Tropical Rainforests

The tropical rainforests have billions of species (kinds) of plants and animals, more than anywhere else on earth. Scientists do not yet know all the species that are to be found in a tropical rainforest and new ones are still being discovered.

The reason there are so many species is because rainforests are very old, some almost 100 million years old, which means dinosaurs probably lived in them. About 10,000 years ago the ice caps at the poles spread out in an Ice Age, but the ice didn't reach the Equator so tropical rainforests survived and their plant and animal species continued to evolve when other places on earth had to start growing plants all over again.

In the tropics it is always hot and it rains every day. Tropical rainforests are the wettest places on earth.

Tropical rainforest plants
Some canopy trees grow over to over 100 metres high. Many have fruit that provides food for animals and people. Many rainforest plants are gathered for food or medicines. This is done without harming the rainforest.

Many 'every day' foods originated in rainforests, including tomatoes, peppers, corn, rice, coconut, banana, coffee, cocoa, cassava (tapioca), beans and sweet potatoes.

Tropical rainforest: Plant Adaptations
In order to survive in the hot, wet tropics, plants of the tropical rainforest have had to develop special features. This is called adaptation.

Because the weather is hot and wet, trees do not need thick bark to slow down moisture loss and have instead thin, smooth bark.

The layers of rainforest are connected by vines and ferns, and mosses grow on the trees. Liana is a climbing vine that grows on rainforest trees, climbing into the canopy so its leaves get more sunlight.

The leaves of rainforest trees have adapted to cope with the large amount of rain. The leaves are big, thick and waxy, and have 'drip tips' to let the rain drain off quickly.

Many large trees have huge ridges called buttresses near the base. They may be 10-12 metres high where they join into the trunk. They increase the surface area of a tree so that it can 'breathe in' more carbon dioxide and 'breathe out' more oxygen. Nutrients in the soil are near the surface, so the big rainforest trees have quite shallow roots. The buttresses support the trees.

Some trees have above-ground roots called prop or stilt roots which give extra support to the trees. These roots can grow about 85 cm in a month.
Buttress roots - photograph © [2007] Jupiterimages Corporation

Some tropical rainforest plants are carnivorous, or meat-eating. They have a cavity filled with either sweet or terrible smelling nectar that attracts insects, especially ants and flies. Inside, the sides are steep and lined with downward pointing hairs. Insects enter and lose their footing or are prevented from leaving because of the hairs. Rafflesia , in Indonesian rainforests, produces the biggest flower in the world.

orchid growing on banyan tree: photograph © [2007] Jupiterimages Corporation

Thousands of flowering plants grow onto trees so they get sunshine. Their roots are not in soil, and the plants get their food from air and water. Plants that do this are called epiphytes (say epp-ee-fights), and include orchids, philodendrons, ferns and bromeliads.

Bromeliads are native to the Americas. Bromeliad leaves form a central 'tank' where water collects. Small creatures such as tiny crustaceans, mosquito and dragonfly larvae, tadpoles, birds, frogs and salamanders often live there. Some bromeliads grow in soil, but most grow on tree branches.

A frog in a bromiliad 'tank'

If you use any part of this in your own work, acknowledge it in your bibliography like this:
Sydenham, S. & Thomas, R. Tropical Rainforests [Online] www.kidcyber.com.au(2002). updated May 2010 ©kidcyber