Although rainforests are such important centres of biodiversity, they cover only about 6% of the Earth's land surface, less than half the area they covered not so very long ago.
What makes a tropical forest?
Tropical rainforests are very wet places, receiving heavy rainfall either seasonally or throughout the year. They are close to the equator and get lots of sunlight and warmth. Temperatures are uniformly high - between 20 and 35°C. They usually receive more than 200 cm rainfall per year.
Rainforest trees are quite different from trees of the temperate forests. In the rainforest, trees grow to gigantic size, supported by strong, strut-like buttresses at the base of the trunk that help to stabilize them in the shallow forest soils. Huge creepers twine themselves around the trunks of trees.
Some are parasites, but others merely use the trees for support. Many rainforest trees have dark green, often leathery, leaves which taper sharply so that water drains quickly from the surface. Flowers like orchids and bromeliads (members of the pineapple family) grow directly on trunks and larger branches - they are called epiphytes.
Birds and butterflies insects easily reach these flowers and act as pollinators. Where rain falls all year round, the forests are evergreen - the trees do not lose their leaves, or do so at different times.
A mature lowland tropical forest consists of several layers. The top layer of vegetation consists of scattered tall trees which tower above a closed canopy layer formed by the crowns of other trees. The canopy is the most exciting part of the rainforest, it is here that most of the flowering and fruiting of the trees takes place, attracting a variety of spectacular creatures.
Below the canopy is a third layer, formed by smaller trees whose crowns do not meet. Below this is a layer is composed of woody and herbaceous shrubs. Finally, there is the ground layer, which receives very little sunlight.
Tropical rainforests have more kinds of trees than any other forests in the world. The richest in plant species are Amazon forests, but in general all tropical forests have an incredible variety of trees.
A hectare of Malaysian rainforest may contain 180 kinds of trees (compare this to a temperate forest where a hectare might have just 10 species of tree). The tropical forests of West and Central Africa have the fewest species of trees, but even here the diversity is high compared to a temperate forest.
Some rainforest trees like mahoganies, teaks, rosewoods and okoumes provide valuable timber, while other rainforest products are nuts, fruits, rubber and rattans.
Rainforests are perhaps the most endangered habitat on earth. Each year, some 140,000 sq km of rainforests are destroyed. Rainforests are being felled for timber by logging companies and cleared by people for farming. The most endangered rainforests are those in West Africa, where human populations are doubling every 20 years, and in Central America and South-East Asia.
Although large areas of rainforest remain in Central Africa and South America, they, too, are disappearing at an alarming rate. Time is short if we are to save the remaining rainforests for future genrations.
WWF is committed to conserving the world's rainforests, not only for the incredible wealth of plants and animals that live in them, but for the benefit of the indigenous peoples who live in them.
WWF has been working to save rainforests for more than 35 years. Today, work continues in key areas like Peru's Manu Biosphere Reserve and the Korup National Park in Cameroon. Assisting tropical countries to save their rainforests - through creating protected areas and exploring ways of using forests wisely - is a priority for WWF.