The study conducted by the International Union for Conservation of Nature (IUCN) also says that the Indian side of Sundarbans is being subjected to various anthropogenic and natural processes affecting the distribution, quality and diversity of its mangroves.
"Human pressures and ecosystem changes are combining to threaten the population of endangered Royal Bengal tigers, one of the iconic species of the Sundarbans," says the report titled 'Sharing Lessons on Mangrove Restoration'.
The Sundarbans, covering 10,000 sq kms of land and water (more than half of it in India, the rest in Bangladesh) in the Ganges delta, contains the world's largest area of mangrove forests. A number of endangered species live in the forests, including tigers, aquatic mammals, birds and reptiles.
Currently, over 4.2 million people live on the fringes of the Indian Sundarbans, resulting in high anthropogenic pressures on the mangroves and their resources.
"In recent years, climate change, regulation of freshwater flow, illicit mangrove felling, poaching and unplanned embankments for settlements have emerged as the main threats to the ecosystem," the report says.
It says that the central part of the Indian Sundarbans receives almost no fresh water because of heavy siltation and clogging of the Bidyadhari channel.
"Seawater intrusion has further affected the growth of dominant mangrove species such as the freshwater-loving Heritiera fomes. The influence of salinity and effects of climate change, though not well-understood, appear to be promoting the invasion of alien species in some parts of the Sundarbans," the report adds.