For three months a year Ratargul Swamp Forest has no floor. The forest stands on the Goain river in the Sylhet division of northeastern Bangladesh, and every monsoon the river swells with rain off the hills of Meghalaya just across the Indian border. It floods the woodland until the trunks stand three to six metres under and the branches come down close to the surface. An ordinary lowland tree would suffocate: floodwater cuts the roots off from air. The koroch and hijol here take months of it, through tissue that carries oxygen down to the roots, and that is the rare talent a freshwater swamp forest is built on. Only a handful of them are left anywhere in the world, and this is the one Bangladeshis know.
Once the water is up there is no path, so you go in low, in a narrow wooden boat. You slip between trunks that disappear into the water with no bank and no root in sight. Where the branches close overhead the channel becomes a tunnel roofed entirely in leaves, the light coming through green and pooling on the water ahead of the bow. When the oar stops, the forest goes quiet and the surface holds the canopy whole. Your boatman points out what is on the branches first: snakes coiled at eye level, monitor lizards basking at the waterline, kingfishers and herons working the shallows, and in winter migrant geese and ducks settling onto the channels. When the raised watchtower is open you climb it, and the canopy from up there is a flat green sea running unbroken to the horizon. Ratargul has been a reserved forest on paper since 1932, but real protection came only in 2015, when a core of two square kilometres was made a wildlife sanctuary. The roads, fencing and concrete built into that core brought protests and court petitions from Bangladeshi environmentalists. By spring the water has gone and the roots stand bare in the mud, and that is when the koroch and the hijol flower.