SUMMARY 



I conducted a demographic study of Astragalus scaphoides , a 

 regional endemic, at one site in southwest Montana and one in 

 adjacent Lemhi County, Idaho. Individual plants were mapped in 

 permanent plots and followed from 1986 through 1993. I used 

 matrix projection models and elasticity analyses to elucidate 

 important life history parameters and the importance of 

 predation, especially livestock grazing, on population growth. 



Astragalus scaphoides is a long-lived perennial. Growth and 

 survival of non-reproductive plants is consistently important to 

 population growth, while recruitment and survival of 

 reproductives are important in some years but not others. These 

 results along with the fact that the grazed A^ scaphoides 

 population became larger during my study suggest that predation 

 of inflorescences by livestock will have only a small negative 

 effect if it is not consistent. Rotation livestock grazing 

 systems should be compatible with long-term persistence of this 

 species in rangelands. 



INTRODUCTION 



Passage of the Federal Endangered Species Act of 1973 and 

 subsequent recognition of the value of conserving biotic 

 diversity (Wilson 1988) have resulted in many government agencies 

 becoming active in species conservation. Surveys to determine 

 the location and size of populations of rare species are being 

 conducted on public lands throughout the west. These surveys are 

 necessary in any species conservation program; however, knowing 

 the location and size of populations at any one point in time is 

 only the first step in a long-term protection strategy (Sutter 

 1986) . Extinction is a process requiring an understanding of 

 population dynamics (Menges 1986) . Periodic inventories can 

 detect trends but will do little to determine causality or help 

 generate predictive hypotheses (Palmer 1987) . Long-term 

 conservation requires a knowledge of many life history parameters 

 including fecundity, recruitment, survivorship, age structure, 

 and population flux. Demographic monitoring techniques can 

 provide information on factors regulating population density and 

 persistence (Palmer 1987) . This information, in turn, provides 

 an essential basis for management decisions. 



Astragalus scaphoides (Jones) Rydb. (Bitterroot milkvetch) 

 is endemic to a small area of east-central Idaho and adjacent 

 Beaverhead County, Montana. It was a candidate for listing as a 

 threatened or endangered species by the U.S. Fish and Wildlife 

 Service but has recently been downlisted to 3C (USDI-FWS 1993). 

 Astragalus scaphoides is listed as sensitive in Idaho (Moseley 

 and Groves 1990) and Montana (Lesica and Shelly 1991) . Most 

 populations of A^ scaphoides in Montana are on public lands 



