Our planet, earth, is occupied by diverse kinds of living organisms. They live in various environments. The world is estimated to have 5 to 30 million species of living organisms. At present about 2.5 million species of living organisms have been given scientific names. Over 1.5 million of them are animal species and out of which 750,000 belong to insect species alone. There are 350,000 species of plants including algae, fungi, mosses and higher forms of plants. Thus the existence of different forms of a species or genus and diverse adaptations for, varied surroundings are referred to as 'biodiversity'.
The survival of such a vast range of living beings could be ensured only when their habitats and environmental conditions remain without alterations. The term ' biosphere' had been coined to highlight the interdependence of living and non-living world. It represents a stable environment of various physical and biological factors which have been operating since the past. The organic continuity of the system rests on a delicate network of inter-dependent relationships. The air, the water, the animals, the plants, the microbes and human beings are all interlinked in a life sustaining system, called theenvironment.
Safeguarding the entire biosphere with all its intricacies is of prime importance today. The nations of the world have convened several conferences and adopted important resolutions for safeguarding the sustainability of earth. In this background, the United Nation's 'Environmental Agency' organised the 'International Conference on Human Environment' at Stockholm in 1972. This conference adopted the motto ' Only one earth'. In 1982, a UN conference on Environment was held at Nairobi. The UN again convened ' Earth summit ' at Rio de Janeiro highlighting ' our common future', in 1992. Once again a world summit on sustainable development was organised in Johannesberg in 2002. One of the agenda commonly placed and accepted in all these meets was the significance of biodiversity and its conservation to ensure sustainable earth.
India's immense biological diversity represents about 7% of world's flora and 6.5% of world's fauna. About 62 % animals in India are endemic to the country. India is one of the 12 countries identified as mega centres of biological diversity.
As per the State Forest Report 1999, based on visual and satellite data from IRS-1B, 1C and 1D, the total forest cover of India is 637,293 sq. km. It is 19.39 % of the total geographic area of the country. It comprises about 64 million hectares.
Indian flora comprises about 15,000 flowering plants of which roughly around 1,500 plant species are threatened. Mammalian fauna of India is 372 species with 63% in Assam. India's 1228 bird species represent about 13% of world's total. Reptilian and amphibian fauna includes 446 and 204 species respectively.
Since the world has a vast range of organisms, identifying the useful, as well as harmful living beings is a need. Differentiating, grouping and giving names to living things has been an ancient activity of every human culture. Without proper classification it would be impossible to deal with enormous diversity of life forms.