Northern Rockies Small Perennial Stream - Draft Account
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General Description
This ecosystem is found in the moderate elevation (1200-2000m), upland foothill streams of the Northern Rockies, Canadian Rockies or Middle Rockies Ecoregions. These moderately confined-channel streams are usually small- to medium-sized (2nd-3rd order, average wetted width=5m), with average summer temperature <15°C). Moderately flowing streams have permanent flow with strong seasonal variability due to melting snowpack from higher elevation mountainous areas. They are often within BLM or National Forest Service boundaries. These streams represent the transitional areas from the headwater or forested stream communities to lower foothills and intermontane rivers, and provide substantial habitat for Montana’s native cutthroat trout populations, which thrive in the cold water temperatures and complex in-stream habitats. The geomorphology of these streams is usually a riffle/run/pool configuration with substrate dominated by boulders and cobbles, and gravel in the short pools. Large woody debris from the surrounding hillslopes can provide significant channel material and additional substrate to these streams. The (L) descriptor on this AES code depicts proximity to a lake outlet or large beaver complex which can have significant effect on the biological community.
Diagnostic Characteristics
The fish community is the Coldwater Transitional Community and the Traditional Trout Stream Assemblage with indicator species of the Intermountian Foothill Stream and Rivers characterized by the native species, Westslope Cutthroat trout, mountain whitefish and Rocky Mountain sculpin, with corridor use by the Bull Trout. 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 Intermountain Foothills Streams and Rivers proceed down gradient, inclusions of the bull trout, longnose sucker, and large scale sucker into the community become apparent if stream quality and connectiveness remain intact. Intermountain Streams and Rivers provide spawning habitat for downstream populations of bull trout during their summer/fall migration and cutthroat trout and suckers in the spring. Macroinvertebrate Community of the Intermountain foothills rivers are dominated by the Traditional Trout Stream Assemblage, with some members of the Medium Mountain Stream Assemblages. The community indicator species are characterized by main channel, fast current mayfly, stonefly and caddisfly species (Caudatella, Epeorus, Drunella spp., Rhithrogena, Pteronarcys californica, Classenia sabulosa, Hesperoperla pacifica, Perlodids, Brachycentrus americanus, Arctopsyche grandis, and Lepidostoma spp.), and the tipulid, Antocha. As Foothills Rivers proceed downstream and begin to warm (>17 °C) or are sediment impaired, degraded or dewatered, they will quickly lose the Traditional Trout Stream Assemblage and shift to the mayfly, stonefly and caddisfly species that form the Medium Montain Assemblage, with its indicator species Hydropsyche, Optioservus, Baetis tricaudatus, Brachycentrus occidentalis, Helicopsyche borealis, Corynoneura, Constempellina, Prosimulium, Amiocentrus aspilis, Lara, Plauditus, and Narpus. Populations of the western pearlshell mussel have been documented in the Intermountain Foothills Transitional river ecosystem, although these populations may be in decline when they lose their cutthroat trout host fish.
Range
This AES within the westside river drainages of the state contains 2718.4 miles of stream. C007 classified streams encompass low to moderate gradient intermountain streams from the Glaciated Columbia Region of the Northern Rockies to the Idaho Batholith in the Bitterroot Basin. Representative streams include the Little Blackfoot River, West Fork Rock Creek, Ninemile Creek, the upper Swan River and Thompson Rivers. C009 AES is the Intermontane Moderate Gradient Stream across the Bitterroot Valley Ecological Section. C010 AES is the Intermontane Moderate Gradient Stream across the Flathead Valley Ecological Section. C011 is the Intermontane Moderate Gradient Streams across the glaciated Northern Rockies Valley Ecological Section.
Density and Distribution
Spatial Pattern
Linear
Dynamic Processes
Beaver played a large role in the ecological processes of this ecological system in the past and provided mediating flood control with their numerous beaver ponds in the watershed. Large riparian willow complexes were indicative of a proper functioning small mountain to foothill transitional stream.
Management
Small dams, water diversions, stock ponds and introduced gamefish species have had the most significant negative impact on this community (Winston et al. 1991). Other threats include heavy cattle intrusions to the riparian areas, which causes bank erosion and subsequent sedimentation and siltation. Anywhere dams occur, even small stock pond earthen dams, the downstream reaches are affected by altered water temperatures, unnatural water level fluctuations, and changes in sediment and nutrient transport.
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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