Middle Rockies Small Perennial Stream - Draft Account
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General Description
This ecosystem is found in the moderate elevation (1200-2000m), upland foothill and valley streams of the Middle Rockies, including the isolated mountain ranges. The smallest sub-type, the Headwaters Foothills River, is a 1st or 2nd order stream tributary to the Small Transitional and Small Foothills River Systems which are small-medium-sized (2nd-4th order, average wetted width=5m), moderately flowing rivers with permanent flow and strong seasonal variability from melting snowpack. These streams represent transitional from high gradient mountain stream communities to the intermontane or prairie rivers in the east. Small Foothills Rivers are tributaries to Intermountain Rivers and maintain average summer temperatures (<20 degrees C) suitable for cool- to coldwater- fish species. In contrast, Small Transitional Foothill Rivers typically enter Prairie Rivers to the eastern part of the state and lose the ability to maintain cool-water fish species at the lower elevations. The surrounding landscape is transitional as well, with coniferous forests giving way to shrubland and sage steppe. Willow- and broadleafed-dominated complexes are common in riparian areas. Beaver pond complexes are often found on these streams. Beavers find suitable conditions and dam building materials as the foothills stream gradient decreases. These ponds provide substantial trout habitat, but can warm beyond the tolerance of cutthroat trout, and the native cutthroats will usually be pushed to the upstream reaches by the more aggressive brook trout. The substrate of these streams is usually boulder/cobble riffles, gravel/sand runs and pools, and silted-in beaver ponds with large woody debris.
Diagnostic Characteristics
The fish community is the Coolwater Transitional Community and the Traditional Trout Stream Assemblage with indicator species of the Headwaters Foothills and Small Foothills Rivers characterized by the native Westslope or Yellowstone Cutthroat trout, mountain whitefish and mottled sculpin. However, the introduced species of the Stocked Trout Assemblage, the brook trout and rainbow trout, tend to dominate and become the focal species of these systems. As Small Foothills and Transitional Foothills Rivers proceed down gradient, inclusions of the longnose sucker, longnose dace and the mountain sucker (Yellowstone drainages) into the community become apparent. Additional fish species (the exotic carp, white sucker, lake chub and fathead minnows of the Core Prairie Stream Assemblage) may be found at the warmer, lower end of the Small Transitional Foothills Rivers in the prairie regions. The shallow riffle areas of the larger foothills rivers entering Intermountain Rivers may provide spawning habitat for downstream populations of brown trout during their fall migration, and suckers, dace and rainbow trout in the spring. The Macroinvertebrate Community/Headwaters and Small Foothills Rivers are dominated by the Traditional Trout Stream Assemblage, with some members of the Medium Coolwater Transitional and Foothills Transitional Assemblages. The community indicator species are characterized by main channel, fast-current mayfly, stonefly and caddisfly species (Pteronarcys californica, Hesperoperla pacifica, Brachycentrus americanus, Rhithrogena, Arctopsyche grandis, and Lepidostoma spp.), and the tipulid, Antocha. As Small Foothills Rivers proceed downstream and begin to warm (>17 °C) or become sediment impaired, degraded or dewatered, they will quickly lose the Traditional Trout Stream Assemblage and shift to the mayfly, caddisfly, beetle and dipteran species that form the Medium Coolwater Transitional Assemblage, with the indicator species Hydropsyche, Optioservus, Baetis tricaudatus, Brachycentrus occidentalis, Helicopsyche borealis, Corynoneura, Constempellina, Prosimulium, Amiocentrus aspilis, Lara, Plauditus, and Narpus. Lower, warmer stretches of Small Transitional Foothills Rivers will begin to pick up species of the Transitional Prairie River Assemblage. Populations of the western pearlshell mussel have been documented in the Foothills Transitional river ecosystem, although these populations may be in decline.
Range
The stream type C002 has been identified in the Custer National Forest (Beartooth District), Pryor Mountains, and foothills of the Belt, Judith and other isolated mountain ranges. The Middle Missouri/ Musselshell drainages contain the most representatives of this community type in the database. The Stream type C004 has been identified in the Helena and Beaverhead-Deerlodge National Forest, the granitic foothills of the Yellowstone Highlands and in other isolated mountain ranges. The upper Missouri/ Musselshell drainages (including the Whitetail, Little Boulder and Bison Rivers)contain the most representatives of this community type in the database.
Density and Distribution
Spatial Pattern
Linear
Dynamic Processes
Beaver played a large ecological role in this system in the past, providing mediating flood control through numerous beaver ponds in the watershed. Large riparian willow complexes are indicative of a proper functioning Small Mountain to Foothill Transitional stream.
Management
Livestock use around the riparian areas of this ecosystem can have strong local effects resulting in sedimentation, which causes a shift of the macroinvertebrate communities from a Traditional Trout Stream Assemblage to the Medium Coolwater Transitional Assemblage, and a shift in fish communities from native cutthroat trout to introduced species, such as brook trout. High-density cattle usage can cause severe degradation, bank erosion, sedimentation and siltation in the riffle habitats and gravel spawning areas downstream. Agricultural water diversions lower in the foothills may be an issue because these streams usually flow onto private lands.
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
Amphibians
References
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