What is a Fen? The Nature of ACRES’ “Springy Places”
“Springy places” the early pioneers called them…probably because the pioneers frequently encountered springs of water emanating from these wet landscapes, or maybe because walking on these bouncy wetlands put a spring in their step. These globally rare ecosystems are also known as “fens” or “prairie fens.”
Prairie fens are found in the glaciated regions of the upper Midwest: predominantly in Indiana, Michigan, Ohio, Illinois, Minnesota, Wisconsin, and southern Ontario, Canada. In Indiana, though a rare landscape type, fens are more common in the lakes region of Steuben, LaGrange, Noble, and Kosciusko Counties.
Essentially wet prairies, fens are unique wetlands on a slope, characterized by plant communities found in sun-drenched landscapes: A continuous flow of cool groundwater in and through fens makes them unique. Over time, these springy places develop a thick layer of peat as the production of roots plus the tops of sedges, grasses and wildflowers greatly outpaces decomposition under the anaerobic or saturated soil. (Saturated soil is produced by groundwater rich in calcium carbonates and magnesium bicarbonates but poor in nutrients.)
Under these conditions, a lush, diverse collection of prairie plant species thrive and accumulate peat…even in summers of drought.
Prairie fens are habitat for many of the Midwest’s rarest plants and animals: These mineral-rich, yet nutrient-poor peatlands are home to poisonous things like Poison Sumac and the federally-endangered Eastern Massasauga Rattlesnakes, as well as demure species such as the ubiquitous Tussuck Sedge, Blue-Joint Grass, Prairie Cord Grass and the beautiful Small White Lady’s Slipper Orchid.
Marsh Blazing Star, Shrubby Cinquefoil, and the federally-endangered Mitchell’s Satyr Butterfly also call fens home.
Interestingly, prairie fens are also home to plants that one would expect in drier uplands. Big Bluestem, Indian Grass, and even Little Bluestem often show up in these saturated peatlands
The hydrology of a fen system is complex: Rather than running off the land, rainwater soaks into the sandy and gravelly soils of the hills and plains near the rim of a glaciated valley. As the water percolates through the soil, it dissolves calcium and magnesium minerals. This mineral-laden “hard water” continues downward through the porous layers of glacial till until it encounters a dense layer such as clay. The groundwater travels along the tilted face of the clay layer until it finds an exit point at or near the base of a hillside. Here, the groundwater springs to the surface and continues its down-slope journey to a receiving body of water such as a stream, river, or lake. This groundwater frequently develops spring runs, or surface streams, as it carves its way through the
ACRES Land Trust members protect dozens of fens: A fen is located on the north shore of Little Gentian Lake at Wing Haven. The Wetland Loop Trail at Beechwood Nature Preserve meanders through a little fen where brush has been managed, and fire has been returned to the landscape. Sauga Swamp Nature Preserve, a closed preserve, in Noble County, Kokiwanee in Wabash County, the newly-acquired Lee Family Perfect Lake Nature Preserve in Steuben County and the Walter H. and E. Marie Myers Nature Preserve on Flowers Creek in Miami County (the latter two are closed preserves) have good examples of fens.
Lots of sunlight, an accumulation of peaty soil, mineral-rich groundwater flowing to adjacent rivers and lakes, a rich diversity of native grasses, sedges, and wildflowers make ACRES’ springy places absolute wonders and reminders of original creation…a pleasure to visit and a pleasure to protect. Will you explore the fens that ACRES members help protect this summer?