A flat region of land that has developed from open stretches of base-rich water that have gradually silted up and passed through the *hydrosere
stage of vegetation. There is a build up of basic peat but the persistence of wet marshy conditions means that large trees cannot grow, resulting in a subclimax community. If the level of peat is raised sufficiently then certain woody plants that can tolerate wet conditions, such as alders (Alnus), willows (Salix), and guelder rose (Viburnum opulus), may become established. These fen woodlands are known as carr. Drained fenland, as for example that of the eastern English counties of Lincolnshire, Cambridgeshire, and Norfolk, is agriculturally very productive.