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Ryan O'Connor
Natural Heritage Inventory Ecologist

Calcareous Fen

State Rank: S3     Global Rank: G3   what are these ranks?


Detailed Community Description from Ecological Landscapes of Wisconsin

General natural community overview

Counties shaded blue have documented occurrences for Calcareous Fen in the Wisconsin Natural Heritage Inventory database.

Calcareous fens occur mostly in southern Wisconsin on sites that are fed by carbonate-enriched groundwater. Fens occur in several landscape settings, including the bases of morainal slopes, on sloping deposits of glacial outwash, in the headwaters areas of spring runs and small streams, and on the shores of alkaline drainage lakes. Most fens are small, covering no more than a few acres, and are often associated and can intergrade with more abundant and widespread wetland communities such as southern sedge meadow, wet-mesic prairie, shrub-carr, emergent marsh, and southern tamarack swamp. An accumulation of peat due to groundwater upwelling can raise the fen surface to a height of several meters above the adjoining lands.

The diverse fen flora is distinctive, containing many calciphiles of restricted distribution. Common or representative plants include sedges (Carex sterilis and C. lanuginosa), marsh fern (Thelypteris palustris), shrubby cinquefoil (Dasiphora fruticosa), shrubby St. John's-wort (Hypericum kalmianum), Ohio goldenrod (Solidago ohioensis), grass-of-Parnassus (Parnassia glauca), twig-rush (Cladium mariscoides), brook lobelia (Lobelia kalmia), boneset (Eupatorium perfoliatum), swamp thistle (Cirsium muticum), and asters (Symphyotrichum spp.). Many fens have a significant number of prairie or sedge meadow components, and some contain plants often associated with bogs, such as tamarack (Larix laricina), bog birch (Betula pumila) and pitcher-plant (Sarracenia purpurea).

Defining Characteristics and Similar Communities

Calcareous fens are distinguished primarily by a constant supply of groundwater high in calcium and magnesium carbonates. They are similar to southern sedge meadows but contain more fen specialists. While both communities may contain tussock sedge, tussocks tend to be taller and more dominant in sedge meadows, reflecting a more variable water table that promotes vertical tussock development. This is a particularly useful feature to distinguish the two communities where they intergrade. Calcareous fens also share similar vegetation with wet-mesic prairies, but are always found on organic soils (peat, sometimes mixed with marl) while prairies tend to occur on mineral soil. Fens are distinguished from shrub-carr and bog relict by having less than 50% cover of tall shrubs, and from southern tamarack swamps by having less than 25% cover of trees (usually much less).

Rare animals

Species of Greatest Conservation Need

Wisconsin Wildlife Action Plan graphic

The following Species of Greatest Conservation Need are listed according to their level of association with the Calcareous Fen natural community type, based on the findings in Wisconsin's 2015 Wildlife Action Plan.

Scores: 3 = high association, 2 = moderate association, and 1 = low association. See the key to association scores for complete definitions.

Pickerel FrogLithobates palustris2

Ants, wasps, and beesScore
Confusing Bumble BeeBombus perplexus1
Rusty-patched Bumble BeeBombus affinis1
Yellow Bumble BeeBombus fervidus1

Aquatic and terrestrial snailsScore
Six-whorl VertigoVertigo morsei3
Deep-throated VertigoVertigo nylanderi1

A Leaf BeetleCryptocephalus venustus2
Cantrall's Bog BeetleLiodessus cantralli2
A Minute Moss BeetleHydraena angulicollis1
A Pear-shaped WeevilFallapion bischoffi1

American WoodcockScolopax minor2
Rusty BlackbirdEuphagus carolinus2
BobolinkDolichonyx oryzivorus1
Eastern MeadowlarkSturnella magna1
Yellow-breasted ChatIcteria virens1

Butterflies and mothsScore
Swamp MetalmarkCalephelis muticum3
Liatris Borer MothPapaipema beeriana1
Midwestern Fen BuckmothHemileuca nevadensis ssp. 31
Silphium Borer MothPapaipema silphii1

Dragonflies and damselfliesScore
Zigzag DarnerAeshna sitchensis3
Sphagnum SpriteNehalennia gracilis2
Forcipate EmeraldSomatochlora forcipata1
Subarctic DarnerAeshna subarctica1

Grasshoppers and alliesScore
Bog ConeheadNeoconocephalus lyristes3
Delicate Meadow KatydidOrchelimum delicatum2
Spotted-winged GrasshopperOrphulella pelidna2

Leafhoppers and true bugsScore
A LeafhopperFlexamia prairiana2
A LeafhopperLimotettix elegans2
A LeafhopperLimotettix pseudosphagneticus1
Yellow Loosestrife LeafhopperErythroneura carbonata1

Big Brown BatEptesicus fuscus2
Northern Long-eared BatMyotis septentrionalis2
Silver-haired BatLasionycteris noctivagans2

Butler's GartersnakeThamnophis butleri3
Eastern MassasaugaSistrurus catenatus3
Blanding's TurtleEmydoidea blandingii1
Plains GartersnakeThamnophis radix1

Please see Section 2. Approach and Methods of the Wildlife Action Plan to learn how this information was developed.

Rare plants

The Natural Heritage Inventory has developed scores indicating the degree to which each of Wisconsin's rare plant species is associated with a particular natural community or ecological landscape. This information is similar to that found in the Wildlife Action Plan for animals. As this is a work in progress, we welcome your suggestions and feedback.

Scores: 3 = "significantly associated," 2 = "moderately associated," and 1 = "minimally associated."
Scientific Name Common Name Score
Agrimonia parviflora Swamp Agrimony 2
Carex suberecta Prairie Straw Sedge 3
Clinopodium arkansanum Low Calamint 2
Conioselinum chinense Hemlock-parsley 3
Cypripedium candidum White Lady's-slipper 3
Cypripedium parviflorum var. makasin Northern Yellow Lady's-slipper 3
Eleocharis quinqueflora Few-flowered Spike-rush 3
Eleocharis robbinsii Robbins' Spike-rush 1
Eleocharis rostellata Beaked Spike-rush 3
Epilobium strictum Downy Willow-herb 2
Equisetum palustre Marsh Horsetail 1
Galium brevipes Swamp Bedstraw 2
Muhlenbergia richardsonis Mat Muhly 3
Scleria verticillata Low Nutrush 3
Spiranthes magnicamporum Great Plains Lady's-tresses 1
Triantha glutinosa False Asphodel 3
Trichophorum cespitosum Tufted Bulrush 3
Triglochin palustris Slender Bog Arrow-grass 3
Valeriana edulis var. ciliata Hairy Valerian 2
Valeriana uliginosa Marsh Valerian 1


The following Ecological Landscapes have the best opportunities to manage for Calcareous Fen, based on the Ecological Landscapes of Wisconsin Handbook.

Map of the Ecological Landscapes of Wisconsin.

Major (3 on map)
A major opportunity for sustaining the natural community in the Ecological Landscape exists, either because many significant occurrences of the natural community have been recorded in the landscape or major restoration activities are likely to be successful maintaining the community's composition, structure, and ecological function over a longer period of time.

Important (2 on map)
Although the natural community does not occur extensively or commonly in the Ecological Landscape, one to several occurrences do occur and are important in sustaining the community in the state. In some cases, important opportunities may exist because the natural community may be restricted to just one or a few Ecological Landscapes within the state and there may be a lack of opportunities elsewhere.

Present (1 on map)
The natural community occurs in the Ecological Landscape, but better management opportunities appear to exist in other parts of the state.


Wisconsin Wildlife Action Plan graphic

What are conservation actions?

Conservation actions respond to issues or threats, which adversely affect species of greatest conservation need (SGCN) or their habitats. Besides actions such as restoring wetlands or planting resilient tree species in northern communities, research, surveys and monitoring are also among conservation actions described in the WWAP because lack of information can threaten our ability to successfully preserve and care for natural resources.

Threats/issues and conservations actions for natural communities


The following are additional considerations for Calcareous Fen in Ecological Landscapes with opportunities for protection, restoration, and/or management. For more information, see the Wildlife Action Plan.

Central Sand Hills

The wetlands bordering some of the spring-fed streams in this Ecological Landscape include a number of important fens, some of them on private lands.

Southeast Glacial Plains

Several exceptional calcareous fens have been identified in and around the kettle interlobate moraine, toward the southeastern edge of the Ecological Landscape. The most notable area is the South Unit of the Kettle Moraine State Forest. The upper reaches of the Mukwonago River also harbor a concentration of fens.

Southern Lake Michigan Coastal

In this Ecological Landscape there are some unusual and highly distinctive variants of this community. Wisconsin's sole example of Lakeplain prairie contains fen-like areas within the complex mosaic of natural communities now protected at Chiwaukee Prairie State Natural Area (Kenosha County). Clay bluffs bordering Lake Michigan in southern Milwaukee County have highly localized patches from which groundwater is discharged. The vegetation in these seepage areas strongly resembles that of the fens, with a number of calciphilic plants present.


Calcareous Fen Photos

Calcareous Fen Photo

Rich calcareous fen bordering Chaffee Creek. Chaffee Creek Fishery Area, Marquette County.

Photo by Matt Brust.

Calcareous Fen Photo

Calcareous fen in Waterloo Prairie State Natural Area, Jefferson County.

Photo by Robert H. Read.

Calcareous Fen Photo

Among the prominent blooming plants in this calcareous fen, in a diverse community complex, are shrubby cinquefoil, Ohio goldenrod, and Kalm's St John's-wort.

Photo by Christina Isenring.

Calcareous Fen Photo

This wire-leaved sedge-dominated calcareous fen contains important microsites such as this alkaline pool. Many rare species have been documented here.

Photo by Thomas Meyer.

Calcareous Fen Photo

Calcareous fen at Clover Valley Fen SNA featuring a marl flat at the top of a peat dome.

Photo by Ryan O'Connor.

Note: photos are provided to illustrate various examples of natural community types. A single photograph cannot represent the range of variability inherent in a given community type. Some of these photos explicitly illustrate unusual and distinctive community variants. The community photo galleries are a work in progress that we will expand and improve in the future.

Last revised: Tuesday, August 30, 2022