of the Sundarban mangroves dates back to the 16th century. It may be noted here that since 1947 the Sundarban mangroves are divided between India and Bangladesh (formerly East Pakistan), as Sundarban in Bangladesh and as Sundarban National Park in India, and the two parts differ considerably in the nature and extent of investigations, conservation and management. They also differ substantially in the level of human exploitation over more than a century. This makes it difficult to integrate the information of the entire Sundarban.
The mangrove-dominated Ganges delta, the Sundarban, named after the dominant species Sundri (beautiful) tree (Heritiera fomes-a mangrove tree that requires freshwater), is a complex ecosystem of mangrove forests in the world. Shared between two neighboring countries, Bangladesh and India, the larger part (62%) is situated in the southwest corner of Bangladesh located between 21°30 َ N to 22°30 َ N and longitude 89° E to 90° E. To the south the forest meets the Bay of Bengal; to the east it is bordered by the Baleswar River, to the west by the Sundarban National Park of India and to the north there is a sharp interface with intensively cultivated land. The forest consists of about 200 islands, separated by about 400 interconnected tidal rivers, creeks and canals. The total area of the Sundarban Reserved Forest (SRF) is 6,017 km2 out of which 4,143 km2 is land area and 1,874 km2 is water area comprising rivers and tidal waterways. This area is approximately half the size of the area of mangrove that existed 200 years ago, the other half being cleared and converted to agricultural land. Rivers in the Sundarban are meeting places of salt water and freshwater. Thus, it is a region of transition between the freshwater of the rivers originating from the Ganges and the saline water of the Bay of Bengal.
The geological setting of the Sundarban ecosystem is a delta of interconnecting large rivers: the Ganges; the Bramaputra, and the Meghna. The sediment is of recent origin, consisting of alluvium washed down from the Himalayas deposited over the older sediments carried by the three rivers. The forest floor is 0.91m to 2.11m above mean sea level. The pH ranges widely from 5.3 to 8.0. Although the Sundarbans soil is in general medium textured, sandy loam, silt loam or clay loam, the grain size distribution is highly variable. Silt loam is dominant textural class. Sodium and calcium contents of the soil vary from 5.7 to 29.8 meq/100g dry soil and are generally low in the eastern region and higher towards the west. The available potassium content of the soil is low, 0.3-1.3 meq/100g dry soil. Organic matter content varies between 4% and 10% in dry soil. Soil salinity increases from east (slight to moderate) to west (highly saline), but the salinity is not uniform from north to south throughout the forest. Its ecosystem is characterized by a very dynamic environment due to the effect of tide, flooding, salinity and even the cyclones.
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 Sundarban 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 Sundarban. The mean annual relative humidity varies from 70% at Satkhira to 80% at Patuakhali. Humidity is highest in June-October and lowest in February. Annual rainfall in the Sundarbans is in the range of 1640-2000 mm, rainfall increases from west to the east. Most rainfall occurs during the monsoon from May to October. Frequent and heavy showers occur from mid-June to mid-September. Often storm accompanied by tidal waves result widespread inundation and cause damage to vegetation and animal life.