16 



The Custer National Forest sites receive a 

 different moisture regime than surrounding 

 areas, and support more successionally advanced 

 habitats. It was noted that A. barrii mats in 

 these habitats tended to be larger, and were 

 often only vegetative. Advanced successional 

 habitats may influence the age class 

 distribution of this species; these populations 

 may contain larger older mats that have lower 

 rates of flowering and fruiting, which may 

 result in reduced seedling establishment. 



6. Dependence on dyneunic aspects of biotic 

 associations and ecosystem features: Unknown. 



7. Other endangered, threatened, rare, or 

 vulnerable species occurring in the habitat of 

 this taxon: None currently known. 



7. Population biology of the taxon. 



A. General summary: The 27 currently known populations 

 of A. barrii in Montana occur in badlands habitats, 

 in the southeastern portion of the state. Some 

 populations in Montana are separated by up to 

 approximately 70 air miles. The largest population 

 occurs in Powder River County. Advancing 

 vegetational succession may be a factor in the age 

 class distribution of this species. 



B. Demography. 



1. Known populations: There are currently 27 

 known populations of A. barrii in Montana. 

 These populations arfe located in 3 counties: 

 Bighorn (2) , Rosebud (6) and Powder River (19) . 

 This species is also known from southwestern 

 South Dakota, and northeastern Wyoming. 



2. General demographic details (Montana): 



a. Biddle (001) 



1. Area occupied by population: Ca. 15 

 acres. 



2. Estimated nvimber of individuals: Ca. 

 200-250 plants (1986). 



3. Density: Unknown. 



4. Presence of dispersed seeds: 

 Unknown. 



5. Evidence of reproduction: Flowering 

 plants observed (1986) . 



6. Evidence of population expansion or 

 decline: Unknown. 



