One criterion for selecting a reserw is density of rare or endangered species 

 (Margules and Usher 1981). We used tlu- geographic information system (GIS) to 

 overlay the distribution maps of the 15 hiuh-priority species (Figure 3). The Gypsum 

 Creek-Crooked Creek area (T9S R27E, \\h R2SB) stands out as having the highest 

 concentration of high-priority species populations. Eight of the 15 high-priority species, 

 Astragalus geyeri, Astragalus oreganus . Camissonia andina . Cleome lutea , Grayia spinosa . 

 Leptodactylon caespitosum , Malacothrix torreyi and Mentzelia pumila , have known 

 populations in this area. The Gypsum Creek-Crooked Creek area is 1250-1580 m (4100- 

 5200 ft) in elevation and contains soils derived from calcareous sandstone, Chugwater 

 sandstone and limestone. Terrain varies from highly dissected foothills with deep 

 canyons to broad alluvial valleys. The appreciable habitat diversity and the large number 

 of populations of both high- and low-priority species make the Gypsum Creek-Crooked 

 Creek area the best choice for a single reserve in the Pryor Mountain Desert. The seven 

 high-priority species not represented in tiiis area occur in widely separated sites 

 throughout the study area (Figure 3) and cannot be protected practically in large 

 reserves. 



In addition to the many species o\' rare plants found in the Prj'or Mountain 

 Desert, we believe that many of the plant communities are rare in Montana, and some 

 may be globally unique. Data from our floristic study provide a basis for delineating 

 special management areas for protecting the biological diversity of the area. However, 

 we believe that classification and mapping of plant communities should also be 

 completed in order to take into account elements of diversity other than plant species. 

 Using GIS, maps locating rare plant communities could be overlain on the existing rare 

 plant maps to better delineate the boundaries of special management areas. This 

 integrated approach will provide an information base that allows managers to protect 

 biological diversity on multiple-use lands. 



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