THE WORLD’S RAINFORESTS are often considered the world’s “hot spots” since they are often found in tropical climates and they are home to the majority of the world’s species. As of 2000, studies and surveillance indicated that rainforests may have from one-half to two-thirds of the world’s species, despite only covering 5–7 percent of the world’s surface. Biodiversity is just 1 of the many advantages that rainforests provide for the planet and that make it worthwhile to protect them. Other contributions from rainforests include carbon sequestration, controlling global warming, preventing soil erosion, minimizing carbon emissions through the photosynthetic process, and preventing desertification. Despite these positive aspects of rainforests, they continue to be threatened by market forces, increased demand for agriculture and a lack of a policy framework in most of the developing countries in which these rainforests are found. Within the tropics, where the temperature lingers at 70 degrees F (20 degrees C) and higher, a rainforest is a common biome to encounter. Tropical zones occur primarily within the equatorial zone, 10 degrees within the equator both north and south. The largest areas of tropical rainforest are in the Amazon Basin of and in western Africa and Indonesia. There are many other smaller areas where rainforests abound throughout Central America and parts of the Pacific. With annual rainfall of over 79 inch (200 centimeter), rainforests are rich with flora and fauna. There may be a dry season that lasts for a month or two, but this is substantially milder than the winter and summer contrast experienced in the temperate zones. Seasonal variation in the rainforests is very slight. The soils found in rainforests are typically old, of decomposed organic matter, and not very fertile to support an abundance of agriculture. Because of the heavy rainfall, leaching of all soluble constituents of the original rock layer occurs, leaving behind a latosol, or a red or yellow soil composed mainly of aluminum and iron oxide. Rainforest soils are not rich in nutrients; the nutrition of the rainforest is lost when logging occurs, since the trees are the main source of nutrients for the ecosystem. The components of a rainforest are numerous and diverse. The upper layer or “story” consists of trees 147 to 180 foot (45 to 55 meter) tall with round or umbrellashaped crowns, and they are referred to as “emergents.” These trees do not necessarily form the canopy characteristic of rainforests; they are tall and small in diameter. The second layer of trees is about 98 to 131 foot (30 to 40 meter) tall. The third layer of vegetation rises about 33 to 82 foot (10 to 25 meter), and this story contains most of the flowering and fruit produce of plants. The shrub story, or the “understory,” includes dwarf palms, bananalike leaves, and 2 flora especially characteristic of rainforests: lianas, or vines rooted in soil that climb to the canopy; and epiphytes, plants that grow on other plants.