But after years of abuse from man and nature, the mangroves seem to be nearing their limits. Illicit logging, mostly for building materials to house the region's booming population, has thinned out the periphery of the forest. At the same time, increasing water salinity caused by the encroaching sea is killing off many higher value, storm-stopping tree species, such as the sundari that gives the forest its name. The salinity assault comes from both land and sea: Upstream dams on rivers in India have reduced freshwater flow into the Sundarbans, while sea-level rise caused by climate change is flushing more salt water into the mangroves.

"The salinity front is just going up and up and up," said Mashfiqus Salehin, a professor at Bangladesh University of Engineering and Technology's Institute of Water and Flood Management. "New areas will salinize, and moderately salinized areas might become unlivable. It's becoming a big problem." In the worst-case scenario, in which sea levels rise by more than six feet this century, Bangladesh alone stands to lose some 800 square miles of mangroves in the Sundarbans. The best-case scenario is a loss of roughly 80 square miles. Salehin and other scientists fear even that much might prove disastrous for a country so poor the forest is besieged by human needs.