Coastal Dunes Milk-vetch

Astragalus tener var. titi

Description

Coastal dunes milk-vetch, Astragalus tener var. titi, is a diminutive annual herb of the pea family (Fabaceae or Leguminosae). The slender, slightly pubescent stems reach 4-8 in (10-20 cm) in height; the pinnately compound leaves are 0.8-2.7 in (2-6.8 cm) long with seven to eleven leaflets, each having a slightly bilobed tip. The tiny lavender to purple flowers are 0.3 in (7 mm) long and are arranged in subcapitate racemes of two to twelve flowers. The seed pods are straight to sickle-shaped and 0.3 to 0.6 in (7-15 mm) long. While annual plants like A. tener var. titi will undergo radical fluctuations in population size as a result of natural environmental conditions, the long-term survival of this taxon depends on maintaining seed production and appropriate habitat for population expansion.

Astragalus tener var. titi, was first collected by Mrs. Joseph Clemens in 1904 along 17-Mile Drive on the Monterey Peninsula near an old hut composed of abalone shells and coal-oil cans. Alice Eastwood named the plant A. titi in 1905 in honor of Dr. F. H. Titus. John Thomas Howell, remarked in 1938 that although A. titi Eastwood has generally been regarded as the same as A. tener, the two plants are not the same. Rupert Barneby published the combination A. tener var. titi in 1950, noting the difference in flower size, habitat, and geographic range between it and A. tener var. tener.

Habitat

Colonies of the milk-vetch occur on a relatively flat coastal terrace within 100 ft (30 m) of the ocean beach and 25 ft (7.6 m) above sea level. The loamy fine sands that comprise a series of shallow swales on the terrace surface support standing water during wet winter and spring seasons. Individual plants are found on the bottoms or sides of the swales growing in association with other low-growing grasses and herbs, including the alien Plantago coronopus (cut-leaf plantain).

Distribution

Two historical locations of this plant from Los Angeles County, Hyde Park in Inglewood and Santa Monica, and two from San Diego County, Silver Strand and Soledad, were annotated by Barneby as A. tener var. titi. It is unlikely that suitable habitat remains at the Los Angeles locations, since the area has been heavily urbanized. The Silver Strand area of Sand Diego County is owned by the Department of Defense for its Miramar Naval Weapons Center, where a section of the property has been used for amphibious vehicle training exercises. Another portion of Silver Strand has been leased by the Navy to the California Department of Parks and Recreation for development of a campground and recreational facilities. Numerous unsuccessful searches for the taxon have been made in these locations since 1980, and it is reasonable to assume that these historical sites have been lost through habitat destruction.

The only known extant population of A. tener var. titi occurs along 17-Mile Drive on the western edge of the Monterey Peninsula on land owned by the Pebble Beach Company and the Monterey Peninsula Country Club. Counts in the 1980s and early 1990s variously identified from 15 to 1,000 individuals in this population. In 1995, four additional colonies of the milk-vetch were located in similarly moist habitats within 1,300 ft (400 m) of the previously known plants. A thorough survey of surrounding patches of suitable habitat was made and a total of 4,000 individuals were counted in 1995 in 11 scattered colonies. These 11 colonies are bisected by 17-Mile Drive, and occur in remnant patches of habitat that are bounded by roads, golf greens, equestrian trails, and a bank covered by the alien plant Carpobrotus edulis (fig-marigold).

Threats

Coastal dunes milk-vetch is currently threatened with alteration of its marine terrace habitat from trampling associated with recreational activities such as hiking, picnicking, ocean viewing, wildlife photography, equestrian use, and golfing.

A. tener var. titi may also be threatened by competition from the alien plants P. coronopus (cut-leaf plantain) and C. edulis.

Due to the fragmented nature of its habitat and the human uses that surround it, the species is also more susceptible to genetic weaknesses and more vulnerable to extinction from random events.

This species occurs with P. coronopus and C. edulis along 17-mile Drive. C. edulis, in particular, spreads rapidly and competes aggressively with native species for space. The Pebble Beach Company has an active C. edulis eradication program in and adjacent to the enclosure on the ocean side of 17-Mile Drive. However, C. edulis has been planted and is being maintained within a few feet of the unfenced portion of the habitat of A. tener var. titi on the inland side of 17-Mile Drive owned by the Monterey Peninsula Country Club.

The Pebble Beach Company, as part of managing the ESHAs in the Del Monte Forest LUP, has constructed fencing around part of the A. tener var. titi occurrences and has implemented a program for control or eradication of alien species within these areas. The DMFF, which manages the Morse Reserve and Huckleberry Hill Open Space area, also has a control program for alien species. Despite these protections, adjacent areas identified for development have damaged and will likely continue to damage the protected areas.

Alteration of habitat due to continuing recreational use of portions of Pebble Beach threaten the small populations of A. tener var. titi there. Trampling by humans and horses can directly damage individuals of this plant, as well as alter soil compaction and erosion in such a way that alien plants increase at the expense of the native ones.

Vandalism is a potential threat for A. tener var. titi. The sites inhabited by this plant are small, easily accessible to people, and highly susceptible to vandalism, an activity that could result in the destruction of a significant portion of the individuals in those populations.

Conservation and Recovery

The only surviving habitats of the coastal dunes milk-vetch occur on privately owned land. Some protective measures have been implemented, including the erection of protective fencing around stands of the rare plant and the local eradication of competing alien plants. However, the coastal dunes milk-vetch is still severely threatened by disturbances associated with land-use practices and recreation in or near its critical habitat. This conflict should be resolved in favor of the endangered plant by protecting larger areas of its habitat. This could be done by acquiring its habitat and designating ecological reserves, or by negotiating conservation easements with the landowners. The populations of the coastal dunes milk-vetch should be monitored, and research undertaken into its biology and ecological needs. Additional populations should be established in suitable habitat, using plants grown from seed in captivity.

Contacts

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

U. S. Fish and Wildlife Service
2493 Portola Road, Suite B
Ventura, California, 93003-7726
Telephone: (805) 644-1766
Fax: (805) 644-3958

Reference

U.S. Fish and Wildlife Service. 12 August 1998. "Endangered and Threatened Wildlife and Plants: Final Rule Listing Five Plants From Monterey County, CA, as Endangered or Threatened." Federal Register 63(155):43100-43116.