Headwater Foothills and Valley Stream
Provisional State Rank
(see reason below)
State Rank Reason
The number of viable stream mile occurrences is unknown, but these stream ecosystems are abundant across the mountain ranges of Western North America, often in protected lands managed by the BLM or US Forest Service.
This ecosystem is found in the mountainous, moderate-to-high elevation (1600-2500m), forested, moderately confined-channel streams of the Middle Rockies Ecoregion, including the isolated mountain ranges. These small-to-medium (1st-2nd order, average wetted width =3m, average summer temperature <15°C) moderately flowing streams have permanent flow with strong seasonal variability due to melting snowpack from higher elevation mountainous areas. These streams represent the transition from forested stream communities to 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 step-pool configuration with a substrate dominated by boulders, 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 (y) descriptor on this AES code depicts the stream is in the Yellowstone River Basin and the (e) descriptor indicates the system along Rocky Mountain Front streams which have retained a slightly different fish community.
The fish community is 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 (AES D001y), mountain whitefish and Rocky Mountain 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. Steep fishless areas provide habitat for the Rocky Mountain Tailed Frog. As s these streams proceed down gradient, inclusions of the longnose sucker, longnose dace and the mountain sucker (D001y Yellowstone drainages) into the community become apparent. 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 reference condition Macroinvertebrate Community Indicators include the Traditional Trout Stream assemblage, with some members of the Medium Cool-Water Transitional Assemblage and the Foothills Transitional Assemblage. The community indicator species are characterized by main channel, fast-current mayfly, stonefly and caddis species, Pteronarcys californica, Hesperoperla pacifica, Brachycentrus americanus, Rhithrogena, Arctopsyche grandis, Lepidostoma spp., and the tipulid, Antocha. As the foothills streams near the valleys and begin to warm (>17 C) or become sediment impaired, degraded or dewatered, they will quickly lose the Traditional Trout Stream community (#4) and shift to the mayfly, caddisfly, beetle and dipteran species that form communities Medium Cool-Water Transitional Assemblage (#1) and #105 with indicator species Hydropsyche, Optioservus, Baetis tricaudatus, Brachycentrus occidentalis, Helicopsyche borealis, Corynoneura, Constempellina, Prosimulium, Amiocentrus aspilis, Lara, Phaenopsectra, Plauditus, and Narpus. Populations of the western pearlshell mussel have been reported from this river ecosystem, although the populations may be in decline.
In Montana, the Headwater Foothills and Valley Stream type is reported from over 150 sites within the Middle Rockies, including the isolated ranges. These include streams in many of Montana’s mountain ranges, including the Beartooths, Absorokas, Elkhorns, Big Belts, Little Belts, Crazys, Gallatin-Madison-Bridgers, Anaconda-Pintlers, Pioneers and the Big Snowy Mountains. These ecosystems typically fall within the boundaries of National Forest Service lands and wilderness areas.
Beaver played a large role in the ecological processes of this ecological system in the past, providing mediating flood control with numerous beaver ponds in the watershed. Large riparian willow complexes are indicative of proper functioning condition.
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 cause 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.