EN
The article deals with contemporary transformations in tropical rain forests, that lead to their degradation, alterations of their range, reduction of the surface they occupy, and in the case of many areas, their complete disappearance. The text aims at the presentation of causing factors of the changes, conditions in which they occur and mechanism of the processes that take place within them. The author's inquiries concentrate on two hypotheses: one - concerning the dominant role of anthropogenic transformation of tropical rain forest vegetation and another, dealing with significant, on the local scale, importance of natural factors (natural disasters among them) that originate degradation of vegetation. The results of studies realised show great regional differentiation of the causes of deforestation and rhythm of the changes in the tropical rain forests range. In Latin America the major part of deforestation in recent years is due to agricultural expansion (and particularly to agricultural colonisation). Extensive cattle breeding is also an important factor (especially in the Amazon). In West Africa and Southeast Asia commercial tree felling and the following process of agricultural occupation of cleared areas seem to play the major role. In all the cases relevance of natural processes degrading vegetation's observed - some of them seem to be indirect results of the environmental transformations induced by human activities.