SUMMARY 



The Pryor Mountain Desert of southern Carbon County has one of the most 

 unusual floras in Montana. The arid climate and unusual and varied soils provide 

 numerous desert-like habitats that are otherwise unknown in the state. Furthermore, this 

 region lies at the north end of the Bighorn Basin, a broad trough that may have served as 

 a migration route from the Red Desert of southern Wyoming. As a result, numerous 

 species of desert plants reach the northern limit of their range in the Pryor Mountain 

 Desert. Many of these species occur nowhere else in the state. For these reasons, the 

 Pryor Mountain Desert is important for the conservation of biological diversity in the 

 Northern Rocky Mountains region. The purpose of our study was (1) to determine 

 which of the rare plants may be threatened or endangered in the area, (2) locate and 

 map these elements of diversity, and (3) use this information to delineate special 

 management areas that efficiently protect the biological diversity of the region. 



We surveyed the 65,000-ha study area for 35 species of vascular plants listed as 

 species of special concern or of limited distribution by the Montana Natural Heritage 

 Program. Efforts were concentrated in areas of high habitat diversity. We mapped 

 locations, estimated population density, and recorded soil and vegetation information for 

 each population observed. 



We located nearly 900 populations of target species, including six rare species 

 previously unknown from the area and four species previously unknown from Montana. 

 From these data, we determined that 26 of the 41 target species were common in the 

 study area. We mapped the occurrences of the remaining 15 high-priority species and 

 determined that a special management area located in ca. one township in the Gypsum 

 Creek-Crooked Creek area would protect populations of half of these species. Sensitive 

 plant species may be threatened by exotic weed encroachment, livestock and feral horse 

 grazing, off-road vehicle use, and oil and gas development. 



