Introduction
The legendary Sinharaja forest covers the steep hills and valleys of Rakwana in the south-western lowlands of Sri Lanka. It is the island's largest expanse of lowland rain forest and the only sizeable, undisturbed remnant. All that remains in the rest of the wet lowlands are the familiar, mist-laden forest patches scattered on hilltops and ridge crests, a mere shadow of the magnificent forests which once covered the entire southwestern sector of the country. Rain forests are the natural vegetation type of the island's ever-wet south-western cjuarter. which covers an area of around 22.500 square kilometres. These forests comprise both lowland rain forests of the hot humid lowlands below 1,000 metres in elevation, and the lower and upper montane rain forests of the cooler mountains, that occur between 1,000 and 2500 metres in elevation.
Climetic Conditions
Rain forests occur under equatorial conditions of constant temperature, high rainMl thai is well distributed the whole year round and suitable soil conditions. In Sri Lanka, the south-western region receives an annual rainMl between 2,500 and 5.000 millimetres and is devoid of a dry period The main sources of rain are the two monsoons that blow over the island, the south-west from May to Jury, and the north-east from November to January. It is the former however that brings the greatest amount of moisture. This wind is intercepted by the central hills of the island, resulting in precipitation on the hill slopes and lowlands of the south-western region.There is little variation in temperature, that of the lowlands being 27 °C to 30 °C while in the upper montane regions at round 1,800 metres in elevation, the temperature can drop to 16°C or 17°C.
The Importance of Rain Forests
The value of these forests is multifold. Of primary importance are the protective benefits they offer as watersheds and ameliorators of climate. The multi-storeyed vegetation of the forest, its leaf litter, root mat and humus-rich, porous top soil all help to trap moisture which accumulates and is then gradually released into rivulets and streams. Rain forests thus help to sustain perennial sources of water such as the major rivers. These forests also make the climate more equitable, the physiological functioning of individual plants helping to moderate temperature, humidity and the level of carbon dioxide in the atmosphere.Man has long recognised that the major benefit of the rain forest is as a source of timber. However continuous and rapid exploitation is fast reducing the available -timber potential of these forests. In Sri Lanka, most of the rain forests were depleted of select hardwoods such as calamander and ebony at the turn of the century. Today the depletion still continues in the lowland rain forests, where a range of light hard woods are being felled to support the plywood industry.
These forests make an important contribution to the national economy. In addition, they are also important to those people who live in, and along their fringes. These people are dependent on the forest for most of their basic needs of food, shelter and medicine. The forest to them is not merely a source of wood for fuel and timber but also a store-house of a host of useful products such as rattan, food, medicine and spices.One value of rain forests often ignored is their recreational value. Forests provide opportunities for human relaxation in surroundings that are peaceful, healthy and above all, beautiful.The protective and commercial value of forests is generally recognised by most people today. However, it is only the scientists perhaps who are aware of the biological importance of rain forests. In Sri Lanka, the rain forest ecosystem is the richest reservoir of flora and fauna of all ecosystems in the country. Furthermore, a high percentage of the plants and animals found in the rain forests are endemic to Sri Lanka and found nowhere else in the world. Of the 25 genera and 830 species of plants that are'endemic to Sri Lanka, i.e. 24% of the island's total flora, as much as 60% is found in the lowland rain forest, and of this 40% appears to be exclusively confined to it.The forests are therefore reservoirs of genetic materials or 'gene pools' and contain a wide variety of plants and animals which are directly or indirectly of use to man. Yet, many are underutilized, and a large majority are as yet unscreened and may perhaps become important in the future. These wild species can be used to breed new strains or improve existing strains of domesticated plants and animals that are of use to man. Many species such as rattan, wild cardamom and medicinal plants such as "went wel" are of commercial importance but are collected solely from the wild and therefore have great potential for domestication and genetic improvement' The fact that the Sri Lankan rain forests contain a high proportion of endemics makes them all the more valuable.The rich complexity of undisturbed rain forests also serves to illustrate the full potential of the land. The rain forest in an undisturbed state is a highly efficient biological system in which individual components are structurally and functionally arranged to maximise the use of the land. If fully understood therefore, these forests can serve as a yardstick for measuring the efficiency of man-made systems such as plantations, agro-forestry systems and agricultural farms. Although they have been unquestionably recognised as the most complex of all ecosystems, the interactions between their physical and biological components are little understood. Thus there is enormous potential for research and education in the rain forest. Much remains to be discovered of the origin, evolution and functioning of these forests. Fortunately, today the rain forest has become the focus of increased scientific speculation, and therefore, there is hope that it will be preserved for future generations.
The value of these forests is multifold. Of primary importance are the protective benefits they offer as watersheds and ameliorators of climate. The multi-storeyed vegetation of the forest, its leaf litter, root mat and humus-rich, porous top soil all help to trap moisture which accumulates and is then gradually released into rivulets and streams. Rain forests thus help to sustain perennial sources of water such as the major rivers. These forests also make the climate more equitable, the physiological functioning of individual plants helping to moderate temperature, humidity and the level of carbon dioxide in the atmosphere.Man has long recognised that the major benefit of the rain forest is as a source of timber. However continuous and rapid exploitation is fast reducing the available -timber potential of these forests. In Sri Lanka, most of the rain forests were depleted of select hardwoods such as calamander and ebony at the turn of the century. Today the depletion still continues in the lowland rain forests, where a range of light hard woods are being felled to support the plywood industry.
These forests make an important contribution to the national economy. In addition, they are also important to those people who live in, and along their fringes. These people are dependent on the forest for most of their basic needs of food, shelter and medicine. The forest to them is not merely a source of wood for fuel and timber but also a store-house of a host of useful products such as rattan, food, medicine and spices.One value of rain forests often ignored is their recreational value. Forests provide opportunities for human relaxation in surroundings that are peaceful, healthy and above all, beautiful.The protective and commercial value of forests is generally recognised by most people today. However, it is only the scientists perhaps who are aware of the biological importance of rain forests. In Sri Lanka, the rain forest ecosystem is the richest reservoir of flora and fauna of all ecosystems in the country. Furthermore, a high percentage of the plants and animals found in the rain forests are endemic to Sri Lanka and found nowhere else in the world. Of the 25 genera and 830 species of plants that are'endemic to Sri Lanka, i.e. 24% of the island's total flora, as much as 60% is found in the lowland rain forest, and of this 40% appears to be exclusively confined to it.The forests are therefore reservoirs of genetic materials or 'gene pools' and contain a wide variety of plants and animals which are directly or indirectly of use to man. Yet, many are underutilized, and a large majority are as yet unscreened and may perhaps become important in the future. These wild species can be used to breed new strains or improve existing strains of domesticated plants and animals that are of use to man. Many species such as rattan, wild cardamom and medicinal plants such as "went wel" are of commercial importance but are collected solely from the wild and therefore have great potential for domestication and genetic improvement' The fact that the Sri Lankan rain forests contain a high proportion of endemics makes them all the more valuable.The rich complexity of undisturbed rain forests also serves to illustrate the full potential of the land. The rain forest in an undisturbed state is a highly efficient biological system in which individual components are structurally and functionally arranged to maximise the use of the land. If fully understood therefore, these forests can serve as a yardstick for measuring the efficiency of man-made systems such as plantations, agro-forestry systems and agricultural farms. Although they have been unquestionably recognised as the most complex of all ecosystems, the interactions between their physical and biological components are little understood. Thus there is enormous potential for research and education in the rain forest. Much remains to be discovered of the origin, evolution and functioning of these forests. Fortunately, today the rain forest has become the focus of increased scientific speculation, and therefore, there is hope that it will be preserved for future generations.
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