Spreading Navarretia

Navarretia fossalis

Description

Navarretia fossalis, (spreading navarretia), a member of the phlox family (Polemoniaceae), is a low, mostly spreading or ascending, annual herb, 4-6 in (10-15 cm) tall. The lower portions of the stems are mostly glabrous. The leaves are soft and finely divided, 0.4-2 in. (1-5 cm) long, and spine-tipped when dry. The flowers are white to lavender white with linear petals and are arranged in flat-topped, compact, leafy heads. The fruit is an ovoid, two-chambered capsule.

Several other species of Navarretia occur within the range of Spreading navarretia. Two of them, Navarretia intertexta and Navarretia prostrata, can occur in similar habitat. Spreading navarretia is distinguished from them by its linear or narrowly ovate corolla lobes, erect habit, cymose inflorescences, size and shape of the calyx, and the position of the corolla relative to the calyx. All Navarretia species can be distinguished by the appearance of the pollen grain surface.

Habitat

The primary habitat of spreading navarretia is vernal pools. This species occasionally occurs in ditches and other artificial depressions, which often occur in degraded vernal pool habitat. In western Riverside County, spreading navarretia has been found in relatively undisturbed and moderately disturbed vernal pools within a larger vernal wetland plain dominated by annual alkali grassland.

Distribution

Spreading navarretia is distributed from northwestern Los Angeles County and western Riverside County, south through coastal San Diego County, California to San Quintin in northwestern Baja California, Mexico. Less than 30 populations exist in the United States. Nearly 60% of these populations are concentrated in three locations: Otay Mesa in southern San Diego County, along the San Jacinto River in western Riverside County, and near Hemet in Riverside County. Others are scattered in southern Riverside County, Los Angeles County, and coastal San Diego County.

The number of individuals of spreading navarretia varies annually in response to the timing and amount of rainfall and temperature. In Riverside County, one population contains 300,000 individuals. Another population contains 75,000 individuals. However, each of these populations occupies less than 8 acres (3 hectares) of habitat. The majority of populations contain fewer than 1,000 individuals and occupy less than 1 acre (0.4 hectares) of habitat. It is estimated that less than 300 acres (121 hectares) of habitat in the United States is occupied by this species. The most pressing threat to spreading navarretia is the ongoing degradation of vernal pools and their outright destruction due to widespread urbanization, agricultural practices, off-road vehicles, and the longer-term threats from flood control and development.

The majority of spreading navarretia populations are on privately owned lands. At least one population occurs on the federally owned Marine Corps Base, Camp Pendleton, and the plant occurs at three locations on Naval Air Station Miramar.

In Mexico, spreading navarretia is known from less than 10 populations clustered in three areas: along the international border, on the plateaus south of the Rio Guadalupe, and on the San Quintin coastal plain.

Threats

The larger of two recently discovered occurrences of spreading navarretia in northwestern Los Angeles has apparently been partially graded, leading to the ongoing deposition of fill material into the vernal pool. In San Diego County, spreading navarretia occurs within vernal pool complexes. These areas have been and continue to be impacted by urbanization and agricultural conversion.

One of the largest concentrations of spreading navarretia occurs on Otay Mesa in San Diego County. At least 37 proposals for development have been filed, which encompass about 80% of the undeveloped portion of the mesa within the jurisdiction of the City of San Diego and all but four of the remaining vernal pool complexes. Several of these projects will impact spreading navarretia. In addition, at least one major transportation project has been proposed for Otay Mesa and could potentially affect vernal pools occupied by spreading navarretia.

Because spreading navarretia is an obligate wet-land species, drainage of the wetlands it inhabits will destroy it. The generally small sizes of vernal pool wetlands render them highly vulnerable to deliberate drainage, as well as to unintentional alteration through changes in drainage that occur during development, and from the physical effects of off-road vehicles and trash dumping. The loss of over 97% of vernal pool habitat in San Diego County occupied, in part, by spreading navarretia, by 1990, shows the intensity of economic and other pressures to develop clay-soil areas with vernal pools. To judge from recent development proposals, the remaining three percent of vernal pool habitat is likely to be lost. On the more extensive alkali wetlands of Riverside County, the effects of agricultural activities, drainage of wetlands, alteration of drainage (from diking and rerouting of drainage) likewise mean that the wetlands remaining available to this plant are much smaller and much more vulnerable to the effects of surrounding development than they were earlier in the century.

Spreading navarretia also occurred historically in the vicinity of Murrieta Hot Springs in Riverside County during the 1920s. Much of the Murrieta Hot Spring area has been urbanized or converted to agriculture resulting in a significant reduction and fragmentation of potential spreading navarretia habitat. While there are no additional confirmed populations of spreading navarretia occurring in the Murrieta area, the continued and rapid urbanization of this area reduces the opportunities to conserve potential habitat for species recovery.

For spreading navarretia, whose 30 known populations in the U.S. are concentrated in Otay Mesa in southern San Diego County, along the San Jacinto River in western Riverside County, and near Hemet in Riverside County, the ongoing degradation of vernal pools and their outright destruction due to widespread urbanization in Otay Mesa is the most pressing threat, followed by agricultural practices and the longer-term threats from flood control and development in the San Jacinto-Hemet areas of Riverside County.

Conservation and Recovery

In 1991, the State of California established the Natural Communities Conservation Planning Program to address conservation needs of natural ecosystems throughout the State. The focus of the current planning program is the coastal sage scrub community in southern California, although other vegetation communities are being addressed in an ecosystem-level approach. Thread-leaved brodiaea and spreading navarretia are currently being considered under the Habitat Conservation Plan of Orange County.

The Multiple Species Conservation Program sets aside preserve areas and provides for monitoring and management for 85 species, including thread-leaved brodiaea and spreading navarretia.

Spreading navarretia could potentially be affected by projects requiring a permit from the Corps of Engineers under the Clean Water Act. In Riverside County, the Corps has not required a permit or mitigation for filling of wetland habitat occupied by spreading navarretia in instances where the land had previously been used for agriculture or where the wetland was determined not to be within the jurisdiction of the Corps. Even if the Corps establishes jurisdiction under the Clean Water Act over vernal pools, this does not ensure their protection. At least two vernal pool complexes that represented suitable habitat for spreading navarretia that were under Corps jurisdiction in San Diego County have been destroyed or degraded without a permit.

The majority of spreading navarretia populations are on privately owned lands. However, at least one population occurs on Federal lands owned by the Department of the Navy. Some of the private land has Federal involvement because spreading navarretia is a covered species under the Multiple Species Conservation Program and populations occur in the Multiple Habitat Conservation Plan area of northern San Diego County.

Spreading navarretia is present at three sites on Marine Corps Air Station Miramar, and both it and thread-leaved brodiaea are present on Marine Corps Base Camp Pendleton. These two facilities comprise some 90% of the remaining vernal pool habitat in San Diego County, so they are essential to the conservation of spreading navarretia. Spreading navarretia is fully protected at the Marine Corps Air Station at Miramar in vernal pool management zones through the Integrated Natural Resource Management Plan. Marine Corps Base, Camp Pendleton has an Isolated Ephemeral Wetlands Management Plan, but it did not prevent the unauthorized filling of a vernal pool in April 1998.

The U.S. Fish and Wildlife Service published a Recovery Plan for the spreading navarretia and other vernal-pool species of southern California in 1998. The key to the survival of the spreading navarretia is the protection of its critical habitats. About 30 populations of this plant survive in the United States and another ten in Mexico. At least one population occurs on the federally owned Marine Corps Base at Camp Pendleton, and three others on Naval Air Station Miramar. These federally owned populations should be protected from any threatening activities. Other U.S. populations of the spreading navarretia are on privately owned land, and are potentially at risk from development and other threatening activities. The largest of these critical habitats should be acquired and designated as ecological reserves, or conservation easements negotiated with the landowners. The populations of the spreading navarretia should be monitored, and research undertaken into its biology and habitat needs.

Contacts

U. S. Fish and Wildlife Service
Carlsbad Fish and Wildlife Office
2730 Loker Avenue West
Carlsbad, California, 92008-6603
Telephone: (760) 431-9440
Fax: (760) 431-9624

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

Reference

U.S. Fish and Wildlife Service. 13 October 1998. "Endangered and Threatened Wildlife and Plants; Determination of Endangered or Threatened Status for Four Southwestern California Plants from Vernal Wetlands and Clay Soils." Federal Register 63 (197): 54975-54994

U.S. Fish and Wildlife Service. 1998. "Vernal Pools of Southern California Recovery Plan." U.S. Fish and Wildlife Service, Portland, Oregon.