Anoka Ecosystems:
Poor Fen
Poor fens are nutrient poor and slightly acidic wetlands which most often occur in the conifer-hardwood forest zone, though they sometimes occur in the deciduous forest-woodland zone. Poor fens are often mistaken for bogs, but unlike bogs which are highly acidic and nutrient-poor, poor fens only have mildly acidic surface water and a higher concentration of nutrients than bogs. Poor fens occur on deep peat which is more than 3 feet deep, and receive little nutrient input from the surrounding uplands. Most commonly, Minnesota poor fens occur when they are adjacent to raised bogs, though they can also occur in any basins which are isolated from runoff or other nutrient input. Typically, this community is transitional between rich fen and open bog communities and will often develop into one of these communities over time.
Vegetation in poor fens is composed of dominantly wiregrass sedge and leatherleaf, though other sedges such as mud sedge and beaked sedge are common. Poor fens are at least half covered by sphagnum moss, and may have up to 70% cover from shrubs such as bog birches and stunted tamaracks. Poor fens are also home to a few more unusual species, such as the pitcher-plant and round-leaved sundew, which are both carniverous, though they use different mechanisms.
Because of their transitional nature, poor fens are very delicate ecosystems which make take decades to recover from disturbances. Regardless of whether the disturbance is human or nature derived, evidence of disturbance may persist for years in poor fens. In addition to their fragility, poor fens are exceptionally reliant on the consistency of nutrient levels. Increased nutrient availability from runoff or or other intputs will fundamentally disrupt species composition and diversity, and species unique to poor fens are quickly crowded out by rich fen species.
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.
