Artemisia tridentata ssp. wyomingensis /Pascopyrum smithii 

 (Elymus lanceolatus) Plant Association 



(syn. Artemisia tridentata ssp. wyomingensis / Agropyron smithii (Agropyron dasystachyum) 

 ARTTSW / PASSMI (ELYLAN); Wyoming big sagebrush / thick-spiked (western) wheatgrass 



MTNHP rank: G4/S? 



Environment: This sagebrush steppe type is probably the single most extensive plant community in 

 Carter County and is especially abundant on BLM lands. It is the dominant vegetation, often 

 extending uninterrupted for miles, in areas with soils derived from shale. It is a major vegetation type 

 on shale ridge systems, particularly northerly slopes, which are less dissected than southerly aspects 

 and have better developed soils. It represents clayey and shallow clay range sites in these settmgs. It 

 occurs as the predominant shrubland association on alluvial terraces in areas of shale-derived soils, 

 where it replaces ARTCAN/PASSMI as subirrigated range sites, and it is also found in areas 

 associated with sandstone outcrops or at least coarser-textured soils (silt loams and loams) as shallow 

 range sites. It also occurs in smaller shallow range site patches on sandstone mesa tops in areas with 

 poorly drained shallow soils perched on level bedrock. 



Vegetation: Wyoming big sagebrush is well represented and there is an undergrowth dominated by 

 thick-spiked wheatgrass {Elymus lanceolatus) and/or western wheatgrass {Pascopyrum smithii). 

 Note: The common upland big sagebrush of Carter County is Artemisia tridentata ssp. 

 wyomingensis, which is distinguished from other subspecies of big sagebrush by its low stature (< 5 

 dm tall) and by its relatively short (mostly < 12 mm long) persistent leaves which have incurved 

 (convex) margins (Dom 1992, Tart 1996). We expect that the dominant rhizomatous wheatgrass of 

 most Carter County big sagebrush communities, at least those in the south on heavy clay soils, is 

 Elymus lanceolatus (syn. Agropyron dasystachyum), however, Pascopyrum smithii (syn. Agropyron 

 smithii) may grow intermixed or be the dominant grass at some sites. We have chosen to include 

 communities with either grass dominant in the same plant association, due to the difficulty of 

 distinguishing the two species, the possibility of hybridization (Great Plains Flora Association 1986), 

 and their apparently overlapping ecological distributions. We refer to the ARTTSW/PASSMI type 

 by the more widely recognized name pending taxonomic and community classification review. 



Six plots were sampled prior to livestock grazing of the season and judged to be in range conditions 

 varying from good to excellent (ungrazed for 12 or more years) to moderately grazed in recent past 

 years. Cover by Artemisia tridentata ssp. wyomingensis ranged from 10 to 25%. Stands with higher 

 sagebrush cover were observed and fenceline contrasts indicate progression towards higher shrub 

 cover with increased grazing. The shrubs Artemisia frigida and Chrysothamnus nauseosus have 

 greater than 50% constancy in the plots. Cover by Elymus lanceolatus, the dominant grass identified 

 in six plots, ranged from about 10% to 60%. Pascopyrum smithii was identified as the dominant 

 grass with about 50% cover in one plot (plot 14 on a pooriy drained position of upland sandstone 

 mesa near Pine Hill in northern Carter County). These two species were not distinguished within 

 plots. A particular previous vegetation study in southern Carter County's Thompson Creek drainage 

 (Ecological Consulting Service 1975) found both Elymus lanceolatus and Pascopyrum smithii in 

 plots of big sagebrush habitat types. In contrast, other studies in the same drainage (MacCracken, et 

 al.l983, Sieg et al. 1983) identified Pascopyrum smithii but not Elymus lanceolatus in plots placed 

 in sagebrush communities. 



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