Endangered Species Recovery Program

F. Bakersfield Cactus (Opuntia basilaris var. treleasei)

• 1. Description and Taxonomy
  • Taxonomy
  • Description
  • Identification
• 2. Historical and Current Distribution
  • Historical Distribution
  • Current Distribution
• 3. Life History and Habitat
  • Reproduction and Demography
  • Habitat and Community Associations
• 4. Reasons for Decline and Threats to Survival
  • Reasons for Decline
  • Threats to Survival
• 5. Conservation Efforts
• 6. Recovery Strategy

1. Description and Taxonomy

Taxonomy.-- The taxonomy of Bakersfield cactus has not been accepted universally, even though it was named nearly a century ago. Originally, Bakersfield cactus was treated as a full species, Opuntia treleasii (Coulter 1896). The type locality was given as "Caliente, in the Tehachapi Mountains" (Coulter 1896, p. 434), which is in Kern County. Shortly thereafter, Toumey (1901) renamed Bakersfield cactus as a variety of beavertail cactus (Opuntia basilaris), resulting in the combination O. basilaris var. treleasii. Griffiths and Hare (1906) considered Bakersfield cactus a distinct species and subdivided it into two varieties, O. treleasii var. treleasii and var. kernii. Britton and Rose (1920) corrected the spelling of the epithet to treleasei to be consistent with the name of the original collector, William Trelease. In the most recent treatment (Parfitt and Baker 1993), the scientific name of Bakersfield cactus is given as O. basilaris var. treleasei. However, some experts consider Bakersfield cactus to be a full species (Bowen 1987, R. van de Hoek pers. comm.).

Description.-- Like other beavertail cacti, Bakersfield cactus (Figure 15) has fleshy, flattened, green stems (pads). The pads of Bakersfield cactus vary in outline from rounded, heart-shaped, or diamond-shaped to nearly cylindrical. A single plant may consist of hundreds of pads, which originate both at ground level and from the tips of other pads. The number of individuals in a population may be difficult to determine because pads from adjacent plants often overlap. Thus, cactus populations usually are described by the number of clumps (groups of pads that are rooted at the same point) rather than as a number of individuals. Clumps of Bakersfield cactus can grow up to 35 centimeters (14 inches) high and 10 meters (33 feet) across (R. van de Hoek pers. comm.). The pads and fruits are dotted with eye-spots, which are rounded structures that contain barbed bristles. Tiny leaves are produced on the youngest pads of beavertail cacti but are shed quickly. Bakersfield cactus has showy magenta flowers. The dry fruits are the size and shape of small eggs and may contain grayish-white seeds (Munz and Keck 1959, Parfitt and Baker 1993). Bakersfield cactus typically has 22 chromosomes, but plants with 33 chromosomes were found in several populations (Pinkava et al. 1977, R. van de Hoek pers. comm.).

Identification.-- Bakersfield cactus is unique among the varieties of O. basilaris in that the eye-spots contain spines in addition to the bristles. Other features of Bakersfield cactus that differentiate it from related beavertail cacti include the smooth pad surfaces, cylindrical pad bases, nonsunken eye-spots, an longer (up to 5 millimeters [0.2 inch]) leaves. The two varieties of O. treleasei differ from each other in that variety treleasei has spines less than 7 millimeters (0.3 inch) long (which may be longer or shorter than the associated bristles) and eye-spots even with the pad surface, whereas variety kernii has spines longer than 7 millimeters (0.3 inch) and raised eye-spots (Griffiths and Hare 1906, ESA Planning and Environmental Services 1986a, Bowen 1987).

Figure 15. Illustration of Bakersfield cactus (from Abrams and Ferris, Vol. 3, 1951, with permission).

2. Historical and Current Distribution

Historical Distribution.-- Bakersfield cactus is endemic to a limited area of central Kern County in the vicinity of Bakersfield. The CDFG (1995) considered the pre-1987 reports to represent approximately 33 occurrences. However, based on written descriptions (Twisselmann 1967), historical photographs (Britton and Rose 1920, Benson 1982), topography, and deductions from plant morphology, the populations most likely were more or less continuous (R. van de Hoek pers. comm.). As of 1987, the northern, southern, eastern, and western limits of the known range, respectively, were Granite Station (R. van de Hoek pers. comm.), Comanche Point, Caliente, and Oildale (CDFG 1995). Reported occurrences of Bakersfield cactus in Los Angeles and San Bernardino Counties, California, and Mohave County, Arizona (Benson 1969) have been attributed to misidentification of other cactus taxa (Bowen in litt. 1987).

Current Distribution.-- Approximately one-third of the historical occurrences of Bakersfield cactus have been eliminated, and the remaining populations are highly fragmented. However, the range was extended to the south when several occurrences were discovered in the late 1980s in south-central Kern County, just north of Wheeler Ridge (Figure 16). The extant occurrences may be grouped into the following areas of concentration: (1) Caliente Creek drainage (Caliente-Bena Hills), (2) Comanche Point, (3) Cottonwood Creek, (4) Fairfax Road - Highway 178 - Highway 184 - Kern Bluffs - Hart Park, (5) Fuller Acres, (6) Granite Station, (7) mouth of Kern Canyon, (8) Oildale - Kern River Oil Field - Round Mountain Road (separated from area #4 by the Kern River), (9) Poso Creek, (10) Sand Ridge, and (11) Wheeler Ridge - Pleito Hills (CDFG 1995, Moe 1989).

Figure 16. Distribution of Bakersfield cactus (Opuntia basilaris var. treleasei).

3. Life History and Habitat

Few details on the life history of Bakersfield cactus are available. The fleshy stems, tiny, short-lived leaves, shallow root systems, and specialized physiology common to most members of the cactus family are adaptations to growth in arid environments (Benson 1982).

Reproduction and Demography.-- Bakersfield cactus is a perennial. The life span of wild plants has not been determined, but clumps in cultivation at the Rancho Santa Ana Botanic Garden in Claremont, California, survived for 48 years, until extremely wet winter weather caused the pads to rot (R. van de Hoek pers. comm.). Bakersfield cactus typically flowers in May (Munz and Keck 1959). Reproductive biology of this taxon has not been studied, but certain other Opuntia species require cross-pollination for seed-set and many are pollinated by bees (Benson 1982, Spears 1987, Osborn et al. 1988). One potential pollinator of Bakersfield cactus is the native solitary bee Diadasia australis ssp. california, which is known to occur in Kern County and which specializes in collecting pollen from Opuntia species (Thorp in litt. 1998). Vegetative reproduction, which is the production of new plants from sources other than seed, is typical in Bakersfield cactus and several related species (Benson 1982). Fallen pads root easily if sufficient water is available (Twisselmann 1967, Benson 1982, Mitchell 1988), but Bakersfield cactus does not survive prolonged inundation (ESA Planning and Environmenta Services 1986a). Bakersfield cactus produces seeds infrequently. Van de Hoek (pers. comm.) noted that the frequency of seed set in extant populations is similar to the proportion of seeds he observed in herbarium specimens. Cactus seeds require warm, wet conditions to germinate, a combination which is extremely rare in the Bakersfield area (Benson 1982). Pads may be dispersed by flood waters (ESA Planning and Environmental Services 1986a), but seed dispersal agents are unknown.

The total population of Bakersfield cactus was not estimated historically. Densely-spaced clumps of cactus once covered an estimated area of 6.5 by 0.8 kilometer (4 by 0.5 mile) from the Caliente Creek floodplain onto Sand Ridge (Twisselmann 1967). Historical photographs showing extensive stands of Bakersfield cactus (Britton and Rose 1920, Benson 1982) are believed to have been taken southwest of Sand Ridge near the eastern margin of the Kern Lake bed (R. van de Hoek pers. comm.). When the known sites were last inventoried, fewer than 20,000 clumps of Bakersfield cactus were estimated to remain. Only 4 areas had populations of 1,000 clumps or more: Comanche Point, Kern Bluff, north of Wheeler Ridge, and Sand Ridge (CDFG 1995, Moe 1989, R. van de Hoek pers. comm.). The metapopulations reported to incorporate the greatest morphological diversity included those in the Bena and Caliente Hills, Kern Canyon, and Sand Ridge (ESA Planning and Environmental Services 1986a, Bowen in litt. 1987, Moe 1989).

Habitat and Community Associations.-- Soils supporting Bakersfield cactus typically are sandy, although gravel, cobbles, or boulders also may be present. Known populations occur on flood plains, ridges, bluffs, and rolling hills (CDFG 1995, ESA Planning and Environmental Services 1986a). Bakersfield cactus is a characteristic species of the Sierra-Tehachapi Saltbush Scrub plant community (Holland 1986, Griggs et al. 1992), but populations near Caliente are in Blue Oak Woodland and the Cottonwood Creek population is in riparian woodland (CDFG 1995, ESA Planning and Environmental Services 1986a, R. van de Hoek pers. comm.). Many Bakersfield cactus sites support a dense growth of red brome and other annual grasses (Cypher 1994a). Sand Ridge is characterized by sparse vegetation (ESA Planning and Environmental Services 1986a, Cypher 1994a) and a preponderance of native species such as California filago (Filago californica) and yellow pincushion (Chaenactis glabriuscula). Historical records indicate that the majority of Bakersfield cactus occurred at elevations ranging from 140 to 260 meters (460 to 850 feet). The highest-elevation population is at 550 meters (1,800 feet) near Caliente and the lowest remaining is at 121 meters (396 feet) at Fuller Acres (CDFG 1995).

4. Reasons for Decline and Threats to Survival

Reasons for Decline.--The primary reason for the decline of Bakersfield cactus was habitat loss. The formerly extensive tracts of Bakersfield cactus near Edison and Lamont were destroyed by conversion to row crops and citrus groves (Twisselmann 1967); much of the conversion occurred prior to 1931 (Benson 1982). Residential development eliminated numerous occurrences in northeast Bakersfield between Mount Vernon Avenue and Morning Drive in recent years (CDFG 1995). Petroleum production has contributed to habitat loss and fragmentation, particularly in the vicinity of Oildale. Populations near Hart Park, the Kern Bluffs, Oildale, Fairfax Road, and parts of Sand Ridge have been degraded by off-road vehicle activity, trash dumping, and sand and gravel mining. Overgrazing may have damaged plants near Hart Park, Mettler, and Caliente, and flooding decimated populations along Caliente Creek and the Kern River (CDFG 1995, Nelson 1983, Bowen in litt. 1987, Mitchell 1988, Moe 1989, R. van de Hoek pers. comm.). Air pollution is suspected to have contributed to the decline of Bakersfield cactus (Messick 1987).

Threats to Survival.-- All the causes of decline continue to threaten existing populations of Bakersfield catus. Almost all the known sites are on private land, much of which has commercial value. Residential development constitutes the most serious threat currently, especially in the greater Fairfax Road-Kern Bluff and Round Mountain Road areas. Conversion for either agricultural or residential use is possible near Wheeler Ridge. Inundation could be an intermittent problem for populations in floodplains and is a remote possibility for occurrences near the California Aqueduct; the largest concentration of clumps in the Wheeler Ridge metapopulation is situated adjacent to an overflow drain for the Aqueduct, which could lead to flooding if an earthquake occurred anywhere along its length (R. van de Hoek pers. comm.). Even the two protected populations (see Conservation Efforts) are adjacent to agricultural land and could be impacted by pesticide drift. Both off-road vehicle use and mining continue to degrade the populations mentioned earlier.

Direct competition from introduced, annual grasses is believed to threaten the survival of mature Bakersfield cactus plants and to hinder the establishment of new plants (ESA Planning and Environmental Services 1986a, Mitchell 1988). Indirect effects from exotic grasses also may threaten Bakersfield cactus in several ways. First, the dense herbaceous growth may promote a greater fire frequency and intensity than would have occurred with the sparse native vegetation typical in historical times. The effect of repeated fires has not been determined. However, survival of Bakersfield cactus plants was monitored following single fire events at Sand Ridge (Hewett in litt. 1987) and near the Rio Bravo Hydroelectric Plant in Kern Canyon (Lawrence 1987, George Lawrence and Associates 1988). All Bakersfield cactus clumps survived the fires at both sites, despite browning and wilting of the pads. During the following spring, cactus plants that were subject to low-intensity flames flowered, but those subject to moderate-intensity flames produced only vegetative growth. The affected cactus individuals near Rio Bravo were still alive 1 year following the fire, but no further observations were made of plants in either treatment area. Second, dense grass cover may harbor insects that damage cactus, which has been demonstrated with related species of Opuntia in Nebraska grasslands (Burger and Louda 1994). Third, the moist microclimate created by dense herbaceous growth may promote growth of decay organisms and cause pads to rot in years of above-average precipitation (E. Cypher unpubl. observ.).

A lack of genetic diversity may threaten some populations of Bakersfield cactus. Contributing factors to this problem include the small size of many populations (Moe 1989), a lack of gene flow between populations, and infrequent sexual reproduction (Messick 1987). Populations low in genetic variation are more vulnerable to diseases and parasites (Burdon and Marshall 1981) and to chance events, including environmental fluctuations, catastrophes, and genetic drift (Menges 1991).

5. Conservation Efforts

Bakersfield cactus was federally and state-listed as endangered in 1990 (USFWS 1990). The Nature Conservancy began preservation efforts for Bakersfield cactus over 25 years ago by purchasing a portion of Sand Ridge (Twisselmann 1969). Recently, The Nature Conservancy doubled the size of the Sand Ridge Nature Preserve, to 111 hectares (275 acres), by acquiring a remnant of the Caliente Creek wash at the eastern base of the ridge. The preserve was transferred to the Center for Natural Lands Management in 1998. Funding levels are insufficient to allow intensive monitoring or management trials, but prescribed burns will be used to control exotic grass competition (G. Hinshaw pers. comm.).

Several colonies of Bakersfield cactus have been acquired for conservation purposes within the past 2 years. The Implementation Trust for the Metropolitan Bakersfield Habitat Conservation Plan protected portions of three metapopulations by purchasing land in the Kern Bluff, Cottonwood Creek, and Oildale areas from willing sellers (R. Reed pers. comm.). The Wildlands Conservancy recently acqured the Pleito Hills population and plans to manage the area for the benefit of Bakersfield cactus and other sensitive species (D. Clendenen pers. comm.). Another portion of the Wheeler Ridge-Pleito Hills metapopulation is protected by the California Department of Water Resources, which has set aside 33 hectares (81 acres) adjacent to the California Aqueduct as a reserve for Bakersfield cactus through consultations with USFWS and CDFG. The only other site on public land is under the control of the Kern County Department of Parks and Recreation, where a few clumps occur adjacent to Hart Park. However, protection of Bakersfield cactus is neither the purpose nor a priority for the site (Moe 1989). Kern County is preparing a Habitat Conservation Plan, which likely will include provisions for protection of additional Bakersfield cactus populations through management agreements, conservation easements, and land acquisition (T. James pers. comm.). A Habitat Conservation Plan in preparation by California Department of Water Resources will address conservation of Bakersfield cactus and other species in the California Aqueduct right-of-way (K. Brown pers. comm.).

Salvage efforts have been undertaken by local members of the California Native Plant Society, who transplanted Bakersfield cactus clumps from sites slated for destruction to Sand Ridge Nature Preserve and the California Living Museum in Bakersfield. Prior to construction of the East Hills Mall in Bakersfield, a few of the cactus clumps growing on the site were removed, then were replanted in a display bed when the mall was completed. Transplanted individuals have not been monitored at any of the sites to determine survival rates or reproductive success (D. Mitchell pers. comm., R. van de Hoek pers. comm.).

6. Recovery Strategy

Due to social and economic considerations, Bakersfield cactus will never occur as widespread as it did historically. Instead, the recovery goal is to maintain self-sustaining populations in protected areas representative of the former geographic and topographic range of the taxon and in a variety of appropriate natural communities. The remaining populations occur in areas sufficiently representative of the former range to achieve this goal, but very little additional loss can be accommodated without compromising the long-term existence of the taxon. Thus, habitat protection is an important action to prevent the extinction or irreversible decline of Bakersfield cactus. Unoccupied habitat within metapopulations also should be protected to facilitate movement of pollinators and seed dispersers. An additional element of the strategy is to avoid fragmenting the few large metapopulations that remain (i.e., Caliente Creek, Comanche Point, Kern Bluff, Sand Ridge, and Wheeler Ridge) into more than two blocks of contiguous, protected natural land each. Land in the other target areas should be protected in blocks of at least 16 hectares (40 acres), and preferably in blocks of 65 hectares (160 acres) or more. The block size is smaller for Bakersfield cactus than for other listed plant species not for biological reasons, but because many of the areas already are so fragmented by development that larger blocks do not exist. Buffer zones of 150 meters (500 feet) or more should be protected beyond the population margins to reduce external influences and to allow for population expansion. Surveys will be necessary to determine the size of natural populations in several of the target areas and the amount of existing occupied habitat. Transplantation of Bakersfield cactus is not a viable substitute for on-site protection. However, where development would destroy entire populations, as many of the clumps as possible should be transplanted to protected areas to salvage potentially unique genetic material, and the transplans should be monitored periodically to determine survival rates and reproductive success.

Demographic studies and matrix projection modeling will be necessary to identify vulnerable stages in the life cycle. Research then will be necessary to determine how to overcome factors that are identified as limiting to population growth. Beause demographic research will take several years to complete and exotic plant competition seems to be detrimental to cactus in several ways, preliminary studies should begin immediately to test the hypothesis that exotic plants are contributing to mortality of Bakersfield cactus. A biosystematic study would determine whether Bakersfield cactus should be recognized as a full species.