Four floors of forest
A tropical rainforest is built in layers, almost like a building. The tallest trees, the EMERGENT layer, poke up above everything else, sometimes more than sixty metres high. Beneath them is the CANOPY, a thick roof of leaves and branches where most of the animals live. Below that is the dim UNDERSTORY of young trees, shrubs and FERNS, and at the bottom the forest floor, where so little light gets through, often only about two per cent, that few plants can grow. VINES and the woody climbing plant called a LIANA wind their way up the trunks towards the light.
It rains most days, often in a heavy afternoon storm, and a rainforest can get more than two metres of RAINFALL in a year. The air is hot and HUMID all year round, because rainforests sit near the EQUATOR, where the Sun is high overhead every day. Our rainforest animals page covers who lives on each floor.
Half the species on six per cent of the land
Tropical rainforests cover only about six per cent of the Earth's land, yet they hold around half of all its SPECIES of plants and animals. In the 1970s the scientist E. O. Wilson found forty-three species of ant living on a single tree in the Peruvian Amazon, about as many as live in the whole of Britain. There are around 28,000 kinds of ORCHID, many of them growing on the branches of rainforest trees rather than in soil.
Rainforest plants have given us important medicines. A small pink flower from Madagascar, the rosy periwinkle, contains chemicals now used to treat some childhood cancers. Our smoothies page covers a fruit from the Amazon that became a breakfast favourite.
The lungs of the planet?
The AMAZON is the largest rainforest in the world, and it is often called the lungs of the planet. That is not quite right. Its trees do make huge amounts of oxygen, but the forest's animals, fungi and bacteria use up nearly all of it again, so it adds very little to the air overall. What it really does is store an enormous amount of carbon in its trees and soil, and help make rain across South America, so cutting it down matters a great deal.
The CONGO rainforest in central Africa is the second largest, home to gorillas, forest elephants and the shy, stripy-legged okapi, and BORNEO has some of the oldest forests in Asia. Australia's DAINTREE, in Queensland, is thought to be around 180 million years old, older than the Amazon. There are temperate rainforests too, in cooler, wet places like the coasts of Canada and Chile, and patches of damp, mossy woodland in western Britain. A single hectare of Amazon forest can hold hundreds of different kinds of tree. The giant kapok tree can grow seventy metres tall, and the fluffy fibre around its seeds was once used to stuff life jackets, because it floats and does not soak up much water. The TOUCAN, the SLOTH, the MAHOGANY tree, the lush FOLIAGE, every HABITAT and the TROPICAL JUNGLE complete the grid.