Santa Cruz Island Dudleya

Dudleya nesiotica

Description

Dudleya nesiotica (Santa Cruz Island dudleya) was described in 1950 as Hasseanthus nesioticus based on a specimen collected earlier that year from a "flat area near edge of sea bluff, Fraser Point," on the west end of Santa Cruz Island. The species was then transferred to the genus Dudleya three years later. Dudleya nesiotica is a succulent perennial in the stonecrop family (Crassulaceae). The plant has a corm-like stem with eight to 16 oblanceolate leaves in a basal rosette from which several flowering stems 1.2 to 4.0 in (3 to 10 cm) tall arise. The white five-petaled flowers and resulting fruits are erect to ascending.

Research from 1996 indicates that the number of flowers per plant ranges from six to 12.

Habitat

Dudleya nesiotica, surviving only in one population on Santa Cruz island, is situated on the lowest marine terrace in coastal scrub and grasslands. The west end of the population is associated with salt bush (Atriplex californica ), slender-leaved iceplant (Mesembryanthemum nodiflorum ), alkali heath (Frankenia salina ), goldfields (Lasthenia californica ), and pickleweed (Salicornia subterminalis ). The east end of the population is associated with Australian salt-bush (Atriplex semibaccata ), brome (Bromus hordeaceus ), goldfields (Lasthenia californica ), purple needlegrass (Nasella pulchra ), and vulpia (Vulpia myuros ).

Distribution

Dudleya nesiotica is known only from one population, the type locality at Fraser Point on the west end of Santa Cruz Island.

Research has indicated that this taxon is more abundant than was once thought. Four sites of high densities were sampled within the general area near Fraser Point, where a total of 32 acres (13 hectares) are occupied by the plant. Based on this field work, estimates from 1994 to 1996 of absolute population size ranged from 30,000 to 60,000. The Nature Conservancy has calculated density, cover, and height of plants within 30 randomly selected plots at this location since 1991. Annual variation in density has ranged from 20.2 to 34.8/sq yard (16.9 to 29.1/sq m). annual variation in cover has ranged from 8.7 to 16.1 %, and annual variation in height of rosettes has ranged from 0.5 to 0.66 in (1.27 to 1.68 cm).

Threats

The Santa Cruz Island dudleya remains vulnerable to soil loss, herbivory by feral pigs, and disturbance by pig rooting. It is also potentially vulnerable to collecting for botanical or horticultural use.

Conservation and Recovery

The Santa Cruz Island dudleya only survives as one population on the west end of Santa Cruz Island. It occurs in an area of about 32 acres (13 hectares), which supports about 30,000-60,000 plants. Although its habitat is being protected from development, the rare dudleya is still threatened by soil loss, the feeding of feral pigs, and habitat alteration by invasive alien plants and other causes. The western 90% of Santa Cruz Island is owned and managed by The Nature Conservancy, a private environmental organization (the other 10% of the island is federal land managed by the National Parks Service). The survival of this endangered plant requires strict protection from the feeding of pigs. This could be done by securely fencing the plants, or by eradicating the pigs from its critical habitat. The abundance of competing non-native plants should also be managed. The populations of the Santa Cruz Island dudleya should be monitored, and research undertaken into its basic biology and ecological requirements.

Contact

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

Reference

U.S. Fish and Wildlife Service. 31 July 1997. "Endangered and Threatened Wildlife and Plants; Final Rule for 13 Plant Taxa From the Northern Channel Islands, California." Federal Register 62 (147): 40954-40974.