Bangladesh is home to much of the Sundarbans, the world's largest mangrove forest, covering an area of 6,000 km2 in the southwest littoral region. It is divided into three protected sanctuaries–the South, East and West zones. The forest is a UNESCO World Heritage Site. The northeastern Sylhet region is home to haor wetlands, which is a unique ecosystem. It also includes tropical and subtropical coniferous forests, a freshwater swamp forest, and mixed deciduous forests. The southeastern Chittagong region covers evergreen and semi-evergreen hilly jungles. Central Bangladesh includes the plainland Sal forest running along the districts of Gazipur, Tangail and Mymensingh. St. Martin's Island is the only coral reef in the country.