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Montana Field Guides

Rocky Mountain Lower Montane-Foothill Riparian Woodland and Shrubland

Provisional State Rank: S4
* (see reason below)

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State Rank Reason
This system has an extensive distribution across Montana, although many occurrences have been impacted by hydrologic modification and adjacent land use, especially in valleys.

General Description

This ecological system is found throughout the Rocky Mountain and Colorado Plateau regions. In Montana, it ranges from approximately 945 to 2,042 meters (3,100 to 6,700 feet), characteristically occurring as a mosaic of multiple communities that are tree-dominated with a diverse shrub component. It is dependent on a natural hydrologic regime, especially annual to episodic flooding. Occurrences are found within the flood zone of rivers, on islands, sand or cobble bars, and on immediate streambanks. It can form large, wide occurrences on mid-channel islands in larger rivers or narrow bands on small, rocky canyon tributaries and well-drained benches. It is also typically found in backwater channels and other perennially wet but less scoured sites, such as floodplains swales and irrigation ditches. In some locations, occurrences extend into moderately high intermountain basins where the adjacent vegetation is sage steppe. Dominant trees may include boxelder maple (Acer negundo), narrowleaf cottonwood (Populus angustifolia), Plains cottonwood (Populus deltoides), Douglas-fir (Pseudotsuga menziesii), peachleaf willow (Salix amygdaloides), or Rocky Mountain juniper (Juniperus scopulorum). Dominant shrubs include Rocky Mountain maple (Acer glabrum), thinleaf alder (Alnus incana), river birch (Betula occidentalis), redoiser dogwood (Cornus sericea), hawthorn (Crataegus spp.), chokecherry (Prunus virginiana), skunkbush sumac (Rhus trilobata), Drummond’s willow (Salix drummondiana), sandbar willow (Salix exigua), Pacific willow (Salix lucida), rose (Rosa species), silver buffaloberry (Shepherdia argentea), or snowberry (Symphoricarpos species). Exotic trees of Russian olive (Elaeagnus angustifolia) and saltcedar (Tamarix species) may invade some stands in southeastern and south-central Montana.

Diagnostic Characteristics
montane, riverine/alluvial, mineral with A horizon less than 10 cm, unconsolidated, short flooding interval (less than 5 years), short persistence ( 50 to 100 years)

Similar Systems

This system is found throughout the mid to low elevations of central and eastern Montana

Ecological System Distribution
Approximately 1,460 square kilometers are classified as Rocky Mountain Lower Montane-Foothill Riparian Woodland and Shrubland in the 2016 Montana Land Cover layers.  Grid on map is based on USGS 7.5 minute quadrangle map boundaries.

Montana Counties of Occurrence

Spatial Pattern

This system is dependent on a natural hydrologic regime, especially annual to episodic flooding. Occurrences are found within the flood zone of major rivers and the associated islands, sand or cobble bars, and along adjacent streambanks. It can occur as a large, wide patch on mid-channel islands in larger rivers or as narrow bands along small, rocky canyon tributaries and on well-drained benches. It is also typically found in backwater channels and other perennially wet but less scoured sites, such as floodplains swales and irrigation ditches. Elevations generally range from 945 to 2,042 meters (3,100 to 6,700 feet) (Hansen et al., 1995). Soils are usually Entisols or, less commonly, Inceptisols with an organic A horizon of less than ten centimeters. Coarse textured substrates allow for rapid movement of highly aerated water. The water table can drop during late summer, but soils remain moist due to capillary action.


Because of the frequent disturbance regime, this system usually occurs as a mosaic of shrub and tree dominant communities. Dominant trees may include boxelder maple, narrowleaf cottonwood, Plains cottonwood, Douglas-fir, peachleaf willow, or Rocky Mountain juniper. In central and eastern Montana, narrowleaf cottonwood frequently dominates the overstory. Dominant shrubs include Rocky Mountain maple, thinleaf alder, river birch, redoiser dogwood, hawthorn, chokecherry, skunkbush, Drummond’s willow, sandbar willow, Pacific willow, silver buffaloberry, rose or snowberry. Russian olive and saltcedar may invade some stands in southeastern and south-central Montana.

The herbaceous understory usually includes colonizing native forbs such as yarrow (Achillea millefolium), Canada goldenrod (Solidago canadensis), American licorice (Glycyrrhiza lepidota), Canada horseweed (Conyza canadensis) and exotics such as Canada thistle (Cirsium arvense) and common dandelion (Taraxacum officinale). Exotic grasses such as redtop (Agrostis stolonifera), Canada bluegrass (Poa compressa), Kentucky bluegrass (Poa pratensis), common timothy (Phleum pratense) and reed canarygrass (Phalaris arundinacea) can dominate the graminoid layer if this system adjoins cultivated areas or disturbed upland communities. Generally, some stands may have a small component of native graminoid species like slimstem reedgrass (Calamagrostis stricta) or wheatgrasses (Elymus species) (Hansen et al., 1995). Wet meadow pataches adjoining or asscociated with this system often contain woolly sedge (Carex pellita), clustered field sedge (Carex praegracilis), Baltic rush (Juncus balticus), and bluejoint reedgrass (Calamagrostis canadensis).

Alliances and Associations
  • (A.3564) (Canada Thistle, Leafy Spurge, Sweetclover species) - Mixed Forbs Herbaceous Alliance
  • (A.1422) (Common Spikerush, Page Spikerush) Seasonally Flooded Herbaceous Alliance
  • (A.947) (Coyote Willow, Sandbar Willow) Temporarily Flooded Shrubland Alliance
  • (A.3539) (Field Horsetail, Variegated Scouring-rush, Common Scouring-rush) Semipermanently Flooded Herbaceous Alliance
  • (A.1407) Alkali Cordgrass Seasonally Flooded Herbaceous Alliance
  • (A.1374) Baltic Rush Seasonally Flooded Herbaceous Alliance
  • (A.341) Box-elder Seasonally Flooded Forest Alliance
  • (A.278) Box-elder Temporarily Flooded Forest Alliance
  • (A.2657) Canadian Horseweed Seasonally Flooded Herbaceous Alliance
  • (A.1419) Clustered Field Sedge Seasonally Flooded Herbaceous Alliance
  • (A.1431) Common Reed Semipermanently Flooded Herbaceous Alliance
  • (A.1405) Creeping Bentgrass Seasonally Flooded Herbaceous Alliance
  • (A.568) Douglas-fir Temporarily Flooded Woodland Alliance
  • (A.636) Eastern Cottonwood Temporarily Flooded Woodland Alliance
  • (A.1329) Great Basin Wildrye Intermittently Flooded Herbaceous Alliance
  • (A.1332) Inland Saltgrass Intermittently Flooded Herbaceous Alliance
  • (A.1382) Kentucky Bluegrass Semi-natural Seasonally Flooded Herbaceous Alliance
  • (A.310) Narrowleaf Cottonwood Temporarily Flooded Forest Alliance
  • (A.641) Narrowleaf Cottonwood Temporarily Flooded Woodland Alliance
  • (A.645) Peachleaf Willow Temporarily Flooded Woodland Alliance
  • (A.565) Ponderosa Pine Temporarily Flooded Woodland Alliance
  • (A.1347) Prairie Cordgrass Temporarily Flooded Herbaceous Alliance
  • (A.2658) Quackgrass Herbaceous Alliance
  • (A.1381) Reed Canarygrass Seasonally Flooded Herbaceous Alliance
  • (A.563) Rocky Mountain Juniper Temporarily Flooded Woodland Alliance
  • (A.506) Rocky Mountain Juniper Woodland Alliance
  • (A.3566) Russian-olive Semi-natural Woodland Alliance
  • (A.842) Salt-cedar species Semi-natural Temporarily Flooded Shrubland Alliance
  • (A.960) Silver Buffaloberry Temporarily Flooded Shrubland Alliance
  • (A.938) Skunkbush Sumac Intermittently Flooded Shrubland Alliance
  • (A.2648) Smooth Horsetail Semipermanently Flooded Herbaceous Alliance
  • (A.936) Water Birch Intermittently Flooded Shrubland Alliance
  • (A.967) Water Birch Temporarily Flooded Shrubland Alliance
  • (A.1414) Woolly Sedge Seasonally Flooded Herbaceous Alliance
  • (A.980) Yellow Willow Temporarily Flooded Shrubland Alliance

Dynamic Processes
Flooding is crucial to the development of establishment sites for cottonwood, and acts as primary control on plant succession. Steep gradients and high-energy flows driven by precipitation cause flooding events that transport coarse sediments. The scouring out and downstream accumulation of sediments constantly creates and destroys sites for the establishment of vegetation. Sediment accumulating in these systems often creates gravel bars at or near the surface of the river, creating bands of mixed vegetation occupying different stages of succession. Increasing vegetation traps even more sediment, so that over time the size and height of the gravel bar increases. Cottonwood and the associated shrub understory are adapted to these flooding events.

Alteration of hydrology by dams and diversions are major influences on the structure, composition, and function of this community. In Montana, dams have eliminated the ability of cottonwood to regenerate by seeds in many places. As the cottonwood stand dies, successional processes will tend toward other communities unless flooding deposits new sediments that support seedling regeneration. Heavy grazing by cattle, or in some cases by elk and deer, along these streams and rivers can result in increased erosion and eliminate the vegetative regeneration of cottonwood sprouts. In sites where there is prolonged disturbance, shrub cover will decrease, resulting in a more open canopy.

Restoration Considerations
Maintaining an undisturbed buffer strip of cottonwood species adjacent to rivers and streams can stabilize riverbanks and will serve as a source for seedling and branch colonization if the hydrology of the river system is restored. Cottonwood requires full sunlight and a moist seed bed for colonization. If the site still has a fairly high water table and a remnant shrub population, the shrubs are capable of resprouting and will stabilize embankments and reduce sedimentation. If the site is highly impacted, seedlings or live cuttings can be used for more intensive restoration practices.

Species Associated with this Ecological System
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (high, medium, or low) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2001, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species’ range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of “observations versus availability of habitat”.
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were associated as using an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  High, medium, and low habitat quality was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species in the literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignments of habitat quality.  If you have any questions or comments on species associations with ecological systems, please contact Bryce Maxell at or (406) 444-3655.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species’ known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2001.  The wild mammals of Montana.  Special Publication No. 12.  Lawrence, KS: The American Society of Mammalogists.  278 p.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana’s amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Original Concept Authors
Natureserve Western Ecology Group

Montana Version Authors
L.K. Vance, C. McIntyre, T. Luna

Version Date

  • Classification and Map Identifiers

    Cowardin Wetland Classification:
    System Palustrine, Riverine or Riparian (non-wetland)
    Class Forested, Scrub-Shrub, Emergent, Unconsolidated Shore
    Water Regime Temporarily flooded, seasonally flooded, semipermanently flooded
    Geographically Isolated Wetland No

    National Vegetation Classification Standard:
    Class Forest and Woodland
    Subclass Temperate Forest
    Formation Temperate Flooded and Swamp Forest
    Division Western North America Flooded and Swamp Forest
    Macrogroup Rocky Mountain and Great Basin Flooded and Swamp Forest

    NatureServe Identifiers:
    Element Global ID
    System Code CES306.821, Rocky Mountain Lower Montane-Foothill Riparian Woodland and Shrubland

    9156: Rocky Mountain Lower Montane-Foothill Riparian Woodland and Shrubland

  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Hansen, P. L., R. D. Pfister, K. Boggs, B. J. Cook, J. Joy, and D. K. Hinckley. 1995. Classification and management of Montana's riparian and wetland sites. Montana Forest and Conservation Experiment Station, School of Forestry, University of Montana, Miscellaneous Publication No. 54. 646 pp. + posters.

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Citation for data on this website:
Rocky Mountain Lower Montane-Foothill Riparian Woodland and Shrubland.  Montana Field Guide.  Retrieved on October 22, 2016, from