The Tropical Rainforests of the world are ancient, complex ecosystem, teeming with diverse life forms. Here there are soaring trees, their trunks are often buttressed; a lofty canopy of branches and leaves, with deep shade below; climbing lianes and palms; plants growing on other plants; a rather bare floor with lumpy roots writhing across it, a dusting of fallen leaves, and scattered ferns and seedlings. Butterflies dance in rare shafts of sunlight from the above, birds make exotic noises, and insects sizzle and click. The term ‘rainforest’ was first coined in 1898 by a German botanist named Schimper, to describe forests that grow constantly wet condition. They can occur wherever the annual rainfall more tat 2500mm (100inches) and evenly spread throughout the year and temperature is constantly high. Rainforests are found to occur in a belt around the equator between the tropics of Cancer and Capricorn.
Worldwide Distribution of Tropical Rainforests:
Rainforests covers about 8.5 million square kilometer, which is 6% of the earth’s land surface. These tropical rainforests are extending from Central America and Amazon Basin through Central, East Africa and South East Asia to Queens land of Australia along the equator between the tropics of Cancer and Capricorn.
Central America:
The seven Central American countries south of Mexico- Belize, Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica and Panama- contain a unique concentration of flora, fauna and people. The rainforests of this region are among the richest habitat on earth in terms of number of species they contain. The rainforests of southern Mexico represent the northern most extent of this habitat.
The Caribbean:
The island s of Caribbean stretching in an area from Florida to Venezuela, are the emergent tops of ancient volcanoes, some which are still active. Before the sixteen century many of the island were almost totally covered in forests,, but now due to the limited land availability and high human density most of the forests has disappeared
The Amazon Basin:
The Amazon Basin contains by far the largest area of tropical forests in the world, covering six million square kilometer in nine countries- 60% in Brazil, and rest in French Guiana, Surinam, Guyana, Venezuela, Colombia, Ecuador, Peru and Bolivia.
Biologically, it is probably richest and most diverse region in the world, containing about 20% of all higher plant species, perhaps same proportion of birds and around ten percent of the world’s mammal. Each type of tree may support more that 400 insects species. Much of the Amazon Basin still remains unknown.
Central, East Africa and Madagascar:
A belt of tropical rainforests spans the center of Africa, running from Cameroon and Gabon on the Atlantic coast to the Kenya and Tanzania on the Indian Ocean. Within this belt, the climate and hence the type of forests, is very varied. Unending vistas of dark, impenetrable jungle are associated with the Central African countries, while East African countries are largely covered with bushland, the rainforests restricted to the fertile mountain regions.
Being separated from its mainland many million years ago and due to very wide Mozambique Channel, no life could raft across from the mainland. As a result, Madagascar’s flora and fauna is unique to the island. Botanically, it is one of the richest areas in the world.
South and South East Asia:
South and South East Asian countries like India, Sri Lanka, Myanmar, Cambodia, Indonesia, Malaysia, Philippines contain rich diversity of rainforests. In India, Western Ghats, Assam and northeast India and Andaman and Nicobar Island are famous for the tropical rainforests.
Rainforests of Northeast India:
The Northeast region of India is cris-crossed by Himalayan ranges flanking the Brahmaputra and Sumatra Valleys. It is the meeting point of the Indian peninsula with the main Asian land serving as a faunal and floral gateway resulting in complex assemblage of species diversity. The region lies between 890 to 980 E longitudes and 220to300 N latitude. Altitude varies from 30 m to 4500 m above mean sea level. The region shares international boundaries with four countries -- Myanmar in the east and southeast, China in the north, Bhutan in the northwest, and Bangladesh in the west and southwest. Brahmaputra and Barrak are two main river and valley systems in the region. Owing to geographical position, it offers a complex variety of habitats and ecosystems. Therefore, it is one of the mega-biodiversity centers in the region and also one of the ten distinct bio-geographic zones of the country. The region comprises of seven sisters namely Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland and Tripura. Sixty four per cent of total geographical area of the region is covered with various types of forests especially rain, tropical wet evergreen, semi-ever green, moist deciduous, sub-tropical broad leafed hill and montane temperate forests. Though the region embodies 7-8% of total geographical area of the country, it contributes 26% of total forest cover of the nation.
Rain forests once covered large areas of the northeast region of India, but as human population has increased, thousands pf square kilometer of forests have been cleared and replaced with scrub jungles. Today, about 43000 square kilometers of rain forests still remain. Shifting cultivation (jhum) is common throughout that region. It was a sustainable form of land use when the local population was much smaller, but as the population pressure increased the situation has deteriorated. Lack of land forced many farmers to shorten the fellow period and in consequence a sever soil erosion can now be found over large areas. Wood is an important source of fuel for 75% of India’s people and its collection is another serious drain on forest resources.
The surviving forests are confined to the Assam valley, foothills of the eastern Himalayas (Arunachal Pradesh) and lower parts of Naga Hills in places where the annual rainfall exceeds 2300mm. Botanically these forests are the richest in the Indian subcontinent. They also support a great variety of mammal and bird species.
Characteristics of Rainforests in Northeast:
Tropical wet evergreen forests are typical rain forests in Northeast India with an annual rainfall above 2500mm. They are composed of very tall trees, usually above 45m high, forming a very dense canopy and are many-storeyed and impenetrable with luxuriant ground vegetation. These forests appear to be climatic complex, being composed of very large number of species that are generally not gregarious. Dominant tree in the upper storey may have few deciduous species, but on account of extremely dense nature of the canopy the evergreen nature of the forests is most prominent. Climbers and wood lianes may be present, and often conspicuous. Bamboos are present. Palms, canes and other climbers are present, forming tangle masses in the undergrowth. Grasses are absent in the forests. Canebrakes usually replace high forests along streams. The trees have smooth barks and plank buttress. They have usually thick and glossy leaves, showing a characteristic pink or white color, when young. Epiphytes of all types of all types are abundant.
The most important trees found in the rainforests of Northeast are Dipterocarpus (Hollong), Mesua (Nahor), Michelia (Titasepa), Dillenia (Outenga), Shorea assamica (Mekai) and so on.
Diversity Of Tropical Rainforests:
Tropical rainforests hold greatest diversity of life of environment on earth. The Amazon, which drains the world’s largest tropical rainforest, is thought to have 3000 species of fish, including the fruit eating fish and electric eel. The tropical forest country of Panama has 1500 species of butterfly, compared with 763 in the USA and is mere 68 in UK. Five times as many kinds of tree grow on the island of Madagascar as in the whole temperate North America. In one ten-hectare (25 acres) plot in central Amazon, researchers have identified over 300 species of trees. A recent study in Malaysia recorded 835 species of tree in 50 hectares. It has been estimated that a typical patch of rain forest of just six kilometer square contain as many as 1500 species of flowering plants, 750 species of trees, 400 hundred species of birds, 150 species of butterfly, 100 species of reptiles and 60 species amphibians. The number of insects is so great that they can only guess at, but one hectare may contain as many as 42,000 species, Tropical forests, therefore, represent the most complex system known in the universe.
Rainforests: Treasure House Of Food, Fodder, Fuel And Medicines:
Rainforests are treasure house of large number of important life saving drugs. The list is endless but here are the few examples. The dainty, pink-flowered Rosy Periwinkle of Madagascar had been used forest people for generations: in 1960 its properties were finally investigated. Drug that cure leukaemia was derived from Rosy Periwinkle. Quinine, the first effective and widely used treatment for malaria, was derived from the bark of South American Cinchona tree. The contraceptive pill is derived from a Mexican yam. Curare, with which the Amazonian Indian poison–tip their arrows, is the basis of muscle relaxant now used extensively in western surgery; while cardiac glycoside of Africa Strophanthus vine seeds, also used in the making arrow poison, are stimulant which are now used in the treatment of heart diseases.
The list goes on, but the important point is these plants, particularly rainforests plants, are sources of an immense range chemicals. Their uninvestigated potential could yield a still greater range of medicines, not to mention other useful substances – foods, perfumes, insecticides, dyes, waxes, fuels, oils and hundred more.
- by Rajib Kalita. Dr Kalita is a Scientist in Rain Forest Research Institute, Jorhat
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