Fen Wetlands

Photo © Joshua Mayer

No other wetlands are as diverse as a fen. Sometimes called rich fens, these saturated environments are fed with mineral-rich groundwater and occur at low points or slopes in the landscape where the soil surface is intercepted by the water table. Like bogs, these unique wetlands occur primarily in the Northeastern U.S., the Great Lakes region, and throughout Canada where glacial activity scoured the landscape thousands of years ago. The cooler, shorter seasons and ample precipitation of the area combine with geology to create the conditions that allow fens to form.


Photo © Cornell Plantations

Like many wetlands, fens are characterized by the presence of water at or near the ground surface throughout most of the year, which helps determine the plant communities that are capable of thriving there. Calcium-rich, or “calcareous,” water flows through a fen, rarely ponding, which separates the plant life into rows and tufts, or small hummocks, of vegetation surrounded by open furrows. Although it may look fairly solid, you’ll likely need a boardwalk to explore this intricate and fragile landscape without getting your feet wet.


Photo © Cornell Plantations

Fens usually lack the sphagnum moss that characterizes bogs and are instead, dominated by brown mosses and herbaceous plants such as grasses, sedges, rushes, and wildflowers. The lack of sphagnum and the addition of groundwater input makes a fen less acidic than a bog, and sometimes even quite alkaline, allowing for even greater species diversity. Above, Joe-pye weed and goldenrod splash color among the asters, cattails, and several tall grasses. Fens also support woody plants, shrubs, and small trees.


Photo © Robert Wesley

The predominantly saturated conditions of wetlands create an environment that produces specialized species incapable of persisting outside of that environment. Fens, like all wetlands, have experienced a dramatic decline in acreage since the 1970’s as they are drained for cropland, mining, and human expansion–threatening the survival of many of the plants and animals that depend on these unique environments. The rare and endangered American Globeflower (Trollius laxus) shown above is found only in a few of the rich fens of New York, New Jersey, Pennsylvania, and one county in Connecticut.

Christopher Porter

Photo © Christopher Porter

The nutrient rich conditions in a fen provide a diversity of plant life, which then supports a number of animal species that thrive in such highly productive habitats. Moose and deer enjoy the lush vegetation while fisher and beaver take advantage of the still waters. Black bear and lynx can often be found fishing around the edges and amphibians are widely abundant throughout. Unlike bogs, fens can have inflow and outflow streams and may support some fish species like trout, walleye, or bluegill. The fish and shallow water draws in wading birds like cranes, herons, and rails and the diversity of plant structure provides food and shelter that attracts owls and songbirds to breed in the rich environment.

Brett Whaley

Photo © Cornell Plantations

The mineral-rich groundwater that supplies fens usually comes from uplands that can be quite a distance from the fen itself. This makes conservation for fens difficult, since a pollution source may be located anywhere along that path between source and fen. Heavy withdrawal of groundwater for municipal or agricultural use can also have negative effects on distant fens. Impermeable surfaces like parking lots, rooftops, and roadways shed rainwater to storm drains and treatment plants reducing the amount that goes into the ground to recharge the water table that fens depend on. Reducing water use and reducing areas of impermeable surfaces are good goals for individuals, communities, and metropolitan areas alike when striving to improve conditions for fens, bogs, and other wetlands.

Map it!

Have a fen on your property? Here’s how to map it!

Use the Wetland habitat tool to outline the Fen. Then set the characteristics for Wetland type to Fen, and set Seasonality to Permanent. You can set the other characteristics to the most appropriate settings. Add a picture and some comments too and really show off that unique habitat!