late April to early June, depending on climate conditions, slope, and aspect. At 

 many sites, extensi\'e vegetative mats were observed without flowers. It is not 

 known if this condition is due to senescence of individuals, advanced 

 succession within the habitat, or mistaken identification of Astragalus 

 hyalinus. 



Flowers or their remnants are necessary to distinguish the two species, and 

 both species may remain in vegetative condition under stress. The phenology 

 of A. hyalinus in the study area is less well understood. While considered to be 

 an early-season species, it did not begin flowering until early July in the 

 relatively cool 1995 growing season (Schmoller pers. comm.). The flowering 

 activity of .4. barhi may have overlapped with that of .4. hyalinus during June 

 of other years. 



2. POPULATION SIZE AND CONDITION: Of the 29 currently knowTi 



populations of ^. banii in Montana, the largest populations occur in Powder 

 River County. In Montana, most populations are large, and range from ca. 50 

 to 3,000 plants (mean ca. 1000). The individual plants of a population are 

 often broadly dispersed across the landscape; therefore, canopy coverage of 

 this species is often low. Population distribution appears to be related to 

 available substrate and may be divided into clusters, or subpopulations that 

 correspond with the local outcrop pattern. 



The Custer National Forest sites receive a different moisture regime than 

 surrounding areas, and support more successionally advanced habitats. Large 

 Astragalus spp. mats in these habitats were noted; because only vegetative 

 material was found, however, identification of these mats remains 

 undetermined. 



3. REPRODUCTIVE BIOLOGY 



a. TYPE OF REPRODUCTION: Reproduction is strictly by seed. 

 Flowers are not necessarily produced every year, perhaps 

 corresponding with climate or competition. Although the potential life 

 span and population age structure for this species is unknown, other 

 members of the group Orophaca can live in excess of 25 years 

 (Locklear 1986). Compared to related species, Barr's milkvetch is 

 considered prolific with fertile pods (Bameby 1964). 



b. POLLINATION BIOLOGY: Insect-pollinated 



c. SEED DISPERSAL AND BIOLOGY: Apparently only one seed 

 reaches maturity within each pod of Astragalus barrii (Bameby 1964 



25 



