45 



dispersal by wind. Dispersal usually occurs 

 in late summer and early fall. 



G. POPULATION ECOLOGY 



1. BIOLOGICAL INTERACTIONS 



a. COMPETITION: Many introduced species of 

 Cirsium are increasers with heavy grazing. 

 Cirsium subniveum occurs at sites where 

 competition is limited by harsh site 

 conditions (loose gravelly moving soils) , and 

 the species may be restricted to these 

 locations through lack of competitive 

 ability. 



b. HERBIVORY: Native plants in the genus 

 Cirsium support a variety of herbivorous 

 fauna including weevils, and several species 

 of moths (Turner et al, 1987a, 1987b) . In 

 addition, young rosettes are grazed by sheep 

 and cattle, but spines protect adult plants. 



H. LAND OWNERSHIP 



1. Laurin Canyon (001) - Bureau of Land Management, 

 Dillon Resource Area. 



2. Elk Lake (002) - Beaverhead National Forest, 

 Dillon Ranger District. 



3. French Creek (003) - Beaverhead National Forest, 

 Dillon Ranger District. 



II. ASSESSMENT AND MANAGEMENT RECOMMENDATIONS 



A. THREATS TO CURRENTLY KNOWN POPULATIONS: 



1. GRAZING: Young rosettes of species in the genus 

 Cirsium are palatable to grazers, but adult 

 flowering plants are often not preferred. Grazing 

 could impact this species if done at high levels 

 early in the season. 



2. MINING: The French Creek (003) population occurs 

 in a historic mining district, which has recently 

 had some renewed attention by geological 

 interests. This population should be considered 

 in any proposed project activities that might 

 affect the area. 



