17 



The average area covered by populations is 

 approximately 101,175 sq. meters (25 acres). 

 Population sizes and condition are summarized in 

 Table 3. 



3 . REPRODUCTIVE BIOLOGY 



a. TYPE OF REPRODUCTION: Little is known of 

 the reproductive biology of A. barrii . 

 Within the group Orophaca a minimum age of 25 

 years was established for individual plants 

 of A. aretioides and even small individuals 

 of A. tridactylicus averaged over 15 years of 

 age (Roberts, 1977) . A perennial species, it 

 may produce a few or no flowers in some years 

 (Locklear, 1986) . This author observed at 

 several sites large mats that bore no 

 flowers, in close proximity to smaller clumps 

 that were flowering. 



b. SEED DISPERSAL AND BIOLOGY: Apparently only 

 one seed reaches maturity within each pod of 

 the flowers of Astragalus barrii (Barneby, 

 1964). Pods dehisce from the base upwards 

 along both the dorsal and ventral sutures. 

 Having no appendages that would aid in long- 

 distance dispersal, it is likely that seeds 

 fall and remain near the parent plant. 



POPULATION ECOLOGY 



1. BIOTIC AND ABIOTIC INTERACTIONS 



a. COMPETITION: Species in the genus 

 Astragalus rarely tolerate direct competition 

 or shade cast by other plants (Barneby, 

 1964). It was observed that populations were 

 most often found on barren ground. Total 

 vegetation cover (by ocular estimation) 

 rarely exceeded 50% and it was often lower. 

 It appeared that sites with large non- 

 flowering mats were those areas where 

 succession was more advanced and total 

 vegetation cover values were somewhat higher; 

 however, the lack of flowering may also have 

 been due to the low rainfall in the area for 

 the past 5 years, or other unknown factors. 



b. FIRE: A large portion of one site (NW 

 Buttress Taylor Butte (017) was within an 

 area that had burned nearly 20 years ago. It 

 is possible that these plants are adapted to 

 fire as fires are common on this portion of 

 the Custer National Forest. However, the 



