Tropical rainforests
Rain forests are home to two-thirds of all the living animal and plant species on the planet. It has been estimated that they contain many millions of new species of plants, insects and microorganisms that are still undiscovered and as yet unnamed by science. Tropical rain forests are called the "jewel of the earth", the "Earth's lungs", and the "world's largest pharmacy" because of the large amount of natural medicines discovered within them.
Located between 5° north and south of the equator, tropical rainforests are found in South America, South-east Asia, West Africa and northern Australia, tropical rainforests are not as hot as deserts, but temperatures are high throughout the year, with an average of 27°C with accompanying high humidity. The average precipitation in tropical rainforests is over 2000 mm per year.
Soils
High rainfall and tropical warmth lead to quick weathering and a deep soil layer. Plant growth is also rapid, so nutrients spend little time in the topsoil. Minerals are washed away, leaving a bright orange-red topsoil that is high in clay and oxides. This soil can only be farmed for a short time (1-2 years) before it is exhausted.
Vegetation adaptations
A hectare of Brazilian rainforest may contain 500 different species of tree and over 1000 different types of plants. The tallest rainforest trees have straight trunks with branches only at the crown (top). These trees, called emergents, form the highest layer of the rainforest at about 50m. (As a comparison the average house is about 8m high).
Trees have wide buttress roots to support their great height.
Leaves are shiny and have pointed `drip tips’ to shed heavy rainfall.
Wildlife
Rainforests are full of animal life. Most of the wildlife live about 30 metres above the forest floor in the canopy layer (birds, monkeys, insects etc). Many of these creatures live their whole lives in the tree-tops.
Human activity
Different tribes of indigenous people have lived in tropical rainforests for thousands of years. These groups live in small communities, usually in remote parts of the forest but close to rivers. They survive by living in harmony with the tropical rainforest. They hunt, fish and gather food like nuts and berries.
But tropical rainforests are at risk of deforestation and this occurs when the world's forests are chopped down, burned, or destroyed. This is done to clear land for to meet growing human needs such as grazing animals and growing crops but also for commercial logging purposes where the wood is sold as timber or pulp. This worldwide problem occurs most often in tropical forests that are situated in relatively poor countries such as Brazil and Indonesia.
Deforestation is also one of the leading causes of habitat and biodiversity loss. The rainforests contain at least half of the Earth’s species and the clearance of these rainforests is causing a dramatic loss of biodiversity. Primate species are highly threatened because of their dependence on large expanses of tropical forest. The accelerating worldwide loss of biodiversity is alarming because no one know how many species inhabit the Earth, and the species are disappearing so fast that many of them are not even named.