Red Rock Lakes National Wildlife 

 Refuge 



Sheep Mountain Research Natural 

 Area 



environment: 



Sheep Mountain RNA represents an 85 acre segment 

 of a unique environment both within the USFWS 

 refuge system in Montana and the state at large. The 

 Centennial Range is Montana's only large mountain 

 range whose main axis is oriented east-west. As such, 

 it is in position to intercept cells of moist air that 

 originate in the Gulf of Mexico and drift northward in 

 mid to late summer. These cells are the source of 

 afternoon thundershowers that can be quite intense 

 and can cause mountain meadows to remain green long 

 into the growing season. Annual precipitation at 

 Lakeview (6,700 ft.), in the Centermial Valley at the 

 very base of the mountains, is 20. 1 inches, which is 

 quite high for a valley location (compare to Wisdom, 

 MT [6,100 ft elevation] which receives 11.8 in. 

 annually). Near the crest of the range armual 

 precipitation probably exceeds 50 inches. About 27% 

 of annual precipitation falls in May and June, which is 

 typical for western Montana's mountainous areas. Soil, 

 snow, winds, and snow slides also shape its uniqueness, 

 as recognized in the original establishment record. The 

 Sheep Mountain RNA, ranging in elevation from 7,600 

 to 8,400 ft., is but a partial representation of a 3,000 

 vertical feet long mountain gradient developed wholly 

 on the calcareous (predominantly Madison limestone) 

 north flank; quartzite is also reported to be present here 

 according to the original establishment record. The 

 limestone-derived soils are generally thin and have a 

 low water holding capacity. An avalanche chute is 

 located along the RNAs north edge. 



VEGETATION: 



The vegetation features of Sheep Mountain RNA are 

 consistent with Society of American Foresters (SAP) 

 cover type (c.t.) targets originally identified for the site, 

 including the Engelmarm spruce-subalpine fir c.t.. 

 Interior Douglas Fir c.t., and limber pine c.t. They are 

 in noteworthy old-growth form. In addition, grassland 



communities and the avalanche chute successional 

 features are present. 



Four tree species are the climax dominants in the forest 

 series on Sheep Mountain RNA: Engelmarm spruce 

 (Picea engelmarmii), subalpine fir (Abies lasiocarpa), 

 Douglas fir (Pseidotsuga menziesii) and limber pine 

 (Pinus flexilis). In addition, a grassland ridgeline 

 opening is near the lower end toward the east, and an 

 avalanche chute is near the upper end toward the west. 

 The predominantly north-facing slopes of the RNA 

 support plant associations of forest series even at the 

 lowest elevations because of the high precipitation. 

 This is in contrast to other portions of southwestern 

 Montana, where at the elevations represented on this 

 RNA, grasslands are prevalent and any forest series 

 present would be only the Pseiddotsuga menziesii or Pinus 

 flexilis series. High elevation sites that have thin soils, 

 are on wind-exposed or ridgeline positions, or have 

 warmer exposures, regularly support the Pseudotsuga 

 menziesii and Finns flexilis series. Pseudotsuga menziesii, 

 Pinus flexilis and even P. engelmannii tend to be favored 

 over Abies lasiocarpa and lodgepole pine {Pinus contorta) 

 by calcareous substrates. In fact, Pinus contorta was 

 rarely seen in the course of our RNA trarisect, which 

 appeared to traverse only limestone. Thus, these three 

 species, Pseudotsuga menziesii, Picea engelmannii, and 

 Pinus flexilis, tend to have greater cover on these mesic 

 slopes than would be predicted from precipitation and 

 temperature alone. Where thin soils combine with 

 exposed positions and warmer exposures, non-forested 

 environments are produced and "usually dominated by 

 bunchgrasses like bluebunch wheatgrass 

 (Pseiuioroegneria spicata) and/or Idaho fescue {Festuca 

 idahoensis). 



Abies lasiocarpa / Thalictrum occider^tak Forest 



[ABILAS/THAOCC] 



subalpine fir / western meadowrue forest 



The vast majority of this RNA is considered to be in 

 various serai stages of this potential or climax plant 

 association. The subalpine fir is used to name the 

 association even though Douglas-fir is strongly 

 dominant in stands representing this type. This naming 

 convention is used because the national vegetation 

 classification, at least in the western United States, has 

 been based, up to now, on plant associations named in 

 the context of potential natural vegetation or habitat 

 types (Pfister and Amo 1980). The existing vegetation 

 or serai associations that occur within habitat types 



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