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Community Field Guide

Scientific Name:
Pascopyrum smithii - Nassella viridula Herbaceous Vegetation

Common Name:
Western wheatgrass - green needlegrass Mixedgrass

Community Description

This association is widespread across most of the northern Great Plains. Stands occur in narrow valleys, stream terraces, and on some upland positions (Jones 1992, USFS 1992). Soils are generally fine-textured, including clays, silts, silty clays, clay loams, or more unusually loams, and are moderately drained. The soil profile is typically well developed. Parent materials usually are siltstone and mixed sedimentary rock (USFS 1992). This association conventionally occurs on level or near-level terrain but sometimes may occur on moderate slopes of all aspects. Most of the documentation of this association comes from unglaciated landscapes; its distribution and environmental parameters in glaciated settings need more work.

In the Bitter and Frenchman Creek area this type was documented from several of the landscapes, usually in valley bottom settings representing highly productive “overflow” range sites. Pascopyrum smithii (western wheatgrass) is the dominant herb, often approaching a sward-like development. The cover for the diagnostic species Nassella viridula (green needlegrass) is highly variable, depending perhaps on past or ongoing grazing regimes. If this species had at least 3% canopy cover, we interpreted this to be a significant amount denoting the presence of this association.

This community is found at the bottom of narrow valleys, on stream terraces, and on rolling uplands (Jones 1992, USFS 1992). Soils are fine-textured (clays, silty clays, clay loams, or rarely loams) and well-drained. The soil profile is typically well-developed. The parent material is siltstone and mixed sedimentary rock (USFS 1992). This community usually occurs on level or nearly level ground but sometimes may be on moderate slopes of any aspect.

This community is dominated by mid grasses, generally between 0.6 and 1 m tall. The vegetation cover tends to be moderate to high, with almost all of the canopy provided by graminoids (Redmann 1975, USFS 1992). The dominant species are Pascopyrum smithii and Nassella viridula, although Elymus lanceolatus (another rhizomatous wheatgrass that is similar in morphology and ecology to Pascopyrum smithii) is the dominant species in some stands. At least 5% canopy cover of Nassella viridula may be diagnostic for this association. Other common grasses are Hesperostipa comata (= Stipa comata), Koeleria macrantha, Poa secunda (= Poa juncifolia), Poa pratensis, Sporobolus cryptandrus, and, on sandier soils, Calamovilfa longifolia. Shorter graminoids are less common, but may include Bouteloua gracilis, Carex duriuscula (= Carex eleocharis), Carex filifolia, Carex inops ssp. heliophila, and Carex pensylvanica. These species are present in many stands, but they usually contribute little cover. The wheatgrass basin association of Nebraska (Steinauer and Rolfsmeier 2000), which may belong to this association, also contains Schizachyrium scoparium. Cheatgrasses (Bromus commutatus, Bromus japonicus, Bromus tectorum) are present in many stands and contribute substantial cover in some. The forbs Symphyotrichum falcatum (= Aster falcatus), Astragalus spp., Achillea millefolium, Sphaeralcea coccinea, Artemisia ludoviciana, Lepidium densiflorum, and Vicia americana are also typical of this community. Artemisia cana ssp. cana or Artemisia tridentata ssp. wyomingensis may be present, often as scattered shrubs contributing little cover. Stands with denser shrubs are transitional to shrub-herbaceous vegetation.

This western wheatgrass - needlegrass community is common across much of the northern Great Plains of the United States and possibly Canada, ranging from Colorado and possibly Nebraska, north to Montana and North Dakota, and possibly Saskatchewan.

Global Rank: G3G4 State Rank: S4

Global Rank Comments:
The G3G4 rank is based on the broad geographic distribution and the relatively broad environmental requirements of this association. The prevalence of cheatgrass in many stands, though, may necessitate a review of this rank.

Community References


K.J. Hirsch, mod. J. Drake and D. Faber-Langendoen, WCS

Bear Creek Uranium Mine Application n.d., DeVelice et al. 1991, Hirsch 1985, Johnston 1987, Jones 1992, Redmann 1975, Stoecker-Keammerer Consultants n.d., U.S. Forest Service (USFS) 1992, Western Resources Development Corporation n.d. (a)

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This information is from the:
Montana Natural Heritage Program
Montana State Library--Natural Resource Information System
1515 East Sixth Ave., Helena, MT 59620-1800
406 444-5354