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Community Field Guide

Scientific Name:
Artemisia tridentata ssp. wyomingensis / Pseudoroegneria spicata Shrub Herbaceous Vegetation

Common Name:
Wyoming big sagebrush / bluebunch wheatgrass Shrub Herbaceous Vegetation

Community Description

Summary:
This bunchgrass vegetation type with an open Wyoming big sagebrush shrub layer occurs in western North Dakota, Montana, Wyoming, Colorado, Idaho, Washington, Oregon (apparently), Nevada, British Columbia, and Canada. It may also occur in Utah and it may occur in South Dakota. Stands occur on moderate- to steep-slopes at low- to mid-elevations, and on a variety of soils. Throughout the range of this association, the vegetation consists of an open to moderately dense shrub layer (about 10% to 25% canopy cover) dominated by Artemisia tridentata ssp. wyomingensis, and an herbaceous layer dominated by Pseudoroegneria spicata with lesser amounts of Poa secunda (sometimes a co-dominant grass). From the Great Plains westward to eastern Idaho and south to Colorado, the sagebrush seldom exceeds 0.5 m in height, but in western Idaho and Washington, the shrubs typically are 1 m tall. Other shrubs (especially Chrysothamnus sp.) and herbaceous species (especially Hesperostipa comata (=Stipa comata) usually are present. Festuca idahoensis is absent or present in amounts too insignificant to be indicative of a more mesic environment. The stands in the eastern half of the geographic range often contain small amounts of Gutierrezia sarothrae, Artemisia frigida, Sphaeralcea coccinea, Phlox hoodii, Koeleria macrantha, and Opuntia polyacantha. Less constant species are Bouteloua spp. (especially Bouteloua gracilis), Carex filifolia, and Pascopyrum smithii (covers a small fraction of Pseudoroegneria spicata value). Missing from these eastern stands is Stipa thurberiana, though Nassella viridula is often present in minor amounts. In the western half of the geographic range, the vegetation generally lacks the associated species listed above and often contains Antennaria dimorpha and Stipa thurberiana. In addition, the stands in Washington often contain large amounts of crustose lichens as ground cover.

Environment:
On the Great Plains of eastern Montana, Wyoming and western North Dakota (Hansen and Hoffman 1988, Thilenius et al. 1995, Jensen et al. 1992), stands of this association occur at 4,400 to 5,000 ft elevation on moderately steep to steep (16% to 45%) slopes and on gentle footslopes with various aspects, though southerly exposures tend to predominate. Soils are loams, sandy loams, and sandy clay loams, often with coarse fragments in the upper horizons. Stands on the Wyoming plains often are on slopes of sandstone or porcelanite buttes (Thilenius et al. 1995). In the basins and foothills of south-central Montana (DeVelice and Lesica 1993) and north-central and central Wyoming (Fisser 1964, Knight et al. 1987, Tweit and Houston 1980), this association mainly occupies gentle to moderately steep (<35%) slopes at 4,000 to 6,000 ft elevation. Soils are moderately deep, usually loamy (although one stand has been described from a clay soil), may have a considerable volume of coarse fragments, and have low electrical conductivity. In central and northcentral Montana this association ranges from being a matrix type on gently rolling terrain to a small patch type on restricted outcrops; it occurs where soils are weathered from coarse sedimentary material, principally sandstone, calcareous and otherwise. In central and northwestern Colorado, stands of this association occupy gentle to steep slopes (to 65%) on a variety of landforms at elevations from about 7,000 to 8,200 ft. Soils are derived from a variety of parent materials and often are gravelly. In southwestern Montana (Mueggler and Stewart 1980, Cooper et al. 1995), stands grow at elevations from 4,000 to 7,500 ft, on slopes up to 54% with various exposures. Soils are shallow to moderately deep and derived from a variety of parent materials. In eastern Washington (Daubenmire 1988), this association occupies silt loam and sandy loam soils on gentle to moderately steep (8% to 38%) slopes with a variety of aspects, up to about 2,700 ft elevation. In British Columbia, this type grows on relatively warm, dry sites (Tisdale 1947), generally from 1,300 to 1,970 ft elevation with stands on steep, south-facing slopes occurring as high as 2,950 ft (McLean 1970). Soils are loams, silt loams, and sandy loams.

This association is poorly documented within the Alkali Creek study area but appears to be exclusively a small patch type found only on sandstone outcrops or sandstone derived colluvium/ Alluvium. It is documented only from mini-mesa tops or associated sandstone escarpments of various aspects. Often the remaining patches (following Alkali Creek Fire) were so small as to represent only a fragment of a community. Soils are apparently shallow, well-drained and of sandy to sandy loam texture. The relatively sparse vegetation cover is reflected in the lack of litter, usually less than 20%, and the high degree of exposed soils, gravel and rock (together averaging about 80%).

Vegetation:
Throughout the range of this association, the vegetation consists of an open to moderately dense shrub layer (about 10% to 25% canopy cover) dominated by Artemisia tridentata ssp. wyomingensis, and an herbaceous layer dominated by Pseudoroegneria spicata with lesser amounts of Poa secunda (sometimes a codominant grass). Other shrubs (especially Chrysothamnus sp.) and herbaceous species (especially Hesperostipa comata) are usually present. Festuca idahoensis is absent or present in amounts too insignificant to be indicative of a more mesic environment. The stands in the eastern half of the geographic range often contain small amounts of Gutierrezia sarothrae, Artemisia frigida, Sphaeralcea coccinea, Phlox hoodii, Koeleria macrantha, and Opuntia polyacantha. Less constant species are Bouteloua spp. (especially Bouteloua gracilis) Carex filifolia, and Pascopyrum smithii (Hansen and Hoffman 1988, Thilenius et al. 1995, Mueggler and Stewart 1980, DeVelice and Lesica 1993, Cooper et al. 1995, Tweit and Houston 1980, Fisser 1964, Knight et al. 1987, Baker and Kennedy 1985, Tiedemann et al. 1987). Missing from these stands is Stipa thurberiana, though Nassella viridula, somewhat of an ecological analogue, is often present in minor amounts. In the western half of the geographic range, the vegetation generally lacks the associated species listed above (although Tisdale (1947) reports that Artemisia frigida in British Columbia often contains Antennaria dimorpha and Stipa thurberiana (Hironaka et al. 1983, Blackburn 1967, Blackburn et al. 1968, Daubenmire 1988, Tisdale 1947, McLean 1970). In addition, the stands in Washington often contain large amounts of crustose lichens as ground cover. Descriptions and photographs of stands show that shrub height also varies across the range of this type. From the Great Plains westward to eastern Idaho and south to Colorado, the sagebrush seldom exceeds 0.5 m in height, but in western Idaho and Washington, the shrubs typically are 1 m tall.

The upper canopy of this community has a open structure with the cover of Artemisia tridentata ssp. wyomingensis ranging from approximately 5 % to 20%; even stands in which the oldest specimens are slightly over 40 years old have cover not exceeding 20%. Other shrubs species that consistently present with a cover seldom greater than 1% to 3% are Artemisia frigida, Gutierrezia sarothrae, and Chrysothamnus viscidiflorus. The undergrowth is dominated by bunchgrasses with Pseudoroegneria spicata at approximately 5% or greater cover as diagnostic, though it and the other major graminoid, Hesperostipa comata, average about 30% and 15% cover, respectively. Carex filifolia, Koeleria macrantha, and Bouteloua gracilis are consistently present, not exceeding about 5% cover. Nassella viridula is inexplicably consistently present, sometimes in greater than trace amounts. Usually Nassella viridula is indicative of mesic environments, whereas in study area sites of this relatively xeric association (having predominantly coarser textured soils and occurring on fractured bedrock) it may be exploiting the opportunity of deeper rooting and available soil moisture. The forb component is depauperate in both species number and in cover, which seldom exceeds 2% to 3% in the aggregate; Phlox hoodii, Psoralea spp. and Opuntia polyacantha are those forbs most consistently present.

Range:
This association is known from Montana, Wyoming, Colorado, Idaho, Washington, Oregon (apparently), Nevada, and British Columbia, Canada. It also occurs in western North Dakota and Utah, and it may occur in South Dakota. This association is known to occur on the Thunder Basin National Grassland and on the Custer National Forest, Ashland District. It may also occur on the Sioux District and the Grand River Districts of the Custer National Forest.

Dynamics:
Though the total vegetative cover is usually less than 50% and litter cover is also relatively light (< 20% of ground surface), this association apparently carried the Alkali Creek Fire quite effectively. The area in which this association was most extensive prior to the Alkali Creek Fire (or other fires) is now predominantly shrub-free grassland. Based on the trace amounts of Bromus japonicus in all inventoried and unburned stands of this type, we speculate that its pre-burn cover was probably minor as well in the areas that did burn. Bromus japonicus apparently did not experience a post-burn surge in cover. It is instructive to note that in southeastern Montana as well, disturbance of this association seems to result in only minor Bromus japonicus cover increases. These observations contrast with the results of disturbing (fire, grazing) the Artemisia tridentata ssp. wyomingensis / Elymus lanceolatus association, which usually responds with a prolific increase in Bromus japonicus. For the Snake River Plains representation of the Pseudoroegneria spicata dominated type, Hironaka et al. (1983) have noted over-grazing does not result in nearly as prolific a response of Bromus tectorum (cheatgrass) as does burning. This difference in response (to burning of this association) may be attributed to many factors but certainly raises the question as to the differential niches of the various annual brome grasses; if one is not present in the landscape of concern it may be advisable to see it remains so. The cover of native increaser species also has remained at low levels in the Artemisia tridentata ssp. wyomingensis / Pseudoroegneria spicata type.

Global Rank: G4 State Rank: S3

Community References

Identifier:
CEGL001535

Author:
WCS; Cooper, S.V. and C. Jean, MTNHP

Citations:
Baker 1983c, Baker and Kennedy 1985, Blackburn 1967, Blackburn et al. 1968b, Brown 1971, Cooper et al. 1995, Daubenmire 1970, Daubenmire 1988, DeVelice and Lesica 1993, Eckert 1957, Fisser 1964, Fisser 1970, Hansen and Hoffman 1988, Hess 1981, Hironaka et al. 1983, Jensen et al. 1992, Johnston 1987, Jones 1992, Knight et al. 1987, Lucky McMine Application n.d., McLean 1970, Mueggler and Stewart 1980, Northwest Resources Co. 1981, Seminoe I Mine Application n.d., Smith n.d., Strong 1980, Thilenius et al. 1995, Tiedemann et al. 1987, Tisdale 1947, Tweit and Houston 1980

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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