Conifer and aspen trees characterize these seasonally flooded mountain riparian woodlands which are confined to sites with specific hydrology and riparian environments at montane to subalpine elevations of the Rocky Mountain cordillera, from southern New Mexico north into Montana, and west into the Intermountain region and the Colorado Plateau. In Colorado, stands are generally found at elevations between 2,280 and 3,660 m (7,500-12,000 ft) bordering mountain streams. Subalpine-Montane Riparian woodlands occur on floodplains or terraces of rivers and streams, in V-shaped, narrow valleys and canyons (where there is cold-air drainage). Less frequently, occurrences are found in moderate-wide valley bottoms on large floodplains along broad, meandering rivers, and on pond or lake margins. These riparian plant communities are dependent on high water tables or overbank flooding to meet their moisture requirements and are also dependent on flooding for the deposition of substrates and nutrients necessary for regeneration, establishment and maintenance of component plant communities. Dominant tree species vary by elevation, and to a lesser extent with latitude. At the highest elevations, Colorado occurrences of these forests are dominated by a mixed subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmannii) tree canopy with a sparse shrub layer and a dense forb cover lining stream banks. With decreasing elevation, quaking aspen (Populus tremuloides) may begin to characterize the tree canopy, replacing subalpine fir and Engelmann spruce, and the streamside forb layer may be replaced by Drummond willow (Salix drummondiana) and/or thinleaf alder (Alnus incana). In the lower elevations of this system, montane zone riparian woodlands are characterized by Colorado blue spruce (Picea pungens) or, in the southern part of the state, white fir (Abies concolor) with understory vegetation dominated by a shrubs such as thinleaf alder and river birch (Betula occidentalis) that is confined to streambanks.

Coniferous and deciduous tree species characterize the canopy in these high elevation riparian woodlands. Common tree species include subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmannii), blue spruce (Picea pungens), Douglas fir (Pseudotsuga menziesii), and quaking aspen (Populus tremuloides). This system occurs as a narrow band of forest lining streams at montane to subalpine elevations.

These riparian woodlands are found at montane to subalpine elevations of the Rocky Mountain cordillera, from southern New Mexico north into Montana, and west into the Intermountain region and the Colorado Plateau. It occurs throughout the interior of British Columbia and the eastern slopes of the Cascade Mountains. In Colorado, occurrences are found throughout the central mountainous portion of the state.

Rocky Mountain Subalpine-Montane Riparian Woodlands are linear systems.

Rocky Mountain Subalpine-Montane Riparian Forests and Woodlands are found throughout the Southern Rocky Mountain ecoregion at elevations between approximately 2,280 and 3,660 m (7,500-12,000 ft). These forests and woodlands are common in the floodplains and terraces of confined V-shaped, narrow valleys and canyons. Less frequently, they are found in moderate-wide valley bottoms on large floodplains along broad, meandering rivers, adjacent to willow carrs, and on pond or lake margins. Soils are generally poorly developed with texture that varies from fine silts on level floodplains to coarse gravels and cobbles interspersed with boulders in steeper canyon bottoms.

Occurrences often contain a mosaic of communities that differ in structure and species composition. Communities in this system may be dominated by white fir (Abies concolor), subalpine fir (A. lasiocarpa), Engelmann spruce (Picea engelmannii), blue spruce (P. pungens), or quaking aspen (Populus tremuloides). Community composition is determined by a combination of characteristics including elevation, floodplain width and steepness, streamflow volume and flooding patterns, and adjacent upland vegetation. At the highest elevations, these forests are characterized by a mixed subalpine fir - Engelmann spruce canopy and are often heavily shaded, lacking shrubs, and have a thick cover of mesic forbs lining the stream edge. With decreasing elevation, quaking aspen (Populus tremuloides) may begin to replace subalpine fir and Engelmann spruce, and the streamside forb layer may be replaced by dense thickets of Drummond willow (Salix drummondiana) and/or thinleaf alder (Alnus incana). In the lower elevations of this system, montane zone riparian woodlands are characterized by Colorado blue spruce (Picea pungens) or, in the southern part of the state, by white fir (Abies concolor) with understory vegetation dominated by a shrub such as thinleaf alder and river birch (Betula occidentalis). Douglas fir (Pseudotsuga menziesii), lodgepole pine (Pinus contorta), aspen, narrowleaf cottonwood (Populus angustifolia), box elder (Acer negundo), and Rocky Mountain juniper (Juniperus scopulorum) may also be present.
Shrub layer cover ranges from sparse to moderate (0-70%) and may include both tall and short shrub species. Associated understory shrub species include Rocky Mountain maple (Acer glabrum), red-osier dogwood (Cornus sericea), currant (Ribes spp.), Geyer willow (Salix geyeriana), mountain willow (Salix monticola), twinberry honeysuckle (Lonicera involucrata), whortleberry, (Vaccinium spp.), and occasionally other willows (Salix ssp.) present in adjacent carrs. Herbaceous cover varies from sparse to dense depending on shading from the tree and canopy cover. Characteristic forb species include Richardson's geranium (Geranium richardsonii), Fendler's cowbane (Oxypolis fendleri), tall fringed bluebells (Mertensia ciliata), common cow parsnip (Heracleum maximum), heartleaf bittercress (Cardamine cordifolia), field horsetail (Equisetum arvense), arrowleaf ragwort (Senecio triangularis), Rocky Mountain hemlock parsley (Conioselinum scopulorum), starry false lily of the valley (Maianthemum stellatum), cutleaf coneflower (Rudbeckia laciniata), Virginia strawberry (Fragaria virginiana), Columbian monkshood (Aconitum columbianum) bluntseed sweetroot (Osmorhiza depauperata), Fendler's meadow-rue (Thalictrum fendleri), common yarrow (Achillea millefolium), largeleaf avens (Geum macrophyllum), brook saxifrage (Saxifraga odontoloma), heartleaf arnica (Arnica cordifolia), and red baneberry (Actaea rubra ssp. arguta). The graminoid layer may be sparse to dense and include bluejoint reedgrass (Calamagrostis canadensis), smallflowered woodrush (Luzula parviflora), sedges (Carex spp.), and rushes (Juncus spp.).

Mammal species reported from these higher elevation riparian woodlands include montane and water shrew (Sorex monticolus and S. palustris), snowshoe hare (Lepus americanus), western jumping mouse (Zapus princeps), meadow and montane vole (Microtus pennsylvanicus and M. montanus), lynx (Lynx canadensis), and beaver (Castor canadensis). Bird species commonly found in these areas are Broad-tailed Hummingbird (Selasphorus platycercus), Dusky Flycatcher (Empidonax oberholseri), Yellow Warbler (Setophaga petechia), MacGillivray's Warbler (Geothlypis tolmiei), Wilson's Warbler (Cardellina pusilla), Lincoln's Sparrow (Melospiza lincolnii), Song Sparrow (Melospiza melodia), Fox Sparrow (Passerella iliaca), Cordilleran Flycatcher (Empidonax occidentalis), Red-naped Sapsucker (Sphyrapicus nuchalis), Hermit Thrush (Catharus guttatus), Ruby-Crowned Kinglet (Regulus calendula), Mountain Chickadee (Poecile gambeli), Warbling Vireo (Vireo gilvus), Western Wood-Peewee (Contopus sordidulus), and American Dipper (Cinclus mexicanus). Boreal toad (Anaxyrus boreas boreas) wood frog (Lithobates sylvatica), and western terrestrial garter snake (Thamnophis elegans) may also occur.

Hydrologic processes, particularly flooding events, are key drivers of geomorphic, biogeochemical, and biological processes in riparian systems. Snowmelt at high elevations contributes a large proportion of water to most wetland types through its influence on groundwater and surface water dynamics. Snowmelt saturates soils, recharges shallow groundwater and produces surface flow and stream flooding, which, in this system, historically has occurred in May and June with volume and duration affected by snowpack levels. Surface flows and flooding are important processes in the formation and maintenance of riparian habitat.
Flood disturbance is the primary driver of this system. Flooding inundates vegetation and supplies water to adjacent floodplain wetlands which store runoff water and can recharge groundwater, and flooding alters channel morphology through lateral erosion and deposition of sediment. Additionally, groundwater recharge from snowmelt creates shallow water tables or seeps that support vegetation for a portion of the growing season. The disturbance processes of overbank flow and erosion and deposition are essential in forming the floodplain and providing habitat for the development of riparian vegetation. Coarse sediments accumulate as gravel bars at or near the surface of the river. These are quickly colonized, eventually creating bands of mixed vegetation representing different stages of succession.
Beaver were historically an important factor in these woodlands, except in reaches with very steep gradients. Beaver are a keystone species whose pond-building activities change adjacent forest structure, elevate local water tables, decrease net flow velocity, and reduce stream erosion and provide valuable habitat for wetland dependent plants and animals. Beaver ponds and associated elevated water tables eliminate most trees in the floodplain as long as ponds are maintained. As beaver colonies fail or move, trees gradually reestablish.

An unaltered hydrologic regime is crucial to maintaining the diversity and viability of the riparian area. Reservoirs, water diversions, ditches, roads, and human land uses in the contributing watershed can have a substantial impact on the hydrology as well as biotic integrity of riparian woodlands. All of these stressors can induce downstream erosion and channelization, reduce changes in channel morphology, reduce base and/or peak flows, lower water tables in floodplains, and reduce sediment deposition in the floodplain. Vegetation responds to these changes by shifting from wetland and riparian dependent species to more mesic and xeric species typical of adjacent uplands (typical of herbaceous species) and/or encroaching into the stream channel.
Human land uses both within the riparian area as well as in adjacent and upland areas can fragment the landscape and thereby reduce connectivity between riparian patches and between riparian and upland areas. Roads, bridges, and development can contribute to fragmentation thereby adversely affecting the movement of surface/groundwater, nutrients, and dispersal of plants and animals. Land use in adjacent uplands, such as forest harvest and grazing, can affect ecosystem processes such as precipitation infiltration and runoff, nutrient cycling and soil erosion. Overgrazing in western riparian systems has left a legacy of riparian ecosystem-level damage that has fundamentally altered ecosystem integrity and function.
Climate factors including the amount, form, and seasonality of precipitation, temperature and wind, and the timing of snow-melt influence stream flow regimes, including flow variability and characteristics such as base, mean, and peak flow volumes, and fluvial geomorphic processes such as sediment erosion and deposition. Global climate change is altering the timing and character of processes that maintain riparian systems. Human-induced warming is resulting in the loss of snowpack which is projected to worsen and trends indicate fundamental impacts on streamflow and water supplies across the western United States.