(Elymns canadensis) and bearded wheatgrass (Elymus 

 trachycaulis) . Starry Solomon-plume (Smilacina stellata) 

 and horsemint (Monarda fistulosa) are uniformly well- 

 distributed, the only forbs among the eight total 

 occurring in greater than trace amounts. Absent are 

 forbs such as purple meadowrue (Thalktrum 

 dasycarpum) , northern bedstraw (Galium aparine) and 

 Sprengel's sedge (Carex sprengeUi) that quite often 

 inhabit these sites; their absence could be attributed to 

 poorly-developed soils or to habitat conditions. [Plot 

 NHMTECRN98SC0007] 



Juniperus horizontalis I Schizachyrium scoparium Dwarf 



Shrubland 



UUNHOR/SCHSCO] 



creeping juniper / little bluestem dwarf shrubland 



This association, both at large and within the RNA, is 

 characterized as a topoedaphic climax, found on 

 moderate to steep, potentially highly erosive slopes of 

 fine sands to sandy loams, with north- to east-facing 

 exposure. In some instances it does occur on flatter 

 slopes, but still the substrate is prone to erosion. For 

 the most part, patch size is dependent upon local 

 vertical relief of appropriate substrate, which is limited 

 in the RNA and thus the type is exemplified by small 

 patches occurring on cooler exposures of steeply incised 

 ravines. There are several other associations having 

 creeping juniper Quniperus horizontalis) dominant but 

 they differ somewhat with regard to the graminoid 

 component. All occur on coarse-textured, erosive soils, 

 but some, such as Juniperus horizontalis I Carex irwps, are 

 confined to steep cool exposures (Hansen and Hoffman 

 1988). 



Juniperus horizontalis generally has greater than 60 % 

 cover at these sites and is the primary substrate binding 

 agent; other shrubs occur in trace amounts. Within 

 the plot, the dominant graminoid is threadleaf sedge 

 (Carex filifolia) but the indicator graminoid is actually 

 bluebunch wheatgrass (Pseudoroegneria spicata) . Across 

 the local landscape there was a fluctuation as to which 

 of these two species is dominant. The grass for which 

 the type is named, little bluestem (Schizachyrium 

 scoparium) , is at best, sporadically distributed in this 

 RNA, though overall its distribution is largely 

 coextensive with that of Pseudoroegneria spicata in 

 considering sites of this nature and in this region (thus 

 its attribution as an indicator species as well). Other 

 grasses present and typical of sandy sites include plains 

 reedgrass (Calamagrostis montanensis) and prairie 

 sandreed (CalamovUfa longifolia) . The forb component 

 is diverse, ranging up to 20 species on a plot, but only 

 one or two species, usually standing milkvetch 



(Astragalus adsurgens) or purple prairie clover 

 (Petalostemon purpureum) , are present in greater than 

 trace amounts. 

 [Plot NHMTECRN98SC0009] 



Rhus aromatica I Pseudoroegneria spicata Shrubland 



[RHUARO/PSESPI] 

 fragrant sumac / bluebunch wheatgrass shrubland 



The sample plot is representative of steep, erosive and 

 high solar intensity slopes, mostly of upper slope and 

 slope shoulder positions. This association occurs 

 predominantly as small patches. This severe and 

 heterogeneous environment has a concomitantly sparse 

 and variable vegetation composition with dominance in 

 the shrub component alternating, in no readily 

 explained manner, between soapweed yucca (Yucca 

 glauca) and fragrant sumac (Ehus aromatica). The soils 

 are fine sands to sandy loams in texture and rills, 

 guUeys and faceted slopes are testimony to their erosive 

 nature. There are at least six closely related plant 

 associations that occur as small patch types on sites 

 with abiotic parameters comparable to those of 

 RHU ARO / threadleaf sedge (Carex filifolia) , 

 RHUARO / little bluestem (Schizachryium scoparium), 

 RHU ARO / plains muhly (Mid^knbergia cuspidata) , 

 Yucca glauca I Calamovilfa longifolia, and Yucca glauca I 

 Pseudoroegneria spicata (Hansen and Hofftnan 1988, 

 Jensen et al. 1992, Schneider et al. 1997, DeVelice et 

 al. 1995). There are no vegetation keys that permit 

 one to unequivocally identify/differentiate these 

 commuiuties, but the site descriptions and vegetation 

 parameters most closely match the RHUARO / PSESPI 

 association described by DeVelice et al. (1995) for 

 northcentral Montana and RHOARO/ PSESPI 

 (Shallow Depth Ecological Type) by Jensen et al. 

 (1992) for western North Dakota. 



Rhus aromatica, Yucca glauca, Juniperus horizcmtalis and 

 Artemisia frigida are ubiquitous shrubs in this type, but 

 only the first three listed exhibit even 5% canopy cover 

 within this landscape; all other shrubs are present in 

 trace amounts. These low shrub coverage values are 

 not in accord with the modal description of the type on 

 a regional basis. For the sample plot, and most of 

 association as developed on the RNA, there is not a 

 dominant graminoid; rather there exists an assemblage 

 of graminoids typical of coarse-textured, well-drained 

 sites. In approximate order of importance, in decreasing 

 cover, these include: plains muhly (Muhlenbergia 

 cuspidata), little bluestem (Schizachryium scoparium), 

 bluebunch wheatgrass 



(Pseu^oegneria spicata) , prairie sandreed (Calamovilfa 

 longifolia) , indian ricegrass (Oryzopsis hymenoides) , 



32 



