Tropical rainforests have the largest biodiversity of all ecosystems on Earth. The soil is rather poor, but it sustains a great variety of plants. It is estimated that 65% of the known plant species are found in rainforests.
During the past three decades, rainforests have been decreasing in size for various reasons, though all of them are connected with human activities. Human populations living near rainforests had the impression that the soil must have been really fertile, as it could sustain such a variety of plants. So, when human started to need more fields for cultivation, they choose rainforests' earth, and thus they set big fires to get rid of big trees and to obtain space. By the time it was understood that the soil wasn't suitable for agriculture, many square kilometres of rainforests had already gone.
Apart from agricultural reasons, the rainforests are cut down in order to provide wood. Most of the paper, toilet paper or furniture manufactured nowadays is based on wood from tropical rainforests. Deforestation also takes place in order to extend cities and build roads. Increasing human needs, due to overpopulation, lead to mass deforestations all over the globe.
The pace with which it's been done is so high, that every year an area of the size of half Greece is lost. 50 years ago rainforests would cover double the area they do today. Thousands of species, whether they are animals or plants become extinct and even more face extinction.
Humanity also depends on rainforests. A variety of building materials, food (bananas, vanilla, coffee), and even caoutchouk come from rainforests. Medical science, from the ancient times till today, also depends on substances from plants that grow there.
Quinine, a range of medicine against pain and stress are only some examples of medicine that require substances from rainforests in order to be manufactured. Nowadays, 20% of the medicines found in pharmacies are produced by the use of plants from rainforests.
Researchers have studied less than the 2% of the 100,000 species of plants that grow in rainforests, and are sure that most of them can be really useful in medicine or other fields. Though most of them point out that ''potentials for the future are endless, as long as scientists and pharmacologists reach the rainforests before chainsaws...''
And let us not forget that rainforests produce oxygen. Tropical rainforests produce 40% of Earth's oxygen. Cutting them down means that oxygen levels decrease, while less CO2 is absorbed by plants and thus increases in the atmosphere, causing the green-house effect. Humanity has to re-examine its needs and reduce them, so that less quantities of substances from rainforests are used. We have to set limits on our activities, otherwise those huge forests will one day belong to history.