Carter County distribution: The occurrence 



record in Carter County represents a 1 943 



collection "from Ekalaka" which is cited in 



Bameby (1964). Field surveys in 1986 and 



1989 in the vicinity of Ekalaka did not relocate 



the species. In the course of this study, we have 



ruled out the likelihood of it occurring on BLM- 



administered land in the vicinity of Ekalaka. We 



have also ruled out the likelihood of it in most of 



northern Carter County, but not in the whole 



county. The timing or extent of baseline survey in 



western ends of the county with potential habitat was not suited for inventorying this species. 



These areas may be similar to the populations along the Powder River breaks in Powder 



River Covmty. 



In the plant association and community type constancy/cover tables (Appendix A), mat 

 forming 3-leaflet milkvetches were provisionally identified as tufted milkvetch (Astragalus 

 gilviflorus; ASTGIL), which is many magnitudes more common as well as more widespread 

 in distribution than Barr's milkvetch. 



HABITAT: Montana habitats of Barr's milkvetch are mostly sparsely vegetated knobs and buttes, 

 usually with dry, fine-textured, often calcareous soils. Many are situated along rivers or streams, 

 where downcutting has exposed shale and siltstone outcrops. It appears to be a poor competitor. The 

 species is often locally confined to specific soil types and rock formations. The highest known 

 numbers are on silty soils of the Midway series, representing calcareous, platy, soft shale with a 

 montmorillonific clay component (Heidel and Marriott 1996). However, it is apparently not 

 restricted to this series in the state. 



The occupied microhabitat represents clayey and shallow clay range site associations that are 

 sparsely vegetated and usually have scattered bunchgrass (bluebunch wheatgrass; Pseudoroegneria 

 spicata, syn. Agropyron spicatum). The surrounding landscape varies from sparsely forested to open 

 plains, with various plant and range associations. The known occurrences span 2950-4160 ft. 



SPECIES BIOLOGY: The potential life span and population age structure for this species is 

 unknown, though other members of the group Orophaca can live in excess of 25 years. Barr's 

 milkvetch is considered prolific with fertile pods (Bameby 1964), though it has been noted that some 

 populations and some drought years have little or no flowering activity (Heidel and Marriott 1996). 



The individual plants of a population are often broadly dispersed across the landscape, with 

 population distribution apparently related to available substrate and local outcrop patterns. There are 

 a few populations that have been documented with over 1000 individuals total. 



OTHER COMMENTS: Barr's milkvetch is known from BLM-administered lands elsewhere in its 

 range. More complete status information is presented in Schassberger (1990) and Heidel and 

 Marriott (1996). This study does not provide any new information for reconsidering its status. 



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