Forests have been exploited over the centuries as a source of wood and for obtaining land for agricultural use. The mismanagement of forest lands and forest resources has led to a situation where the forest is now in rapid retreat. The main aspects of the situation are: serious shortages in the supply of industrial wood; the catastrophic erosion and floods accompanying the stripping of forests from mountainous land; the acute shortages of fuel wood in much of the developing world; the spread of desert conditions at an alarming rate in the arid and semi-arid regions of the world; and the many environmental effects of the destruction of tropical rainforests.