Grasslands 



30. Aqropyron spicatum / cushion plant c.t. 



(AGRSPI/cushion; bluebunch wheatgrass/cushion plant) 



(17 stands) 



Environment- Windswept mesas, ridgetops and upper slopes in the 

 outwash plains and foothills on the south side of the Pryor 

 Mountains are often dominated by cushion plant-grasslands. 

 Elevations range from 4,100 to 5,500 feet Adjacent plant 

 communities are often Utah juniper or limber pine woodlands in 

 more protected sites. ARTTRI/AGRSPI may also occur nearby where 

 soils are deeper. 



Vegetation- Shrubs are rare in this community type. The 

 subshrubs Ceratoides lanata and Gutierrezia sarothrae were 

 present in the majority of stands but their mean cover did not 

 exceed 2%. Aqropyron spicatum was present in all stands with a 

 mean canopy cover of 13%. Koeleria pyramidata is common in some 

 stands. The most common forbs are cushion plants, including 

 Arenaria hookeri, Hymenoxys acaulis . Phlox hoodii and P. 

 muscoid.es. Cryptantha cana and Erioqonum mancum are common in 

 some stands, and Machaeranthera qrindelioides , Townsendia 

 spathulata and Astragalus spatulatus are present in the majority 

 of stands but have low mean cover. Lichens are relatively common 

 in this type. 



Soils- AGRSPI/cushion generally occurs on moderately deep soils 

 derived from limestone or calcareous sandstone. They are very 

 gravelly or cobbly with a loamy to clay texture. The soil 

 subgroup at both of the soil characterization sites was Ustic 

 Torriorthent . High concentrations of carbonate are present in 

 all horizons. pH varied from 7.2 to 7.6, and conductivity ranged 

 from 200 to 680 uhmos/cm^ (2 stands) . 



Other Studies- Knight et al. (1987) describe this community type 

 from Bighorn Canyon NRA and refer to it as windswept plateau 

 grassland. Similar shallow-soil grasslands dominated by 

 Aqropyron spicatum have been described for northwest Montana 

 where the codominant forb is Erioqonum ovalifolium (Lesica 1988) 

 and for Oregon and Idaho in which the codominant is E. 

 heracleoides (Bourgeron and Engelking 1992). 



Natural Heritage Program Rank- G3/S3 



32 



