22 

 II. ASSESSMENT AND MANAGEMENT RECOMMENDATIONS 



A. THREATS TO CURRENTLY KNOWN POPULATIONS 



1. GRAZING: Grazing by domestic livestock is not 

 known to pose any current threat to Cirsium 

 lonqistvlum populations. 



2. TIMBER HARVEST: Timber harvest is not known 

 currently to pose a threat to any Cirsium 

 lonqistvlum populations. 



3. WEED CONTROL: A weevil, Rhinocvllus conicus , 

 which was introduced as a biological control for 

 musk thistle (Carduus nutans ) , has attacked the 

 seed heads of some Cirsium lonqistylum plants in 

 the Little Belt Mountains. The effect on seed 

 production and population viability is not known. 

 This insect could pose a threat to Cirsium 

 lonqistylum in the long term, and its effect 

 should be fully evaluated. A preliminary study 

 has been begun. 



4. HYBRIDIZATION: This is currently only a 

 speculative threat since it is not clear that 

 hybridization is occurring or that it is 

 threatening the integrity of C. lonqistvlum as a 

 distinct species. However, introgressive 

 hybridization (Anderson 1953) with a more numerous 

 species could potentially swamp C. lonqistylum as 

 a distinct genetic entity. Introgressive hybrids 

 typically occur in disturbed areas ('hybridized 

 habitats') and with increasing disturbance can 

 increase their population size and contact between 

 the parent species to the point that parent 

 populations can be overwhelmed genetically. 

 Introgression is often a natural process but may 

 also be triggered or increased by human 

 disturbance. Studies are needed to determine if 

 hybridization is, in fact, occurring and, if so, 

 to determine its effect on C. lonqistvlum . 



B. MANAGEMENT PRACTICES AND RESPONSE: No information is 

 available on responses to specific management actions. 

 However, C. lonqistylum seems able to occupy lightly 

 disturbed sites, but is as often found in native 

 habitat. 



C. RECOMMENDATIONS FOR MAINTAINING VIABLE POPULATIONS: 

 The following recommendations are made to ensure that 

 the long-term viability of Cirsium lonqistylum 



