The Rainforest cREMedia 1994 All Rights Reserved. What are rainforests? Rainforests occur in both temperate and tropical regions. Tropical rainforests occur in three major regions: Asia, Africa and in Central and South America. The name 'tropische Regenwald' meaning 'tropical rainforest' was first defined in 1898 by A Schimper, a German botanist. Most of the world's rainforests fall either side of the Equator between the Tropic of Capricorn and the Tropic of Cancer. Forests close to the Equator which receive year round drenchings are known as evergreen equatorial rainforests. Rain in these areas falls at a rate of between 160 and 400 inches a year; there is no winter, days and nights are equal in length and a consistently high temperature of around 80 degrees is maintained. The further a rainforest is from the equator the greater are the changes in temperature and rainfall. Seasonal changes give rise to semi-deciduous rainforests in which most, and sometimes all, the trees lose their leaves during the dry season. Tropical 'moist' forests are called monsoon forests in South East Asia. Although extremely rich in wildlife and vegetation they do, however, contain fewer animal and plant species than the evergreen equatorial rainforests. There is no clear demarcation line between equatorial evergreen forests and the tropical moist forests as they blend one into the other without noticeable change although trees tend to be smaller in stature in moist tropical forests. Rainforest layers Rainforests are usefully divided into four layers; the emergent layer, the canopy, the understory and the forest floor. Each level is home to a unique variety of animals many of whom rarely cross between the different layers. The emergent layer gets its name because trees emerge randomly from the main forest roof. Most of the trees at this level reach 160 feet but some attain heights of 200 feet or more. Pavilion trees are able to withstand burning sun, strong winds and torrential rainshowers. The crowns of trees in the canopy form an almost closed roof on the forest below. It is often further divided into upper and lower canopy. Because the top of the canopy basks in almost constant sunlight and can absorb light more easily trees tend to have smaller leaves than those at a lower level. Usually trees are very straight and reach heights of between 100 and 150 feet. The lower canopy is the richest layer in terms of animal and plant life. Most of the mammals that live in the canopy are nocturnal. The understory extends from the forest floor up to about 80 feet and contains a mix of saplings, tall shrubs, vines and palms. Leaves are often long and pointed, the ends of which form 'drip tips' allowing excess water to run off quickly. Little sunlight filters into the understory which makes it dark and humid. Plant growth on the forest floor is very limited because only between 1-2% of sunlight filters down to this level. The floor of the rainforest teems with life. Millions of termites, beetles, centipedes and ants can be found in one acre of rainforest. Lowland rainforest Scientists have identified more than 40 types of lowland rainforest. They cover a greater land area than other types of rainforest, the two largest regions being in Africa and South America. These forests are found at altitudes of under 1,000 ft, although in Amazonia some forests below 6,000 ft are also called 'lowland rainforests'. Some lowland rainforests contain swamp forests. Life is so abundant in lowland rainforests that a single acre may hold as many as 15,000 separate plant and animal species. Trees in lowland rainforests can grow to heights of 150 ft or more which are often supported by enormous buttress roots. Montane rainforest Montane rainforests are divided into two types; lower montane growing at elevations above sea level of between 1,000 and 3,000 ft, and upper montane rainforests growing at an altitude of between 3,000 and 10,000 ft. Montane forests are given the name 'cloud' forest because they are constantly shrouded in mist. Rainfall increases and temperature decreases at these higher elevations. Trees become shorter and grow crooked rather than upright, and their leaves are smaller. Tropical species give way to those found more commonly in temperature forests such as oak, beech and conifer trees. Mangrove rainforest Mangrove forests are found at the edge of the sea where regular flooding occurs. Mangrove trees live in a silt-rich soil and use pitchfork-like roots which grow out from the lower part of their trunks for additional support. These roots, known as stilt or prop roots, trap debris which provide the trees with nutrients but are also important for stabilizing the shoreline. Mangrove forests range in stature from shrubs a few few high to trees which can reach heights of 80 ft. Mangroves are home to many bird species and molluscs. Custodians of the forests Indigenous people are the true custodians of the forest. They know which forest plant and animal species are safe to use as food and medicines, knowledge which may help us in our search for cures for disease and illness and food for our growing world population. Every single year a tribe in Brazil alone has become extinct this century. According to a report by the World Bank, Brazil's Indian population was five million in 1500. Today it is under 200,000. Attempted 'pacification' of tribespeople has proved fatal to many. The introduction of diseases, sometimes deliberately, such as influenza and smallpox to which they have no immunity, has wiped out hundreds. In 1977, a measles epidemic wiped out half of the Yanomami tribe of the Amazon region. In the 1980s the government of Brazil had been promised an enormous grant by the World Bank to build five hydroelectric dams on the Xingu river. The natives of South America affected by this began actively protesting to protect their homelands. In 1988 one of the Kayapo Indian leaders, Paulinho Paiakan, travelled to Washington DC to discuss the plans with leaders of the World Bank. This meeting received worldwide attention and preceded a major protest gathering the following year at Altimira on the Xingu river. Meeting together were various Indian tribe leaders, including Paiakan, ecologists, environmentalists and government officicials. The Indians successfully highlighted their plight and the World Bank agreed to postpone their funding of the proposed dams. What do the rainforests give us? Many of the foods found in our kitchen at home were first discovered in the rainforest. Although most are now cultivated outside of the rainforests, some even in our back gardens, wild populations still grow in the forest. When crops are struck by disease scientists sometimes need to go back to plants grown in the wild to procure disease resistant strains which when bred with cultivated varieties may transfer resistance to disease. There are still hundreds of fruits and crops eaten only by native people but that we may one day find on our supermarket shelves. One quarter of the medicines used by doctors today originate from rainforest plant species. There are still many more that are unknown to us. Indigenous people have learned to use thousands of plants as medicines. The US National Cancer Institute has identified 3,000 plants which may turn up potential cures for cancer, half of which come from tropical rainforests. Some pharmaceutical companies are conducting research into chemicals extracted from rainforest plants to find cures for a variety of diseases. Besides food and medicines the rainforest also provides us with many other items including oils, dyes, waxes, flavorings, fibers and rubber. These are only a very few of the many resources that are obtainable through sustainable extraction.