16 



It appears that Astragalus barrii is not 

 restricted to a particular geologic stratum but 

 may be restricted by a chemical characteristic of 

 the soil such as soil pH . Soil samples from two 

 sites were tested by the Colorometric Method and 

 found to have a pH near 8.0. This is a fairly 

 high soil pH. A more comprehensive soil study 

 might better reveal any ecological influence this 

 may have on the plants. 



4. REGIONAL CLIMATE: The summer climate of 



southeastern Montana is predominantly hot and dry. 



Summer storms are largely convective, a common 



characteristic of areas with continental climates. 



Winters are cold and dry with precipitation 



occurring mostly in the form of snow. For areas 



on the Custer National Forest where A. barrii is 



located, the nearest long term climatological 



station is in Broadus (923 m (3,029 ft.) in 



elevation), located 64 km (40 mi.) to the east of 



the Custer National Forest. The mean annual 



temperature for the time period 1951-1980 is 6.9 

 o o 

 C (44.5 F) . The mean minimum and maximum 



temperatures for July were 12.9 and 30.6 °C (55.3 



and 87.0 °F) while for January it was -15.8 and - 



1.1 °C (3.6 and 30.0 °F) for the same time period. 



Mean annual precipitation was 33.9 cm (13.84 in.). 



Most of this precipitation occurs in the form of 



rain falling from April through August (U.S. 



Department of Commerce, 1982). 



POPULATION DEMOGRAPHY AND BIOLOGY 



1. PHENOLOGY: An early-blooming species; Astragalus 

 barrii flowers from early May to the first part 

 of June, depending on climatic conditions, 

 latitude, and slope aspect. At many sites 

 extensive vegetative mats were observed without 

 flowers. It is not known if this condition is due 

 to senescence of the individuals through natural 

 aging, advanced succession within the habitat 

 (i.e., increased overstory cover), or other 

 unknown factors. 



2. POPULATION SIZE AND CONDITION (MONTANA): 

 Populations of A. barrii range in size from about 

 70 individual plants, up to sites with several 

 subpopulations totaling 3,050 plants. The average 

 population size is approximately 1,000 

 individuals. 



