Wetland Plants and Plant Communities of Minnesota and Wisconsin

III.D. CALCAREOUS FENS

Calcareous fens are the rarest wetland plant community in Minnesota and Wisconsin, and probably one of the rarest in North America. These are plant communities of wet, seepage sites that have an internal flow of groundwater rich in calcium and magnesium bicarbonates, and sometimes calcium and magnesium sulfates as well (Curtis 1971). The calcium and magnesium bicarbonates and sulfates precipitate out at the surface, creating a harsh, alkaline soil condition. Only a select group of calcium-tolerant plants, referred to as calciphiles, can tolerate these conditions. Characteristic species include shrubby cinquefoil, sterile sedge, wild timothy, beaked spike-rush, Ohio goldenrod, common valerian and lesser fringed gentian. Also included are species disjunct from the tundra, alpine meadows, and salt marshes. Therefore, calcareous fens have been referred to as a hybrid community by Curtis (1971).

Calcareous fen communities in general have a disproportionate number of rare, threatened, and endangered plant species compared to other plant communities in the Great Lakes Region.

Trout streams are often associated with calcareous fens because of the cold, pure water provided by the springs and seepages.

Active springs are frequently associated with calcareous fens. The example shown by the photograph is within Nicols Meadow Fen in Dakota County, Minnesota. Note the water cress (Rorippa nasturtium-aquaticum).

VEGETATION: The calcareous fen community shown in the photograph supports 5 species listed as threatened (T) by the State of Minnesota, as well as 2 species listed as being of special concern (SC): sterile sedge (Carex sterilis) (T); beaked spike-rush (Eleocharis rostellata) (T); fen beak-rush (Rhynchospora capillacea) (T); whorled nut-rush (Scleria verticillata) (T); common valerian (Valeriana edulis var. ciliata) (T); twig-rush (Cladium mariscoides) (SC) and white lady-slipper (Cypripedium candidum) (SC). Additional species present include hummock sedge (Carex stricta), hardstem bulrush (Scirpus acutus), Grass-of-Parnassus (Parnassia glauca), lesser fringed gentian (Gentianopsis procera), brook lobelia (Lobelia kalmii), wild timothy (Muhlenbergia glomerata), swamp thistle (Cirsium muticum), blazing star (Liatris ligulistylis), Riddell's goldenrod (Solidago Riddellii), giant goldenrod (Solidago gigantea), shrubby cinquefoil (Potentilla fruticosa), sage willow (Salix candida), beaked willow (Salix bebbiana) and red-osier dogwood (Cornus stolonifera).

Two Eurasian shrubs, glossy buckthorn (Rhamnus frangula) and common buckthorn (R. cathartica), have become established at scattered locations within this fen and many other fens in Minnesota and Wisconsin. Without control measures, buckthorns can form dense thickets that shade out many of the calcareous fen species including the rare species.

SOILS: Seelyeville muck (Typic Borosaprists), sloping, calcareous. Muck "domes" created by upwelling groundwater pressure are present within the sloping, organic layer that is up to 25 feet in depth overlaying dolomite bedrock. Muck deposits of calcareous fens in Minnesota and Wisconsin have been found to be 5,000 to 10,000 years old.

HYDROLOGY: Upwelling, calcareous groundwater discharge. Small, calcareous streams originate in the fen complex due to the groundwater discharge. Seelyeville soils (sloping) are typically saturated to the surface.

LOCATION: Savage Fen Scientific And Natural Area, Scott County, Minnesota.

SPECIES ACCOUNTS:

Sterile Sedge (Carex sterilis Willd.)
Beaked Spike-rush (Eleocharis rostellata (Torr.) Torr.)
Narrow-leaved Cottongrass (Eriophorum angustifolium Honck.)
Wild Timothy (Muhlenbergia glomerata (Willd.) Trin.)
Grass-of-Parnassus (Parnassia glauca Raf.)
Common Valerian (Valeriana edulis var. ciliata (T. & G.) Cronq.)
Ohio Goldenrod (Solidago ohioensis Riddell)
Swamp Thistle (Cirsium muticum Michaux)
Brook Lobelia (Lobelia kalmii L.)
White Lady-slipper (Cypripedium candidum Willd.)
Nodding Ladies' Tresses Orchid (Spiranthes cernua (L.) Richard)
Lesser Fringed Gentain (Gentianopsis procera (Holm) MA)
Shrubby Cinquefoil (Potentilla fruticosa L.)
Sage Willow (Salix candida Willd.)

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