{Chenopodium leptophyllum) , and Russian thistle (Salsola 

 kali). The shoreline is interrupted by scattered, high 

 cutbanks. 



OVERALL BIODIVERSnT SIGNIFICANCE: 

 York Island is a small but representative example of the 

 Missouri River Breaks segment of the Great Plains 

 biome. As such, it affords a rangeland reference area for 

 land managers and ecology researchers. The island is 

 small and vertical relief is limited, and though there are 

 two or three major substrate types, overall biological 

 diversity of the uplands is limited. 



bird use, and forms dense populations in limited upland 

 areas. It is currently the most abundant non-native 

 species and may have the potential to occupy virtually 

 all habitats on the island, with or without disturbance, 

 as evidenced by its mainland patterns of distribution. 



The survival of Hotsprings Phacelia {Phacelia thermalis) 

 on York Island is confiimed, restricted to relatively 

 sparse, successional vegetation zones created by the 

 Fort Peck Reservior; including scoured beaches and the 

 drawdown zone in wetland backwaters. Places where 

 Montana rare plant species of special concern are 

 confined to zones of man-made disturbance raise 

 questions whether the disturbance mimics natural 

 habitat conditions or the species is adventive by nature. 

 One other collection of this species has been made on 

 the Refuge, in Douglas-fir habitat near the former 

 Slippery Anne Guard Station (E0#001), suggesting 

 that the species occupies natural habitat elsewhere and 

 the York Island disturbance may mimic natural habitat 

 conditions. The Refuge is the only place where this 

 species occurs on public land in Montana, and even 

 though York Island does not have biodiversity 

 significance as a representative site for this species' 

 conservation, it points to the possibility of finding such 

 sites elsewhere on the Refuge. 



OTHER VALUES: 



York Island is also a Fort Peck Reservior landmark and 

 shelter for boaters. Archeological artifacts may be 

 present. Wildlife values were not evaluated. 



LAND USE: 



This landscape has been grazed in the past and the 

 Juniperus scopulorum woodland was probably cut for 

 fencing/firewood. }urdperus scopulorum stem density 

 probably approaches pre-disturbance conditions. No 

 signs of grazing were evident. It is otherwise idle except 

 for occasional visits by passing boaters. 



MANAGEMENT COMMENTS: 

 Exotic species present included Canada thistle {Cirsium 

 arvense) at scattered shoreline and backwater locations, 

 and minor upland populations of cheatgrass {Brotnus 

 tectorum) and Japanese brome {Bromus japorucus) . 

 Yellow sweetclover {Melilotus officinalis) dominates 

 beach vegetation where it may interfere with shoreline 



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