Fen Mapping

Fens are as groundwater-fed wetlands with organic soils that typically support sedges and low stature shrubs. In the mountain west, organic soil formation can take thousands of years and long-term maintenance of fens requires protection of both hydrology and plant communities. Given the sensitivity of fens, they are a high priority for conservation and restoration. However, few land management agencies have a complete inventory of fens within their lands.

A fen in Livingston Park, Routt County.

To fill this data gap, CNHP has mapped fens for both the U.S. Forest Service (USFS) and the Colorado Department of Transportation (CDOT) through a series of contracts. To date, fen have been mapped on four National Forests, with work underway for six additional Forests, and along the entire CDOT right-of-way. For each project, potential fens are identified from digital aerial photography. Each potential fen polygon is hand-drawn in ArcGIS based on the best estimation of fen boundaries and attributed with a confidence value of 1 (low confidence), 3 (possible fen) or 5 (likely fen). CNHP photo interpreters rely on multiple image sources, as well as ancillary data such as topographic maps and wetland mapping form the National Wetlands Inventory.

A 130 acre fen within one polygon (to the left) among a complex of likely and possible fens. This complex is in an area called Victoria Lake in Conejos County, in the Rio Grande National Forest.

From these projects, the data show that fen density is strongly related to elevation and landforms. In general, fens are concentrated between 9,000–12,000 feet in elevation in the subalpine zone. Fens form at the base of slopes, on valley margins, and in old kettle ponds. Geospatial data on fen locations will help both USFS and CDOT avoid potential impacts and target rare plant surveys in these important wetland habitats.

A fen near Loveland Pass (Summit/Clear Creek counties) mapped and surveyed as part of the CDOT roadside fen project.

All fen mapping by CNHP has been combined with fen mapping by partners into one seamless map of fens in Colorado. See the Colorado Wetland Inventory Mapping Tool to access the data.

Left-click to view, and right-click to download.

Below are links to Fen Mapping Reports

For information, contact Gabrielle Smith.