Prior to European settlement, the Lower Mississippi Valley was covered with over 24 million acres (97,000 km2) of bottomland hardwood forest that supported a rich diversity of fish and wildlife species. Historically, the dominant forest type was oak-gum-cypress. covered the broader flats on slightly higher ground, forming extensive nearly pure stands beneath huge bottomland hardwood trees. Settlers began clearing the forest in the early 19th century. Today more than 75% of the forest coverage has been lost to land clearing operations for agriculture, transportation, industrialization, and urbanization. The remaining 4.8 million acres (19,000 km2) of forest are isolated islands of habitat surrounded by cotton, corn, rice, and bean fields. Most of the surviving forests now occupy low ground dominated by water tolerant species.