similar colluvial setting. In Carter County, the largest population at Medicine Rocks is in early 

 successional habitat of active sand dunes. The two BLM populations are more isolated and are 

 confined to southerly aspects below sandstone outcrops. The outcrop settings support scattered 

 ponderosa pine and grassland mosaics with Cyperus schweinitzii occupying ecotones of the 

 dominant community types with rock outcrop. Dominant grass species in these habitats include 

 prairie reedgrass (Calamovilfa longifolia), little bluestem {Schizachyrium scoparium; syn. 

 Andropogon scoparium) and needle-and-thread {Stipa comata). The threadleaf sedge {Carex filifolia) 

 is sometimes a dominant species. Other species associated with its sandy habitat include spiderwort 

 {Tradescantia occidentalis) and yucca {Yucca glauca). 



SPECIES BIOLOGY: Carter County BLM populations are small, the Pine Hill occurrence had an 

 estimated 100 aerial stems across about 1 acre of habitat, while the Mill Iron site had only 1 1 stems 

 confined to the south side of a small outcrop. Since the plants are rhizomatous, these numbers are 

 high estimates of the actual number of genetically distinct individuals. The population is larger at 

 Medicine Rocks State Park (over 500 stems), and largest and far more extensive in Sheridan County 

 in the Medicine Lake Sandhills complex (Cooper and Heidel 1998). 



OTHER COMMENTS: Range conditions in the vicinity of BLM Carter County populations was at 

 the low end, and grazed by sheep. The population areas are confined to steep or rocky areas that are 

 less heavily grazed. No browsed plants were seen. It is difficult to assess the impact of grazing on 

 Cyperus schweinitzii because the area of these populations (Mill Iron and Pine Hill vicinities) has 

 among the longest histories of grazing in Montana. Whether the current small populations are relict 

 numbers protected by topography, or are naturally small and limited by other habitat constraints, is 

 uncertain. The large population at Medicine Rocks State Park is protected from grazing. Due to 

 uncertain population trends and responses, we recommend that BLM Watch status be retained. 



This is one of several sand-loving species in the county that are often found with other species of 

 special concern where the habitat is extensive and/or in good condition. 



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