kingii , Carex rupestris , and Poa interior . This community 

 type has been described in Montana in very general terms by 

 Pfister et al. 1977. 



Within the shrubland and grassland zone the following three 

 additional communities were sampled: 



4) Atriplex conf ertif olia 



This community was sampled at one steep mid slope location 

 at an elevation of 4,600 feet. Atriplex conf ertif olia and 

 Haloqeton qlomeratus were the only species that were well 

 represented. This community type has not been previously 

 described in Montana. Similar communities occur in Nevada 

 (Bourgeron and Engelking 1992). 



5) Sporobolus cryptandrus 



This community was sampled at one valley bottom location on 

 at an elevation of 4,800 feet. Sporobolus cryptandrus , 

 Opuntia polyacantha , and Haloqeton qlomeratus were all well 

 represented. This community type has not been previously 

 described . 



6) UNCLASSIFIED 



One steep mid slope sample at an elevation of 4,500 feet was 



not characterized by any single species or group of species. 



The only species present with canopy cover values up to 5% 



were Suaeda nigra , Atriplex conf ertif olia , and Atriplex 

 nuttallii. 



DISCUSSION 



Rarity and Biogeography 



Using a combination of two-way indicator species analysis 

 (TWINSPAN) and detrended correspondence analysis (DCA) 33 

 vegetation types were identified among the 197 study plots. 

 Comparisons with a "comprehensive" listing of vegetation types of 

 the western United States revealed that 9 of the types from the 

 Pryor Mountains region had not been reported from elsewhere and 

 14 are rare globally. This concentration of rare vegetation 

 types, in combination with previously documented occurrences of 

 rare plant species, highlight the significant biodiversity values 

 of the Pryor Mountains. 



Specifically, the globally rare types identified in the 

 study area were: 



Abies la siocarpa / Clematis columbiana (G3/S3) 

 Pseudotsuaa msnziesii / Cercocarpus ledifolius (G3/S3) 



36 



