Hemizonia increscens ssp. villosa
|Listed||March 20, 2000|
|Description||Gray-green, soft, yellow flowered annual herb.|
|Habitat||Coastal grasslands and sage scrub.|
|Threats||Development and habitat loss.|
The Gaviota tarplant, also known as the grassland tarweed, is a soft, hairy, gray-green plant that is 12-35 in (30-90 cm) tall. Stems branch near the base, and leaves are approximately 2-3.4 in (5-8.6 cm) long. The yellow flower head is rounded to flat-topped with 13 ray flowers and 18 to 31 disk flowers that are usually sterile.
There are two other subspecies, Hemizonia increscens ssp. increscens and H. increscens s sp. foliosa, which can be distinguished from the Gaviota tarplant by their stiff-bristly, deep-green foliage. However, the best means to differentiate between these species is to test their chemical composition.
Gaviota tarplant is associated with the rare needlegrass grasslands, which intergrade with coastal sage scrub. Primary habitat lies on an uplifted, narrow marine terrace 150-200 ft (46-60 m) above sea level. Acidic, fine, sandy loams sit upon a layer of clay, which is a reservoir of water for a typically dry habitat. Associates include the purple needlegrass in the grasslands and the California sagebrush, coyote bush, and sawtooth golden bush in the coastal sage scrub ecosystem.
Historically, the Gaviota tarplant was found near Gaviota, approximately 15 mi (24 km) from Santa Barbara. Localized to western Santa Barbara County, the plant occupies a narrow, 2.2 mi (3.5 km) long band of coastal terrace between the Santa Ynez Mountains and the ocean.
There is one scattered population on 60 acres (24 hectares) of habitat, the patches often separated by no more than 330 ft (100 m). A few colonies occur on land owned by the California Department of Parks and Recreation.
The Gaviota tarplant is primarily threatened by habitat loss, development of oil and gas facilities, and competition with non-native plants. The narrow coastal terrace on which it occurs is bisected lengthwise by Highway 101, a railroad, and several pipelines.
The majority of habitat lies on the north side of the highway, on private lands owned by the petroleum industry. Construction of new pipelines and a drilling station proposed as of 2000, as well as installation of a water pipeline and the maintenance of pipelines and facilities will continue to disturb habitat and encourage invasion by non-native species.
Recreational and urban development also threaten the Gaviota tarplant. One proposal is for a coastal bike path, which would create a corridor for non-natives to enter. At the same time, as oil and gas companies are abandoning their facilities, proposals for campgrounds, golf courses, a convention center, and residential housing are being planned.
Another threat is heavy grazing, which has reduced the stature and the number of seeds produced by the Gaviota tarplant. Grazing has been displacing this species of tarplant for another more common species of tarplant.
A smaller threat is an unidentified flower beetle. It has been known to infest some of the Gaviota tarplants.
Conservation and Recovery
Measures have been taken to protect the habitat of the Gaviota tarplant. A preserve area has been established by the oil industry within the corridor, yet it is small and preventing entry of non-native plants is difficult. Other projects to encourage recovery include salvaging seedbank and topsoil for transfer to a habitat creation site, seeding of areas disturbed by facility and pipeline construction, and enhancing areas with low density of this species.
The Gaviota tarplant does not compete well against non-native species, due to its need to germinate and become established in open habitat. Therefore the relocated plants need intensive maintenance for non-native species.
The California Exotic Pest Plant Council has taken steps to identify non-native invasive plants that negatively impact habitat.
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
Ventura Fish and Wildlife Office
U. S. Fish and Wildlife Service
2493 Portola Road, Suite B
Ventura, California 93003-7726
Telephone: (805) 644-1766
Fax: (805) 644-3958
U.S. Department of the Interior. 20 March 2000. "Endangered and Threatened Wildlife and Plants: Final Rule for Endangered Status for Four Plants from South Central Coastal California." Federal Register 65 (54): 14888-14898.
University of California, Berkeley. " Hemizonia increscens ssp. villosa." CalFlora Database Project: A Botanical Resource for California on the Internet. (http://dlp.cs.berkeley.edu/calflora.) Accessed July 6, 2000.
"Gaviota Tarplant." Beacham's Guide to the Endangered Species of North America. . Encyclopedia.com. (April 18, 2019). https://www.encyclopedia.com/environment/science-magazines/gaviota-tarplant
"Gaviota Tarplant." Beacham's Guide to the Endangered Species of North America. . Retrieved April 18, 2019 from Encyclopedia.com: https://www.encyclopedia.com/environment/science-magazines/gaviota-tarplant
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