Damage due to feral horses was observed west of the mouth of Big Coulee. Steep slopes 

 and banks had been severely terraced and destabilized. Both livestock and feral horse 

 grazing increases the likelihood of exotic weed encroachment. 



At the present time there is relatively little off-road vehicle use in th'e Pryor 

 Mountain Desert area. However, the topography and sparseness of the vegetation is 

 suitable for this sort of recreation. If off-road vehicle use increases substantially, it could 

 damage some populations of rare plants by disrupting plants, compacting soil, and 

 increasing erosion. 



Bentonite claims have been made on public lands in the Pryor Mountain Desert 

 area and some strip mining has occurred in just south of the border in Wyoming. Oil 

 and gas development has occurred south and west of Warren. Drilling and the 

 associated road-building and development could destroy populations of rare plants. 

 Sensitive plant surxeys should be conducted in association with any proposed 

 developments. 



Protecting Biological Diversity 



Species that are at risk due to their rarity or other aspects of their biology should 

 be given high priority for protection (Jenkins 1981). Based on the results of our study, 

 vascular plants of special concern and limited distribution in Montana occurring in the 

 study area can be divided into two groups: (1) high priority - species that are rare in the 

 study area and in Montana (15 species) and (2) low priority - species of limited 

 distribution in Montana that are common in the study area (26 species). Our knowledge 

 of the distribution of these species, especially high priority species, in the Pryor Mountain 

 Desert can be used to identify areas that are critical for protecting the biological diversity 

 of this northern outlier of intermountain desert vegetation. 



Although low-priority species ha\e little chance of becoming extirpated in the 

 Pryor Mountain Desert region and should not he given special protection status, they can 

 provide information on the occurrence of the unusual desert-like habitats in which they 

 occur. Of the 26 low-priority species, Astragalus chamaeleuce . Camissonia minor , 

 Cryptantha cana, Cryptantha flavoculata . Hrigeron allocotus , Streptanthella longirostris , 

 Townsendia incana , Wvethia scabra are confined to the area on the south side of the 

 Pryor Mountains in the Drainage of the Bighorn River (T9S R28E, 27E, 26E, 25E), while 

 none are confined to the areas north and west of Warren in the drainage of the Clarks 

 Fork of the Yellowstone. These results suggest that the area directly south of the Pryors 

 contains important habitats not found in the rest of the study area. This effect may be 

 due to greater topographic relief as well as the presence of calcareous sandstone and 

 Chugwater sandstone not present elsewhere. 



