Atriplex gardneri / Elymus lanceolatus Plant Association 



ATRGAR / ELYLAN; (syn. A. nuttallii / Agropyron dasystachyum); 



Gardner's saltsage / thick-spiked wheatgrass 



MTNHP rank: to be determined 



Environment: This is a distinctive community type which occupies relatively large areas on 

 eroded, low relief bentonite/shale ridge systems in southern Carter County. They represent salt- 

 affected upland range sites. It is mostly confined to ridgetops and southerly exposed side ridges and 

 convex slopes. ATRGAR/ELYLAN was sampled by three plots on BLM land in the Cottonwood 

 Creek drainage (North Fork and Duncan Creek). Patches dominated by Atriplex gardneri were also 

 observed on Carter Coimty BLM on steep south facing shale slopes in the breaklands in the 

 southeast comer of the county (Wymonkota). 



Vegetation: These highly erodable, sparsely vegetated sites are dominated by the low, mound- 

 forming shrub Atriplex gardneri (syn. A. nuttallii). This species is salt and drought tolerant (Branson 

 et al. 1970). While the landscape superficially appears barren, we recorded shrub cover values 

 ranging from 30-50% canopy cover. Sometimes the shrubs grow in rows between shallow erosion 

 gullies giving the community a distinctive vertically striped pattern visible from a distance. The 

 grass component is sparse (up to about 1 0% cover) and patchy, dominated in our plots by Elymus 

 lanceolatus (syn. Agropyron dasystachyum) and Elymus elymoides (syn. Sitanion hystrix). There is 

 low diversity of and only trace cover by forbs in the plots, but one plot included two species that 

 were formerly Montana Species of Special Concern that are of biogeographical interest. 

 Haplopappus multicaulis and Xylorhiza glabriuscula, the former which is a regional endemic to this 

 area of the Great Plains, and the latter which is a Great Basin species at its northern limits. 



Downslope gully bottoms and lower slopes with better-developed soils are occupied by grasslands 

 (PASSMI and PASSMI / STIVIR) and ftuther downslope alluvial plains are occupied by 

 greasewood communities (SARVER / ELYLAN). Northerly aspects of these ridge systems are less 

 eroded and less dissected and support sagebrush steppe (ARTTSW/PASSMI). 



Soils: Branson et al. (1970) characterized shale-derived soils supporting Atriplex gardneri 

 communities in northeastern Montana as having high soluble salt and sodium content, high total 

 moisture stress, and low infiltration rates. Derived primarily from bentonite (sedimentary deposits of 

 montmorillonitic mineralogy (clay texture) resulting from in-place weathering of volcanic ash), 

 study area soils have a high shrink-swell capacity and once wet, a very low permeability. Low 

 infiltration rates result in extensive and intensive sheet, rill, and gully erosion and almost no profile 

 development. The high, but less than 8.5 pH values, and electrical conductivities less than 4 

 mmhos/cm indicate, respectively, a high sodium content and, technically speaking, a non-saline 

 condition, though values are approaching saline. 



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