Flora

The vegetation is largely of mangrove type and encompasses a variety of plants including trees, shrubs, grasses, epiphytes, and lianas. Being mostly evergreen, they possess more or less similar physiological and structural adaptations. Most trees have pneumatophores for aerial respiration. The prominent species is Sundari (Heritiera fomes) and Gewa (Excoecaria agallocha). Prain (1903) recorded 334 species under 245 genera. Of these 17 are pteridophytes, 87 monocotyledons and the rest are dicotyledons. The plant species include 35 legumes, 29 grasses, 19 sedges, and 18 euphorbias. Of the 50 true mangrove plant species recorded, the Sundarbans alone contain 35. Almost all mangrove plant species are evergreen, dwarf, shrubby or tall trees, and grow gregariously without leaving any space on the floor.

In the Sundarbans the saltwater forest is situated in the south-western part where Gewa (E. agallocha), Goran (Ceriops decandra), Keora (Sonneratia apetala), Ora (S. caseolaris), Passur (Xylocarpus mekongensis), Dhundul (X. granatum), Bain (Avicennia alba, A. marina, A. officinales), and other rhizophores, and Hantal (Phoenix pelludosa) dominate. The typical mangrove species dominate the central part of the forest. The moderate saltwater forest covers most of the southern parts of Khulna and Bagerhat districts where Sundari is the dominant species.

There is a thick mat of the nipa palm or 'Golpata' (Nipa fruticans) by the side of almost all the canals. The moderately freshwater zone results from the large amount of water, which flows down the Passur, Haringhata and Burisher, maintaining the surface water at a lower level of salinity.

The Sundarbans shows some distinct phyto-succession, where the newly formed lands are occupied by some pioneer species viz Leersia hexandra, wild rice (Potresia species), followed by Avicennia, Sonneratia and Aegiceras. The secondary succession occurs due to Ceriops, Excoecaria, Bruguiera, Heritiera, Xylocarpus and Rhizophora. Tiger fern (Achrostichum aureum) mostly covers the ground floor, which is common in saltwater and moderately saltwater zones. Tigers use these bushes to camouflage themselves.

Fauna

The Sundarbans hosts a large variety of animals. It is the last stronghold of the bengal tiger (Panthera tigris). Within the forest habitats there are about 50 species of mammals, about 320 species of inland and migratory birds, about 50 species of reptiles, 8 species of amphibians, and about 400 species of fish.

Besides the spectacular Royal Bengal Tiger, the other notable mammalian fauna are Spotted deer (Cervus axis), Barking deer (Muntiacus muntjak), Rhesus macaque (Macaca mulatta), Jungle cat (Felis chaus), Leopard cat (Prionailurus bengalensis), the Indian porcupine (Hystrix indica), Otter (Lutra perspicillata), and wild boar (Sus scrofa). deer and wild boar constitute the main prey for the tiger. Some species including the Bengal tiger are endangered.

The ecological diversity of the Sundarbans supports a large variety of birds. Among the total number of species recorded, most are resident. Over 50 species are known to be migratory and are mostly represented by the waterfowls. The egrets, storks, herons, bitterns, sandpipers, curlew, and numerous other waders are seen along the muddy banks. There are many species of gulls and terns, especially along the seacoast and the larger waterways. Accipitridae (kites, eagles, vulture, harrier etc) is represented by about 22 species. Nine species of kingfishers are available in the forest. The rich avifaunas of the forest include species of woodpeckers, barbets, owls, bee-eaters, bulbul, shrikes, drongos, starlings, mynas, babblers, thrush, oriole, flycatchers, and many others.

Of about 50 species of reptiles the largest member in the Sundarbans is the Estuarine crocodile (Crocodylus porosus), some of which may attain a length of about seven metres. Although once they were abundant in this mangrove habitat, their total number is now estimated to be around 250. Species of lizards, including the Monitor Lizards Varanus, turtles, and snakes are well-represented. Among the snakes, the King Cobra (Ophiophagus hannah), Russell's Viper (Vipera russellii), Rock python (Python molurus), Banded Krait (Bungarus fasciatus) and several species of sea snakes are notable.

Only eight species of amphibians have been reported from the Sundarbans. The green frog (Euphlyctis hexadactylus) is mostly observed in Chandpai area of the mangrove forest. The other forest amphibians include the Skipper frog (E. cyanophlyctis), Cricket frog (Limnonectes limnocharis), Tree frog (Polypedates maculatus), and the common toad.

The Sundarbans suports nearly 400 species of fishes in its varied aquatic habitats; these include both the pelagic and demersal fishes. Many species use these habitats as nursery grounds. No aquaculture or fish farming is allowed in the Sundarbans. The Forest Department controls the fish catch from the area.

Among the invertebrates some molluscs and crustaceans constitute important fisheries resources. About 20 species of shrimps, 8 species of lobsters, 7 species of crabs, several species of gastropods, and 6 species of pelecypods have been reported from the Sundarbans. Among the shrimps Penaeus monodon and Metapenaeus monoceros and the mud crab Scylla serrata are commercially important. Insects are varied, the most important being the honeybee Apis dorsata. Locally known as 'Mouals', the professional bee collectors gather honey for three to four months during the flowering season taking permission from the Forest Department. The forest is very rich in its spider fauna (Araneae). Nearly 300 species under 22 families have been recorded from the mangrove forest habitats.

Source: http://banglapedia.search.com.bd