3 

 Arabis fecunda is threatened by livestock trampling (Lesica 

 and Shelly 1991a) and encroachment of habitat by the aggressive 

 exotic Centaurea maculosa (spotted knapweed) at the Ravalli 

 County sites. It also occurs in areas of historic mining 

 activity in Beaverhead and Sliver Bow counties (Schassberger 

 1988) . Arabis fecunda is a candidate for listing as a threatened 

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

 (USDI-FWS 1990) and is considered threatened in Montana (Lesica 

 and Shelly 1991b) . 



Centaurea maculosa Lam. (Asteraceae) is a native of Eurasia, 

 widely introduced in North America, and has become a serious pest 

 of semi-arid grasslands in the Pacific Northwest and 

 intermountain valleys of the Northern Rocky Mountains (Watson and 

 Renney 1974, French and Lacey 1983). Its ability to invade and 

 replace native plants is well-documented (Morris and Bedunah 

 1984, Harris and Cranston 1979, Tyser and Key 1989). In 

 addition, leachates of Centaurea maculosa inhibit germination of 

 grass and conifer seedlings (Kelsey and Locken 1987) ; however, 

 concentrations high enough to inhibit germination would seldom be 

 found in natural environments (Kelsey and Bedunah 1989) . 

 Centaurea maculosa was introduced into western Montana in the 

 1920 's and has since come to dominate large areas of rangeland 

 (French and Lacey 1983). Like A^ fecunda . it is a rosette- 

 forming, taprooted perennial with an average life-span of 3-5 

 years (Watson and Renney 1974, Boggs and Story 1987). 



