Sundarbans is the largest mangrove forest in the world, located in the southern part of Bangladesh. It lies on the Ganges-Brahmaputra Delta at the point where it merges with the bay of bengal. With its array of trees and wildlife the forest is a showpiece of natural history. The forest consists of about 200 islands, separated by about 400 interconnected tidal rivers, creeks and canals.

The Sundarbans was originally measured (about 200 years ago) to be of about 16,700 sq km. It is now estimated to be about 4,110 sq km, of which about 1,700 sq km is occupied by waterbodies. The forest lies under two forest divisions, and four administrative ranges viz Chandpai, Sarankhola, Khulna and Burigoalini and has 16 forest stations. It is further divided into 55 compartments and 9 blocks. The Sundarbans was declared as a Reserve Forest in 1875. About 32,400 hectares of the Sundarbans have been declared as three wildlife sanctuaries, and came under the UNESCO World Heritage Site in 1999.

The Bangla word ban means forest, and the name Sundarban was coined either from the forests of Sundari tree ie Sundari-ban, or from the forests of the samudra (sea) ie, Samudra-ban, or from its association with the primitive tribe Chandra-bandhe which was corrupted into Sundarban. The generally accepted explanation, however, is its derivation from the sundari tree, the most common tree in these forests.

Climate Since the forest is located on the south of the Tropic of Cancer and bounded by the northern limits of the Bay of Bengal, it is classified as tropical moist forest. The temperatures in the Sundarbans are fairly equable than those of the adjacent land areas. The average annual maximum and minimum temperatures vary between 30º and 21ºC. High temperatures occur from mid-March to mid-June and low in December and January. The mean maximum temperature for the hottest months has been recorded as 32.4ºC at Patuakhali, in the east of the Sundarbans.

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.      

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.
Economic value, tourism and forest dwellers The most important value of the Sundarbans lies in its protective role. It helps hold coastlines, reclaim coastal lands, and settle the silt carried by the rivers. The estuary is a good breeding centre for many fishes. Several plant-based industries have been developed here. The most important ones are the newsprint and hardboard mills in Khulna. The raw material for the former is gewa and for the latter sundari. Other important plant-based industries are match factories and boat building. The forest is a good source of fuel, tannins, thatching, wooden articles, medicinal plants, and fodder. The forest is also a major source of honey and bee wax.

Most frequently visited sites in the Sundarbans include Katka, Hiron Point (known commonly as Nilkamal), Dublar Char and Tiger Point (Kachi Khali). Katka attracts tourists for its landscape and wildlife. There is a forest rest house here and an observation tower. Hiron Point also has a rest house and an observation tower. Dublar Char is an island with a beautiful beach. The other attraction of the island is the fishing activities that take place every year between mid-October and mid-February. Fishermen from other places of the country, especially from Chittagong, assemble here during the period to catch fish and dry them on the sunny beach. The honey collectors go into the forests during April-May.

Salinity of the area apparently influences the regeneration density which decreases with increasing level of salinity. There is year to year variation in recruitment. However, salinity appears to have little influence on these variations. Variation in seedling recruitment among the three salinity zones seems to be significant. Seedling recruitment for H. fomes, E. agallocha, and other species shows highly fluctuating values over the years. Such fluctuation might be due to the existence of periodicity in the seed production of some species. (source-Banglapedia)