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Montana Field Guides

Greasewood Flat

Provisional State Rank: S4
(see reason below)

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State Rank Reason
The major threat to this system is drought, followed by grazing effects (trampling, pugging, hummocking)

General Description

This system occurs in central, north-central and eastern Montana and as a minor occurrence in southwestern Montana. Elsewhere, it occurs throughout the western U.S. including the Intermountain Basin states, the Columbia Plateau, the Rocky Mountains and the western Great Plains. It is found on nearly level, older alluvial terraces on broad or narrow floodplains and coalescing alluvial fans in valleys. It may also occur on broad expanses along lake shores and playas. Sites typically have saline soil and a shallow water table. They flood intermittently, but the surface is dry for most of the growing season. The water table remains high enough to maintain vegetation, despite salt accumulations. Sites occur where overland flow or soils or a combination of both allow for greater than normal moisture regime. In many cases, fine textured soils result in a perched water table. The structure of this system usually consists of open to moderately dense shrubs dominated by greasewood (Sarcobatus vermiculatus) with a sparse graminoid understory most commonly consisting of western wheatgrass (Pascopyrum smithii).

Diagnostic Characteristics
Partially isolated wetland, shrubland, lowland, toeslope/valley bottom, alkaline soil, deep soil, xeromorphic shrub

This system occurs throughout the western U.S. including the Intermountain Basin states, the Columbia Plateau, the Rocky Mountains and the western Great Plains. It occurs in central, north-central and eastern Montana and as a minor occurrence in southwestern Montana.

Ecological System Distribution
Approximately 1,187 square kilometers are classified as Greasewood Flat 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, Dawson, Fallon, Fergus, Garfield, Glacier, Golden Valley, Hill, Judith Basin, Lewis and Clark, Liberty, Mccone, Meagher, Musselshell, Petroleum, Phillips, Pondera, Powder River, Prairie, Rosebud, Stillwater, Sweet Grass, Teton, Toole, Treasure, Valley, Wheatland, Wibaux, Yellowstone

Spatial Pattern
Large or Small Patch

In Montana, this ecological system represents one of the driest extremes of the riparian/wetland zone. It occurs on nearly level, older alluvial terraces on broad or narrow floodplains and coalescing alluvial fans in valleys. It may also occur on broad expanses along lake shores and playas. Sites typically have saline or alkaline soils and a shallow water table. They flood intermittently, but remain dry for most of the growing season. However, the underlying water table stays high enough to maintain vegetation, despite salt accumulations. The system occurs where overland flow or soils or a combination of both allow for a greater than normal moisture regime. High water tables are common, typically within 25 to 30 centimeters (10 to 12 inches) of the soil surface. Soils are fine textured, poorly drained and are alkaline or saline. Soil texture ranges from silt to clay. Sites range in elevation from 655 to 1,067 meters (2,150 to 3,500 feet) (Hansen et al., 1995).


Greasewood (Sarcobatus vermiculatus) is the dominant shrub, although overall canopy cover may be low. Other shrubs present in some occurrences include four-wing saltbush (Atriplex canescens), shadscale saltbush (Atriplex confertifolia), Gardner’s saltbush (Atriplex gardneri), Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis), big sagebrush (Artemisia tridentata ssp. tridentata), silver sage (Artemisia cana ssp. cana), green rabbitbrush (Chrysothamnus viscidiflorus), rubber rabbitbrush (Ericameria nauseosa) or winterfat (Krascheninnikovia lanata).

Perennial grasses are the most common herbaceous cover, with western wheatgrass (Pascopyrum smithii) tending to dominate in undisturbed communities. Other graminoids commonly occurring in this system include slender wheatgrass (Elymus trachycaulus), prairie cordgrass (Spartina pectinata), Nutall’s alkaligrass (Puccinellia nuttalliana), Sandberg’s bluegrass (Poa secunda), inland saltgrass (Distichlis spicata), alkali sacaton (Sporobolus airoides), prairie sandgrass (Calamovilfa longifolia), basin wildrye (Leymus cinereus) and occasionally common spikerush (Eleocharis palustris). Common forb species include yarrow (Achillea millefolium), one-flowered groundsel (Pyrrocoma uniflora), boreal sagewort (Artemisia frigida), western sagewort (Artemisia ludoviciana), goosefoot (Chenopodium species), scarlet globe mallow (Sphaeralcea coccinea), western saltwort (Salicornia rubra) and curlycup gumweed (Grindelia squarrosa).

Adjacent drier communities are dominated by upland shrub or grassland communities such as mixed salt desert scrub, big sagebrush (Artemisia tridentata) shrublands, or three tip sagebrush (Artemisia tripartita) shrublands. Wetter adjacent communities may be dominated by inland salt grass (Distichlis spicata) or willow-cottonwood (Salix-Populus species) dominated communities. In Montana, this system can occur near alkaline lakes or in overflow washes.

National Vegetation Classification Switch to Full NVC View

Adapted from US National Vegetation Classification

A0870 Atriplex confertifolia Scrub Alliance
A1046 Sarcobatus vermiculatus Intermountain Wet Shrubland Alliance
CEGL001359 Sarcobatus vermiculatus - Artemisia tridentata Wet Shrubland
CEGL001360 Sarcobatus vermiculatus - Atriplex gardneri Wet Shrubland
CEGL001363 Sarcobatus vermiculatus - Distichlis spicata Wet Shrubland
CEGL001366 Sarcobatus vermiculatus - Leymus cinereus Wet Shrubland
A1329 Leymus cinereus - Leymus triticoides Alkaline Wet Meadow Alliance
CEGL001479 Leymus cinereus Alkaline Wet Meadow
A1332 Distichlis spicata Alkaline Wet Meadow Alliance
CEGL001770 Distichlis spicata Alkaline Wet Meadow
A1334 Sporobolus airoides - Muhlenbergia asperifolia - Spartina gracilis Alkaline Wet Meadow Alliance
CEGL001685 Sporobolus airoides Southern Plains Wet Meadow
CEGL001799 Puccinellia nuttalliana Salt Marsh
A3196 Ericameria nauseosa Steppe & Shrubland Alliance
A3807 Eleocharis palustris - Eleocharis acicularis Marsh Alliance
CEGL001833 Eleocharis palustris Marsh
A3905 Sarcobatus vermiculatus Great Plains Wet Shrubland Alliance
CEGL001508 Sarcobatus vermiculatus - Pascopyrum smithii / (Elymus lanceolatus) Shrub Wet Meadow
A3978 Sarcobatus vermiculatus Great Plains Badlands Alliance
CEGL001367 Sarcobatus vermiculatus - Pseudoroegneria spicata Shrubland
A4071 Salicornia rubra Wet Meadow Alliance
CEGL001999 Salicornia rubra Salt Flat
*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

Soil-water dynamics within this system support a restricted range of species. Communities in good condition typically have 30 to 40 % shrub cover. Under continued disturbance, greasewood and western wheatgrass decrease in cover, while species such as foxtail barley (Hordeum jubatum) and yarrow (Achillea millefolium), and exotics like cheatgrass (Bromus tectorum), Japanese brome (Bromus japonicus) and Kentucky bluegrass (Poa pratensis), increase in cover.

Overgrazing practices can significantly impact vigor and cover of principal shrub species, leading to an increase in cheatgrass and other exotics, although herbaceous cover in this system is often too low to attract cattle away from surrounding uplands. Off road travel can be a disturbance, especially in the early season, when clayey soils are still soft. In any season, heavy off road travel can be harmful to very slow growing dominant shrub species.

Restoration Considerations
In cases where the system has been impacted by heavy grazing, a rest-rotation regime with limited fall grazing may allow this system to recover by allowing regrowth of principal graminoid and shrub species. Severely impacted sites should be re-seeded to decrease soil erosion potential, to re-establish a native community, and to decrease weedy invasion by exotic species. Western wheatgrass can be used as the principal restoration species and can be seeded or transplanted as plugs. Once established this species spreads vigorously by rhizomes. Both greasewood and western wheatgrass exhibit excellent soil erosion control characteristics. Replanting with greasewood shrub seedlings may be necessary due to the slow recovery time within this system and low rates of natural seedling recruitment.

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
C. McIntyre, L.K. Vance, T. Luna

Version Date

  • Classification and Map Identifiers

    Cowardin Wetland Classification:
    System Palustrine
    Class Scrub-Shrub
    Water Regime Temporarily flooded to intermittently flooded
    Geographically Isolated Wetland Partially isolated

    NatureServe Identifiers:
    Element Global ID 28618
    System Code CES304.780, Inter-Mountain Basins Greasewood Flat

    9103: Inter-Mountain Basins Greasewood Flat

  • 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:
Greasewood Flat — Inter-Mountain Basins Greasewood Flat.  Montana Field Guide.  Retrieved on , from