of average annual precipitation (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: 



The great majority of the island was at one time a 

 black-tailed prairie dog {Cynomys ludovicianus) colony, 

 that has been extirpated as the result of sylvatic plague. 

 During the colony's existence or following its demise, 

 Bromus tectorum established in dense swards over the 

 area occupied, or once occupied, by the colony. OiJy 

 two plots were established to document the island's 

 vegetation composition, one representing this 

 community within historic prairie dog colony, and the 

 other representing the probable undisturbed native 

 vegetation. 



Bromtts tectorum Disturbance Vegetation 



[BROTEC] 



cheatgrass disturbance vegetation 



only four forbs present, scarlet globemallow 

 (Sphaeralcea coccinea) is the dominant. The presence of 

 silver sagebrush (Artemisia cana) probably reflects the 

 high water table. This site has also received some past 

 disturbance, as evidenced by several alien species being 

 present. [Plot NHMTECRN98SC0005]. 



The unvegetated sandy shore ends abruptly in cutbank 

 with no intervening vegetation gradient between it and 

 the grassland. 



OVERALL BIODIVERSITY SIGNIFICANCE: 

 This site has limited merit as an RNA due to the 

 explosion of weed populations, particularly Bromus 

 tectorum (cheatgrass). This condition may reflect the 

 combined history of prairie dog use and surrounding 

 land use. Even if this site were in pristine condition, it 

 would have limited vegetation significance because it 

 represents a single major community type; one that is 

 best represented as part of a large, contiguous 

 landscape. 



Cheatgrass (Bromus tectorum) is the dominant species 

 in the area formerly occupied by prairie dog colony. 

 Cheatgrass cover is variable, but generally is in excess 

 of 60% and ranges as high as 90%. A number of species 

 that were once prominent on the site, inferred ft-om 

 composition of adjacent landscape, are still present, 

 including silver sagebrush (Artemisia cana) , fringed sage 

 (Artemisia frigida) , blue grama (Bouteloua gracilis) , 

 needle-and-thread (Stipa comata) , Indian ricegrass 

 (Oryzopsis hymenoides) and scarlet globemallow 

 (Sphaeralcea coccinea). However, the site is dominated 

 by weedy, increaser species that also include common 

 dandelion (Taraxacum officinale), tumblemustard 

 (Sisymbrium altissimum) , goat's beard (Tragopogon 

 dubius), Russian thistle (Salsola kali), and rough 

 pennyroyal (Hedeoma hispidum). [Plot 

 NHMTECRN98SC0004] 



Stipa comata - Bouteloua gracilis - Carex filifolia 



Herbaceous Vegetation 



[STICOM - BOUGRA - CARFIL] 



needle-and-thread — blue grama - threadleaf sedge 



grassland 



This is the prevailing grassland where sandy deposits 

 are extensive, as at Prairie Dog Island. The 

 composition of the sampled site, representing the 

 fraction of vegetation not impacted by the "dog town", 

 matches the modal conditions described for this plant 

 association with Stipa comata dominant and Bouteloua 

 gracilis and Carex filifolia being subsidiary graminoids 

 (Hansen and Hoffman 1988, Jensen et al. 1992). Of 



The presence of colonial nesting birds was evident and 

 warrants enumeration. Cutbanks on the leeward 

 (southeastern) shore were favored as perches and 

 shoreline nest sites. The original establishment record 

 said that this site also provides habitat for burrowing 

 owl; it is unclear whether this meant that breeding of 

 this species had been documented or suspected. 

 Existing and potential wildlife significance may warrant 

 further consideration. 



OTHER VALUES: 



Like the Manning Corral RNA, this site could be used 

 to track plant succession in the wake of prairie dog use, 

 or be considered for prairie dog reintroduction. 



LAND USE: 



Grazing by large ungulates, if it occurs at all, would be 

 confined to winter when the frozen-over reservoir 

 provides the only access, but it was once part of primary 

 range for livestock grazing. Until recently, it was also 

 subject to foraging from prairie dogs in the main colony. 



MANAGEMENT COMMENTS: 

 Weeds and increaser species are prevalent on this site. 

 Native graminoids and forbs are present, but there is no 

 indication that they can outcompete the weed 

 population to reestablish their dominance. Though 

 there are various theories on cheatgrass invasion 

 (Young and Allen) , the projections are similar. On 

 comparable sites of the Columbia Basin and Great 

 Basin, despite a 40 year hiatus in disturbance, 

 cheatgrass (Bromus tectorum) has continued - and even 



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