10 



sagebrush ( Artemisia tridentata ) and bluebunch wheatgrass 

 ( Elymus spicatus ) . Other shrub species which are 

 subdominant or in some cases replace big sagebrush in these 

 habitats include three-tip sagebrush ( Artemisia tripartita ) , 

 low sagebrush ( Artemisia nova ) , and grey rabbitbrush 

 Chrysothamnus nauseosus) . Other common or subdominant 

 grasses at the sites include needle and thread ( Stipa 

 comata) , indian ricegrass ( Oryzopsis hymenoides ) , Idaho 

 fescue ( Festuca idahoensis ) , and Sandberg's bluegrass ( Poa 

 secunda) . Among the most conspicuous associated forbs are 

 other milkvetches, including Astragalus adsurgens . 

 Astragalus drummondii , and Astragalus atropubescens . 



J. Topography: Barneby (1964) describes the settings of 



Astragalus scaphoides throughout its range as "open valleys, 

 low hills, (and) canyon benches ... from 3,500-6,000 feet." 

 This describes the landforms where the species occurs in 

 Montana, however, the elevation at some sites is somewhat 

 higher and populations are often confined to warm, southerly 

 facing aspects or micro-aspects. 



I. Soil relationships: In Montana, Astragalus scaphoides grows 

 in relatively well developed, dry soils ranging from clayey 

 to gravelly and stony loams. The soils are derived from 

 limestones, volcanics, and basin sediments. The soil of the 

 occurrence near Bannack is heavy and gravely. 



POPULATION DEMOGRAPHY AND BIOLOGY 



. . Demographic details: Most populations in the state are 

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

 population nearest Bannack was estimated in 1983 to consist 

 of fewer than 50 plants. A population further downstream 

 near the Bon Accord mine was larger, estimated to consist of 

 between 200 and 300 plants in 1984. Neither of these 

 populations has been recently surveyed. 



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

 numbers of successfully reproducing plants at many sites 

 suggests that seed production is a major limitation to 

 population size and distribution of Astragalus scaphoides in 

 Montana. This conclusion is supported by data from several 

 Montana populations over several years, where low 

 percentages of flowering plants and high percentages of 

 aborted flowers have been documented. Browsing of flowering 

 heads (and entire plants), probably by cattle, has been 

 observed at several sites. Bitterroot milkvetch flowers in 

 June and produces fruit from June to July. 



