Explain why slash-and-burn farming must constantly shift to new areas, when rainforests are normally ...

Rainforest trees supply the tropical soils with most of the nutrients that the trees themselves need for growth. As leaves, flowers, and branches fall to the ground or roots die, numerous soil-dwelling animals and bacteria act on them, transforming forest litter into organic matter with vital nutrients. However, if the trees are removed, there is almost no replenishment of these nutrients and no natural barrier (forest litter and root systems) to prevent large amounts of rainwater from percolating through the soil. Percolating water dissolves and removes nutrients and minerals from the topsoil. The intense activities of microorganisms, worms, termites, ants, and other insects cause rapid deterioration of remaining organic debris, and soon all that remains is an infertile soil with a mixture of insoluble aluminum, iron, and manganese compounds.