Introduction

Summary

The tropical region lies between the Tropic of Cancer and the Tropic of Capricorn, 23° north and 23° south of the equator respectively. In this area, the sun's rays fall directly and because of the direct sunrays throughout the year, the temperature of this region remains high. Along with this, it also receives the highest amount of rainfall. The closer one gets to the Tropics of Cancer and Capricorn, the more noticeable are the dry periods. As one moves farther north or south of these lines, the more slanted the sun's rays fall resulting in lower temperatures. Within the tropical belt, on land, from east to west, there are various kinds of tropical ecosystems: from tropical rain forests to tropical open woodlands, deciduous forests, spiny or desert forests, savannah, semi-deserts and other habitats. There are often significant areas of biodiversity and species endemism can also be seen.

The Indian subcontinent along with Myanmar is the second richest region in the world after Brazil, in terms of the number of endemic plant species. It is effectively isolated from the rest of Asia by a desert along the western flank of Pakistan, and a continuous wall of mountains, dominated by the Himalayas, to the north and the east. The great basins of the Indus and Ganges separate this mountain fringe from the rolling plateau of the Indian peninsula, which is bordered by a line of coastal hills, the Eastern and Western Ghats. Sri Lanka is separated from India by a narrow channel of sea formed by the Palk Strait and the Gulf of Mannar. The subcontinent's position at the confluence of three biographic realms is the main reason for this remarkable diversity of life forms that include elements of African, European, Chinese and Indo-Malayan flora.

The Indian region (8°–38° N and 68–97.5° E) with a total area of about 329 million hectares, representing only 2.2 per cent of the world's land surface, is indeed very rich in biological diversity. It is estimated that about 45,000 plant species occur in our country. The vascular flora, which forms the conspicuous vegetation cover, is itself composed of 15,000 flowering species, of which more than 60 per cent are endemic and are largely concentrated in two principal biographical regions of India, namely the Himalayas (about 4,200 species) and peninsular India (about 2,600 species).