Coastal fen is a sedge- and rush-dominated wetland that occurs on calcareous substrates along Lake Huron and Lake Michigan north of the climatic tension zone. The community occurs where marl and organic soils accumulate in protected coves and abandoned coastal embayments and grade to moderately alkaline glacial tills and lacustrine sediments lakeward. Sediments along the lakeshore are typically fine-textured and rich in calcium and magnesium carbonates. Vegetation is comprised primarily of calcicolous species capable of growing on wet alkaline substrates.
County Distribution Map
Global Rank: G1G2 - Rank is uncertain, ranging from critically imperiled to imperiled
State Rank: S2 - Imperiled
Coastal fen occurs along the flat, saturated shorelines of northern Lake Huron, Lake Michigan, and the Georgian Bay on glacial lakeplains and where thin, discontinuous layers of glacial till overlay limestone. The community frequently develops where groundwater seepage percolates from either calcareous uplands or joints in the underlying limestone bedrock. Coastal fens frequently occur as part of a larger wetland complex that may include Great Lakes marsh, wooded dune and swale complex, rich conifer swamp, and northern fen. The surrounding uplands are typically dominated by mesic northern forest and boreal forest and can contain a significant component of northern white-cedar (Thuja occidentalis).
Soils of coastal fen may range from neutral to moderately alkaline, fine-textured sand to clay in areas immediately adjacent to the lake, to marl and organic sediments in protected coastal embayments less influenced by storm waves. When lake levels rise, areas closer the lakeshore become inundated and storm waves can wash away loose organic and marl sediments.
Coastal fens are minerotrophic wetlands that receive groundwater inputs rich in calcium and magnesium carbonates. The high mineral content of the groundwater is derived from the limestone and dolomite of the Niagaran escarpment and calcareous glacial tills and lacustrine clays exposed by wave action along the Great Lakes shoreline. The hydrologic regime of coastal fens is directly linked to that of the Great Lakes. As such, the water table is not stable, being subject to seasonal fluctuations in Great Lakes water levels, short-term changes due to seiches and storm surges, and long-term, multi-year lake level fluctuations. Windthrow caused by severe storms along the shoreline of Lakes Michigan and Huron can expand coastal fen farther inland, especially during Great Lakes high-water periods.
Marl forms as a calcium carbonate precipitate through the metabolic activity of algae growing in hard water lakes and calcareous wetlands. In coastal fens, extensive marl flats develop in protected areas farther from the shoreline, where marl accumulates in shallow water and eventually becomes sparsely vegetated by a unique suite of species able to survive in wet alkaline conditions.
Coastal fens share the herbaceous flora of northern fens, but lack the diverse moss flora and tall shrub and tree layers in areas immediately adjacent to the Great Lakes. Most of the graminoids of coastal fens are rhizomatous, an adaptation well suited to the dynamic environment of the Great Lakes shoreline. The most abundant grasses and sedges include twig-rush (Cladium mariscoides), bluejoint grass (Calamagrostis canadensis), little bluestem (Schizachyrium scoparium), hair grass (Deschampsia cespitosa), hardstem bulrush (Schoenoplectus acutus), tufted bulrush (Trichophorum cespitosum), Baltic rush (Juncus balticus), golden-seeded spike-rush (Eleocharis elliptica), beaked spike-rush (E. rostellata), white beak-rush (Rhynchospora alba), and sedges (Carex flava, C. viridula, C. lasiocarpa, C. buxbaumii, C. capillaris, and C. eburnea).
The common forbs of coastal fen include many species occurring in other calcium-rich habitats along northern Lake Michigan and Lake Huron including false asphodel (Triantha glutinosa), Kalm’s St. John’s-wort (Hypericum kalmianum), low calamint (Clinopodium arkansanum), Kalm’s lobelia (Lobelia kalmii), grass-of-Parnassus (Parnassia glauca), Ohio goldenrod (Solidago ohioensis), bog goldenrod (S. uliginosa), common bog arrow-grass (Triglochin maritima), Indian paintbrush (Castilleja coccinea), dwarf Canadian primrose (Primula mistassinica), balsam ragwort (Packera paupercula), small-fringed gentian (Gentianopsis virgata), mermaid-weed (Proserpinaca palustris), bastard toadflax (Comandra umbellata), large yellow lady-slipper (Cypripedium parviflorum var. pubescens), grass-leaved goldenrod (Euthamia graminifolia), common water horehound (Lycopus americanus), and white camas (Anticlea elegans). Several carnivorous plants grow in the coastal fens, including sundew (Drosera rotundifolia), pitcher-plant (Sarracenia purpurea), common butterwort (Pinguicula vulgaris, state special concern), and bladderworts (Utricularia cornuta and U. intermedia). These carnivorous species can survive in habitats where nitrogen supplies are limited and are well adapted to the calcareous environment of coastal fens.
Shrubs found in coastal fen include shrubby cinquefoil (Dasiphora fruticosa), Labrador tea (Rhododendron groenlandicum), sweet gale (Myrica gale), large cranberry (Vaccinium macrocarpon), creeping juniper (Juniperus horizontalis), and soapberry (Shepherdia canadensis). Shrub-sized northern white-cedar (Thuja occidentalis), tamarack (Larix laricina), balsam poplar (Populus balsamifera), and paper birch (Betula papyrifera) are often scattered throughout the fen but are often killed when Great Lakes water levels rise, especially in low areas and those adjacent to the lake.
Vegetation changes quickly when water levels change. Among the species that appear in large numbers when the water level drops are butterwort, Kalm’s St., John’s-wort, low calamint, Kalm’s lobelia, grass-of-Parnassus, Indian paintbrush, bird’s-eye primrose, and Houghton’s goldenrod (Solidago houghtonii, federal/state threatened).
Numerous butterflies and moths are restricted to fens because their food plants occur within these wetland systems, but inventories have not been done within the coastal fen community to determine if these species utilize this open shoreline habitat. In addition, many land snails are associated with coastal fens, including the rare species listed below.
- Cacalia plantaginea (prairie Indian-plantain, state special concern)
- Carex scirpoidea (bulrush sedge, state threatened)
- Drosera anglica (English sundew, state special concern)
- Pinguicula vulgaris (butterwort, state special concern)
- Solidago houghtonii (Houghton’s goldenrod, federal/state threatened)
- Ardea herodias (great blue heron, protected by the Migratory Bird Treaty Act of 1918)
- Botaurus lentiginosus (American bittern, state special concern)
- Catinella exile (Pleistocene catinella, state special concern)
- Circus cyaneus (northern harrier, state special concern)
- Emydoidea blandingii (Blanding’s turtle, state special concern)
- Euconulus alderi (land snail, state special concern)
- Merolonche dolli (Doll’s merolonche moth, state special concern)
- Pandion haliaetus (osprey, state threatened)
- Phyciodes batesii (tawny crescent, state special concern)
- Planogyra asteriscus (eastern flat-whorl, state special concern)
- Sistrurus c. catenatus (eastern massasauga, federal candidate species and state special concern)
- Somatochlora hineana (Hine's emerald, federal/state endangered)
- Somatochlora incurvata (incurvate emerald, state special concern)
- Terrapene c. carolina (eastern box turtle, state special concern)
- Vertigo elatior (tapered vertigo, state special concern)
- Vertigo morsei (six-whorl vertigo, state special concern)
- Vertigo pygmaea (crested vertigo, state special concern)
- Williamsonia fletcheri (ebony boghaunter, state special concern)
Biodiversity Management Considerations
Protecting the hydrology of coastal fens is critical to their long-term viability. Increased surface flow and reduction in groundwater recharge can be prevented by establishing no-cut buffers around coastal fens and avoiding road construction and complete canopy removal in stands immediately adjacent to fens. In addition, road construction through fens should be avoided to prevent hydrologic alterations; roads can impede surface flows and result in significant changes in species composition and structure as a result of sustained flooding on one side of a road while the other side becomes drier and subject to increased shrub and tree encroachment. Off-road vehicles can create deep ruts in the loose soils of coastal fen, altering surface flows and species composition, and creating opportunities for invasive plants to establish.
Particularly aggressive invasive species that have the potential to threaten diversity and structure of coastal fens include glossy buckthorn (Frangula alnus), purple loosestrife (Lythrum salicaria), narrow-leaved cat-tail (Typha angustifolia), hybrid cat-tail (Typha xglauca), reed canary grass (Phalaris arundinacea), and reed (Phragmites australis subsp. australis). Monitoring and control efforts to protect and remove invasive plants before they become widespread will help maintain the ecological integrity of coastal fens and surrounding natural communities.
Species composition of coastal fen varies depending on gradients in nutrient levels and water chemistry. For most coastal fens in Michigan, there is limited observable groundwater flow, but for others such as Thompson’s Harbor in Presque Isle County and Peck Bay in Mackinac County, groundwater seepages are clearly visible. Coastal fens are located where Devonian, Silurian, and Ordovician limestone and dolomite are at or near the surface, providing a source of carbonate-rich groundwater. Differences in bedrock characteristics determine the prevalence of seepages and springs. Calcium-rich lacustrine clays and tills also provide suitable substrates for development of coastal fens.
Similar Natural Communities
- Albert, D.A., G. Reese, S. Crispin, L.A. Wilsmann, and S.J. Ouwinga. 1987. A Survey of Great Lakes marshes in Michigan's Upper Peninsula. MNFI report for Land and Water Management Division of Michigan DNR, Coastal Zone Management Program. 73 pp.
- Albert, D.A., G. Reese, M.R. Penskar, L.A. Wilsmann, and S.J. Ouwinga. 1989. A survey of Great Lakes marshes in the northern half of Michigan's Lower Peninsula and throughout Michigan's Upper Peninsula. MNFI report for Land and Water Management Division of Michigan DNR, Coastal Zone Management Program. 124 pp.
- Albert, D.A., and L.D. Minc. 2001. Abiotic and floristic characterization of Laurentian Great Lakes’ coastal wetlands. Proceedings of the International Association of Theoretical and Applied Limnology. Stuttgart, Germany. Verh. Internat. Verein. Limnol. 27: 3413-3419.
- Amon, J.P., C.A. Thompson, Q.J. Carpenter, and J. Mines. 2002. Temperate zone fens of the glaciated Midwestern USA. Wetlands 22(2): 301-317.
- Bedford, B.L., and K.S. Godwin. 2003. Fens of the United States: Distribution, characteristics, and scientific connection versus legal isolation. Wetlands 23(3): 608-629.
- Boelter, D.H., and E.S. Verry. 1977. Peatland and water in the northern Lake States. North Central Forest Experiment Station. USDA, Forest Service General Technical Report NC-31. 26 pp.
- Minc, L.D. 1997. Great Lakes coastal wetlands: An overview of abiotic factors affecting their distribution, form, and species composition. A report in three parts. Michigan Natural Features Inventory, Lansing, MI. 307 pp.
- Schwintzer, C.R. 1978. Vegetation and nutrient status of northern Michigan fens. Canadian Journal of Botany 56: 3044-3051.
- Schwintzer, C.R, and T.J. Tomberlin. 1982. Chemical and physical characteristics of shallow ground waters in northern Michigan bogs, swamps, and fens. American Journal of Botany 69(8): 1231-1239.
- Siegel, D.I. 1988. Evaluating cumulative effects of disturbance on the hydrologic function of bogs, fens, and mires. Environmental Management 12(5): 621-626.
- Zoltai, S.C., and D.H. Vitt. 1995. Canadian wetlands: Environmental gradients and classification. Vegetatio 118: 131-137.
For a full list of references used to create this description, please refer to the natural community abstract for coastal fen.
Kost, M.A., D.A. Albert, J.G. Cohen, B.S. Slaughter, R.K. Schillo, C.R. Weber, and K.A. Chapman. 2007. Natural Communities of Michigan: Classification and Description. Michigan Natural Features Inventory, Report No. 2007-21, Lansing, MI.