, coffee, vanilla, cashews and many spices first came from rainforests |
| People | Home to many Indigenous peoples |
Threats
Deforestation is the biggest threat. Forests are cleared for:
- cattle ranching (the leading cause in the Amazon)
- crops like soybeans and palm oil
- logging
- mining and roads
Deforestation releases carbon dioxide, destroys habitats and can change rainfall patterns. Scientists worry that if too much of the Amazon is cleared, parts could dry out and turn into savanna.
Solutions
- Protecting forests in parks and Indigenous territories
- Buying products certified as sustainable (wood, coffee, chocolate, palm oil)
- Replanting forests
- Supporting laws against illegal logging
Common mistakes
- Thinking rainforest soil is rich. It’s actually poor.
- Thinking all rainforests are tropical. Canada has temperate rainforests on the BC coast.
- Thinking the Amazon produces most of the world’s oxygen. Ocean plankton produce about half; the Amazon uses most of the oxygen it makes.
Try it yourself
- Draw the four layers of the rainforest and add two animals to each.
- Check your kitchen for foods that originally came from rainforests.
- Pour water on a leaf with a pointed tip and one with a round tip. Which drains faster?
Quick recap
- Tropical rainforests are hot, wet forests near the equator.
- They have the highest land biodiversity on Earth.
- Four layers: emergent, canopy, understory and forest floor.
- Plants and animals are adapted for competition, light and humidity.
- Deforestation is the biggest threat to rainforests.