Biogeography is the study of distribution of biological species and ecosystems in geographical space and geological time. Organisms and the biological communities often vary in a regular manner along geographic gradients of latitude, and altitude creating gradients of climatic conditions (temperature and rainfall). Also the geographical barriers like seas, oceans, mountains affect distribution of organisms. India represents a large geographical region (area 3.28 million sq. km) and is the seventh largest country in the world.
India exhibits a great variety of climatic conditions owing to its geographical position w.r.t. equator and proximity to seas, geographical extent (latitudinal variation), and topography (altitudinal variation). It lies in the northern hemisphere extending between 8o04′ N – 37o06′ N latitudes and 68o07′ E – 97o25′ E longitudes. It is bounded by the Indian Ocean in the south, Arabian Sea in the west, Bay of Bengal in the east and the Himalayan mountain range in the north.
Most part of India is situated in tropical to subtropical zone, that results in conducive temperatures for plant growth and development. The rainfall, second important climatic factor, also varies hugely in different parts of the country. India receives rains from the southwest monsoons originating in the Arabian Sea as well as the Bay of Bengal. The range of topography, further affects temperature and rainfall in different parts of the country. Consequently, a great variety of climates are found across the country and this has resulted in great variety of plant and animal species, communities, habitats, or ecosystems (biological diversity) on the Indian subcontinent.
India is has been divided into 10 bio-geographic zones such that each biogeographic zone represents a geographical area having similar species of plants and animals, communities, ecosystems, and ecology. Each biogeographic zone is further divided into biotic provinces and each biotic province contains different biomes. Rodgers and Panwar (1988), first described 10 biogeographic zones and 25 biotic provinces in India. Rodgers, Panwar and Mathur (2002), revised this classification and defined 10 biogeographic zones and 27 biotic provinces.
Biogeographic Zones of India
Zone 1: The Trans-Himalayan
This zone is located in the rain-shadow zone beyond the Greater Himalaya covering 5.6% of total geographical area of India. It is divided into three biotic provinces: Ladakh Mountains (Kargil, Nubra, and Zanskar in Jammu & Kashmir, and Lahaul and Spiti in Himachal Pradesh), Tibetan Plateau (eastern Ladakh and adjacent parts of Spiti), and Sikkim Plateau. The Greater Himalaya blocks the annual monsoon-bearing winds, creating arid conditions on the leeward side. This zone receives annual rainfall of less than 350 mm, and has average elevation of 5000 – 6000 m. This zone is referred as ‘high-altitude cold desert’ with characteristic sparse tree-less vegetation viz. Alpine steppe (Stipa purpurea, Artimisia capillaris); Alpine herbaceous formations (Caragana-Lonicera-Artimisia). Characteristic fauna of this zone includes wild sheep and goat species, wild yak, ass, gazelle, and four- horned antelope, snow leopard, Tibetan wolf, endemic lesser cat (Pallas’ cat), Himalayan marmot, and black-necked crane.
Zone 2: The Himalaya
The Himalaya (Sanskrit meaning the abode of snow) are the mountain range that separates plains of Indian subcontinent from Tibetan plateau. They are spread over 2,400 km in length across nations of Afghanistan, Pakistan, India, Nepal, China, Bhutan, and Myanmar. In India, the Himalaya are spread over states of Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Sikkim, West Bengal, and Arunanchal Pradesh, accounting 6.41 % of India’s total geographic area. This zone is divided into four biotic provinces – North-West Himalaya, West Himalaya, Central Himalaya, and East Himalaya. The annual mean temperature ranges from -30o C to 25o C. The annual precipitation ranges from 1500 mm in the west to > 4800 mm in the east. The Himalaya exhibit longest altitudinal gradient of earth (0 – 8,850 m) and so has variety of ecosystems ranging from species-rich tropical and sub-tropical broadleaf wet forests equivalent to tropical rain forests (Myristica, Artocarpus, Syzigium, Mesua) at <1000 m elevations in Eastern Himalaya and dry forests (Shorearobusta, Terminalia, Acacia catechu, Dalbergia); at around 2000 m elevation, sub-tropical mixed conifer forest (Pine-Oak forest); at 2000 – 3800 m, the moist temperate coniferous forests (Blue pine, deodar, Spruce, Silver fir) and moist temperate broadleaf forest (Oak, Rhododendron, Aesculus indica, Acer) occur; at 3800 – 4500 m elevation, sub-alpine shrublands and meadows (Rhododendron) occur; and at 4500 – 5000 m elevation alpine scrubs (dwarf Rhododendron, Cassiope, Juniper) occur. Beyond 5000 m, snow and ice is present even through the summers. Characteristic fauna of the Himalayan zone includes Tibetan Ass, Sikkim Stag, Himalayan Musk Deer, Sambar, Tahr, Beharal, Ibex, Mishmi Takin, Sun Bear, Wild Boar, Gibbon, Binturong, Red Pandas, Lesser Cats, Jungle Fowl, Markhor, Serow, Koklas, and Himalayan Monal.
Zone 3: The Indian Desert
This zone occupies northwestern India spreading over western Rajasthan and the Rann of Kutchh in Gujarat, accounting 6.5 % of India’s total geographical area. This zone is divided into two biotic provinces – the Thar desert and the Kutch. The Thar desert is spread partly over northwestern India (85%) and Eastern Pakistan (15%). The southwest monsoon that brings rain to most parts of India, bypass the Thar desert creating arid conditions. The annual rainfall ranges from < 100 mm in the west to 500 mm in the east. High temperatures, extremely low rainfall and strong winds result in rolling sand dunes in the Thar desert. Desert vegetation includes thorn scrub and grasslands (Acacia, Balanites roxburghii, Zizyphus nimmularia, Capparis decidua, Tecomella, Prosopis cineraria, Salvadora oleoides, Euphorbia caducifolia and grasses like Panicum antidotale, Eleusine sp., Cenchrus sp.). These vegetation support blackbucks, chinkara, quail, and Great Indian bustard. The Great Rann of Kutch lies to the south of Thar desert at transboundary of India and Pakistan, stretching southeast into the Little Rann of Kutch. The Rann of Kutch represent unique ecosystem, the desert wetland or seasonal salt marshes that remain flooded during rainy season and remain dry as salt-flats during rest of the year. It is important as it supports the last population of the endangered Asiatic wild ass (Equus hermionus) and the one of the world’s largest breeding colonies of the greater and lesser flamingos (Phoenicopterus ruber and P. minor).
Zone 4: The Semi-Arid
This zone encompasses 16.6 % of the total geographical area of India spreading over the states of Punjab, Haryana, Delhi, eastern Rajasthan, North-West Madhya Pradesh, Gujarat, and small part of southwest Jammu & Kashmir, and Himachal Pradesh also. This zone is divided into two biotic provinces – the Punjab plains, and Gujarat, Rajputana. Topographically, it has plain area, and the ancient Aravalli hill range. Vegetation of this area is basically represented by tropical thorn forests on the hills (with low thorny trees Acacia, Anogeissus, Balanites, Capparis, Grewia, etc.) and grasslands with interspersed trees and shrubs in the plains. Wildlife comprises of larger herbivores- Blackbuck, Chowsingha, Nilgai, and Gazelle, and carnivores- Lions, Cheetah (now extinct), Caracal, Jackal, and Wolf. There is high pressure of livestock and agriculture leading to local extinction of wildlife.
Zone 5: The Western Ghats
This biogeographic zone is divided into two biotic provinces, Malabar plains and the Western Ghat Mountains, both running parallel to the west coast of Indian peninsula, approximately 30-50 km inland eastwards from the Arabian Sea. They lie between 8 °20’N – 20°40’N and 73 °- 77°E, stretching 1600 km north-south beginning from the south of Tapti river valley, Gujarat to Kannyakumari, Tamil Nadu. They traverse the states of Gujarat, Maharashtra, Goa, Karnataka, Kerala, & Tamil Nadu. They are interrupted only by the 30 km Palghat Gap at around 11°N. The northern Western Ghats are also known as Sahyadri ranges. The altitude of the Western Ghats ranges from 35 to 2685 m above MSL and annual rainfall ranges from 2000 to 7000 mm. Anamudi is the highest peak (2695 m) of Indian Peninsula occurring in southern Western Ghats. They act as barriers to the southwest monsoon into the Deccan Plateau as the moisture-laden winds from Arabian Sea rise up to 900-1200 m elevation over the Western Ghats, and become cool and consequently precipitate most of the moisture as heavy rainfall in the windward slopes of these hills and coastal plains. As dry wind crosses the Western Ghats and descends, it gets heated and further becomes drier, thus east side of the Western Ghats and the Deccan Plateau receives very little rainfall (rain-shadow area). Due to tropical position, proximity to sea, and relief (coastal plains and mountains), the Western Ghats have very unique climatic variation leading to an exceptionally high level of biological diversity and endemism. Thus, it is recognized as a UNESCO World Heritage Site and one of the world’s eight ‘hottest hotspots’ of biological diversity. The major vegetation types found in the Western Ghats are tropical evergreen forests, temperate moist deciduous forests, temperate dry deciduous forests, the Sholas, high altitude grasslands, the dry scrub vegetation. This zone has about 4000 plant species accounting 27% of the India’s 15000 species, and of these about 1800 plant species are endemic to this zone. Some endemic tree species of this zone are Memecylon, Litsea, Cinnamomum, Syzygium, Grewia, Diospyros, and Dalbergia. The Western Ghats region is also a rich in wild relatives of important crop plants viz. cereals & millets, legumes, tropical & sub-tropical fruits, vegetables, spices & condiments. Important fauna of the region are Asian Elephant, Gaur, Tiger, lion-tailed Macaque, Nilgiri Tahr and Nilgiri Langur.
Zone 6: The Deccan Peninsula
Deccan Paninsula is India’s largest biogeographic region accounting 42 per cent of the total geographical area of India. This zone is divided into 6 biotic provinces- Central Highlands, Chotta Nagpur, Eastern Highlands, Central Plateau, Deccan South. It includes states of Madhya Pradesh, Chhattisgarh, Jharkhand, Orissa, Maharashtra, Karnataka, Telangana, Andhra Pradesh, & Tamil Nadu. It is bordered from north by Vindhya and Satpura ranges, in the east by the Eastern Ghats, and in the west by the Western Ghats. The average elevation is about 600 m, sloping generally eastward and the principal rivers are Godavari, Krishna, and Cauvery that flow from the Western Ghats eastward to the Bay of Bengal. It has an overall semi-arid condition as it falls in the rain-shadow area of the Western Ghats. The vegetation of this zone is mostly dry deciduous forests, with some dry thorn scrub towards west, and moist deciduous forests towards northeast. Important plant species of this zone are Hardwickia binata, Albizia amara, Tectona grandis, Boswellia serrata, Lannea coromandelica, Anogeissus latifolia, Albizia lebbeck, Lagerstroemia parvifolia, Diospyros tomentosa, and Acacia catechu. Important fauna includes Tiger, Chital, Sambar, Nilgai, Chowsingha, Elephant, Wild Buffalo, Hard Ground Swamp Deer, Gharhial, Rusty Spotted Cat, and Wolf.
Zone 7: The Gangetic Plain
The Gangetic plains are one of the most fertile areas of the world, formed by alluvium brought by Himalayan rivers, Ganges and Brahmaputra and their tributaries. And so are form the robust agricultural lands of the world, and are also one of the most densely populated areas of the world. It accounts for 10.8 % of the total geographical area of India, stretching from the Yamuna river eastwards spreading over mainly the states of Uttar Pradesh, Bihar, West Bengal, and the coastal plain of Orissa. This zone is divided into two biotic provinces- Upper and Lower Gangetic Plains. This zone is topographically homogeneous. Important crops grown in this zone are rice and wheat, which are grown in rotation and others include maize, sugarcane and cotton.
Natural vegetation includes Sal (Shorea robusta) forests along the foothills of Himalaya, and mixed dry decidous forest in the plains. This zone lacks in endemic species. Wildlife has decreased due agriculture expansion and high population density. Some important fauna of the zone includes Nilgai, Blackbuck, and Chinkara, Sambar, and Chital.
Zone 8: The Coasts
India has vast coastline of 7516.6 Km (6100 km of mainland coastline & 1197 km of Indian islands) touching 13 States and Union Territories (UTs). This zone accounts for 2.5% of the India’s total geographical area and is divided in three biotic provinces – West Coast, East Coast, and Lakshadweep. The west coast extends from the Gulf of Cambay (Gulf of Khambhat) in the north to Cape Comorin (Kanniyakumari) in the south. The east coast extends from the Ganges river delta in the north to Kannyakumari in the south. The coasts have a diverse set of communities like Mangroves in the estuaries or deltas, sand beaches with distinctive plant communities like Casuarina-Calophyllum-Pandanus, raised coral and rocky coastline, and the marine angiosperm pastures. Wildlife of this zone includes Dungdong and Hump-back Dolphin of estuarine waters, Salt-Water Crocodile and Batagur Basker Turtle of Sunderbans estuary, and Huge soft-shell Estuarine turtle of Utkal-Begal coast.
Zone 9: North-East India
North-East India is the richest biogeographic zone of India in terms of plant communities and endemism. This zone accounts for 5.2 % of the India’s total geographical area, and is divided into two biotic provinces – the Brahmaputra Valley (Assam), and the North-East Hills (spread over Nagaland, Manipur, Tripura, Mizoram, Meghalaya and southern part of Assam). This zone is unique as is situated at the confluence of three regions – Indian, Indo-Malayan, and Indo-Chinese regions and is also the meeting place of the Himalaya and the Indian Peninsula. This makes this zone highly rich in biodiversity and endemism. Khasi-Jaintia Hills (Meghalaya) are known to be richest in biodiversity in Asia. Vegetation types found in this zone include tropical and sub-tropical evergreen forest, temperate rain forests, sub-alpine and alpine vegetation. The North-East region (including Eastern himalayas, Arunanchal Pradesh) harbors the richest diversity in orchids, zingibers, yams, rhododendrons bamboos, canes and wild relatives of cultivated plants. More than 8,000 species out of 15,000 (in India) of flowering plants are found in this region. The five insectivorous plant genera including Nepentheskhasiana (endemic) are found in this region. Some important plant species of this North-East India – biogeographic zone specifically include rhododendrons, bamboo, and orchids. Typical fauna of this zone includes Rhinoceros, Buffalo, Elephant, Swamp Deer, Hog Deer, Pygmy Hog, Hispid Hare, Hornbill, and Waterfowl.
Zone 10: The Islands
India has two group of islands in its political boundary – i) Andaman and Nicobar Islands located in the Bay of Bengal, and ii) Lakshadweep islands located in the Arabian Sea. The latter one has very little remaining natural vegetation. The Andaman and Nicobar Islands unlike Lakshadweep islands are not much populated and have natural vegetation as Tropical rain forests. This zone accounts for 0.3 % of the total geographical area of the country and is divided into two biotic provinces – Andamans, and Nicobars. This zone (Andaman & Nicobar) stretches 590 km north to south (13o 45′ N to 6o 45′ N) and consists of 348 islands. The Andamans show biogeographical affinities with Myanmar, and the Nicobars show biogeographical affinities with Indonesia, and South-East Asia. The tropical rain forests here exhibit unique assemblages different from Indian mainland due to its geographical isolation. Some important plant species are Dipterocarpus (tropical rain forests), Terminalia and Lagerstroemia (deciduous and semi-evergreen forests). This zone shows high species richness and endemism for plant and bird species. Some important fauna of this zone are: Andaman pig, Nicobar Macaque, Nicobar tree shrew, Narcodium Hornbill, Nicobar pigeon, Andaman wood pigeon, Nicobar parakeet, marine turtles, fish and coral communities, dolphins and whales.