Type of "forestry practice" which involves the permanent removal of forests and their undergrowth so that the land can serve another purpose. This practise has had a profound effect on global environmental problems (air pollution, global warming), soil erosion, desertification, sedimentation of water courses, alteration of climate and hydrological cycles, alteration of the atmospheric oxygen and carbon dioxide balance and has caused many species to become extinct, reducing worldwide biodiversity. A common deforestation practise is to simply burn the forest while clearing the land for a seasonal crop. This also creates a large-scale release of carbon dioxide further compounding the global warming effect. Since most of the available nutrients are contained in the forest biomass the newly cleared land does not support a crop for more than a few seasons before adjacent land must be deforested.