The natural Upper Mississippi River (UMR) and its tributaries flowed and meandered freely across large floodplain landscapes. Processes such as flooding, erosion, and sedimentation were powerful natural forces that shaped and maintained some floodplain forest communities. Beginning in the early nineteenth century, the UMR and its floodplain have been modified by navigation structures and agriculture. As a consequence of human modifications, a large portion of the UMR floodplain is no longer periodically inundated and the hydrologic patterns in the river, as well as on the floodplain, have changed. In general, agriculture and urban development have greatly reduced floodplain forest acres, especially in river reaches where a mainline levee system has been established. Compared to presettlement forest composition, our present floodplain forests are generally less diverse. Silver maple has dramatically increased in abundance and pioneer forests have probably been greatly reduced throughout much of the UMR floodplain.