Great Plains Alkaline Fen
Global Rank:
GNR
State Rank:
S2?
(see reason below)
External Links
State Rank Reason
These very uncommon peatland habitats on the Great Plains are likely imperiled because of their very small area of occupancy, as well as from past declines and potential and/or on-going threats to the few remaining areas. Additionally, they are sensitive habitats, which are not tolerant of nor capable of regenerating quickly following disturbance. They require very specific environmental and hydrological conditions for their formation and persistence on the landscape. Additional documentation of their occurrence and extent within MT is needed.
General Description
This National Vegetation Classification Group is composed of alkaline peatlands on the plains and prairies. They occur within a grassland mosaic and they are confined to specific environments defined by groundwater discharge, soil chemistry, and peat accumulation. 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). The water chemistry of alkaline fens, also known as rich and extremely rich fens ranges from neutral to alkaline and is usually distinctly calcareous with higher concentrations of dissolved minerals. Marl deposits (precipitated calcium carbonates) are common in these habitats.
These habitats are rare in MT and have been documented from only a handful of sites from the Rocky Mtn Front to the North Dakota border including on the Blackfeet Reservation (Luna and Bahls 2017) and in Sheridan County (Heidel, Cooper and Jean 2000).
Diagnostic Characteristics
Peatlands; Rich and Extremely Rich Fens; Calcareous Fens; True Moss (Brown Mosses)-dominated; Herbaceous-or Shrub dominated; Minerotrophic; Permanently Saturated Organic Soils gen with >40cm Peat, Neutral to Alkaline Soil Water pH; Great Plains Region
Typical Dominants: Sedges (Carex nebrascensis, Carex pellita, Carex simulata, or Carex utriculata), Eleocharis spp. (Eleocharis quinquefolia, Eleocharis palustris)
Similar Systems
Range
Alkaline Fens are very widely scattered in the Great Plains region, extending from the Rocky Mtn Front to the North Dakota Border and primarily north of the Missouri River.
In MT, G1216 occurs within Level III Ecoregions: 42 (Northwestern Glaciated Plains) and likely also in 43 (Northwestern Great Plains).
In Montana, G516 occurs or likely occurs within these Major Land Resource Areas: 46 - Northern and Central Rocky Mountain Foothills, 52 (Brown Glaciated Plains), 53A (Northern Dark Brown Glaciated Plains), 53B (Central Dark Brown Glaciated Plains), 58A (Northern Rolling High Plains, Northern Part).
Density and Distribution
Based on 2025 land cover layer. Grid on map is based on USGS 7.5 minute quadrangle map boundaries.
Mapped Distribution by County
Glacier
Based on 2025 land cover layer.
Spatial Pattern
Small Patch
Environment
This group occurs in the Great Plains where the climate is semi-arid to temperate. Sites occur within a grassland context where groundwater is close to the surface and saturates the soils year-round, resulting in organic soils consisting of peat or muck. Groundwater pH is neutral to alkaline. Sites can be found along at the headwaters of other wetland types such as streams or lakes, or along hillsides where groundwater emerges.
Fens are confined to specific environments defined by groundwater discharge, soil chemistry, and peat accumulation of at least 40 centimeters (15 inches), although peat accumulations in areas overlain by gravel, cobble or bedrock may be less. Soils are typically organic histosols with 40 centimeters or more of organic material if overlying a mineral soil, or less if overlying bedrock, cobbles or gravels. Histosols range in texture from clayey-skeletal to loamy-skeletal and fine-loams. 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 accumulations of organic material. Alkaline (Rich and extremely rich) fens are found in areas underlain by limestone. Water chemistry ranges from only slightly acidic to alkaline and is usually distinctly calcareous. Marl deposits (precipitated calcium carbonates) are common in these habitats. Tufa deposits or terraces can be seen in some rich fens and are composed of virtually pure calcium carbonate at the soil surface, formed by continuous discharge and evaporation of calcite saturated groundwater.
Vegetation
Sites are typically dominated by medium or low-statured, rhizomatous graminoids. Open to dense graminoids less than 1 m tall comprise the majority of the vegetation. Forbs are often less dominant in height and cover. Bryophytes often provide a significant ground cover. Pools of water can provide microsites for aquatic vascular plants and bryophytes. Low to medium- statured shrubs are often scattered but rarely dominant. Dominant vegetation may vary by zones within a single site. Common species include sedges (Carex aquatilis, Carex nebrascensis, Carex pellita, Carex simulata, or Carex utriculata) and spikerushes (Eleocharis quinqueflora and Eleocharis palustris). Other graminoids present often include rushes (Juncus spp.), bulrushes (Schoenoplectus spp.), Triglochin maritima, Glyceria striata and cattails (Typha latifolia). In open pools, Chara spp. and Utricularia spp. may be found. Forb species are highly variable rangewide but often include Lobelia spp., Helianthus spp., Mimulus spp., Scutellaria spp., Symphyotrichum boreale and Viola spp. Equisetum spp. are often present as well. Low to medium shrubs may be present and include willows (Salix exigua, Salix bebbiana and Salix serissima), red-osier dogwood (Cornus sericea), and birch (Betula pumila).
Dynamic Processes
Fens act as natural filters, cleaning ground and surface water. They maintain stream water quality through denitrification and phosphorus absorption. Fens also act as sponges by absorbing heavy precipitation, then slowly releasing it downstream, minimizing erosion and recharging groundwater systems. Persistent groundwater and cold temperatures allow organic matter to accumulate, forming peat.
Management
Land uses surrounding fens can potentially alter the hydrology and nutrient inputs of these habitats, thus changing their underlying processes. Increased land use within 100 meters has been found to be correlated with increased nutrient levels in peatlands in Montana, suggesting that setbacks should be 100 meters or more for adequate protection (Jones 2003). Draining, heavy cattle use, and irrigation practices can also alter hydrology and result in the loss of species diversity.
These fens may be susceptible to invasive plants that occur in nearby wet prairie or wet meadows including Agrostis stolonifera, Phalaris arundinacea, and Sonchus arvensis.
Restoration Considerations
Cattle use in fen habitats can alter the hydrology by damaging soils within the fen. Soil compaction and pugging within the peat layer will change surface water flow. Cattle use can also alter the successional processes within the sedge-dominated area of a fen. Cattle hoof action can lead to pugging and hummocking, creating microsites where shrubs can become established, changing the sedge-dominated meadow to carr shrubland.
Species Associated with this Community
- How Lists Were Created and Suggested Uses and Limitations
Animal Species Associations
Please note that while all vertebrate species have been systematically associated with vegetation communities, only a handful of invertebrate species have been associated with vegetation communities and invertebrates lists for each vegetation community should be regarded as incomplete. Animal species associations with natural vegetation communities that they regularly breed or overwinter in or migrate through were made by:
- Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Werner et al. 2004, Adams 2003, and Foresman 2012);
- Evaluating structural characteristics and distribution of each vegetation community relative to the species' range and habitat requirements;
- Examining the observation records for each species in the state-wide point observation database associated with each vegetation community;
- Calculating the percentage of observations associated with each vegetation community relative to the percent of Montana covered by each vegetation community to get a measure of "observations versus availability of habitat".
Species that breed in Montana were only evaluated for breeding habitat use. Species that only overwinter in Montana were only evaluated for overwintering habitat use. Species that only migrate through Montana were only evaluated for migratory habitat use. In general, species are listed as associated with a vegetation community if it contains structural characteristics known to be used by the species. However, species are not listed as associated with a vegetation community if we found no support in the literature for the species’ use of structural characteristics of the community even if point observations were associated with it. If you have any questions or comments on animal species associations with vegetation communities, please contact the Montana Natural Heritage Program's Senior Zoologist.
Plant Species Associations
Please note that while diagnostic, dominant, or codominant vascular plant species for a vegetation community have been systematically assigned to those communities and vascular plant Species of Concern were systematically evaluated for their associations with vegetation communities, the majority of Montana’s vascular plant species have not been evaluated for their associations with vegetation communities and no attempt has been made to associate non-vascular plants, fungi, or lichens with vegetation communities. Plant species associations with natural vegetation communities were made in a manner similar to that described above for animals, but with review of Lesica et al. (2022) and specimen collection data from the Consortium of Pacific Northwest Herbaria. If you have any questions or comments on plant species associations with vegetation communities, please contact the Montana Natural Heritage Program's Program Botanist.
Suggested Uses and Limitations
Species associations with vegetation communities should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning. These potential lists of species should not be used in place of documented occurrences of species or predicted habitat suitability models (this information can be requested at: https://mtnhp.mt.gov/requests/), or systematic surveys for species and onsite evaluations of habitat by trained biologists. Users of this information should be aware that the land cover data used to generate species associations is based on satellite imagery from 2016 and was only intended to be used at broader landscape scales. Land cover mapping accuracy is particularly problematic when the vegetation communities occur as small patches or where the land cover types have been altered over the past decade. Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections). Finally, although a species may be associated with a particular vegetation community within its known geographic range, portions of that vegetation community may occur outside of the species' known geographic range.
Literature Cited
- Adams, R.A. 2003. Bats of the Rocky Mountain West; natural history, ecology, and conservation. Boulder, CO: University Press of Colorado. 289 p.
- Consortium of Pacific Northwest Herbaria. https://www.pnwherbaria.org/ Last accessed May 30, 2025.
- Dobkin, D. S. 1992. Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34. Missoula, MT.
- Foresman, K.R. 2012. Mammals of Montana. Second edition. Mountain Press Publishing, Missoula, Montana. 429 pp.
- Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998. Montana atlas of terrestrial vertebrates. Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT. 1302 p.
- Hutto, R.L. and J.S. Young. 1999. Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32. 72 p.
- Lesica P., M. Lavin, and P.F. Stickney. 2022. Manual of vascular plants, 2nd Edition. Brit Press. 779 p.
- Maxell, B.A. 2000. Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species. Report to U.S. Forest Service Region 1. Missoula, MT: Wildlife Biology Program, University of Montana. 161 p.
- Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath. 2004. Amphibians and reptiles of Montana. Missoula, MT: Mountain Press Publishing Company. 262 p.
- Species of Concern Associated with this Community
Vascular Plants
Mammals
Birds
Reptiles
Amphibians
Invertebrates
- Diagnostic, Dominant, or Codominant Plant Species for this Community
Vascular Plants
- Other Native Species Commonly Associated with this Community
Vascular Plants
Mammals
Birds
Reptiles
Amphibians
Invertebrates
- Other Native Species Occasionally Associated with this Community
Mammals
Birds
Reptiles
Invertebrates
Original Concept Authors
Vinge-Mazer et al. (2025)
Montana Version Authors
S. Mincemoyer
Version Date
7/5/2025
References
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