The mixedwood forest wetlands consist mainly of bogs, fens and marshes. Habitats of the valleys and floodplains include woodlands, marshes, fens, and species-rich limestone grasslands. Other habitat types include wetlands, grasslands, bogs, fens, scrub habitats, coastal and marine habitats. The common sundew thrives in wetlands such as marshes and fens. When peat accumulates, bogs and fens arise. The boreal forest also has vast areas of wetland, particularly bogs and fens. This area is a patchwork of alpine heaths, herbfields, feldmarks, bogs and fens. Wetland productivity (marshes and fens) is similarly measured. Ireland possesses almost of actively growing bogs and fens. The resulting stagnant water is conducive to the formation of bogs and fens. Much of the county was once wet fenland (see The Fens). It is a rather flat countryside that was once full of fens and swamps. Peats continued to develop in the freshwater wetlands of the interior fens. Wicken Fen features the last surviving wooden windpump in the Fens. Since the 19th century, all of the acid peat in the Fens has disappeared.