Chrysothamnus nauseosus / Eriogonum pauciflorum Community Type 



CHRNAU / ERIPAU; rubber rabbitbrush / few flowered buckwheat 

 MTNHP rank: to be determined 



Environment: This previously poorly documented community type was sampled by 4 plots on 

 BLM land in southern Carter County. It appears to be an early successional community on eroded 

 alluvial and residual soils with shale parent material. It occurs in small, scabby, eroded patches on 

 hillsides dominated by grasslands (PASSMI / STIVIR) and in larger patches where it represents an 

 edaphic climax on alluvial outwash flats and low gradient drainages surrounded by sagebrush 

 (ARTTSW/PASSMI) and greasewood (SARVER/ELYLAN) communities. Erosion, often severe, is 

 evident at all sites, indicated by elevated rootstocks of the dominant subshrub, Eriogonum 

 pauciflorum. 



Vegetation: These sparsely vegetated communities are typically dominated by evenly spaced plants 

 of the low, mat-forming subshrub Eriogonum pauciflorum with few other species present. (Note: 

 Eriogonum pauciflorum is included under forbs in the constancy/cover tables (Appendix A)). Three 

 plots sampled on alluvial outwash suggest a serai relationship between the named codominants. Two 

 plots have sparse cover (about 20-30%) by Eriogonum pauciflorum and few other plants present, 

 except the annual Atriplex suckleya which was well represented in one plot (putative earliest serai 

 stage) and Chrysothamnus nauseosus was present in the other along with trace amounts of four grass 

 species (Koeleria macrantha, Poa compressa, P. juncifolia, and P. secunda). In the third plot 

 (putative most advanced serai stage) Chrysothamnus nauseosus was becoming well established 

 (about 10% cover), and grew exclusively on elevated soil in clumps of dead Eriogonum pauciflorum, 

 live plants of which persisted in trace amounts, and the rhizomatous wheatgrass Elymus lanceolatus 

 was evenly scattered in the plot with about 10% cover. The fourth plot on scabby upland hillside is 

 somewhat different, with higher shrub cover, Eriogonum pauciflorum (about 30% cover) sharing 

 dominance with Gutierrezia sarothrae (about 20% cover). The bunchgrass Oryzopsis hymenoides, 

 usually indicative of sandy sites, is common in this plot, and there is higher forb diversity (10 

 species), including the BLM Watch species and selenium indicator Astragalus racemosus. 



Soils: The visual impression of these sites is expanses of bare soil (90 % plus) with scattered sub- 

 shrubs, beneath the canopy of which and closely applied at the stem bases are trace amounts of litter. 

 Judging by the tabulated results (see inset below) soils of all plots are at least slightly saline and 

 three plots are derived from acid shales and one from non-acidic shale. Plot JV029 with non-acidic 

 soils represents the atypical hillslope position with higher grass cover. Our soil values accord well 

 with those of Branson et al. (1970) who correlated distribution of a similar Eriogonum pauciflorum 

 community with acidic, shale-derived (Bearpaw Shale) soils having high gypsum (CaS04) content 

 and relatively low clay content considering the parent material is platy shale. Mechanical weathering 

 of some shales results in it fissuring into small plates, which in aggregate mimic a coarse-textured 

 soil (resulting in relatively high infiltration rates and low fertility). Hydrolysis of gypsum causes the 

 slightly acidic (pH 4.0-5.0) soil reaction. Note that the textural classes of our CHRNAU / ERIPAU 

 soils are varieties of clays but that the percent clay composition is much less (49-58 %) than for the 

 Atriplex gardneri-dommaied sites (64-80 %). The high calcium concentration of a gypsiferous 

 environment renders phosphate relatively unavailable as the calcium phosphate precipitate, which 



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