Great Plains Floodplain
Provisional State Rank
This system occurs along the Missouri and Yellowstone Rivers and their larger tributaries, including parts of the Little Missouri, Clark’s Fork Yellowstone, Powder, Tongue, Bighorn, Milk, and Musselshell rivers. These are the big perennial rivers of the region, with hydrologic dynamics largely driven by snowmelt and rainfall originating in their headwater watersheds, rather than local precipitation events. In the absence of disturbance, periodic flooding of fluvial and alluvial soils and channel migration will create depressions and backwaters that support a mosaic of wetland and riparian vegetation, whose composition and structure is sustained, altered and redistributed by hydrology. Dominant communities within this system range from floodplain forests to wet meadows to gravel/sand flats, linked by underlying soils and flooding regimes. In the western part of the system’s range in Montana, the overstory dominant species is black cottonwood (Populus balsamifera ssp. trichocarpa) with narrowleaf cottonwood (Populus angustifolia) and eastern 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 relatively undisturbed stands, willow (Salix species), redosier dogwood (Cornus sericea) and common chokecherry (Prunus virginiana) form a thick, multi-layered shrub understory, with a mixture of cool and warm season graminoid species below. Box elder (Acer negundo) and green ash (Fraxinus pennsylvanica) form a tree understory in mid-seral and late-seral stands.
In Montana, many occurrences are now degraded to the point where the cottonwood overstory is the only remaining natural component. The hydrology of these floodplain systems has been affected by dams, highways, railroads and agricultural ditches, and as a result, they have lost their characteristic wetland /riparian mosaic structure. This has resulted in a highly altered community consisting of relict cottonwood stands with little regeneration. The understory vegetation is dominated by non-native pasture grasses, legumes and other introduced forbs, or by the disclimax western snowberry (Symphoricarpos occidentalis) and rose (Rosa species) shrub community.
Floodplains; meandering channels with alluvial bar formation; vegetation occuring in bands or zones reflecting past deposition
This system is found in the northwestern Great Plains through southern Canada. In Montana, it is characteristic of the big river floodplains in the Missouri River Basin. It is found along the Missouri and Yellowstone Rivers and their larger tributaries, including parts of the Little Missouri, Clark’s Fork Yellowstone, Powder, Tongue, Bighorn, Milk, and Musselshell rivers. Elsewhere, this system is found in northern Nebraska and the Dakotas on the Niobrara, upper Missouri, White, Cheyenne, and Little Missouri rivers; and in the prairie provinces of Canada on the Saskatchewan River.
Ecological System Distribution
Approximately 1,712 square kilometers are classified as Great Plains Floodplain 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, Fergus, 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
This system may occur as relatively broad and extensive forests, as seen along the lower stretches of the Missouri and Yellowstone Rivers, or more narrow bands, as seen along the Milk, Little Missouri, Tongue and Powder Rivers. The elevational range of this system is from 579-1,310 meters (1,900-4,300 feet) (Hansen et al., 1996). These are the big perennial rivers of the region, with hydrologic dynamics largely driven by snowmelt and rainfall originating in their headwater watersheds, rather than by local precipitation events. In an undisturbed state, periodic flooding of the fluvial and alluvial soils and channel migration will create alluvial bars, depressions and backwaters supporting zones or mosaics of wetland and riparian vegetation, whose composition and structure is sustained, altered and redistributed by hydrology. Soils can be Entisols, Inceptisols and Mollisols on older stabilized sites. Often there is up to 1 meter of soil overlying river gravels and cobble. Water tables can drop to within 1 meter of the soil surface in summer months.
In the western part of the system’s range in Montana, the overstory dominant species is black cottonwood, with narrowleaf cottonwood and Plains cottonwood occurring as co-dominants in the riparian/floodplain interface near the mountains. Further east, narrowleaf cottonwood and Plains cottonwood become dominant.
In less disturbed occurrences, willow species such as yellow willow (Salix lutea) planeleaf willow (Salix planifolia), and peachleaf willow (Salix amygdaloides) co-dominate the shrub layer with common chokecherry (Prunus virginiana), redosier dogwood (Cornus sericea), serviceberry (Amelanchier alnifolia) and currant (Ribes spps). Boxelder (Acer negundo), green ash (Fraxinus pennsylvanica), and American elm (Ulmus americana) are common in mid- to late-seral stands, and will generally succeed Plains cottonwood in the rivers of the Southeast. Sandbar willow (Salix exigua) and shrubby cinquefoil (Dasiphora fruticosa) frequently colonize recent alluvial bars in central and eastern Montana, while silverberry (Elaeagnus commutata), thinleaf alder (Alnus incana) and Drummond’s willow (Salix drummondiana) are colonizers in black cottonwood-dominated floodplains near the mountains and riparian/floodplain interface. Common graminoids associated with these floodplain systems include big bluestem (Andropogon gerardii), wooly sedge (Carex pellita), streamside wild rye (Elymus lanceolatus), old switch panicgrass (Panicum virgatum), western wheatgrass (Pascopyrum smithii), little bluestem (Schizachyrium scoparium), and sand dropseed (Sporobolus cryptandrus). Forbs include Drummond’s dryad (Dryas drummondii), yarrow (Achillea millefolium), starry solomon’s seal (Maianthemum stellatum) and aster (Symphyotrichum species). Because of the disturbance regimes typical in these systems, they are highly susceptible to invasion by exotic species. Russian olive (Elaeagnus angustifolia) and cheatgrass (Bromus tectorum) have become established in many stands, and leafy spurge ( Euphorbia esula) is a common invasive.
National Vegetation Classification Switch to Full NVC View
Adapted from US National Vegetation Classification
A0636 Populus deltoides Floodplain Woodland Alliance
A3423 Populus deltoides Floodplain Forest Alliance
CEGL000657 Populus deltoides - Cornus sericea Floodplain Forest
CEGL000658 Populus deltoides - Fraxinus pennsylvanica Floodplain Forest
A3493 Spartina pectinata Great Plains Wet Meadow Alliance
CEGL001477 Spartina pectinata / Carex spp. Wet Meadow
A3769 Salix boothii - Salix geyeriana - Salix lutea Montane Wet Shrubland Alliance
A3800 Salix exigua - Salix irrorata Shrubland Alliance
A3805 Carex nebrascensis - Carex vesicaria - Carex pellita Wet meadow Alliance
CEGL001813 Carex nebrascensis Wet Meadow
A4036 Prunus virginiana - Symphoricarpos occidentalis - Amelanchier alnifolia Great Plains Shrubland Alliance
CEGL001131 Symphoricarpos occidentalis Shrubland
A4131 Fraxinus pennsylvanica - Ulmus americana - Populus deltoides Floodplain Forest Alliance
*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
In Montana, many occurrences are now degraded to the point where the cottonwood overstory is the only remaining natural component. The hydrology of these floodplain systems has been affected by dams, highways, railroads and agricultural ditches. As a result, they have lost their characteristic wetland /riparian mosaic structure. This has resulted in a highly altered community consisting of relict cottonwood stands with little regeneration. In the system’s disturbed/altered hydrological state and/or under heavy grazing pressure, there will be an increase in shrub species such as western snowberry and rose and a corresponding decrease in willow species, redosier dogwood, currant, serviceberry and common chokecherry.
Successional processes create a community resembling adjacent upland communities; western snowberry and rose may persist, but will be joined by other native shrubs from adjacent upland communities, such as silver sagebrush (Artemisia cana)and big sagebrush (Artemisia tridentata). In addition, exotic shrub species such as salt cedar (Tamarix ramosissima) can invade disturbed floodplain systems. Russian olive has become a dominant overstory tree in many areas, shading out native species. In these disturbed floodplains, the understory vegetation is dominated by a mixture of pasture grasses such as smooth brome (Bromus inermis), common timothy (Phleum pratense), redtop (Agrostis stolonifera) and Kentucky bluegrass (Poa pratensis), as well as non-native forbs such as sweetclover (Melilotus species), clovers (Trifolium species), Canadian thistle (Cirsium canadensis) and common dandelion (Taraxacum officinale). Once exotic grasses become dominant, especially in the absence of episodic flooding, these systems cannot return to their original state without substantial management intervention.
Cottonwoods and willows are the dominant tree species in these Great Plains Floodplain Systems, creating a highly productive and important habitat type. Since they are specifically adapted to infrequent large flooding events that promote dispersion and colonization of newly formed alluvial bars, management efforts need to begin with identifying the frequency and duration of the flows necessary for colonization to succeed (Scott et al, 1994). Great Plains floodplain systems have been substantially impacted by the development of both groundwater and surface water for irrigation, isolating rivers from their adjacent floodplains. Unless water management can restore periodic flooding, floodplains and riparian areas may become dominated by late-seral communities, and nutrient cycles may be disrupted without floodwaters depositing organic material (Decker, 2007). In addition, management efforts need to target aggressive non-native shrubs like salt cedar and Russian olive that can drastically alter ecological processes. 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. Early detection and rapid response are necessary to prevent its spread. Prescribed spring grazing by sheep has been effective in controlling leafy spurge along some rivers, particularly the upper Powder.
Restoration strategies are dependent on the degree and type of disturbance event. Restoration efforts must first concentrate on restoring hydrologic processes or simulating large flood events. Instream habitat enhancement (e.g., additions of logs or boulders) can be employed after restoring natural processes or where short-term improvements in habitat are needed (e.g., for species in recovery).
Removing or limiting grazing will allow the system to recover if hydric soils have not been lost due to soil compaction, pugging, or downcutting of stream channels, and if there are existing populations of herbaceous native species (Carex, Juncus, and native grasses) with rhizomatous root systems capable of re-colonizing bare soils. 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 (Trifoliumspecies) 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 small enough that an adequate stand of native graminoids and forbs can become established on the site if reseeding efforts are used. With reseeding, grazing must 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 floodplain 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 seed bank.
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:
- 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);
- Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
- Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
- 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: mtnhp.org/requests
) 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.
- 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.
- Native Species Commonly Associated with this Ecological System
- Native Species Occasionally Associated with this Ecological System
Original Concept Authors
Montana Version Authors
- Classification and Map Identifiers
Cowardin Wetland Classification:
||Palustrine, Riverine or Riparian (non-wetland)
||Forested, Scrub-Shrub, Emergent, Unconsolidated Shore
||Temporarily flooded, seasonally flooded, semipermanently flooded
|Geographically Isolated Wetland
|Element Global ID
||CES303.676, Northwestern Great Plains Floodplain
9159: Northwestern Great Plains Floodplain
- 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.
- Friedman, J. M., M. L. Scott, and G. T. Auble. 1997. Water management and cottonwood dynamics along prairie streams. Pages 49-71 in: F. L. Knopf and F. B. Samson. Ecology and Conservation of Great Plains Vertebrates. Springer-Verlag, New York, NY.
- 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.
- 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.
- Hauer, F Richard, and Mark S Lorang. 2004. "River regulation, decline of ecological resources, and potential for restoration in a semi-arid lands river in the western USA". Aquatic Sciences. 66 (4): 388.
- Junk WJ, Welcomme RL. 1990. Floodplains. p 491-524 in: Patten BC, editor. Wetlands and Shallow Continental Water Bodies. The Hague, The Netherlands: SPB Academic Pub.
- 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.
- Scott, M. L., G. T. Auble, and J. M. Friedman. 1997. Flood dependency of cottonwood establishment along the Missouri River, Montana, USA. Ecological Applications7:677-690.
- Ward, J V, and J A Stanford. 1995. "Ecological Connectivity in Alluvial River Ecosystems and its Disruption by Flow Regulation". Regulated Rivers. 11 (1): 105.