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What is a Rainforest

Tropical rainforests have evolved over tens of millions of years into highly complex ecosystems, which contain over half of the world's species of plants and animals.

Rainforest, Costa Rica. Image courtesy of Chris Perrett, naturesart

Rainforest, Costa Rica. Image courtesy of Chris Perrett, naturesart

Millions of years in the making

Many trees in the rainforests are hundreds of years old. Radiocarbon dating methods, used in the Amazon, indicate that half of all trees greater than 10 centimetres in diameter are more than 300 years old and that some trees are over 1,000 years old [1].

Daintree Rainforest in Queensland, Australia is believed to be the oldest living rainforest at a grand old age of around 135 million years [2]. To put this into context, the first hominids (human-like primates) did not appear until around 5-8 million years [3]. This time has allowed rainforests to evolve into highly complex ecosystems with unparalleled and globally important levels of biodiversity.

Where are they?

By definition, tropical rainforests lie between the Tropic of Capricorn and the Tropic of Cancer, 22.5° North and 22.5° South of the equator. Almost half of the remaining tropical rainforest is found in tropical America, a bit more than a third in Asia and Oceania, and fifteen percent in Africa. In total, over 80 countries are considered rainforest owning nations. However, three countries - Brazil, Indonesia and the Democratic Republic of Congo - contain almost half of the world's tropical rainforests.

Tropical Rainforests of the World

The structure of a rainforest

Home to an incredibly diverse range of species and plant life, the structure of rainforests is complex and highly evolved, making them the most biologically rich ecosystems to be found on the planet. Rainforest trees can reach heights of over 60m (200 ft) high. From the tips of their branches down to the base of their trunks, around four to five distinct forest strata can be found, each providing a specific habitat for plants and animals. Click here to read more.


As the name suggests, rainforests experience high levels of rainfall and are often covered by clouds and mist. This humid climate is partly created by the trees themselves. The combined activity of animal and plant life releases huge quantities of volatile organic compounds, which create the fine condensation nuclei around which water droplets form. Moisture is held in these humid, cool ecosystems and evaporates slowly to make clouds, which helps maintain regular rainfall.

1 Bourgeron, Patrick S. (1983) "Spatial Aspects of Vegetation Structure", in Frank B. Golley: Tropical Rain Forest Ecosystems. Structure and Function 14A, Ecosystems of the World, Elsevier Scientific, 29-47
2 http://www.daintreerainforest.com/ (accessed May 2008)
3 http://anthro.palomar.edu/earlyprimates/first primates.htm; http://www.mc.maricopa.edu/dept/d10/asb/anthro2003/origins/bipediality.html (accessed May 2008)
4 http://news.bbc.co.uk/1/hi/sci/tech/4947350.stm (accessed May 2008)
5 http://www.runet.edu/~swoodwar/CLASSES/GEOG235/biomes/rainforest/rainfrst.html (accessed May 2008)
6 BBC Anatomy of a Rainforest (http://news.bbc.co.uk/1/hi/sci/tech/7127687.stm, accessed May 2008)


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