LUNA, T., VANCE, L.K. & C. McINTYRE(2010)

Montana Field Guides: Rocky Mountain Subalpine-Montane Fen.

Montana’s Official State Website.


General Description:

Fens occur infrequently throughout the Rocky Mountains from Colorado north into Canada. They are confined to specific environments defined by groundwater discharge, soil chemistry, and peat accumulation. This system includes poor fens, rich fens and extremely rich fens. Fens form at low points in the landscape or near slopes where groundwater intercepts the soil surface. Groundwater inflows maintain a fairly constant water level year-round, with water at or near the surface most of the time. Constant high water levels lead to accumulation of organic material, usually greater than 40 centimeters (15 inches), except on sites underlain by limestone bedrock. In addition to peat accumulation and perennially saturated soils, extremely rich and iron fens have distinct soil and water chemistry, with high levels of one or more minerals such as calcium, magnesium, or iron. Fens maintain stream water quality through denitrification and phosphorus absorption. They are among the most floristically diverse of all wetland types, supporting a large number of rare and uncommon bryophytes and vascular plant species, and provide habitat for uncommon mammals, mollusks and insects. Fens usually occur as a mosaic of herbaceous and woody plant communities. In herbaceous communities, there are several plant associations dominated by sedges (Carex species), spikerushes (Eleocharis species), and rushes (Juncus species). Bryophyte diversity is generally high and includes sphagnum (Sphagnum species). Forb diversity is especially high in extremely rich and iron fens. The woody community is typically composed of willow (Salix species) and birch (Betula nana) carr shrubland. The surrounding landscape may be ringed with other wetland systems: fens often grade into marshes, wet meadows or riparian shrublands, and can be surrounded by conifer swamps or wet to mesic coniferous forests. In very rare cases, fens can occur within prairie grasslands in the glaciated Great Plains. Fens are found in scattered locations along the Rocky Mountain Front, in the Rocky Mountains and and intermountain valleys, in the small isolated central mountain ranges, and at higher elevations on the Beartooth Plateau in the southern portion of the state.

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