India is a mega-biodiversity country. Variety of physiographic and climatic conditions has attributed India with rich biodiversity.
Biogeographically, India is situated at the tri-junction of three realms, namely, Afro-tropical, Indo-Malayan and Palaeo-arctic realms.
Therefore, India has characteristic elements from each of them.
This assemblage of three distinct realms probably is a fact which is believed to partly account for its rich and unique biodiversity. India also represents three major biomes, viz., tropical humid forests, tropical dry forests/deciduous forests and warm forests/semi-arid desert (Joshi and Joshi, 2004).
Based on available species data, India ranks tenth in the world and fourth in Asia in plant diversity and ranks seventh in the number of endemic species of higher vertebrates in the world (MoEF, 1999 and 2001).
The Wildlife Institute of India (WII) divides India into 10 biogeographic zones or regions. These are: Trans-Himalayan, Himalayan, Indian Desert, Semi-arid, Western Ghats, Deccan Peninsula, Gangetic Plain, North-east India, Islands and Coasts (Figure 1.6).
1. Trans-Himalayan:
It is an extension of the Tibetan plateau, harboring high-altitude cold desert in Laddakh (Jammu & Kashmir) and Lahul Spiti (Himachal Pradesh). It comprises about 5.7 per cent of the country’s landmass.
2. Himalayan:
The entire mountain chain, running from north-western to north-eastern India, comprises a diverse range of biotic provinces and biomes. It covers 7.2 per cent of the country’s landmass.
3. Desert:
This is an extremely arid area, which is mainly in the west of the Aravalli hills range, comprising both the salty desert of Gujarat and the sand desert of Rajasthan. It covers about 6.9 per cent of the country’s landmass.
4. Semi-arid:
The zone lies between the desert and the Deccan plateau, including the Aravalli hills range. It covers 15.6 per cent of the country’s landmass.
5. Western Ghats:
The hill ranges and plains running along the western coastline, south of the Tapti river, cover an extremely diverse range of biotic provinces and biomes. It is extended on 5.8 per cent of the country’s area.
6. Deccan Peninsula:
This is largest of the zones, covering much of the southern and south-central plateau with predominantly deciduous vegetation. About 4.3 per cent of the country’s landmass is under this province.
7. Gangetic Plain:
This is defined by the Ganga river system. These plains are relatively homogenous in surface characteristics. It covers about 11 per cent of the country’s landmass.
8. North-east India:
The plains and non-Himalayan hill ranges of north-eastern India have wide variation of vegetation. This zone is one of the highly diverse regions in terms of species richness and endemism covering about 5.2 per cent of the country’s geographical area.
9. Islands:
This includes Andaman and Nicobar Islands in the Bay of Bengal, with a highly diverse set of biomes comprising of 0.03 per cent of the country’s landmass.
10. Coasts:
A large coastline distributed both to the west and east, with distinct differences between the two; Lakshadweep islands are included in this with the percentage area being negligible. India is one of the 12 identified mega-biodiversity centres of the world.
It also harbours two of twenty-five identified biological diverse centres termed as ‘Hot Spots’; the Eastern Himalaya covering Indo-Burma region and Western Ghats in South India and Sri Lanka. Hot Spots are the areas that are extremely rich in species, have high degree of endemism and are under constant threat called ‘loss of biodiversity”. These areas are very rich in faunal and floral diversity.
Hot Spots in India include (Ministry of Environment and Forests, 2001):
Eastern Himalaya:
Phytographically, the Eastern Himalaya forms a distinct floral region. The area comprises Nepal, Bhutan and neighbouring states of north-east India. Although all Eastern Himalayan forests lie north of tropic of cancer and some of them are at the altitude of 1,780 to 3,500 metres, they can be considered as tropical forests since they occur largely within the climatic tropics.
1. This region is the meeting ground of Indo-Malayan and Indo-Chinese biogeographic realms as well as the Himalayan and peninsular Indian elements, formed when the peninsula plates struck against the Asian plate.
2. Around 30 per cent flora is endemic to India. Of these endemic species, 3,500 are found in this region. Many deep and isolated regions are exceptionally rich in endemic plant species. In Sikkim, 60 per cent of plants species are endemic. In India’s sector of the area, there are about 5,800 species of which about 2,000 (36%) are endemic.
3. In Nepal, there are 7,000 plant species, many of which overlap with India and Bhutan. Of these species about 500 are believed to be endemic. In Bhutan Himalaya about 15 per cent of plant species are considered to be endemic to Eastern Himalaya.
Western Ghats:
Western Ghats extends parallel to the western coasts in north-south direction. Average altitude ranges between 900-1,100 m and average width is 50 to 80 km. About 40 per cent of endemic species are found in a 17,000 sq km strip of forests along the seaward side of Western Ghats in Maharashtra, Karnataka, Tamil Nadu and Kerala.
Forests tracts up to 500 m in elevation, comprising one-fifth of the entire forests expanse, are mostly evergreen while those in the 500-1,500 m range are semi-evergreen.
There are two main centres of diversity, the Agastyamalai hills and Silent valley:
1. About 62 per cent of known amphibian species are endemic with the majority occurring in the Western Ghats. Nearly 50 per cent of lizards of India are endemic with high degree of endemism in the Western Ghats.
2. There are currently seven national parks in Western Ghats with a total area of 2,073 sq km and 39 wildlife sanctuaries covering an area of about 13,862 sq km.
3. The status of management of wildlife sanctuaries in this part of India varies enormously. Nilgiri wildlife sanctuary, for example, has no human inhabitant, while the Paramikulam wildlife sanctuary in Kerala includes considerable area of commercial plantation with heavy resources exploitations (Joshi and Joshi, 2004).
India has a large network of protected areas that gives priority to conserve and protect the remaining biodiversity centres (natural forests). Altogether, there are 14 biosphere reserves, out of them three are in the world network of biosphere reserve—Sunderban, Gulf of Mannar and Nilgiris. Also, there are about 100 national parks and about 500 wildlife sanctuaries.
The forests in India range from tropical evergreen forests in Andaman and Nicobar Islands, Western Ghats and north-eastern states to dry alpine scrub in high Himalaya. Between the two extremes, the country has semi-evergreen rain forests, deciduous monsoon forests, thorn forests, subtropical pine forests in lower mountain zone and temperate mountain forests. Western and Central India is characterized by dry and thorn forests (Table 1.4).
North-eastern states, viz., Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, Sikkim and Tripura, parts of states to the western side of Western Ghats, coastal plains and islands, etc., have very rich forests and biodiversity. Each of these states has more than 70 per cent area under forest cover.
These regions are mainly having tropical evergreen forests. Some tribal and hill states, viz., Orissa, Chhattisgarh, Uttarakhand and Himachal Pradesh have also a large area under forest cover. On the other end, Punjab, Haryana, Uttar Pradesh, Bihar and Rajasthan, each having less than 10 per cent of their geographical area under forest cover, are very poor in terms of forest cover (Table 1.5).
Geographical distribution of forest cover is depicted in Figure 1.7. It can be concluded from the figure that Eastern Himalaya, Western Himalaya, Western Ghats, islands have substantial area under forest cover. Eastern parts of Central Indian upland, i.e., Orissa, Chattisgarh, Jharkhand, Eastern Madhya Pradesh, etc., are also characterized by dense forests. North-western parts of the country, Indo-Gangetic plain and rain shadow parts of South India are very poor in terms of forest cover (Figure 1.7).
The number of plant (flowering and non-flowering) species in India is estimated to be over 47,000 representing about 12 per cent of world’s flora. These are categorized in different taxonomic divisions including over 1,500 flowering plants.
Estimates for lower plants are: 64 gymnosperms, 2,843 bryophytes, 1,012 pteridophytes, 1,940 lichens, 12,480 algae and 23,000 fungi. Some 5,150 species of flowering plants are endemic to the country. Among the endemic species, 2,532 species are found in Himalaya and adjoining areas followed by 1,782 species in peninsular India.
About 1,500 endemic species are facing varying degrees of threat. In India, tropical forests harbour around 89,451 animal and 49,219 plant species. Forests are rich in floral and faunal diversity and are regarded as home of the biodiversity because most of the biodiversity occurs in the forests particularly tropical forests among terrestrial systems have a great number of species.