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Community Field Guide

Scientific Name:
Pascopyrum smithii - Eleocharis spp. Herbaceous Vegetation

Common Name:
Western wheatgrass - spikerush spp. Mixedgrass Prairie

Community Description

Summary:
This association includes stands of herbaceous vegetation growing in periodically inundated, small playas on the northern Great Plains. The sites supporting this association are closed basins (playas) of <1 ha with fine-textured soils that impede drainage; consequently the playas are flooded periodically. The small basins supporting this association have standing water during "the wet seasons," presumably mainly in the spring and also after heavy summer rains. Pascopyrum smithii and Eleocharis spp. (Eleocharis acicularis or Eleocharis palustris or both) dominate the vegetation, and Hordeum brachyantherum, Juncus balticus, and Alopecurus spp. often are present. Stands of this type typically include two zones, resulting from differences in the period of inundation. The lowest part of the stand, which is inundated most often and for the longest time, is dominated by Eleocharis acicularis, and may contain Hordeum brachyantherum, Juncus balticus, and Alopecurus aequalis or Alopecurus carolinianus. Bare soil accounts for about 75% of the ground surface. The higher part of the stand is dominated by Pascopyrum smithii and may contain substantial amounts of Carex douglasii and Vulpia octoflora var. octoflora (= Festuca octoflora). Other species common in the surrounding vegetation are absent from stands of this type, or contribute little cover.

Vegetation:
This type includes low herbaceous vegetation growing in closed basins. Pascopyrum smithii and Eleocharis acicularis generally dominate, and the plants common in the surrounding steppe generally are absent or contribute very little cover. Stands of this type typically include two zones, resulting from differences in the period of inundation. The following information is from two stands surveyed by Jones (1997): the lowest part of the stand, which is inundated most often and for the longest time is dominated by Eleocharis acicularis and may contain Hordeum brachyantherum, Juncus balticus, and Alopecurus aequalis or Alopecurus carolinianus, and bare soil accounts for about 75% of the ground surface. The higher part of the stand is dominated by Pascopyrum smithii and may contain substantial amounts of Carex douglasii and Vulpia octoflora (= Festuca octoflora). According to Thilenius et al. (1995), Hordeum jubatum occurs on the margins of the stands.

Range:
This association has been described from a small area (about 250 square miles) in northeastern Wyoming, mainly on the divide between the Belle Fourche River drainage and the Cheyenne River drainage. Two stands apparently have been described from the area of the Montana - South Dakota border as well (Hansen and Hoffman 1988, Table A-5, stands 61 and 136), suggesting that the range of the type may extend into southeastern Montana and western South Dakota. It has been confirmed from northcentral Montana, just south of the Saskatchewan border.

Global Rank: G1 State Rank: S?

Global Rank Comments:
This association has been described from a small area (ca. 250 square miles) in northeastern Wyoming, mainly on the divide between the Belle Fourche River drainage and the Cheyenne River drainage. The range of the type may extend into eastern Montana and western South Dakota, but further inventory and classification work are needed to confirm this. The area covered by stands of this association is estimated to be <100 acres because the playas are each 2 acres or smaller, and less than 50 occur in northeastern Wyoming where the association is best known. Enough additional stands may exist in other Northern Great Plains states (eastern Montana and the western Dakotas) to increase the estimated area to 100-1000 acres. The rank has been changed from G2G3 to G1 to reflect the very limited known distribution, the small number of stands, and the small proportion of stands that are undisturbed.

Community References

Identifier:
CEGL001581

Author:
G.P. Jones, WCS

Citations:
Bergman and Marcus 1976, Bureau of Land Management 1979, Caballo Rojo Mine Application n.d., Hansen and Hoffman 1988, Hansen et al. 1984, Holpp 1977, Jones 1997, Mine Reclamation Consultants 1977, Paris and Paris 1974, Soil Conservation Service 1986, Thilenius et al. 1995, Western Resources Development Corporation n.d.

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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