There are many ecosystems on earth not rich in vegetation and other organisms. This is natural wherever there is low rainfall and hostile ground. However, there are other areas, in theory able to sustain a variety of living organisms, with enough rainfall and mild climate, but which have as little variety as the first category. Their soil remains poor and unsuitable for vegetation. Such ecosystems have been eroded by human activities, often to the point of desertification.

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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.

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