Small Forested Mountain Streams
Provisional State Rank:
S5
(see reason below)
External Links
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 National Park Service or US Forest Service.
General Description
This system 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 (2nd to 3rd order, average wetted width less than 7 meters, 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 alpine 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.
Diagnostic Characteristics
The D002 Montane Forested stream type originates in the Rocky Mountain Front Ranges of the upper Missouri River Drainages. The D003 Montane Forested stream type has origins in the isolated mountain ranges of the Missouri River drainages and the D004/D004y Forested stream type begins in the Granitic Mountain Ranges of the upper Missouri Basin and the volcanic yellowstone highlands of the Yellowstone basin. The fish community is the Traditional Trout Stream Assemblage, specifically the Small Trout Stream Assemblage. There are typically westslope cutthroat trout and Rocky Mountain sculpin in reference quality Missouri and upper Columbia drainage streams, while Yellowstone cutthroat trout and sculpin are found in the Yellowstone Mountain Stream Assemblage (D004y). Unfortunately, the introduced brook and rainbow trout have pushed out many native cutthroat trout populations through aggressive competition (brook trout) and hybridization (rainbow trout). Rocky Mountain sculpin usually persist in all of these types, but single species assemblages of westslope and Yellowstone cutthroat trout occur in many streams that have sufficient downstream barriers to prevent the dispersal of the sculpin upstream. Interestingly, these downstream barriers have allowed the persistence of high quality, intact small mountain stream communities by impeding the colonization of introduced species into the pure cutthroat trout areas. The diverse macroinvertebrate community of coldwater stenotherms makes up the Mountain Stream and Medium Mountain Stream Assemblages. The community indicator species are characterized by intolerant, main channel, fast-current mayfly, stonefly and caddisfly species (Baetis bicaudatus, Caudetella spp., Drunella spp., Epeorus spp, Cinygmula, Zapada spp., Megarcys, Doroneuria, Sweltsa, Paraperla, Micrasema, Neothremma, Parapsyche, Neophylax spp., and numerous Rhyacophila spp. groups) and the cold-water dipterans (Rhabdomastix, Bibiocephela, and Glutops). As mountain streams warm in downstream reaches(>15 °C), a dominance shift occurs to the Medium Mountain Stream Assemblage. Populations of western pearlshell mussel have been reported from this stream type and this ecosystem may be their stronghold in the state east of the Continental Divide.
Range
In Montana, the Mountain Stream type is reported from over 100 sites within the Middle Rockies and Isolated Ranges Ecoregions. 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.
Spatial Pattern
Linear
Dynamic Processes
This diverse community of coldwater stenotherms consists of the Mountain Stream and Medium
Mountain Stream Assemblages. The community indicator species are characterized by intolerant, main
channel, fast current mayfly, stonefly and caddisfly species (Baetis bicaudatus, Caudetella spp.,
Drunella spp., Epeorus spp, Cinygmula, Zapada spp. Megarcys, Doroneuria, Sweltsa, Paraperla,
Micrasema, Neothremma, Parapsyche, Neophylax spp., and numerous Rhyacophila spp. Groups) and
the cold-water dipterans (Rhabdomastix, Bibiocephela, and Glutops). As mountain streams proceed downstream and begin to warm (>15 °C), a dominance shift occurs to the Medium Mountain Stream Assemblage. Populations of western pearlshell mussel have been reported from this stream type and this ecosystem may be their stronghold in the state east of the continental divide.
Management
Due to the confined valley nature of these streams, the largest management issue involves keeping the riparian zone intact. Disturbances in the riparian zone (e.g., logging) can have severe water quality impacts from bank erosion, sedimentation, increased stream temperatures, silt deposits and loss of large woody debris. Livestock use around the riparian areas can have strong local effects resulting in sedimentation and stream widening at cattle crossings.
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