10 



This describes the landforms where the species occurs in 

 Montana, however, the elevation at some sites is somewhat 

 higher (over 6,800 feet on Bachelor Mountain) and 

 populations are often confined to warm, southerly facing 

 aspects or micro-aspects. 



3. Soil relationships: In Montana, Astragalus scaphoides grows 

 in dry soils ranging from clayey to gravelly and stony 

 loams. The soils are derived from limestones, volcanics, 

 and basin sediments. 



E. POPULATION DEMOGRAPHY AND BIOLOGY 



1. Demographic details: Most populations in the state are 

 small and local, consisting of fewer than 500 plants. The 

 occurrence to the north of Clark Canyon Reservoir (008) is a 

 relatively large, dense, and healthy population with the 

 number of plants estimated between 1,000 and 10,000 in 1994 

 (1.500-2,000 in 1986). On Bachelor Mountain (005), the 

 subpopulations have a total of over 1,000 plants covering 

 around 100 acres, but most of these were small vegetative 

 plants at both survey dates (1984 and 1994). The newly 

 discovered occurrences in the northern Tendoys (011) and 

 along Rawhide Creek (013) consist of 500 or fewer plants, 

 covering 15 or fewer acres at each site. 



2. Reproductive biology: Reproduction is by seed. The low 

 numbers of successfully reproducing plants at many sites 

 suggests that seed production may be a major limitation to 

 population size and distribution of Astragalus scaphoides in 

 Montana. This conclusion is supported by data from the 

 study area as well as from other Montana populations in 

 other years, where low percentages of flowering plants and 

 high percentages of aborted flowers have been documented. 

 The population north of Clark Canyon Reservoir (008) is an 

 exception where large plants with mature fruit were common; 

 this reproductive success is reflected by the large and 

 dense population. Browsing of flowering heads (and entire 

 plants), probably by cattle, has been observed at several 

 sites. Astragalus scaphoides flowers in June and produces 

 fruit from June- July. 



F. MANAGEMENT CONSIDERATIONS 



Astragalus scaphoides has one of the narrowest global 

 distributions of plant species in Montana. The species is 

 locally plentiful in Idaho (Barneby 1964, Lesica and Elliott 

 1987) but is uncommon in Montana. Although new populations were 

 discovered in the state in 1994 (this report and Vanderhorst 

 1995a), most of these were small or otherwise in poor shape. 

 Only three of the currently known populations in the state 

 (including one in this study area) are large and prolific. The 



