Mexican Flannelbush

Fremontodendron mexicanum

Description

Mexican flannelbush, Fremontodendron mexicanum, a member of the cacao family (Sterculiaceae), is a small tree or shrub 5-19 ft (1.5-5.8 m) tall with evergreen, palmately lobed leaves (leaflets radiating from one point) 1-2 in (2.5-5.1 cm) wide. The flowers may reach a width of approximately 2.7 in (6.9 cm) wide and lack petals. The showy orange to dark yellow sepals are sometimes reddish toward the bases. F. mexicanum is distinguished from F. californicum by its orange sepals with basal pits generally lacking long hairs, and shiny black, smooth seeds that lack outgrowths.

Habitat

Native populations of this species occur primarily in closed-cone coniferous forest and southern mixed chaparral dominated by Tecate cypress, often in association with metavolcanic soils at elevations between 900 and 3,000 ft (300 and 900 km).

Distribution

Mexican flannelbush is found only in southern San Diego County in California, and northwestern Estado de Baja California in Mexico. Fewer than 10 historical native locations have been reported in the United States. Apparently at least two historical populations have been extirpated. Both locations were in San Diego County—at Boundary Monument near the Pacific coast, and in the Jamul Mountains. Reliable distribution records for the species indicate that it is currently only known from Cedar Canyon on Otay Mountain in southern San Diego County and at Arroyo Seco, north of San Quintin, Estado de Baja California, Mexico. This species has not been relocated during surveys of other historical localities. The U.S. Bureau of Land Management (BLM) manages most of the Cedar Canyon population.

The total number of remaining plants of Mexican flannelbush in the United States is estimated to be fewer than 100 individuals. Two additional native historical populations are reported from Mexico; however, one population was not observed in the late 1990s. The other location, at Arroyo Seco, may have been extirpated by a substantial flood.

Threats

The only confirmed extant native occurrence for Mexican flannelbush in the United States is located in Cedar Canyon on Otay Mountain in southern San Diego County near the Mexican border. About 50% of the habitat occupied or potentially suitable for restoration of Mexican flannelbush populations exists on lands administered by the BLM as an area of critical environmental concern and a research natural area. The remaining portion of this habitat is located within the privately owned Otay Ranch, on lands zoned as natural open space.

The Cedar Canyon areas were designated for the preservation of Mexican flannelbush by BLM in 1994 as part of the South Coast Resource Management Plan. The area is a right-of-way avoidance area, which is not available for mineral material sales or livestock grazing, and is closed to motorized vehicle use. Natural conditions are maintained by allowing ordinary physical and biological processes to operate without human intervention. Some management activities are authorized to maintain the unique features for which the plan was designated.

Although urbanization and associated habitat loss and further habitat fragmentation are no longer significant direct threats to Mexican flannelbush, the single known population is vulnerable to a variety of threats. This species is likely susceptible to adverse genetic effects because of the low number of individuals in the population, which is estimated to be below 100.

Because Mexican flannelbush is known from one small population in the United States, with perhaps fewer than 100 individuals remaining, it continues to be vulnerable to extinction caused by random events, such as hot, slow-burning fires or fires that occur too frequently. Although Mexican flannelbush also has evolved in association with natural fire cycles, alteration of fire patterns can significantly affect the viability of this species by destroying plants and the seed bank, thereby reducing the genetic diversity of the species. A single fire event could severely impact the chance for recovery of this species.

Conservation and Recovery

The management proposal for the Cedar Canyon conservation area includes the use of fire as part of the management strategy as well as restricted access. A fire management plan reflective of a natural fire regime promises to benefit Mexican flannel-bush. Other areas of occupied or potential habitat for reestablishment of Mexican flannelbush are zoned as natural open space and are within the privately owned Otay Ranch. The future management and protection associated with this designation will likely reduce the threats of urbanization and off-road vehicle traffic.

Contact

Regional Office of Endangered Species
U. S. Fish and Wildlife Service
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232
http://pacific.fws.gov/

Reference

U. S. Fish and Wildlife Service. 13 October 1998. "Endangered or Threatened Status for Three Plants from the Chaparral and Scrub of Southwestern California." Federal Register 63 (197): 54956-54971.