The upper canopy is relatively open, with large spaces between treetops. The next lowest layer is a more enclosed canopy, entangled with lianas and strangler figs, and at the forest floor there are relatively few plants. Rain forests are the most diverse ecosystems on earth because of the enormous numbers of animal species present. Most of this animal diversity is made up of insects, and the bulk of it is found in the trees. Even some large vertebrates spend most of their lives in the trees.
Scientists consider rain forests to be more valuable intact than when converted to pastures.
Managed rain forests can provide huge amounts of valuable timber, retain their thin topsoil layers, regulate runoff, and stabilize local climate. Their plants and animals represent giant gene banks that can provide new drugs, foods, and other products. However, only a very small part of rain forests have thus far been assayed for potential chemical value. Human Impact Human activities such as logging, mining, and farming threaten the survival of rain forests. Since the 1970s the rate of tropical deforestation has accelerated, and some unique rain forests have been almost totally destroyed.