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 is a candidate for listing as a 

 threatened or endangered species (C-2) by the U.S. Fish and 

 Wildlife Service (USDI-FWS 1990) . It 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 administered by the Bureau of Land Management and 

 are subject to livestock grazing (Lesica and Elliott 1987) . 



Previous studies have indicated that inflorescence predation 

 and seed predation by insects may be adversely affecting A. 

 scaphoides fecundity (Lesica and 'Elliott 1987, 1989). Lowered 

 fecundity is thought to be the cause of local rarity in a number 

 of plant species (Greig-Smith and Sagar 1981, Hester and 

 Mendelssohn 1987, Cabin et al. 1991). The purpose of this 

 demographic monitoring study is to track population trends of 

 Astragalus scaphoides in Montana and Idaho and gather life 

 history information that will enable interpretation of these 

 trends. 



METHODS 



Study Sites 



The Sheep Corral Gulch population occurs in southern 

 Beaverhead County, Montana on a gentle south-facing slope at 

 6,300 ft (T8S R12W S16) . Mean July and January temperatures at 

 Dillon, 20 miles to the northwest at 5,400 ft, are 66.2° and 

 20.1°F respectively. Mean annual precipitation is 9.5 in. 



