Anoka Ecosystems:
Rich Fen
Rich fens are wetlands which develop on generally level and poorly drained ground and may be mostly open communities or may be covered with grasses and sedges with a few woody species present. Rich fens with a woody component are usually classified as rich fen shrubs subtype, and will be composed of grasses and sedges, as well as shrubs such as bog birch, shrubby cinquefoils and willows. Rich fens generally have two distinct regions, a Transition Zone and a Boreal Zone. The Transition Zone has a relatively shallow layer of peat and sometimes even a wet mineral soil that has a significant amount of organic matter. The Boreal Zone typically has very deep peat and contains species such as bulrushes, pitcher-plants, and other northern species. Unlike poor fens, however, rich fens do not have a layer of sphagnum moss. If the soil in the Transition Zone is a wet mineral soil, it often can allow the presence of some wet prairie species.
Rich fens have a high species diversity which is variable based on the type of nutrients available and soil type. If it occurs in association with poor fens, common species including wiregrass will dominate. In rich fens that are closer to streams, a diverse composition of sedges, grasses and forbs will occur and often grade into wet meadows, where species such as marsh bellflower, northern marsh fern, blue-joint, and others can be found.
In the mid-1800's, original Anoka county surveyors referred to extensive "floating marshes," which are likely to have been rich fens or possibly cattail rafts. However, it is unclear exactly how extensive they were across the county. Historically, they have been found most commonly in large wetland systems, but today they are found only in small, isolated areas shaped like bowls or narrow bands. In Anoka County, the area with the most notable rich fen is the Carlos Avery Wlidlife Management Area.
Sources:
"Minnesota Land Cover Classification System: User Manual." Version 5.3 Minnesota Department of Natural Resources, Central Region, 2004.
"Minnesota's Native Vegetation: A Key to Natural Communities" Version 1.5 Minnesota Department of Natural Resources, Natural Heritage Program, 1993.
Wovcha, D, Delaney, B, Nordquist, G. Minnesota's St. Croix River Valley and Anoka Sandplain: A Guide to Native Habitats Minneapolis: University of Minnesota, 1995.
