Great Lakes Shore Fen

Definition

Detailed Community Description from Ecological Landscapes of Wisconsin

General natural community overview

This open peatland community occurs along the shorelines of the Great Lakes, near the mouths of estuarine streams, and in association with sandspit landforms. Great Lakes shore fen is locally common along the southwestern shore of Lake Superior because the basin is slowly subsiding due to differential isostatic rebound from the last episode of Pleistocene glaciation. This has created conditions along the Wisconsin shore that favor the development of drowned river mouths, sandspits, and extensive peatland complexes. Shore fens are generally in direct contact with clear, cold, circumneutral (pH ~7) waters of low nutrient status.

A characteristic floating sedge mat is dominated by wire-leaved graminoid plants, including woolly sedge (Carex lasiocarpa), twig-rush (Cladium mariscoides), sweet gale (Myrica gale), and buckbean (Menyanthes trifoliata). Other common herbs in the floristically diverse coastal fens of the Lake Superior region include marsh horsetail (Equisetum palustre), marsh bellflower (Campanula aparinoides), intermediate bladderwort (Utricularia intermedia), lesser bladderwort (Utricularia minor), water bulrush (Schoenoplectus subterminalis), elliptic spike-rush (Eleocharis elliptica), narrow-leaved willow-herb (Epilobium leptophyllum), water-parsnip (Sium suave), and bog willow (Salix pedicellaris). Sooty beak-rush (Rhynchospora fusca) and the rare coast sedge (Carex exilis) are locally common in some coastal fens on the Apostle Islands. The floating sedge mat is often bordered on the downslope side by a lagoon that supports marsh vegetation composed of varying mixtures of submergent, floating-leaved, and emergent species. Toward higher ground and in the shallower portions of the peatland basins, the mat is grounded. Sphagnum mosses become increasingly important and accumulate as peat, and there are significant changes in fen composition. These sphagnum-based, herbaceous peatland communities are classified as poor fens.

Defining Characteristics and Similar Communities

Great Lakes shore fens are distinguished by their circumneutral to calciphitic flora and their proximity to the Great Lakes, located in embayments, lagoons, and river mouths with water levels influenced by Great Lakes hydrology. They are distinguished from the more acidic open bogs and poor fens (which may adjoin them in the same wetland complex) by their scarcity or lack of Sphagnum moss species, low ericad cover, higher pH, and the presence of a direct hydrologic connection to the waters of the Great Lakes. They are distinguished from boreal rich fens by their lower pH and the absence of "rich" peatland indicator species such as linear-leaved sundew (Drosera linearis), grass-of-parnassus (Parnassia glauca), common bog arrow-grass (Triglochin maritima), and false asphodel (Triantha glutinosa). Great Lakes shore fens also share similarities with northern sedge meadows, especially when dominated by wiregrass sedge (Carex lasiocarpa), but occur in drowned river mouths or coastal embayments, often have a floating mat, and have a high prevalence of calciphiles (see description), all of which are atypical for sedge meadows.

Rare animals

Species of Greatest Conservation Need

The following Species of Greatest Conservation Need are listed according to their level of association with the Great Lakes Shore 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.

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.

Landscapes

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

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.

Threats/Actions

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

Considerations

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

Northern Lake Michigan Coastal

Only a few fen-like peatlands occur on the Lake Michigan shore in direct contact with the waters of Lake Michigan. Toft Point State Natural Area (Door County) is one good example. More vegetation sampling is needed to define the community level affinities. However, detailed species lists obtained from several sites on the Door Peninsula have many similarities with the Lake Superior sites.

Superior Coastal Plain

Great lakes coastal fens occur with other peatland types in coastal embayments that are concentrated on the northern edge of the Bayfield Peninsula, in the Apostle Islands archipelago (Apostle Islands Sandscapes State Natural Area and Big Bay State Park (Bayfield County). There are also coastal fens at the mouths of the two largest rivers entering Lake Superior from Wisconsin: the St. Louis and the Bad. Even the more degraded sites (e.g., parts of the St. Louis River Estuary, Douglas County) have retained attributes of high value to some wildlife species. The intact sites merit the strongest level of protection possible.

Photos

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Great Lakes Shore Fen Photos

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.