Biological diversity in the state of West Bengal could be presented at species as well as at ecosystem levels. The geographical location of the state has bestowed major representative ecosystem within it. The wide variety in physical feature and climate situations have resulted in a diversity of ecological habitats in West Bengal, like forests, grasslands, wetlands; coastal and marine ecosystems, which harbour and sustain the immense biodiversity. Measured in terms of area, its incidence is higher than that of India. The mountain ecosystem in the Darjeeling (Himalayas) in the north, the forest ecosystem, semi-evergreen, deciduous, dry moist and tidal varieties extending over the major part of the state, the freshwater ecosystem (spread over rivers, wetland and estuaries), the semiarid ecosystem of Purulia-Bankura-Birbhum region, the mangrove ecosystem of the Sunderbans and coastal-marine ecosystem along North and South 24Parganas and Midnapore districts are the examples of the largest assemblages of habitats for floral and faunal diversity.
Five distinct types of grasslands recognized in India harbour about 1256 species belonging to 245 genera. Out of these, three types are found in West Bengal, vjz. Phragmites-Saccharum-Imperata type. Themeda-Arundirtella type and Temperate-Alpine type.In Jaldapara Wildlife Sanctuary pure grassland extends over 30.55 Sq.km,. (14.11% of the PA area), along with Kharir-Sissoo succession over 42.90 Sq.km. (19.81%1 and with Simul-Siris succession over 22.59 Sq.km.110.03%), which is the important habitat (grazing ground) of Rhino, Hog deer, Spotted deer, Sambar, Barking deer, Elephant and Gaur.In Buxa Tiger Reserve, the riverine grasslands and savannah woodlands occupy a considerable part. The total coverage of grassland in BTR as per satellite imageries is 51.34 Sq.km., which offers grazing ground for cheetal, sambar, barking deer, hog deer, gaur and elephant.The riverine grassland and Savannah woodland occupy about 20% of the total plant cover of Gorumara National Park, which is the grazing ground of wild herbivores.The first seral stage of vegetation succession by grass is found in the riverbeds. This type is met on the clear land formed due to erosion and washing away of the forest cover by the Teesta as seen in Samardanga forest block. The main grasses found here are Phragmitis karka and Saccharum munja. In Sunderban Tiger Reserve, the sea facing areas have a long line of Saccharum grassland ideally suited for tiger and its prey species.
These ecosystems encompass diverse and heterogeneous habitats ranging from rivers, flood plains and rain fed lakes to swamps, estuaries and salt marshes. India has about 4.1 million ha. of wetlands (excluding paddy fields nod mangroves) of which 1.5 million ha, are natural and 2.6 million ha. are man-made. The predominant wetland types of the State are marshes, jheels, terai swamps and char lands of the Gangetic plains, wetlands in Islands of Bay of Bengal and coastal brackish water wetlands. These wetlands harbour enormous diversity of floral and faunal species, many of which are endangered.Wetlands are a highly productive ecosystem, which serve as habitat for a variety of plants and animals. Wetlands perform essential functions including flood control, natural sewage treatment, stabilisation of shorelines against wave erosion, recharging of aquifers and supporting rich biodiversity. Many wetlands serve as the winter habitats for migratory birds.Wetlands are subjected to reclamation, agriculture runoffs, pesticides, construction of dams and barrages, etc.
Coastal and Marine Ecosystem
The coastline of India including those of Andaman and Nicobar Islands and Lakshadweep Islands extend over 7500 km. West Bengal has a coastline of 650 kms. in the northern part of Bay of Bengal within Medinipur and S. 24 Pgs. districts. The marine ecosystem in India covers 2.1 million Sq.km. area. The available data on faunal diversity reveals that it represents more than 15% of the total fauna of the country. Such ecosystem in the State is located in Sunderbans in S. 24 Pgs. district under Tiger Reserve and Biosphere Reserve areas.
The total area covered by mangroves in India is estimated at about 6700 Sq.km. i.e. about 7% of the World's mangroves. The largest stretch of mangroves in the country lies in the Sunderbans of West Bengal covering an area of about 4200 Sq.km. The predominant mangrove species are 'Avisennia officinalis, Excoecana agallocha, Herittera Tomes, Brugutera parviflora, Cenops decandia, Rhtzophora mucronata and Zylocarpus granatum. Mangroves also harbour a number of molluscs, polychaetes and honeybees.Mangroves constitute an important economic resource providing fodder, fuel wood, tanbarks, edible fish, hides; honey, wax, various chemicals and medicines which are important sources of livelihood for people. Mangroves play an important role in stabilizing shorelines and protecting these from cyclones. Over-exploitation of fisheries and other fauna also has adverse impact on mangrove biota. Increase in sewage and industrial effluents has deleterious impact on the biodiversity harboured by mangroves. Aquaculture with its high inputs of organic matter, fish feed etc. accelerates eutrophication of mangrove areas.
Coastal and Marine Ecosystem