shrub-dominated communities are parts of the ravine, 

 and small, scattered woodlands are characteristic of 

 north-facing ravine slopes and segments of the narrow 

 bottoms. The semi-arid continental climate has peak 

 precipitation in June followed by July and May, and a 

 mean annual precipitation of 11.6 inches (Climate data 

 from Fort Peck Power Plant, Western Regional Climate 

 Center, 1956-1997). 



VEGETATION: 



Represented on this site are at least three major 

 grassland plant associations and many other types of 

 small size or restricted ravine habitats. They readily 

 sort by topographic position, slope, and aspect; but the 

 highly dissected nature of the setting fosters a 

 complicated vegetation pattern. 



Stipa comata - Bouteloua gracilis - Carex fiUfoUa 



Herbaceous Vegetation 



[STICOM - BOUGRA - CARHL) 



; needle-and-thread - blue grama - thread-leaved sedge 



grassland 



This grassland association occupies the rolling uplands 

 and upland benches with well-drained soils derived 

 from sandstone; it also occurs on moderate to steep 

 slopes, usually those with a southerly aspect. 



This association is consistently dominated by needle- 

 and-thread (Stipa comata). Cover of the major co- 

 dominant species, threadleaved sedge (Carex filifoUa) 

 and blue grama (Bouteloua gracilis), is highly variable 

 and factors controlling this variation have not been 

 identified. Forbs constitute very little cover in this or 

 the following grassland types scarlet globemallow 

 (Sphaerakea cocdnea), rush skeletonweed (Lygodesrrua 

 juncea), and silver scurfpea (Psoralea argophylla) are the 

 forbs with greatest cover and corwtancy. Together with 

 the western wheatgrass - needle-and-thread grassland 

 (Pascopyrum snuthii - Stipa comata Herbaceous 

 Vegetation) , they comprise the great majority of the 

 upland landscape. There was some western wheatgrass 

 (Pascopyrum srruthii) present in nearly every upland site. 

 While there are characteristically steep gradients from 

 Pascopyrum smit/iij-dominated sites to those dominated 

 by Stipa comata in western Montana, these gradients are 

 diffuse in eastern Montana. The break-point coverage 

 between these two associations is placed by Hansen 

 and Hoffman (1988) at the point where dominance (in 

 terms of canopy cover) shifts from one to the other 

 principal species. [Plots NHMTECCR97SC000 1 , 

 NHMTECCR97SC0002, NHMTECCR97BH0003] 



Pascopyrum smithii - Stipa comata Herbaceous 



Vegetation 



[PASSMI- STICOM] 



western wheatgrass - needle-and-thread grassland 



This is the other major grassland association within the 

 RNA; it occurs on benches, concave topography to 

 swales and is associated with slightly finer-textured soils 

 (silt loams or finer, usually shale-derived) than is 

 STICOM- BOUGRA -CARFIL. It grades to the 

 STICOM - BOUGRA - CARFIL type of drier 

 exposures, coarser textured soils, and under intensive 

 grazing pressure. In more moist positions, such as 

 swales, it grades to the PASSMI - NASVIR 

 association. 



Calamovilfa longifolia - Carex inops 



Herbaceous Vegetation 



[GALLON -CARINO] 



prairie sandreed - sun sedge grassland 



[Plot NHMTECCR97BH0002] This community type 

 constitutes the most extensive vegetation on exposed 

 sandy slopes, though its representation on the RNA has 

 very reduced vegetative cover and much more exposed 

 substrate compared to literature descriptions of the type 

 (Hansen and Hoffman 1988, DeVelice et al. 1995). It 

 borders on the RHUARO / PSESPI and STICOM - 

 BOUGRA - CARFIL associations; often the ecotone 

 between these types is abrupt due to the rhizomatous 

 nature of both Calamovilfa longifolia (prairie 

 sandreed) and Carex inops (sun sedge) , both typically 

 forming dense clones. RNA examples of these sites are 

 highly erosive and this may constitute the difference 

 between this type and the adjoining plant associations 

 as well as explain the differences between the Limber 

 Pine RNA expression of the type and those literature 

 descriptions of the type. There are questions as to 

 whether an association should accommodate this much 

 variation in site parameters. Calamovilfa longifolia is 

 typically the site dominant, though shrub cover of 

 golden currant (Ribes aureum) and yucca (Yucca 

 glauca) may rival that of the graminoids. 



Rhus aromatica I Pseudoroegr\eria spicata Shrubland 



[RHUARO /PSESPI] 

 fragrant sumac / bluebunch wheatgrass shrubland 



This community is associated with sandy, somewhat 

 unstable soils of the steep-slope ravines, particularly 

 southeast- through southwest-facing exposures. It is 



19 



