Cushenbury Milk-vetch

Astragalus albens

Description

Astragalus albens (Cushenbury milk-vetch) is a small silvery-white perennial herb in the pea family (Fabaceae). The slender stems are decumbent, grow to 12 in (30 cm) in length, and support leaves comprised of five to nine small leaflets. Its purple flowers bloom from March to May towards the ends of the branches in five to 14 flowered racemes, developing pods with eight to 11 seeds.

Habitat

Cushenbury milk-vetch is typically found on carbonate substrates along rocky washes and gentle slopes within pinyon woodland, pinyon-juniper woodland, Joshua tree woodland, and blackbrush scrub communities. Parish's daisy and Cushenbury buckwheat are associated with Cushenbury milk-vetch at several locations. Most occurrences are found between 5,000-6,600 ft (1,500-2,000 m) in elevation on soils derived directly from decomposing limestone bedrock. Three occurrences are found below 5,000 ft (1,500 m) in elevation in rocky washes that have received limestone outwash from erosion higher in the drainages. According to a 1992 survey, the Gordon Quarry and Granite Peaks populations occur on granite substrates and the Cactus Flat population occurs on granite and quartzite. Other habitat characteristics include an open canopy cover with little accumulation of organic material, rock cover exceeding 75%, and gentle to moderate slopes between 5-30% in inclination.

Distribution

Cushenbury milk-vetch is currently known from less than 20 occurrences scattered over a range of 15 mi (24 km) throughout the eastern half of the carbonate belt, running from Furnace Canyon southeast to the head of Lone Valley.

Although the number of Cushenbury milk-vetch individuals was estimated at 2,000 during a drought in 1988, this number is likely to be greater in years of substantial rainfall. Several known populations comprised a larger number of individuals during the 1992 field season than had previously been reported. This circumstance may have been due to heavy and favorable rainfall received during March 1992 that resulted in a large establishment of seedlings; it also might reflect a more thorough survey effort than in previous years. Of particular significance was the extension of a population in the Top Spring-Smarts Ranch Road area; several thousand individuals were found in this area, making it the primary population center for the species. Population estimates for 1992 place the total number of individuals between 5,000 and 10,000.

Threats

Cushenbury milk-vetch is restricted primarily to carbonate and adjacent carbonate/granitic substrates occupied by pinyon-juniper woodland on the northern side of the San Bernardino Mountains. The imminent and primary threat facing this species is the ongoing destruction of the carbonate substrates on which it grows by activities associated with limestone mining, including direct removal of mined materials, disposal of overburden on adjacent unmined habitat, and road construction. Additional threats to its habitat include off-highway vehicle use, urban development near the community of Big Bear, development of a ski run, and energy development projects.

Conservation and Recovery

There are about 20 known habitats of the Cushenbury milk-vetch, almost all of which occur on federal land managed by the Forest Service, and to a lesser degree the Bureau of Land Management. The largest of these critical habitats should be protected from mining and other disturbances. This could be done by appropriate modifications of the management plan for the San Bernardino National Forest. The populations of the Cushenbury milk-vetch should be monitored, and research undertaken into its biology and habitat requirements.

Contacts

U.S. Fish and Wildlife Service
Ventura Fish and Wildlife Office
2493 Portola Road, Suite B
Ventura, California 93003-7726
Telephone: (805) 644-1766

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Building
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

References

U.S. Fish and Wildlife Service. 24 Aug 1994. "Endangered and Threatened Wildlife and Plants; Five Plants From the San Bernardino Mountains in Southern California Determined to be Threatened or Endangered." Federal Register 59.