Tropical Wet Forests


Nature Gallery (Eco Regions)
Tropical Wet Forests
Tropical wet forests-the famous rainforests-grow in an equatorial belt, where conditions for life are as uniform as is possible on land: temperature, precipitation, and hours of daylight hardly vary from season to season. The combination of warm temperatures, high rainfall, and days of unvarying length creates an environment in which plant growth and reproduction is essentially independent of the time of year. This means that leaves, flowers, and fruit are always available to feed the animal population. These wet forests are frequently, if wrongly, called "jungles", a name that actually applies to the tangled growth that invades after primary forest is cut. The crowns of the rainforest trees form a continuous canopy. An understorey of shorter trees and a tangle of woody vines, or lianas, produce a forest of such complex internal structure that many animals, including some large ones, rarely or never descend to the ground. Within the forest, competition for light is intense, and many plants get closer to the sun by climbing up the larger trees or growing as epiphytes on their branches and trunks.

Despite the myth of the rainforest as an impenetrable tangle of vegetation, the floor is so deeply shaded that comparatively few plants can grow, except in the sun-drenched clearings created when a tree falls due to strong wind, landslide, or chain-saw. The ground is carpeted with fallen leaves, twigs, and branches, which an army of termites and other decomposers break down, providing nutrition to the roots of the trees from which they came. Because of this rapid recycling of nutrients into the vegetation, rainforest soils are notoriously poor. Although the diversity of rainforest species is well-known, many of the trees are superficially quite similar. Water-shedding leaves with pointed tips are a feature of a host of unrelated species. Because there is no need for a thick, waterproof covering in the humid forest, bark tends to be thin. Buttresses and spreading roots may enhance stability in shallow or waterlogged soils. With increasing distance from the equator, seasonal differences become more pronounced and the number of deciduous species rises. However, because each kind drops its leaves at a different time, the similarity between fully and semi-evergreen forests is close. The wet forests of the Amazon Basin are often regarded as the essential rainforests, and they are extraordinarily diverse in both plant and animal species, most of which science has yet to catalogue. The area of rainforests in the Amazon is the largest on Earth, and despite the encroachment of people in many places, it remains comparatively intact. In other parts of the Americas, a ribbon of continuous forest once ran from the Pacific coast of Ecuador through Central America into southern Mexico, and another forest, the mata atlântica, extended from northeastern Brazil south into Paraguay. Human use of both these forests has fragmented and degraded them, and the forest of Brazil along the Atlantic Ocean is so critically threatened that it is now the subject of an intensive conservation campaign. Apart from these continental forests, remaining patches of Caribbean rainforest still cover parts of the Greater and Lesser Antilles. In Africa, a western zone of rainforest extends from Guinea to Ghana, where the savannahs of the Dahomey Gap separate it from the larger Congo forest in Nigeria, Cameroon, and the countries of the Congo Basin. A substantial portion of the Congo forest remains, but the Guinea and Nigerian forests have been logged, as have the island forests of eastern Madagascar. The most intact wet forests in Asia and Oceania are on the islands of Borneo and New Guinea. Otherwise, tropical rainforest runs in an interrupted swathe from the Western Ghāts of India to Sri Lanka and Bangladesh, and through Southeast Asia and the Malay Archipelago to northeastern Australia and many of the islands of the tropical Pacific Ocean, including Hawaii.