M04 Ecosystems - Tropical Rainforests
Rainforests of the World
Rainforests cover 6% of the Earth’s land surface and most are found in the equatorial regions between the tropics of Cancer and Capricorn. Some rainforest types also extend north and south to Canada and Chile. They are considered to be amongst the most biodiverse and productive ecosystems on the planet, and have long been exploited to various degrees for natural resources by humans.
Over half of the world’s rainforest lies in the Brazilian Amazon River basin of South America which in turn holds about a third of the remaining tropical rainforest. Another 20% is found in Indonesia and the Congo basin in Central Africa and the balance scattered around the tropical regions of the globe.
Generally, most rainforests are characterized by high rainfall and temperatures generally above 18°C for most of the year. This is typical for the tropics which receive high sunlight throughout the year and continuous warmth. There are no true seasons although many forests may have a ‘drier’ season for some months of the year.
There are other types of rainforest such as cloud and temperate rainforest. Cloud forest is generally found at higher altitude (Montane forest) with has a higher rainfall and lower temperatures. The trees in cloud forest tend to be shorter and hardier as they have to endure a wider range of physical (abiotic) conditions. Cloud forests also have many plants that live on the trunks and branches of trees known as epiphytes. Temperate rainforests often have coniferous trees replacing broadleaved species and are mainly found in coastal regions and the average temperatures are much lower.
It has been estimated that there may be millions of species of plants, insects and microorganisms yet to discover and it is thought that over half of the world’s total species are indigenous to rainforests. It is also believed that half of the medicines we use are derived from plants endemic to the rainforest, and many future pharmaceutical discoveries are expected to come from species living in tropical rainforests.
However, rainforests are being destroyed at a high rate, particularly through deforestation for the timber industry and for land clearance, and it has been suggested that 60% of the Amazonian rainforest could disappear by 2030 (WWF – A. Benjamin – December 2007), a very worrying thought indeed.