Hickman's Potentilla

Potentilla hickmanii

Description

Potentilla hickmanii (Hickman's potentilla) is a small perennial herb in the rose family (Rosaceae) that annually dies back to a woody taproot. The leaves are pinnately compound into generally six paired, palmately cleft leaflets each 0.1-0.3 in (0.3-0.8 cm) long and to 0.1 in (0.3 cm) wide. Several reclining stems 2-16 in (5-40 cm) long support two to four branched cymes (flowering stems) each of which has less than 10 flowers. The flowers consist of five yellow obcordate petals 0.2-1 in (0.5-2.5 cm) long and 0.2 in (0.5 cm) wide, with typically 20 stamens and about 10 styles. Potentilla hickmanii is separated from Potentilla anserina var. pacifica and Potentilla glandulosa, two other potentillas that occur on the Monterey Peninsula, by a combination of its small stature, size and shape of leaflets, and color of the petals.

Hickman's potentilla was originally collected by Alice E. Eastwood in 1900 near the reservoir which supplies Pacific Grove, Monterey County, California, along the road to Cypress Point. The reference to a reservoir could refer to Forest Lake in Pebble Beach but more likely refers to the Pacific Grove reservoir. Eastwood described the species two years later, naming it after J. B. Hickman who was her guide on that collecting trip.

Habitat

Hickman's potentilla is currently known from only one location in Monterey County and one in San Mateo County. On the Monterey Peninsula, Potentilla hickmanii grows in an opening within Monterey pine forest. Loamy fine sandy soils support a meadow community of alien grasses and several introduced and native herbs. The San Mateo County population grows on grassland slopes on private lands.

Distribution

Only three historical locations for the plant are known, two in Monterey County and one in San Mateo County. A collection was made by Ethel K. Crum in 1932, apparently in the vicinity of East-wood's original collection on the Monterey Peninsula. The area surrounding the Pacific Grove reservoir was surveyed in 1992, but he found no Hickman's potentilla plants or suitable habitat for the species. An extant population is known from the western edge of the Monterey Peninsula on lands owned by Pebble Beach Company. This species was collected from one other location, at "Moss Beach" near Half Moon Bay in San Mateo County by Katherine Brandegee in 1905 and in 1933 by Mrs. E. C. Sutliffe. This population was presumed extirpated until it was rediscovered in 1995 by biologists from the California Department of Transportation surveying for a highway project.

Twenty-four individuals of Potentilla hickmanii were located during 1992 surveys of the Monterey site. The site was surveyed on two occasions in 1995 and no more than 21 plants were found. Sampling in a portion of this occurrence indicated that neither recruitment of new individuals nor mortality of existing individuals had occurred in the sampled area in the past two years. The San Mateo County population was estimated to have between 2,000 and 3,000 individuals in 1995 and 1996.

The Pebble Beach Company has maintained management responsibilities for the Monterey population, located in an open space area called Indian Village, although ownership of the land has been transferred to the Del Monte Forest Foundation. Indian Village is available for use by residents and has been developed as an outdoor recreation area. Although a fence was constructed in the 1970s to limit access by recreationists, the fenced area contained only a portion of the population, and recreation-induced damage continued through the mid-1990s. The Pebble Beach Company installed additional fencing in 1996 to protect this population from recreational activities.

Threats

Hickman's potentilla is currently threatened by a proposed residential development in the Del Monte Forest which could alter hydrology at the Monterey site. Invasive alien species at both the Monterey and San Mateo sites may be competing with this taxon. The extremely small number of individual plants remaining at the Monterey site also make Potentilla hickmanii vulnerable to extirpation from random events like genetic drift, poor years of reproduction, and tree fall.

Hickman's potentilla on the Monterey Peninsula is known from one occurrence of about 25 plants that grow in a meadow area designated as open space and used for recreation. In the 1970s, habitat occupied by Potentilla hickmanii was lost and degraded by fill brought in for a ball field; habitat trampling during recreational activities was noted as recently as 1995. The Pebble Beach Company built an additional wood fence in 1996 to exclude recreational activities from the remainder of the population. Development of an 18-acre (7.3-hectare), 21-lot residential subdivision is being proposed in Monterey pine forest within 330 ft (100 m) of the occurrence. This subdivision could harm Potentilla hickmanii by increasing the amount of human use in the area and by altering the hydrology of the site; a small watercourse and freshwater marsh that likely influence the meadow habitat of Potentilla hickmanii are located about 1,300 ft (396 m) upslope from the occurrence and are within the proposed lot development area. Mitigation proposed to reduce this threat is the elimination of the three lots that cover and border the marsh and riparian areas. Nevertheless, runoff into the meadow may be affected by upslope development.

Both populations of Hickman's potentilla may be threatened by alien species. The population on the Monterey Peninsula occurs at Indian Village where Ferreira in 1995 noted four alien grass taxa associated with it: Aira caryophylla, Bromus mollis, Festuca arundinacea, and Lolium multiflorum. The Festuca may have been introduced in a "meadow mix" used on adjacent fairways; its stature and invasiveness appear to compete with Potentilla hick-manii. Plantago coronopus is another alien present at this site that may be competing with Potentilla hick-manii. The alien grass Phalaris aquatica is also found at the San Mateo site, as is Genista monspessulana, an invasive alien shrub that occurs on the surrounding slopes. Potentilla hickmanii, at this location, is reported in greatest concentrations in those areas that support the most intact native habitats with the fewest annual grasses; whether lower densities elsewhere are due to competition from annual grasses has not yet been explored.

Alteration of habitat due to continuing recreational use of portions of Pebble Beach threaten the small populations of Hickman's potentilla there. Trampling by humans and horses can affect this taxa directly, as well as alter soil compaction and erosion to such a degree that alien taxa increase at the expense of native ones.

Vandalism is a potential threat for Hickman's potentilla. The sites that this plant inhabits are small, easily accessible, and highly susceptible to vandalism, an activity that could destroy a significant portion of these populations.

The inability of existing regulatory mechanisms to adequately protect this species has contributed to its status. In managing the habitat for this species in the Del Monte Forest Land Use Plan, the Pebble Beach Company has constructed fencing around part of the Potentilla hickmanii occurrences and has a program for control or eradication of alien species found within these areas. The Del Monte Forest Foundation, 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 already been harmed, as well as the protected areas themselves.

Conservation and Recovery

The Hickman's potentilla survives only at two sites, both of which are privately owned and at risk of development and other threatening activities. One habitat owned by the Del Monte Forest Foundation is located within an area called Indian Village, which is being managed as open space for outdoor recreation. Although the small population of Hickman's potentilla there is enclosed within a protective fence, it is still threatened by nearby recreational activities and potential residential development, and also by invasive alien plants. Both critical habitats of the Hickman's potentilla should be better protected. This could be done by acquiring the private land and establishing ecological reserves, or by negotiating conservation easements with the landowners. The populations of the Hickman's potentilla should be monitored, and research undertaken into its biology and habitat needs, including methods of beneficial management. The rare plant should be propagated in captivity, with the aim of providing stock for out-planting to augment the tiny natural population, and to establish new ones in areas of suitable habitat.

Contacts

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

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/

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.