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Montana Field Guide

Montana Field Guides

Rocky Mountain Front Foothill and Valley Rivers

Provisional State Rank: S4
(see reason below)

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State Rank Reason
Although widespread and with many representative river reaches in the state, this ecosystem has been negatively affected by small dams, water diversions, stock ponds and introduced gamefish species. Therefore, it is fairly rare to find biologically intact river miles of this ecological system.

General Description
This ecosystem is found in moderate elevation (1200-2000m), upland foothill areas of the Middle Rockies ecoregion, including isolated mountain ranges. The smallest sub-type, the Headwaters Foothills River, is a 1st or 2nd order stream tributary; those feed small- to medium-sized (2nd-4th order, average wetted width = 5m), moderately flowing rivers with permanent flow and strong seasonal variability that depends on melting snowpack from higher elevations. Rocky Mountain Front Foothill and Valley Rivers are transitional between high gradient mountain stream communities and 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 Foothills 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 shrublands and sage steppe, and riparian woodlands and shrublands. Beaver pond complexes are often characteristic habitats 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, or silted-in beaver ponds with large woody debris. The (e) descriptor on this AES code depicts the system along Rocky Mountain Front streams which have retained a slightly different fish community.

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 Cutthroat trout, mountain whitefish and Rocky Mountain sculpin. The AES C002H system that flows from the Rocky Mountain Front to the Hudson River (Belly River Drainages) has a unique assemblage that includes the bull trout and the spoonhead 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 mountain whitefish into the community become apparent. Additional fish species (the exotic carp, white sucker, flathead chubs and fathead minnows of the Coolwater Transitional Community) 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 for suckers, dace and rainbow trout in the spring. The Macroinvertebrate Community/Headwaters and Small Foothills Rivers is dominated by the Traditional Trout Stream Assemblage, with some members of the Medium Coolwater Transitional and Foothills Transitional Assemblage. 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. This Assemblage is indicated by 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.

This C001E stream type has been identified in the Rocky Mountain Front portion of the Lewis and Clark National Forest, and in the foothills of the Belt, Judith and other isolated mountain ranges. The upper Sun, Teton, Badger-Two Medicine and Dearborn Rivers contain the most representatives of this community type in the database.

Spatial Pattern

Dynamic Processes
Beaver once 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, loss of these riparian features represent non-functional or functional-at-risk ecosystems.

Livestock use around the riparian areas of this ecosystem can have strong local effects resulting in sedimentation, 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 riffle habitats and gravel spawning areas downstream. Lower in the foothills, agricultural water diversions may be an issue where these streams usually flow onto private lands.

  • Classification and Map Identifiers

    1314: Rocky Mountain Front Foothill and Valley Rivers

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Citation for data on this website:
Rocky Mountain Front Foothill and Valley Rivers.  Montana Field Guide.  Retrieved on , from