GRAMINOID- and FORB-DOMINATED VEGETATION TYPES 



Artemisia iongifolia / Oryzopsis hymenoides Community Type 



ARTLON /ORYHYM; long leaved sagewort / Indian ricegrass 

 MTNHP rank: G2/S2 



Environment: This plant community is a localized feature of breaklands and badlands on slopes 

 and benches. It was sampled at one site on barren, dissected, acid shale uplands above Keith Creek, a 

 headwaters tributary of the Powder River in the west-central segment of the county. In the study area 

 it occurs in very small bands and patches restricted to steep, eroding ridge shoulders. We interpret it 

 to occur on Pierre Shale formations directly overlying the erodable Hell Creek Formation, based on 

 general bedrock geology maps (Ross et al. 1955). The sampled plot has a north aspect but the 

 community was observed nearby on a variety of aspects. Outside Carter County it has been 

 documented only from north-central Montana badlands (DeVelice 1995, Faber-Langendoen et al. 

 1997, and citations therein). 



Vegetation: The plot corresponds floristically in other respects to the community type described 

 from north central Montana (DeVelice et al. 1995), though lacking the indicator Indian ricegrass 

 {Oryzopsis hymenoides). The herbaceous to sub-shrub sagewort, Artemisia Iongifolia, dominates 

 with about 30% cover, while Eriogonum pauciflorum is codominant with about 10% cover. Also 

 present in trace amounts are the short stature Rosa arkansana, the only true-shrub present, and the 

 forb Thermopsis rhombifolia, which are considered diagnostic of the type (Faber-Langendoen 1997). 

 In our plot, the forb Iva axillaris is common with about 3% cover. Grasses occur only in trace 

 amounts. 



Adjacent, less erodable slopes are occupied by Juniperus scopulorum (JUNCON/ORYMIC) and 

 Pinus ponderosa (PINPON/JUNSCO) communities. The ridgetops are nearly devoid of vegetation 

 or support annuals such as Atriplex suckleya or Suaeda calceoliformis, or are infested with Melilotus 

 officinalis. Draw and gully bottoms are dominated by rhizomatous wheatgrass (Elymus lanceolatus 

 and/or Pascopyrum smithii) community types. 



Soils: All known occurrences of this community type are on acid marine shales or bentonite. Our 

 one sampled site is no exception, as can be seen from the inset below; pH is moderately acidic, the 

 texture is clay, and the electrical conductivity indicates substantial amoimts of salt, though not 

 enough to qualify soils as being saline. These substrates are quite similar to those of the CHRNAU / 

 ERIPAU community type but, more highly eroded, suggesting perhaps that ARTLON / ORYHYM 

 may represent an early serai stage of CHRNAU / ERIPAU, or at least an analogous environment. 



Comments: This community type is provisionally identified as a rare type known only from 

 Montana (Faber-Langendoen et al. 1997). It is not a significant rangeland resource. We maintain that 



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