Montana Field Guide

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 medium (2nd-3rd order, average wetted width less than 4m, 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.

The typical headwater source stream is steep, shallow and fishless with significant barriers to fish colonization (natural waterfalls or impassable culverts); dominant bioloigical communities are amphibians and macroinvertebrates. However, pioneering members of the Headwater Trout Stream Assemblage, specifically Westslope Cutthroat Trout, may migrate up these small tributaries if barriers are permeable. Unfortunately, the introduced brook trout may also migrate up and aggressively compete with the native cutthroats in this limited habitat. The Macroinvertebrate Community consists of coldwater stenotherms characteristic of the shredder and predator functional groups of the Mountain Stream Assemblage. The community indicator species include intolerant, moderate current mayflies (Baetis bicaudatus, Ameletus, Caudetella spp., and Drunella spinifera), stoneflies (Yoraperla, Zapada colombiana, Despaxia augusta, Leuctridae, and Megarcys), caddisflies (Neothremma alicia, Parapsyche, Cryptochia, Lepidostoma, and Neophylax splendans), cold-water dipterans (Bibiocephela and Glutops), and the non-insect turbellarian Polycelis coronata. The (L) subclass of this ecological system denotes up- or downstream connections to natural lakes which can have very different habitat for the first 100 meters; lake outlets can hold some unique assemblages of aquatic insects (Newell, pers. comm. 2009).

In Montana, this Headwater Source Stream type is reported from over 100 sites within the Northern and Middle Rockies Ecoregions and particularly the Bitterroot Ecological Section. The D009 system includes headwater streams in many of Montana’s western mountain ranges, including the Bitterroots, Beaverheads, Garnets, Anaconda-Pintlers, Pioneers and the Sapphire Mountains. The D010 system includes streams particularly within the Flathead Ecological Section. The D011 AES includes the glaciated Northern Rockies Valley Ecological Section. These ecosystems typically fall within the boundaries of National Forest Service lands and wilderness areas.

Linear

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., timber harvest, roads) can have severe water quality impacts, such as 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.