Osterhout Milk-vetch

Astragalus osterhoutii

Description

Osterhout milk-vetch, Astragalus osterhoutii, is a tall herbaceous annual with several bright green stems up to 41 in (104 cm) high and clusters of showy, white flowers. Each inflorescence (flowering stalk) bears 12-25 large flowers, 1 in (2.5 cm) long.

Habitat

This species is endemic to a limited area of badlands of shale and siltstone sediment at an elevation of about 7,450 ft (2,250 m).

Distribution

The Osterhout milk-vetch has been found only within a 15-mi (24-km) area in Middle Park, a sagebrush basin in north-central Colorado. It was first collected in 1905 by George Osterhout, an early Colorado botanist. Until the 1980s, this milk-vetch had been collected only five times. The largest population was discovered in 1940, along Muddy Creek, about 6 mi (9.7 km) north of Kremmling in Grand County, Colorado.

The species remains geographically confined to the Middle Park region in Grand County. The Muddy Creek population was further surveyed during the 1980s and was found to contain an estimated 25,000-50,000 plants. This represents approximately 90% of the total known species population. During the late 1980s small populations were discovered along Troublesome Creek and the north side of the Colorado River.

Threats

About two-thirds of the principal Muddy Creek population occurs on federal land administered by the U. S. Bureau of Land Management (BLM). Most of the remaining one-third is on privately owned land; a small number occurs on state land. The species is likely a remnant of a previous extension of the Wyoming flora southward during glacial periods. As such, it is naturally restricted to the small area of suitable habitat still available to the plants in Middle Park. Expansion and migration to possibly suitable habitats elsewhere is blocked by the high mountains surrounding Middle Park.

A portion of the Muddy Creek population is threatened with flooding by the proposed Muddy Creek Reservoir. Two different dam heights are under consideration. The higher would inundate about 14% of the Muddy Creek population; the lower proposal would flood about 8%. During flood stages there would be short-term flooding of an undetermined number of additional plants.

Recreational use of the reservoir and associated development would also threaten this population. The U. S. Fish and Wildlife Service (FWS) believes that a high level of recreational use may cause more damage to the Osterhout milk-vetch than the reservoir construction itself.

Conservation and Recovery

During a public hearing held in Kremmling before the final listing of the Osterhout milk-vetch, the Grand County government and the local water district, concerned with the future of the reservoir, voiced opposition to adding the species to the federal list of threatened and endangered species.

Under provisions of the Endangered Species Act, before the construction of the Muddy Creek Reservoir can proceed, the BLM and the U. S. Army Corps of Engineers must consult with the FWS to ensure that plans are developed and implemented to mitigate damage to the Osterhout milk-vetch. Such a plan might call for intensely managing the remaining habitat around the reservoir, fencing population sites, and redesigning recreational facilities to minimize impact on the species.

The 1992 recovery plan for the Osterhout milk-vetch—which also covers the rarer Penland beard-tongue (Penstemon penlandii ), an endangered plant with an overlapping habitat—states that the primary recovery objective is the conservation of existing populations for the foreseeable future. Removal of the species from the list of endangered and threatened species (delisting) is considered unlikely because of the species' small natural populations, limited habitat, and the persistent nature of potential threats.

The recovery plan describes a number of efforts recommended to conserve existing populations, including the establishment of land management designations and development and implementation of habitat management programs for known populations of both species on private and public lands. The inventory of any remaining unsurveyed suitable habitat will also aid in conservation, as will research into the species' life history and ecology and the monitoring of existing populations. The adjustment of management practices will be undertaken as necessary and indicated by a downward trend of populations or evidence of physical habitat degradation.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 25486
Denver Federal Center
Denver, Colorado 80225
http://www.r6.fws.gov/

References

Barneby, R. 1964. "Atlas of North American Astragalus. " Memoirs New York Botanical Garden 13: 429, 434-436.

Karron, J. D. 1987. "The Pollination Ecology of Cooccurring Geographically Restricted and Widespread Species of Astragalus (Fabaceae)." Biological Conservation (London) 39: 179-193.

Peterson, J. S., et al. 1981. "Status Report on Astragalus osterhoutii. " State of Colorado Natural Areas Program, Denver.

U. S. Bureau of Land Management. 1989. "Biological Assessment for the Muddy Creek Reservoir Project, Grand County, Colorado." U. S. Bureau of Land Management, Craig, Colo..

U. S. Fish and Wildlife Service. 1992. "Osterhout Milk-vetch and Penland Beardtongue Recovery Plan." U. S. Fish and Wildlife Service, Grand Junction, Colo.

U. S. Forest Service. 1987. "Biological Assessment for the Rock Creek/Muddy Creek Project, Routt and Grand Counties, Colorado." U. S. Forest Service, Rocky Mountain Region, Lakewood, and Rout National Forest, Steamboat Springs, Colo.