Charles M. Russell National Wildlife Refuge 



Fourth Ridge Research Natural Area 



environment: 



The Fourth Ridge RNA spans 1,480 acres representing 

 one among a repeating series of shale ridges at the 

 northeast end of Fort Peck Reservoir. Outcrops of 

 Bearpaw Shale are exposed at the surface. Soils have 

 developed from this parent material and thus are 

 heavy-textured with clays predominating. The shale 

 outcrop landscape is predominantly gently rolling with 

 parts of the landscape prominently erosion-sculpted 

 with pitches and rolls that would be registered orJy on 

 a large-scale map. The semi-arid continental climate 

 has peak precipitation in June followed by July and May 

 (mean armual precipitation of 11.6 inches; climate data 

 from Fort Peck Power Plant, Western Regional Climate 

 Center, 1956-1997). 



VEGETATION: 



The vegetation is made up of two extensive upland 

 plant associations that compose a mosaic of shrubland 

 and open woodland. The RNA does not include 

 ponderosa pine {Pinus potvierosa) vegetation types as 

 indicated in the establishment report, raising the 

 question of whether boundaries need to be reviewed. 



Artemisia tridentata ssp. wyomingensis I Pascopryrum 



smithii Shrubland 



[ARTTSW/PASSMI] 



Wyoming big sagebrush / western wheatgrass shrubland 



This is the prevailing vegetation type on Fourth Ridge 

 RNA. Its occurrence is close to defining the 

 northeastern-most distribution of big sagebrush 

 (Artemisia tridentata) as a species and as a vegetation 

 type in North America, regardless of subspecies (Shultz 

 1984). This shrubland occurs on benches and gentle 

 backslopes with fine-textured soils (silty clays to silty 

 clay loam) weathered firom shale and claystone. The 

 amount of bare ground and litter is inversely related 

 and highly variable, perhaps depending on past grazing 

 history. The shrub layer is dominated by Wyoming big 

 sagebrush (Artemisia tridentata ssp. wyomingensis; the 

 Great Plains subspecies) but total canopy cover ranges 

 between 10-20 %, seldom exceeding 25 %, so that 

 according to the National Vegetation Classification 

 Standard (1997) this community is technically 

 grassland with a shrub component. The dominant and 



diagnostic grass is western wheatgrass (Pascopyrum 

 smithii) with subordinate graminoids like threadleaved 

 sedge (Carex fdifolia) , Sandberg's bluegrass (Poa 

 secunda), andjunegrass (Koeleria macrantha) attaining 

 only a fraction of the 40 % plus canopy cover of the 

 dominant graminoid. The highly palatable green 

 needlegrass (Nasella viridula) is present in only trace 

 amounts. Forb diversity is low, not surpassing 15 per 

 plot and individual cover values seldom exceed trace 

 amounts; American vetch (Vicia americana), white 

 otuon (A/!ium textile), bastard toadflax (Commarvira 

 umbellata), prickly pear (Opuntia polyacantha) , and 

 yellow sweetclover (MeUhtus officiruilis) have high 

 constancy in the community. Melilotus officiruilis is 

 uncommon and widely scattered in this type, and may 

 be increasing. [Plots NHMTECFR97SC0001, 

 NHMTECFR97SC0003, NHMTECFR97SC0006] 



Junipenis scopulorum /Artemisia tridentata ssp. 



11 wyomingensis Woodland 



[JUNSCO/ARTTSW] 



Rocky Mountain juniper / Wyoming big sagebrush 



woodland 



Rocky Mountain juniper / Wyoming big sagebrush 

 woodland (Juruperus scopulorum I Artemisia tridentata 

 ssp. wyominger\sis Woodland) is an extensive type 

 within this landscape, generally occurring on higher 

 positions with silty clay soils derived from one of the 

 subsidiary shale members of the Bearpaw Shale. 

 JUNSCO / ARTTSW is ranked globally imperiled (G2; 

 Schneider et al. 1997) and is cited to occur only in 

 Montana, Wyoming and Colorado. It is noted to grade 

 most frequently to the ARTTSW / PASSMI 

 community type, which occupies similar positions in 

 the landscape. Sometimes the difference in these 

 communities may reflect past disturbance, such as fire, 

 but the mosaic pattern at Fourth Ridge as it 

 cortesponds with gentle dips may indicate edaphic 

 microhabitat differences. The Bearpaw Shale includes 

 mostly non-calcareous members but also has calcareous 

 and bentorutic shale beds. 



]uniperus scopulorum is the only tree present, occurring 

 as short-statured and highly branched forms and in a 

 rather clumped distribution. Canopy height ranged 

 from 5-10 ft. At Fourth Ridge, as elsewhere along this 

 area of the Missouri River, its growth form is rounded 

 and generally without a central axis. It is not known if 



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