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Community Field Guide

Scientific Name:
Pascopyrum smithii - Distichlis spicata Herbaceous Vegetation

Common Name:
Western wheatgrass - inland saltgrass Saline Prairie

Community Description

The Pascopyrum smithii - Distichlis spicata association has been described mainly for unglaciated landscapes in Wyoming, North Dakota and Nebraska where it is found typically in depressions and on steam terraces on deep, moderately saline soils. It is also present in the alkali lake systems of the prairie pothole region. It can be considered a wetland type when it occurs on soils that are saturated for part of the year and may flood periodically. This community is graminoid dominated with Pascopyrum smithii usually the more abundant of the two diagnostic grasses. Forbs seldom exceed 5% canopy cover in the aggregate with the most constant being Aster falcatus (white-prairie aster), Plantago patagonica (Indian-wheat), Iva axillaris, and Helianthus petiolaris (prairie sunflower). Woody species constitute a very minor component, and the most characteristic are Gutierrezia sarothrae (broom snakeweed) and Artemisia cana (silver sagebrush).

Within the Bitter and Frenchman Creek area this association was most frequently associated with glacial depressions and stream terraces on soils of silty clay or clay loams. It was also found as very small pockets in salt-affected glacial outwash in what were hypothesized to be upland sites, though soils and hydrology information was lacking. In depression sites this association occurs on positions slightly drier than typified by the Pascopyrum smithii - Eleocharis spp. association. Salt efflorescence is occasionally visible in the stream terrace sites.

This community is found in depressions and on stream terraces, including ephemeral streams. Stands contain moderately saline silt loam and sandy loam soils, sometimes with a clay subsoil (Hanson and Whitman 1938, Johnston 1987, Steinauer and Rolfsmeier 2000). Hirsch (1985) found the clay layer to be 0-25 cm below the surface. The soils are wet for part of the year and may flood periodically.

The vegetation is dominated by graminoids, which may be as tall as 1 m, but typically are less than 0.6 m. The depth to the clay layer affects the height and amount of vegetation, and the deeper the clay layer is buried, the taller the vegetation (Hirsch 1985). The dominants are Pascopyrum smithii and Distichlis spicata. Other common graminoids include Bouteloua gracilis, Koeleria macrantha, Hesperostipa comata (= Stipa comata), Hordeum jubatum, and Carex duriuscula (= Carex eleocharis). Forbs that may be present are Iva annua, Helianthus petiolaris, Plantago patagonica, Gutierrezia sarothrae, and Aster spp. (including Symphyotrichum falcatum (= Aster falcatus)). Woody plants are rare. In Wyoming, some stands may have scattered Artemisia frigida or Artemisia cana ssp. cana. In Nebraska stands may have scattered Populus deltoides. There, alkaline indicators, such as Muhlenbergia asperifolia and Sporobolus airoides, may also be present. Exotic species, principally Atriplex micrantha (= Atriplex heterosperma) and Cirsium arvense, are ubiquitous and may contribute substantial cover in many stands (Steinauer and Rolfsmeier 2000).

This western wheatgrass saline prairie type is found in the northern Great Plains of the United States, extending from perhaps Montana south to Nebraska.

Global Rank: G4 State Rank: S?

Global Rank Comments:
The G4 rank is based on a large geographic range and rather general environmental requirements. In light of the ubiquity of exotic plants in this type and the large proportion of stands in Nebraska (and perhaps elsewhere) that have been heavily disturbed by livestock (Steinauer and Rolfsmeier 2000), the rank probably should be reviewed.

Community References


J. Drake, mod. D. Faber-Langendoen, WCS

Hanson and Whitman 1938, Harner-White Consultants n.d., Hirsch 1985, Johnston 1987, Jones 1992, NVS Corporation n.d., Steinauer and Rolfsmeier 1997, Stoecker-Keammerer Consultants n.d. (a), Stoecker-Keammerer Consultants n.d.(a), Western Resources Development Corporation n.d., Western Resources Development Corporation n.d. (b)

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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