Land Use Planning Information>Fens, Marshes, and Bogs

Fens, Marshes, and Bogs

These three specialized wetland systems are considered rare and a high priority for preservation in southern Michigan. They might even be considered "extreme" wetlands, because they occur only under specific conditions related to their source of water and location in the landscape. photo (c) Michael Kucinich [Click here to view full size picture]

Prairie Fens
Coastal Plain Marshes
Why Protect These 'Extreme' Wetlands?

Prairie Fens

photo by William Westrate [Click here to view full size picture] Prairie fens are peat-covered wetlands that are often springy when walked upon. These fens are fed by a constant flow of mineral-rich groundwater that seeps to the surface and flows through and over the accumulated peat. The groundwater, rich in both calcium and magnesium, contributes to the alkaline soil condition.

Historically, dry upland communities such as mixed oak savannas were subject to fire, which also burned into the adjacent prairie fens. Plants found in fens are adapted to alkaline soils, periodic fire, and a constant flow of cool groundwater.

Typical plants in a prairie fen are big bluestem, Indiangrass, tamarack, shrubby cinquefoil, bog birch, poison-sumac, and many species of sedges and rushes. The extremely alkaline soils limit the variety of plants found in fens, but alkaline-tolerant plants like grass-of-Parnassus, Kalm's lobelia, round-leaved sundew, and pitcher plant may be found. Prairie fens also harbor a number of rare plant species, including Indian plantain, white ladies'-slipper, common valerian, prairie dropseed, and rosinweed.

A number of animals make their homes in or around fens. The Mitchell's satyr butterfly, a federally endangered species, is one of the more special finds in the fens of southwest Michigan. Other common finds are dragonflies, water snakes, and turtles.

There are 85 known prairie fens in Michigan, totaling about 2,000 acres. Although prairie fens are not considered to be globally imperiled, they are often found only in very small, isolated pockets, and good quality sites can be very difficult to find. In the southern Lower Peninsula of Michigan, prairie fens occur primarily in areas with a lot of topographic relief.

Coastal Plain Marshes

Photo by William Westrate Coastal plain marshes occur in relatively narrow bands around softwater ponds and depressions having gradually sloping shores and warm water temperatures. Soils range from sandy to muck and are very acidic.

Annual and seasonal water level fluctuations are what make coastal plain marshes unique. Many of the characteristic plant species are annuals, plants that live only for one growing season. They are adapted to the periodic natural draw-down of water levels, which exposes bare soils for germination.

Shallow water or recently emerged shore, due to draw-down, contains coastal plain marsh species like the purple spike rush and tooth-cup. More than 40 threatened or endangered plant species are associated with coastal plain marshes in Michigan. Cross-leaved milkwort, meadow beauty, tall beak rush, umbrella grass, and Hall's bulrush are just a few of the rare plants in this unique habitat.

These marshes are very rare in Michigan and are considered by many conservation organizations to be critically threatened. Most records indicate the majority of coastal plain marshes are in the western Lower Peninsula.


photo by William Westrate Bogs are composed of saturated peat soils that are low in nutrients and very acidic. Bogs originate in a shallow lake as a floating mat of sedges that becomes colonized by sphagnum moss. As the mat gradually thickens and stabilizes, it is invaded by shrubs and trees. Over time, the bog mat expands until no open water is visible. This transformation from open water to forest is very slow and can take thousands of years.

The peat is typically covered by a low-growing carpet of sphagnum moss. Low nighttime temperatures in bogs (often 30 degrees cooler than the surrounding uplands) are ideal for sphagnum moss, which acts as an insulator for the roots of other plants. Plants typically found in bogs include sedges and shrubs such as bog rosemary, Labrador tea, bog laurel, lowbush blueberry, and leatherleaf.

Carnivorous plants like pitcher plants and sundew are common in bogs. Bogs are also home to turtles, frogs, salamanders, and snakes. The spotted turtle and the red-bellied snake are two of the rarer finds in a bog, and they are protected by the State of Michigan.

Why Protect These 'Extreme' Wetlands?

photo by Emma Pickham Pitcher [Click here to view full size picture]
  • The "extreme" wetland systems are particularly important because they occur only under specific circumstances.
  • They are not the type of wetland that can be created, and restoration can be challenging.
  • The variety of plants and animals that occupy these systems is unique and specialized.

For more information on conserving fens and bogs Contact your county Conservation District.
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