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Community Field Guide

Scientific Name:
Artemisia cana ssp. cana / Pascopyrum smithii Shrub Herbaceous Vegetation

Common Name:
Silver sagebrush / western wheatgrass Shrub Prairie

Community Description

Summary:
This association has been described from the Great Plains of central and eastern Montana, far western North Dakota, northwestern South Dakota, and northeastern Wyoming. It occupies terraces and floodplains along streams, where alluvium contains more soil water than is available in the uplands. Artemisia cana ssp. cana dominates the shrub layer, which may also include small amounts of Symphoricarpos occidentalis, Sarcobatus vermiculatus, or Chrysothamnus sp. The undergrowth typically is dense and composed mainly of graminoids, with forbs contributing little cover. Pascopyrum smithii often dominates, and in many stands several other species may codominate, especially Nassella viridula, Poa pratensis, and Bromus japonicus (or another exotic, annual brome grass). Exotic grasses (Poa pratensis, Bromus japonicus) dominate the undergrowth in many stands. Bouteloua gracilis and Carex filifolia, both more typically upland species, may contribute substantial cover. Common forbs are Taraxacum spp. (exotic), Achillea millefolium, Artemisia ludoviciana, and Vicia americana.

Environment:
This community is found on flat to gently sloping alluvial terraces and fans near larger creeks and rivers. Thilenius et al. (1995) found that most stands were raised at least 1 m above the general floodplain. Soils are formed from alluvium and are medium- to fine-textured. Flooding may occur frequently.

Vegetation:
This community is dominated by moderately dense to dense graminoids less than 1 m tall. Pascopyrum smithii is usually the most abundant among these. Poa pratensis, Bouteloua gracilis, and Nassella viridula are also common. Calamovilfa longifolia, Hesperostipa comata (= Stipa comata), and Achnatherum hymenoides (= Oryzopsis hymenoides) are sometimes present. Short shrubs, especially Artemisia cana and sometimes Symphoricarpos occidentalis, have 10-25% cover. Forbs and nonvascular species are generally rare.

Range:
This association is known to occur from northern Montana as far south as central Wyoming, and from central Montana as far east as west-central South Dakota.

Global Rank: G4 State Rank: S?

Global Rank Comments:
This association seems to be common within a large geographic range, occurring from northern Montana as far south as central Wyoming, and from central Montana as far east as west-central South Dakota. It is restricted to mesic swales, terraces and floodplains along streams of nearly any size, where soils are deep and have low to moderate amounts of salts. However, the presence of exotic species Poa pratensis and Bromus japonicus (or other annual brome grasses) in many of the stands is cause for concern. The global rank has been changed from G3? to G4. Prolonged, heavy grazing by livestock may pose a threat to this association by favoring the grazing-tolerant exotic species.

Community References

Identifier:
CEGL001556

Citations:
Bourgeron and Engelking 1994, DeVelice et al. 1991, Driscoll et al. 1984, Hansen and Hoffman 1988, Hansen et al. 1984, Hansen et al. 1995, Jones and Walford 1995, Thilenius et al. 1995

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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
http://mtnhp.org
mtnhp@mt.gov