Fire suppression was identified in the original 

 establishment record as needed to maintain the 

 vegetation. 



There is currently not a weed threat to the area, but 

 the introduced yellow sweetclover {Melilotus officinalis) 

 is aggressive and can be seen invading environments as 

 disparate as PSEMEN / ORYMIC and ARTLON / 

 ORYHYM. While it has the greatest potential for 

 expansion on the shrub and grassland sites within the 

 area, it could also proliferate with fire or other major 

 changes to forested commuruty structure. 



The Knox Ridge road is a maintained BLM road 

 ruiming through the area that is a potential corridor for 

 new invasions of exotic species. Any road-grading work 

 on such a steep-sided, narrow ridge also presents the 

 possibility of destabilizing the slopes that drop off on 

 either side. 



York Island Research Natural 

 Area 



ENVIRONMENT: 



York Island is a 120 acre island in the eastern end of 

 Fort Peck Reservoir in a highly exposed setting at the 

 juncture of the main reservoir and the Dry Arm. Its 

 highest point rises less than 80 feet above water level. 

 The undulating to sharply incised surface is typical of 

 Missouri River Breaks Subsection (f ) of the 

 Northwestern Glaciated Plains Section (33 ID, Nesser 

 et al. 1997) where dissected river breaks have formed in 

 shale, sandstone and siltstone. Most of the island's 

 communities are developed on soils weathered from 

 fine-textured sedimentary parent materials, including 

 montmorillinitic clay, i.e. bentonite, a water deposited 

 volcanic ash. The climatic regime is Continental with 

 hot summers and frigid winters; 35% of average annual 

 precipitation (total 11.5 in.) occurs in May and June 

 (data averaged over years 1956 to 1998, from Fort Peck 

 Power Plant, Western Region Climate Center). 



VEGETATION: 



This site has two major community types, both 

 dominated by Wyoming big sagebrush (Artemisia 

 tridentata ssp. wyomingensis) . While the cover of this 

 species is quite variable, it averages in the mid-20% 

 range, i.e., close to the 25% threshold for distinguishing 

 between shrubland and herbaceous vegetation (Federal 

 Geographic Data Committee — Vegetation 

 Subcommittee 1997.) We have described only the 



Artemisia tridentata shrub associations (shrub canopy 

 cover > 25%) because they appeared to be more 

 prevalent and their intergradation with the herbaceous 

 associations is structurally and compositionally 

 overlapping without a discretely different herbaceous 

 type at another extreme. 



Artemisia tridentata ssp. wyomingensis I Fascopyrum 



smithii Shrubland 



[ARTTSW / PASSMI] 



Wyoming big sagebrush / western wheatgrass shrubland 



This is the most extensive of the island's vegetation 

 types, occurring on ftne-textured silt and clay loams 

 derived from shale and siltstone, and found on upland 

 benches and gently to moderately inclined slopes of all 

 aspects. Its varies between the more densely vegetated 

 undulating uplands and more sparsely vegetated south- 

 facing slopes, inversely related to the amounts of 

 exposed soil and gravels (less than 20% - over 80%, 

 respectively). Traces of scattered rounded rock are 

 testimony to past glaciation but veneers of till were not 

 found as part of the soil profile. 



Upland sites have a notably well-developed microbiotic 

 crust, including crustose lichens and algae, that 

 constitute as much as 80% cover. This is circumstantial 

 evidence that the site is a refiige from grazing 

 ungulates, and previously had light use when it was 

 contiguous with the mainland. 



As noted above, Wyoming big sagebrush (Artemisia 

 tridentata ssp. wyomingensis) dominates the shrub 

 component, coverages varying from approximately 15 

 to 30% but giving a distinct impression of a shrubland. 

 Other shrubs/subshrubs present, generally in less than 

 trace amounts, are fringed sage (Artemisia frigida) , 

 broom snakeweed (Gutierrezia sarothrae) , and fragrant 

 sumac (Rhus trilobata) . The graminoid component is 

 dominated by western wheatgrass (Pascopyrum smithii) 

 with higher coverages (to 60-70%) occurring on rolling 

 uplands. Other graminoids commonly present but in 

 amounts not exceeding 5%, include: narrowleaved 

 sedge (Carex sterwphylla) , sun sedge (Carex inops), 

 needle-and-thread (Stipa comata) , blue grama 

 (Bouteloua gracilis) , and prairie junegrass (Koeleria 

 macrantha). Green needlegrass (Nasella viridula) is 

 sporadically present; higher coverages of hlasella 

 viridula, generally on lower north-facing slopes or 

 toeslope postions, indicate a transition to more mesic 

 and relatively scarce habitats (and the ARTTSW / 

 PASSMl-NASVIR association) . The forb component 

 constitutes little cover, the most constant species being ^ 

 scarlet globemallow (Sphaeralcea cocdnea), northern 



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