Soils are another important environmental factor. Tropical forests grow on a huge range of soil types, from highly fertile soils in volcanic areas and on river floodplains, to infertile peat and sand. Most tropical soils are between these extremes, however, and can support forest only
because of the rapid and efficient recycling of nutrients (see below). From an agricultural point of view, such soils are best suited to traditional shifting cultivation or to tree crops, such as oil palm or rubber.