Fens – the Rocky Mountain’s unique high altitude wetlands

Collecting plant data from a fen located at 11,000 feet near Mount Emmons, Crested Butte, Colorado.

It is a scenic spot, this wet meadow thick with mats of sedges, rushes and some beautiful wildflowers lying in the shadows of Sheep Mountain near Trout Lake, Colorado.  This lush, high altitude wetland, rich in plant diversity is a unique habitat in Colorado. The Grand Mesa Uncompahgre and Gunnison (GMUG) National Forests’ lead hydrologist, Gary Shellhorn explains that this wet meadow is called a fen. 

Fens are mostly a northern hemisphere phenomenon, occurring in the northeastern United States, the Great Lakes region, the Rocky Mountains, and much of Canada -- and are generally associated with low temperatures and short growing seasons where excessive moisture accumulates from rain or snow.   Fens are peat-forming wetlands. Peat forms when wetland plants die creating mats of dead and decaying plant matter.  Fens are sustained by mineral enriched groundwater which is less acidic.  For this reason fens support a more diverse plant and animal community.  In southern Colorado, it takes about 2,000 years to accumulate 8 inches of peat at a fen.  This suggests that most fens are 4,000 to 10,000 years old.  

Ben Stratton, a hydrologist with the GMUG National Forests, was part of a team of specialists that inventoried the forest for the occurrence and condition of fens.  The team searched for fens across the 3 million acre forest.  It was estimated that about 1,700 fens covering 11,000 acres may occur on the GMUG National Forests.  “About 90% of the fens found are between 9,000 and 12,000 feet in elevation and most fens are geologically associated with glacial drift or mass wasting,” Stratton explains.

Fen inventory team at work collecting plant data at a fen near Engineer Pass, Ouray, Colorado (Red Mountain  #3 in the background).

In the late 1800s and early 1900s, many peat lands were flooded by reservoir construction or drained for farming and other land uses.  Of the nearly 150 fens surveyed, six fens had no apparent disturbances. The majority had been disturbed by flooding, de-watering, grazing, off highway vehicle tracks, roads, and even campsites.  Last summer the GMUG hydrologists experimented with a couple creative “fen restoration” projects. The surface flows to one fen had been channelized, partially drying up the area. By installing straw bales in channelized sections, the flows spread across the fen to inundate about 13 acres of the previously dewatered wetland.

“Our goal is to understand how to restore the function of impaired fens that took thousands of years to form” said Gary Shellhorn.  Fens, like all wetlands, provide important benefits in a watershed. By slowing runoff, fens helps reduce flooding; the vegetation filters pollutants, improving water quality; and lush wetlands provide habitat for unique plants and animals.  “Through the fen restoration efforts, our successes will improve the condition of our watersheds which will ultimately benefit the water quality and quantity for the public,” Shellhorn added.  For the GMUG National Forest fen report: "The Inventory of Fens in West Central Colorado" go to: http://www.fs.usda.gov/goto/gmug/fens

Preparing the channelized section of the fen for straw bale placement. These organic check dams spread out surface flows over a de-watered fen.