Fen mapping at the Pike and San Isabel National Forests

Fens are a special type of wetland – they are fed by groundwater, support vegetation that is very different from the plants on the surrounding uplands and some contain water that is alkaline (high pH values) or mineral rich. Fens are often dominated by rushes and sedges and they can support mosses, willows and even some trees.   

During the warm seasons between 2004 and 2009, fen expert David Bathke surveyed wetlands that could potentially contain fens on the Pike and San Isabel National Forests.  He visited places that been identified as emergent and shrub wetlands in the National Wetland Inventory to see if any of these wetlands contained fens. The resulting surveys contained a wealth of information: fen determinations and boundaries, lists of plant species, soil measurements, and observations on hydrologic processes at each site.  CNHP recently got involved when the US Forest Service requested that we use our photo-interpretation and GIS expertise to convert these data (that only existed on paper) into digital geospatial data (GIS data).  This data will help the US Forest Service better understand and protect the fens on their land.

A fen complex in Pike/San Isabel National Forest.
The fens are outlined in yellow, the  NWI wetland is outlined in purple.
The fen complex pictured above contained a diverse array of plant species including water sedge (Carex aquatilis), peat moss (Sphagnum angustifolia), white water-crowfoot (Ranunculus aquatilis), diamondleaf willow (Salix planifolia), and resin birch (Betula glandulosa).
Iron fens at Geneva Creek, note the terracing of the unvegetated surface.

Iron fens are a special type of fen that occur on iron-rich substrates, and are unique to Colorado.  The water that flows the iron-rich substrate is acidic and mineral rich, and forms limonite (iron saturated peat) which forms terraces and ledges. Note the small forested fen in the bottom left corner of the above photo: this forested iron fen is dominated by dwarfed Engelmann spruce (Picea engelmanni).