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Montana Field Guides

Great Plains Riparian

Provisional State Rank: S3

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General Description

This system is associated with perennial to intermittent or ephemeral streams throughout the northwestern Great Plains. In Montana, it occurs along smaller tributaries of the Yellowstone and Missouri rivers, as well as tributaries to the large floodplain rivers that feed them (e.g. the Milk, Marias, Musselshell, Powder, Clark’s Fork Yellowstone, Tongue, etc). In areas adjacent to the mountain ranges of central and southeastern Montana, and near the Rocky Mountain Front, it grades into Rocky Mountain Lower Montane-Foothill Riparian Woodland and Shrubland systems. This system is found on alluvial soils in highly variable landscape settings, from confined, deep cut ravines to wide, braided streambeds. Channel migration occurs in less-confined areas, but within a more narrow range than would occur in broad, alluvial floodplains. Typically, the rivers are wadeable by mid-summer.

The primary inputs of water to these systems include groundwater discharge, overland flow, and subsurface interflow from the adjacent upland. Flooding is the key ecosystem process, creating suitable sites for seed dispersal and seedling establishment, and controlling vegetation succession. Communities within this system range from riparian forests and shrublands to tallgrass wet meadows and gravel/sand flats. Dominant species are similar to those found in the Great Plains Floodplain System. In the western part of the system’s range in Montana, the dominant overstory species is black cottonwood (Populus balsamifera ssp. trichocarpa) with narrowleaf cottonwood (Populus angustifolia) and Plains cottonwood (Populus deltoides) occurring as co-dominants in the riparian/floodplain interface near the mountains. Further east, narrowleaf cottonwood and Plains cottonwood become dominant. In wetter systems, the understory is typically willow (Salix spp.) and redosier dogwood (Cornus stolonifera) with graminoids such as western wheatgrass (Pascopyrum smithii) and forbs like American licorice (Glycyrrhiza lepidota). In areas where the channel is incised, the understory may be dominated by big sagebrush (Artemisia tridentata) or silver sagebrush (Artemisia cana). Like floodplain systems, riparian systems are often subjected to overgrazing and/or agriculture and can be heavily degraded, with salt cedar (Tamarix ramosissima) and Russian olive (Eleagnus angustifolia) replacing native woody vegetation and regrowth. Groundwater depletion and lack of fire have resulted in additional species changes.

Diagnostic Characteristics
Forest and Woodland

Similar Systems

This system extends north into Alberta, Saskatchewan and Manitoba, east into the Dakotas and Nebraska, and south into Wyoming. In Montana, it occurs in the Yellowstone and Missouri River drainage basins along small rivers and perennial, intermittent and ephemeral streams. In areas adjacent to the mountain ranges of central and southeastern Montana, and near the Rocky Mountain Front, it grades into Rocky Mountain Lower Montane-Foothill Riparian Woodland and Shrubland systems.

Ecological System Distribution
Approximately 5,938 square kilometers are classified as Great Plains Riparian in the 2017 Montana Land Cover layers.  Grid on map is based on USGS 7.5 minute quadrangle map boundaries.

Montana Counties of Occurrence
Big Horn, Blaine, Carbon, Carter, Cascade, Chouteau, Custer, Daniels, Dawson, Fallon, Fergus, Gallatin, Garfield, Glacier, Golden Valley, Hill, Judith Basin, Lewis and Clark, Liberty, Mccone, Musselshell, Park, Petroleum, Phillips, Pondera, Powder River, Prairie, Richland, Roosevelt, Rosebud, Sheridan, Stillwater, Sweet Grass, Teton, Toole, Treasure, Valley, Wheatland, Wibaux, Yellowstone

Spatial Pattern


The primary inputs of water to these systems include groundwater discharge, overland flow, and subsurface interflow from the adjacent upland. Flooding is the key ecosystem process. It creates suitable sites for seed dispersal and seedling establishment, and controls vegetation succession. This system is associated with small rivers and perennial to intermittent or ephemeral streams that flow only during part of the year. In the Great Plains, the water source is primarily local precipitation and groundwater inflow (Decker, 2007); in systems receiving flow from central and southeastern mountain ranges, snowmelt and summer thunderstorms provide a significant portion of flows. The boundaries of these riparian areas extend beyond the limits of flooding into streamside vegetation (Gregory, 1991). They are important links between terrestrial and aquatic ecosystems, acting as ecotones between upland and wetland, and connecting ecological processes and plant communities.


Like the Western Great Plains Riparian system of Wyoming, Colorado and New Mexico, Montana’s Great Plains Riparian systems may include riparian forests or woodlands, as well as shrublands, tallgrass or mixedgrass wet meadows, herbaceous wetlands, and gravel/sand flats (Decker, 2007). Vegetation may be a mosaic of communities that are not always tree- or shrub-dominated. At lower elevations (e.g. along the Little Powder River and Mizpah Creek in southeastern Montana), forested communities may form galleries dominated by Plains cottonwood. Narrowleaf cottonwood occurs at intermediate elevations and black cottonwood tends to be prevalent at higher elevations (Hansen et al., 1996). Willows commonly associated with this system include sandbar willow (Salix exigua), yellow willow (Salix lutea), peachleaf willow (Salix amygdaloides), and diamondleaf willow (Salix planifolia). Other shrubs include redosier dogwood, western snowberry (Symphoricarpos occidentalis), chokecherry (Prunus virginiana), and woods rose (Rosa woodsii). In areas where the channel is incised, the understory may be dominated by big sagebrush or silver sagebrush. The herbaceous stratum is variable. Subirrigated areas may support tallgrass meadows dominated by big bluestem (Andropogon gerardii) or fresh water cordgrass (Spartina pectinata). Other graminoids include wooly sedge (Carex pellita), little bluestem (Schizachyrium scoparium), western wheatgrass, porcupine needlegrass (Hesperostipa spartea), northern dropseed (Sporobolus heterolepis), and panic grass (Panicum virgatum). American licorice and Canada goldenrod (Solidago canadensis) are common understory forbs within all cottonwood riparian systems. These sites are prone to invasion by exotic grasses and forbs, the most widely established being creeping bentgrass (Agrostis stolonifera), cheatgrass (Bromus tectorum), quackgrass (Agropyron repens), Canada thistle (Cirsium arvense), clovers (Melilotus species), leafy spurge (Euphorbia esula) and common dandelion (Taraxacum officinale).

National Vegetation Classification Switch to Full NVC View

Adapted from US National Vegetation Classification

A0636 Populus deltoides Floodplain Woodland Alliance
CEGL000660 Populus deltoides - Symphoricarpos occidentalis Floodplain Woodland
A3423 Populus deltoides Floodplain Forest Alliance
CEGL000657 Populus deltoides - Cornus sericea Floodplain Forest
CEGL000658 Populus deltoides - Fraxinus pennsylvanica Floodplain Forest
A3492 Panicum virgatum - Pascopyrum smithii Wet Meadow Alliance
A3586 Artemisia cana ssp. Cana Wet Shrubland Alliance
CEGL001072 Artemisia cana - Pascopyrum smithii Wet Shrubland
*Disclaimer: Alliances and Associations have not yet been finalized in the National Vegetation Classification (NVC) standard.  A complete version of the NVC for Montana can be found here.

Dynamic Processes

Fluvial processes play a key role in the dynamics of Great Plains streams. The nature of these processes is often indicated by channel morphology. Meandering channels generally have a shallow gradient, low flow variability, and sediment loads dominated by silt and finer particles, while braided channels are characterized by a steep gradient, high flow variability, and a sediment load dominated by sand and coarser particles (Friedman, 2002). Flooding is the key ecosystem process whereby establishment sites for riparian vegetation are created, seeds are dispersed and vegetative succession is controlled. However, since Euro-American settlement, natural fluvial processes have been disrupted in many of these systems by dams and diversions. Fire has been suppressed, agricultural activities have increased siltation rates and introduced both non-native species and chemical changes, and native grazers have been largely replaced by domestic cattle. Consequently, there has been a direct loss of woody plant diversity. Furthermore, both channel incision and channel widening have altered flooding regimes, leading to establishment of flood-intolerant species in many areas.


The quality and quantity of ground and surface water input into riparian areas is almost entirely determined by the condition of the surrounding landscape. Therefore, the integrity of riparian ecological systems is partly determined by processes operating in the surrounding landscape, especially in the local watershed. Different types of land use can alter surface runoff and recharge of local aquifers, and introduce excess nutrients, pollutants, or sediments. Great Plains riparian systems have been substantially impacted by the development of both groundwater and surface water for irrigation. Alteration of natural hydrological processes by dams, diversions, ditches, roads, etc., and abiotic resource consumption through groundwater pumping have considerably altered the presettlement condition of the Great Plains. Vegetation responds to hydrologic changes by shifting from wetland- and riparian-dependent species to more mesic and xeric species typical of adjacent uplands and/or encroaching into the stream channel. When periodic flooding is eliminated by water management, riparian areas may become dominated by late-seral communities due to the inability of pioneer species (e.g., cottonwood and willow) to regenerate (Decker, 2007). Pollution from agricultural runoff can introduce excess nutrients into riparian areas. Increased nutrients can alter species composition by allowing aggressive, invasive species to displace native species. Nutrient cycles may also be disrupted by water management that eliminates normal flooding cycles and prevents deposition of organic material from floodwaters (Decker, 2007). Riparian vegetation is also affected by climatic drought that reduces soil moisture in the unsaturated zone and decreases streamflows, which reduces recharge and lowers the alluvial water table (Friedman et al. 1997). The elimination of beavers from most of the plains watersheds probably decreased water storage and increased variability in plains streams (Friedman et al. 1997). The replacement of native grazers, especially bison, with fenced cattle has changed the regeneration patterns of cottonwood. In addition, salt cedar and Russian olive can drastically alter ecological processes in these plains riparian areas. Tamarisk is an early successional species with dispersal strategies and habitat requirements similar to native cottonwood and willow (Lesica and Miles, 2004). It can replace the native cottonwood and willow where natural flow regimes have been altered.

Restoration Considerations

Restoration strategies are dependent on the degree and type of disturbance event. Restoration efforts must first concentrate on restoring thestream's hydrology, so the floods can re-occur. In-stream habitat enhancement (e.g., additions of logs or boulders) should be employed after restoring natural processes or where short-term improvements in habitat are needed (e.g., for species in recovery).

Removingor eliminating grazing from this ecological system will allow the system to recover if hydric soils have not been lost due to extensive soil compaction, pugging, or down cutting of stream channels, and if there are existing populations of herbaceous native species (Carex, Juncus, and native grasses) that possess rhizomatous root systems capable of re-colonizing bare soils. The presence of rhizomatous, highly adaptable exotic grasses such as Kentucky bluegrass (Poa pratensis), common timothy (Phleum pratense) and smooth brome (Bromus inermis) and pasture forbs such as clovers (Trifolium species) and common dandelion (Taraxacum officinale) however, will persist on the site and may compete with existing populations of native graminiods and forbs. In these cases, land managers must decide if the exotic density is low enough that an adequate stand of native graminoids and forbs can become established on the site if reseeding efforts are used. In all cases, grazing should be excluded for several years to allow adequate re-growth and recovery of existing shrubs and the herbaceous understory.

Because all major shrub species within this riparian system are capable of re-sprouting and typically possess extensive, spreading root systems, modified land management practices in areas of low to moderate impact can minimize additional restoration needs. Vigor, health and degree of vegetative regeneration of existing trees and shrubs must be evaluated to determine if these components of the community are capable of recovery in an acceptable time frame. Intensive revegetation efforts should be limited to sites where a catastrophic wildfire or prolonged heavy grazing has destroyed existing trees, shrubs and the seedbank.

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 (common or occasional) 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 2012, 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 observation 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 listed as associated with 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 listed as 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.  Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific 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 assignment of common versus occasional association.  If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.

    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.  2012.  Mammals of Montana.  Second edition.  Mountain Press Publishing, Missoula, Montana.  429 pp.
    • 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

    NatureServe Identifiers:
    Element Global ID 28534
    System Code CES303.677, Northwestern Great Plains Riparian

    9326: Northwestern Great Plains Riparian

  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Decker, Karin. 2007. Western Great Plains riparian woodland and shrubland ecological system ecological integrity assessment. Ft. Collins, Colo: Colorado State University, Colorado Natural Heritage Program.

    • Covich, A. P., S. C. Fritz, P. J. Lamb, and R. D. Marzolf. 1997. "Potential Effects of Climate Change on Aquatic Ecosystems of the Great Plains of North America". Hydrological Processes. 11 (8): 993.
    • Dodds, W. K., K. Gido, M. R. Whiles, K. M. Fritz, and W. J. Matthews. 2004. Life on the edge: The ecology of Great Plains prairie streams. BioScience 54: 205–216.
    • Friedman, J. M., and V. J. Lee. 2002. Extreme floods, channel change, and riparian forests along ephemeral streams. Ecological Monographs 72:409-425.
    • Friedman, J. M., M. L. Scott, and G. T. Auble. 1997. Water management and cottonwood forest dynamics along prairie streams. Pages 49-71 In F. L. Knopf, and F. B. Samson, editors. Ecology and Conservation of Great Plains Vertibrates. Springer-Verlag, New York.
    • Friedman, J. M., W. R. Osterkamp, M. L. Scott, and G. T. Auble. 1998. Downstream effects of dams on channel geometry and bottomland vegetation: regional patterns in the Great Plains. Wetlands 18:619-633.
    • Gregory, S. V., F. J. Swanson, W. A. McKee and K. W. Cummins. 1991. An ecosystem perspective of riparian zones. BioScience 41(8):540-551.
    • 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.
    • Lesica, P., and S. Miles. 2004. "Ecological strategies for managing tamarisk on the C.M. Russell National Wildlife Refuge, Montana, USA". Biological Conservation. 119 (4): 535-543.
    • Reed, P. B. Jr. 1988. National list of plant species that occur in wetlands: Northwest (Region 9). U. S. Fish and Wildlife Service Biological Report 88 (26.9). USDI Fish and Wildlife Service, Research and Development, Washington, DC. 89 pp.
    • Woods, A. J., J. M. Omernick, J. A. Nesser, J. Shelden, J. A. Comstock, and S. H. Azevedo. 2002. Ecoregions of Montana, 2nd edition (color poster with map, descriptive text, summary tables, and photographs). Environmental Protection Agency, Office of Research and Development, Durham, North Carolina.

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Citation for data on this website:
Great Plains Riparian — Northwestern Great Plains Riparian.  Montana Field Guide.  Retrieved on , from