Bangladesh has five ecoregions:
- Sundarbans mangroves
- Sundarbans freshwater swamp forests
- Lower Gangetic Plains moist deciduous forests
- Mizoram-Manipur-Kachin rain forests
- Myanmar coastal rain forests
The ecoregion lies in the vast delta formed by the confluence of the Ganges, Brahmaputra, and Meghna rivers. The maze of mangrove channels extends across southern Bangladesh and India's West Bengal State.The Sundarbans Mangroves ecoregion is the world's largest mangrove ecosystem.
Named after the dominant mangrove species Heritiera fomes, locally known as sundri, this is the only mangrove ecoregion that harbors the Indo-Pacific region's largest predator, the tiger (Panthera tigris).
Unlike in other habitats, here tigers live and swim among the mangrove islands, where they hunt scarce prey such as chital deer (Cervus axis), barking deer (Muntiacus muntjak), wild pig (Sus scrofa), and even macaques (Macaca mulatta). Quite frequently, the people who venture into these impenetrable forests to gather honey, to fish, and to cut mangrove trees to make charcoal also fall victim to the tigers.
But the ecoregion's importance is not based solely on its role as a priority tiger conservation area. Mangroves are a transition from the marine to freshwater and terrestrial systems. They provide critical habitat for numerous species of fishes and crustaceans that are adapted to live, reproduce, and spend their juvenile lives among the tangled mass of roots, known as pneumatophores, that grow upward from the anaerobic mud to get the trees' supply of oxygen.
Bangladesh supports one of the world's highest human population densities. About half of this ecoregion's mangrove forests have been cut down to supply the fuelwood and other natural resources extracted from these forests by this large population. Despite the intense and large-scale exploitation, the ecoregion still is one of the largest contiguous areas of mangroves in the world.
There are seven protected areas that cover almost 2,700 square kilometers (km2), or 15 percent of the ecoregion (table 2). Despite the high proportion of the ecoregion being within the protected area system, only one of these, Sajnakhali, is large enough to support a space-dependent species such as the tiger. Many of the protected areas also lack trained and dedicated personnel and infrastructure to adequately manage them.
This ecoregion represents the brackish swamp forests that lie behind the Sundarbans Mangroves where the salinity is more pronounced. The freshwater ecoregion is an area where the water is only slightly brackish and becomes quite fresh during the rainy season, when the freshwater plumes from the Ganges and Brahmaputra rivers push the intruding salt water out and also bring a deposit of silt. Like the vast mangrove ecoregion, the freshwater swamp forest ecoregion also straddles the boundary between Bangladesh and India's state of West Bengal.
The Sundarbans Freshwater Swamp Forests ecoregion is nearly extinct. Hundreds of years of habitation and exploitation by one of the world's densest human populations have exacted a heavy toll of this ecoregion's habitat and biodiversity.
Because it sits in the vast, productive delta of the Ganges and Brahmaputra rivers, the annual alluvial deposits make the ecoregion exceptionally productive. Therefore, most of the natural habitat has long been converted to agriculture, making it almost impossible to even surmise the original composition of the ecoregion's biodiversity.
This ecoregion is nearly extinct, the victim of large-scale clearing and settlement to support one of the densest human populations in Asia. There are two protected areas that cover a mere 130 square kilometers (km2) of the ecoregion
The Lower Gangetic Plains Moist Deciduous Forests lie along the confluence of two of Asia's largest rivers, the Ganges and Brahmaputra rivers, which run the length of the Himalayan foothills and drain its breadth. It once harbored impressive populations of tiger (Panthera tigris), greater one-horned rhinoceros (Rhinoceros unicornis),Asian elephant (Elephas maximus), gaur (Bos gaurus), swamp deer (Cervus duvaucelli), and Bengal florican (Eupodotis bengalensis). Today, the ecoregion supports one of the densest human populations on Earth, and the fertile alluvial plains have been cleared and intensely cultivated. The human activities that date back thousands of years have taken a very heavy toll on the natural biodiversity of the ecoregion, and many of these species have disappeared from the ecoregion.
Despite hundreds of years of human settlement, much forest still remained until the early twentieth century. Since then deforestation has accelerated, and now the ecoregion's natural habitat borders on the verge of extinction. Only about 3 percent of the ecoregion is now under natural forest, and only one large block of intact habitat (south of Varanasi) remains in this ecoregion. Although more than forty protected areas are represented in the ecoregion, they cover only about 3 percent of the ecoregion, and more than half of these protected areas are small, being less than 100 km2 in area
This large ecoregion represents the semi-evergreen submontane rain forests that extend from the midranges of the Arakan Yoma and Chin Hills north into the Chittagong Hills of Bangladesh the Mizo and Naga hills along the Myanmar-Indian border, and into the northern hills of Myanmar. It divides the Brahmaputra and Irrawaddy valleys, through which two of Asia's largest rivers flow.
The Mizoram-Manipur-Kachin Rain Forests has the highest bird species richness of all ecoregions that are completely within the Indo-Pacific region. (The only ecoregions that have more birds are the Northern Indochina Subtropical Forests and South China-Vietnam Subtropical Evergreen Forests that extend into China.) Except the pioneering explorations of Kingdon-Ward (1921, 1930, 1952) and Burma Wildlife Survey made by Oliver Milton and Richard D. Estes (1963), few scientific surveys have been made in this ecoregion. Once exception has been the recent Wildlife Conservation Society (WCS) and Smithsonian Institution's reptile survey in northwestern Myanmar. Therefore these rugged mountains' biodiversity remains largely unknown.
Almost half of this ecoregion's natural habitat is still intact, especially in the eastern areas within Myanmar. There are fifteen protected areas that cover about 3,700 km2 (3 percent) of the ecoregion (Table 3). Nonetheless, several other intact habitats should be incorporated to create a more comprehensive and representative protected area network that includes the diverse habitats and biodiversity contained within this ecoregion.
This ecoregion represents the lowland evergreen and semi-evergreen rain forests of the western side of Arakan Yoma and Tenasserim ranges along the west coast of Myanmar. A small area extends into southeast Bangladesh.
The Myanmar Coastal Rain Forests are a diverse set of climatic niches and habitats that include flora and fauna from the Indian, Indochina, and Sundaic regions. Though low in endemism, this ecoregion has a tremendous species diversity. However, the forests have been increasingly destroyed to make way for agriculture, and poaching has become the dominant threat to the remaining wildlife populations.
Most of the seasonal evergreen forest and almost all the freshwater swamp of this ecoregion has been cleared for agriculture, especially along the fertile, densely populated plains of the Irrawaddy. Heavy degradation is evident around Myeik (Mergui) and Dawei (Tavoy). Further north, large tracts of forest have been cut, including the gorges of the Thanlwin (Salween) River where it enters the Andaman Sea at Mawlamyine, an area that once harbored many local or endemic species of orchids, begonias, and other herbs. This ecoregion is inadequately protected; there are five proposed protected areas that cover about 2,700 km2 (4 percent) of the ecoregion area (Table 2). Of these one, Pegu Yomas, shared with Irrawaddy moist deciduous forests accounts for almost 2,500 km2. Along Myanmar's western coast, extensive areas of forest remain that are worthy of conservation and should be brought under protection and managed effectively to increase representation in this diverse ecoregion.Types and Severity of Threats
The continued development of flat, lowland areas for irrigated paddy rice and subsistence crops such as hill rice, cassava, yams, and vegetables on hilly ground will be a major threat in the future. Forests are being exploited extensively for timber because the country is hungry for foreign currency.
Wildlife trade and poaching are a major threat to the rapidly declining large mammals and medicinal plants in both regions of Arakan and Tenasserim coasts. Tigers are almost extinct in the northern part of the ecoregion along the Arakan Yoma because of intense demand in China and Thailand.
Ecoregions are areas that:
 share a large majority of their species and ecological dynamics;
 share similar environmental conditions; and,
 interact ecologically in ways that are critical for their long-term persistence.
Scientists at the World Wildlife Fund (WWF), have established a classification system that divides the world in 867 terrestrial ecoregions, 426 freshwater ecoregions and 229 marine ecoregions that reflect the distribution of a broad range of fauna and flora across the entire planet.