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SPECIES:  Hesperoyucca whipplei
Chaparral yucca in an urban-wildland interface. Photo by G.A. Cooper @ USDA-NRCS PLANTS Database.


SPECIES: Hesperoyucca whipplei
AUTHORSHIP AND CITATION : Tirmenstein, D. A. 1989. Hesperoyucca whipplei. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: []. ABBREVIATION : HESWHI SYNONYMS : Hesperoyucca whipplei (Torr.) Baker [5] Yucca newberryi McKelvey Yucca whipplei Torr. [46,51,52] Yucca whipplei subsp. caespitosa M.E. Jones [17,31,51,52] Yucca whipplei subsp. eremica Haines and Epling [18,45] Yucca whipplei subsp. intermedia A.L. Haines [17,31] Yucca whipplei subsp. newberryi (McKelvey) Webber [18,45] Yucca whipplei subsp. parishii M.E. Jones [17,31] Yucca whipplei subsp. peninsularis (McKelvey) Webber [18,45] Yucca whipplei subsp. percursa A.L. Haines [17,31] Yucca whipplei subsp. whipplei [17,31,51,52] SCS PLANT CODE : HEWH COMMON NAMES : chaparral yucca Our Lord's candle Our-Lord's-candle quixote plant TAXONOMY : The currently accepted scientific name of chaparral yucca is Hesperoyucca whipplei (Torr.) Trel. (Agavaceae) [49,52]. Natural hybridization is common in chaparral yucca and other Yucca species, and numerous intermediate forms occur [45]. The yuccas have received only limited attention from past researchers, and many taxonomic questions remain [11]. In many areas, hybridization and gene flow occur freely across chaparral yucca populations, while in other areas, populations are isolated by geographic barriers [18]. As a result, this species exhibits much variation in growth habit, general ecology, reproductive strategies, phenology, and gross morphology. LIFE FORM : Shrub FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY


SPECIES: Hesperoyucca whipplei
GENERAL DISTRIBUTION : Chaparral yucca occurs from coastal southern California across portions of the Mohave Desert southward into Mexico [24,40,41,45].  ECOSYSTEMS :    FRES21  Ponderosa pine    FRES30  Desert shrub    FRES34  Chaparral - mountain shrub    FRES35  Pinyon - juniper STATES :      CA  MEXICO BLM PHYSIOGRAPHIC REGIONS :     3  Southern Pacific Border     7  Lower Basin and Range KUCHLER PLANT ASSOCIATIONS :    K005  Mixed conifer forest    K023  Juniper - pinyon woodland    K033  Chaparral    K035  Coastal sagebrush    K041  Creosotebush    K045  Ceniza shrub SAF COVER TYPES :    239  Pinyon - juniper    241  Western live oak    245  Pacific ponderosa pine    255  California coast live oak SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : Chaparral yucca in Tulare County chaparral. Photo by Mark W. Skinner @ USDA-NRCS PLANTS Database.
Chaparral yucca is listed as a dominant in a number of coastal sage
scrub and chaparral communities of southern California.  Common
codominants include California broomsage (Lepidospartum squamatum),
thickleaf yerba-santa (Eriodictyon crassifolium), and California
sagebrush (Artemisia californica) [33].


SPECIES: Hesperoyucca whipplei
IMPORTANCE TO LIVESTOCK AND WILDLIFE : The flowers and fruits of chaparral yucca are used by a number of small birds and mammals [2,9].  This species provides little browse for domestic livestock or wild ungulates [9], although some use of the flowers has been reported [1].  It presumably provides some cover for smaller birds and mammals. PALATABILITY : Fruits of chaparral yucca are highly palatable to many species of birds, the dusky-footed woodrat, and numerous other small mammals [2,9]. Flowers and flowerstalks are apparently favored by mule deer in some locations [1]. NUTRITIONAL VALUE : Little specific information is available on the food value of Our Lord's candle.  Nutritional values for the genus Yucca are as follows [7,32]:                                         %                water   ash   crude   crude   fat   n-free  ether protein                              protein fiber         extract extr. n x6.25   young stem, dry --    5.55   7.50    16.13  1.54   69.28    --      -- old stems       --    9.15   3.07    19.59  0.93   67.26    --      -- fresh stems    72.1   1.55   2.09     4.50  0.43   19.33    --      -- fresh flowers   --    8.7     --     13.3    --    53.3    4.4     20.3 COVER VALUE : NO-ENTRY VALUE FOR REHABILITATION OF DISTURBED SITES : Little documentation exists on the potential value of chaparral yucca for rehabilitation.  Studies indicate that seedlings can be successfully transplanted [45].  However, Webber [45] emphasizes the importance of not overwatering young plants, and notes that propagation of this species is sometimes difficult. OTHER USES AND VALUES : Native Americans made flour from the seeds and used fibers from the leaves to weave rope, nets, and baskets.  They roasted the very young flowerstalks to produce a food that tasted like baked apple.  The roots have a high component of saponin; when soaked and pounded they produce copious suds [12].  The flowers of chaparral yucca are sometimes made into various novelty products [45]. OTHER MANAGEMENT CONSIDERATIONS : NO-ENTRY


SPECIES: Hesperoyucca whipplei
GENERAL BOTANICAL CHARACTERISTICS : Chaparral yucca is a highly variable, rosette-forming, perennial shrub [23,45].  Plants are distinguished by growth form (caespitose or solitary) and color, size, and shape of leaves and flowers [10,13,17]. Chaparral yucca may also differ in phenological development, fruit set, and growth habit.  Varying forms occur in most populations [23].  RAUNKIAER LIFE FORM : Geophyte REGENERATION PROCESSES : Chaparral yucca reproduces both by seed and by sprouting [23].  Many populations have mixtures of monocarpic, caespitose, and rhizomatous growth forms [23]. Flowering and fruiting:  Attractive, creamy-white or sometimes purplish-tinged flowers are borne on flowerstalks which generally grow 8 to 21 feet (2.5-3 m) in height [45].  The inflorescence is a pedant panicle made up of one hundred to several thousand flowers [40].  Size of the showy inflorescence is varible; it may average 3 feet in length and 13 inches in diameter, or sometimes, be twice that large (averaging 6.5 feet in length and 2 feet in diameter)[17].  The lower portion of the panicle develops fruit while the upper part is still flowering [40].  Each dehiscent fruit contains approximately 150 to 200 flat, smooth, dull black seeds, which are dispersed by wind [40,45]. Germination:  Germination rates are variable [23], ranging from 0 to 100 percent in controlled laboratory experiments [4].  When viability is high, germination may be rapid.  Germination of seed presoaked in water for 24 hours began within 3 days of treatment [42].  Despite the occurrence of chaparral yucca in fire-prone chaparral, seed is vulnerable to high temperatures.  Significant reductions in germination have been noted after even brief exposure to high temperatures [18]. Pollination:  One of the most interesting and well-studied aspects of yucca ecology centers on the symbiotic relationship between yuccas and their yucca-moth pollinators.  Chaparral yucca relies solely on the yucca moth (Tegeticula maculata), which consumes a small percentage of flowers while in the larval stage, for pollination [3].  Seed production is limited not only by the resources available to the parent plant, but by pollinator numbers as well [2,14,41].  Many of the regenerative strategies used by Chaparral yucca reflect competition for potentially scarce pollinators [40]. Vegetative:  Chaparral yucca regenerates vegetatively by producing multiple, densely packed rosettes from axillary buds early in development; these rosettes are attached to a small caudex [23].  This mode of regeneration allows it to persist or increase even on harsh sites.  Some populations rarely, if ever, forms rhizomes [23,45].  Some plants regenerate vegetatively via axillary branching, which occurs only after plants are mature; the base of the stem and roots persist after flowering to form the subterranean portion of the new plants [13,17].  Some plants or populations reproduce vegetatively through thick, underground rhizomes [13,21,23].  Rhizomes average 2 to 6 feet (0.6-1.8 m) in length, and sprouting often results in the formation of dense clone [17,23].  SITE CHARACTERISTICS : Chaparral yucca grows from 980 to 8,200 feet (300-2,500 m) elevation [49]. Topography includes dry, stony slopes on foothills, coastal plains [2,31], bare, rocky, mountain slopes or mesas [21,23,45], and desert fringes of southern California and Mexico [2,31]. It grows particularly well on mountain slopes and alluvial fans [31].  Soils:  Chaparral yucca grows well on a variety of soil types including unconsolidated or granitic substrates [24].  Growth is most common on very porous, shallow soils or on rocky outcrops [17]. It is a common understory species in maritime [18], coastal sage shrub, chaparral [17,31], California juniper (Juniperus californica) woodlands, and in desert shrub [17,31,45], and into ponderosa pine (Pinus ponderosa) forests [17,31]. Plant associates:  Coastal sage - sage (Salvia spp.), lemonade sumac (Rhus integrifolia), California scrub oak (Quercus dumosa), chokecherry (Prunus spp.), mountain-mahogany (Cercocarpus betuloides), California broomsage (Lepidospartum squamatum), and thickleaf yerba-santa (Eriodictyon crassifolium) [24,40].  Desert scrub - creosotebush (Larrea tridentata).  Chaparral - oaks (Quercus spp.), ceanothus (Ceanothus spp.), manzanita (Arctostaphylos spp.), chamise (Adenostoma fasciculatum), and red shank (A. sparsifolium) [40]. SUCCESSIONAL STATUS : The successional role of chaparral yucca has not been well documented. It probably occurs as a climax species on some fairly harsh sites, and is well adapted to persist in fire-prone chaparral communities. SEASONAL DEVELOPMENT : Our Lords's candle generally flowers from late February to early June [1,10].  Only some plants in a particular area flower in any given year, while the rest undergo vegetative growth.  This annual variation in reproductive effort may represent an adaptation for greater overall reproductive success despite limited pollinator availability or aberrant weather patterns. Flowering:  Individual plants flower for 2 to 7 weeks [1], but the population flowers for 2 or less commonly 3 months [5,41].  Flowering tends to be influenced by factors such as rainfall, floral structure, and elevation [5,10,42].  Flowering generally begins later at higher elevations, and during extremely dry years, most stands have few if any individuals which produce flowers [10].  Chaparral yucca may only bloom for 10 days on very dry sites, while plants on more mesic sites flower for up to 30 days [40].  Each flower on the inflorescence is only open for a few days [1].  Flowers at the bottom of the panicle begin development much earlier than those above [14.] Fruiting:  Fruit development begins at the bottom of the panicle several weeks after the first flowers have wilted but while the upper flowers are still in bloom [42].  Fruit set tends to be low, but is somewhat higher in fruit at the bottom of the panicle [14].  Fruits reach full size within a month; seed pods mature, turning dry and gray-brown, by late summer or fall [40].  The first pods dehisce while the last flowers are wilting [3].  Wind dispersal usually begins by mid-August [10]. The monocarpic plants turn brown and die by late summer or fall in the year of flowering [10].  These plants generally complete their life cycle within 4 to 7 years [10,28].


SPECIES: Hesperoyucca whipplei
FIRE ECOLOGY OR ADAPTATIONS : The specific fire adaptations of chaparral yucca vary greatly within and among populations.  Even individuals within a given population may exhibit varying adaptations to fire.  Diverse regenerative strategies of chaparral yucca may represent local adaptations to the fire frequency most common in the habitat occupied by that population.  Genetic variation present within populations may have allowed chaparral yucca to persist or spread despite climatic shifts leading to changes in fire frequency or subsequent geographic isolation. Chaparral yucca is generally well adapted to persist in fire-prone environments, and is closely associated with chaparral types [43].  However, chaparral yucca often grows in openings within chaparral communities where fuel levels are lower than those of surrounding areas [10].  This may result in lighter fires and increased survival.  On some extremely harsh, rocky sites occupied by the species, fire may be infrequent due to insufficient fuels. Large, densely packed leaf bases provide some protection from fire [36]. Fairly vigorous sprouting has been noted after many fires [29,35,38,38], but in other instances, little if any sprouting has occurred and high mortality has been observed [20].  Plants frequently survive and resume growth if only lightly damaged [9,19,48].  Specific plant morphology may largely dictate the probability of survival and most typical mode of postfire response.  Conditions which favor rhizomatous or caespitose forms of chaparral yucca are generally not conducive to seedling germination and establishment [18].  Some popultaions exhibit a larger leaf area than most, which may allow for more rapid growth rates in fire-free years, a characteristic of selective value in fire-prone habitats [23].  Also, although seed of chaparral yucca is in general very sensitive to heat damage, seeds of some popultaions are more resistant to exposure to high temperatures (up to 230 degrees Fahrenheit [110 deg C]) than others [23].  Reestablishment is probably through surviving on-site or off-site wind-dispersed seed. Rhizomes vary in depth, length, and thickness but are probably well protected from fire by overlying soil.  Plants can probably sprouting rapidly after fire.  Many of the populations of chaparral yucca sprout vigorously and rapidly, even after fires of high intensity.  Plants with a caespitose growth form may show best survival in areas experiencing lighter fires.  Undamaged or slightly damaged portions of the clump would survive and resume growth, permitting fairly rapid reestablishment [23]. Some plants grow in a dense clump of rosettes with secondary rosettes forming from underground portions of older plants [17,45].  These underground plant parts are presumably protected from the damaging effects of heat by overlying soil.  These adaptations suggest that plants with rosettes can survive and resume growth, particularly after light fires. FIRE REGIMES :
Find fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes". POSTFIRE REGENERATION STRATEGY : Secondary colonizer - off-site seed Rhizomatous shrub, rhizome in soil


SPECIES: Hesperoyucca whipplei
IMMEDIATE FIRE EFFECT ON PLANT : The effect of fire on chaparral yucca probably varies according to such factors as fire intensity and severity, climate, site characteristics, and genetic makeup of a particular population.  Although major differences among populations have been documented with respect to botanical characteristics and regenerative strategies, little is known about these differences influence plant repsonses to fire. The literature reports variable and seomtimes contradictory information on effects and response of chaparral yucca to fire.  Some researchers have observed low postfire mortality of chaparral yucca (< 25%) [37,38], while others have reported low survival (10%) [19,20].  Much of the variability in fire effects is probably due to genetically based differences in growth habit and regeneration strategies. Postfire mortality is probably high in semelparous, monocarpic plants.  A fire which consumes aboveground vegetation would presumably kill the plant, although some individuals might survive if the foliage was only lightly damaged. Survival is probably more likely in plants that are not monocarpic, since they have the ability to survive and regrow if portions of the dense clump or clone remain undamaged.  Some plants or populations form new secondary rosettes from underground portions of older plants; fires which occur after the formation of these buds but prior to emergence may have little effect on the buds themselves. Postfire mortality is presumably low in rhizomatrous plants because the rhizomes are afforded some protection from heat by overlying soil, allowing the plant to survive even when aboveground vegetation is consumed by fire. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : NO-ENTRY PLANT RESPONSE TO FIRE : Postfire response of chaparral yucca is extremely variable.  This diverse species shows extreme variability, and many growth forms can be observed in a single population.  More research is needed to sort out the complex interrelationships between genetic and environmental factors which influence postfire regenerative strategies of chaparral yucca. Postfire response of chaparral yucca may be rapid.  Sprouts or seedlings appeared within 2 years after a September fire removed all aboveground vegetation [8].  Sprouting, when it occurs, can be vigorous. As many as 262 to 1,690 sprouts per hectare were observed only 1 year after a July wildfire in a chaparral-desert ecotone of southern California [37,38].  On certain sites which had a prefire density of 27 per hectare, sprout densities were averaged 20 per hectare.  Each plant produced an average of 18 to 85 sprouts [37,38], suggesting increased density in burned stands.  Basal sprouting appears to be most likely when foliage is not "severely burned" [9].  Limited evidence suggests that where chaparral yucca is capable of sprouting, this mode of regeneration allows for much more rapid and complete recovery than would be expected in populations which regenerate through seed alone [27].  In many instances, chaparral yucca appears to be capable of surviving and resuming growth if only slightly damaged by fire [9,19,48].  Some lightly burned stands produce an abundance of flowers within 1 or 2 years after fire [9]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : Recovery:  Vegetative regeneration of chaparral yucca through sprouting apparently permits a much more rapid and vigorous postfire recovery than is possible through seedling establishment.  Specific documentation of recovery following a fall fire of variable intensity in a coastal sage scrub community is as follows [27]: site #            % cover (#/ha)             mean size (cm sq)              sprout     seedling        sprout      seedling   1             4.3          --           2,344           156   3            12.1          0.1          1,875           156   4             8.8          0            1,562           469   5             4.3          --             937           --   6            10.8          0            1,719           156 Postfire recovery of chaparral yucca cover through seed alone may take more than 4 years in many southern California chaparral communities [19]. Although evidence is lacking, the likelihood of vegetative regeneration in individuals or populations capable of such a response may depend largely on fire severity.  Conrad [9] reports that basal sprouting can occur only if plants are not severely burned. FIRE MANAGEMENT CONSIDERATIONS : One year after a summer wildfire in a California chaparral-desert shrub ecotones, postfire productivity ranged from 0.05 pounds per acre (57 g/hectare) in winter to 11 pounds per acre (1,196 g/hectare) in spring [37,38].


SPECIES: Hesperoyucca whipplei
REFERENCES :  1.  Aker, Charles L. 1982. Regulation of flower, fruit and seed production        by a monocarpic perennial, Yucca whipplei. Journal of Ecology. 70:        357-372.  [5842]  2.  Aker, Charles L. 1982. Spatial and temporal dispersion patterns of        pollinators and their relationship to the flowering strategy of Yucca        whipplei (Agavaceae). Oecologia. 54(2): 243-252.  [5760]  3.  Aker, C. L.; Udovic, D. 1981. Oviposition and pollination behavior of        the yucca moth, and its relation to the reproductive biology of Yucca        whipplei (Agavaceae). Oecologia. 49(1): 96-101.  [5807]  4.  Arnott, Howard J. 1962. The seed, germination, and seedling of yucca.        Berkeley, CA: University of California Press. 96 p.  [4317]  5.  Krueger, William C.; Sharp, Lee A. 1978. Management approaches to reduce        livestock losses from poisonous plants on rangelands. Journal of Range        Management. 31(5): 347-350.  [1379]  6.  Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals,        reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's        associations for the eleven western states. Tech. Note 301. Denver, CO:        U.S. Department of the Interior, Bureau of Land Management. 169 p.        [434]  7.  Brockway, Dale G.; Topik, Christopher; Hemstrom, Miles A.; Emmingham,        William H. 1985. Plant association and management guide for the Pacific        silver fir zone: Gifford Pinchot National Forest. R6-Ecol-130a.        Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific        Northwest Region. 122 p.  [525]  8.  Christensen, Norman L.; Muller, Cornelius H. 1975. Effects of fire on        factors controlling plant growth in Adenostoma chaparral. Ecological        Monographs. 45: 29-55.  [4923]  9.  Conrad, C. Eugene. 1987. Common shrubs of chaparral and associated        ecosystems of southern California. Gen. Tech. Rep. PSW-99. Berkeley, CA:        U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest        and Range Experiment Station. 86 p.  [4209] 10.  Cox, George W. 1981. The yucca with the big bang. Environment Southwest.        493: 12-16.  [5762] 11.  Cronquist, Arthur; Holmgren, Arthur H.; Holmgren, Noel H.; [and others].        1977. Intermountain flora: Vascular plants of the Intermountain West,        U.S.A. Vol. 6. The Monocotyledons. New York: Columbia University Press.        584 p.  [719] 12.  Dale, Nancy. 1986. Flowering plants: The Santa Monica Mountains, coastal        and chaparral regions of southern California. Santa Barbara, CA: Capra        Press. In coooperation with: The California Native Plant Society. 239 p.        [7605] 13.  DeMason, Darleen A. 1984. Offshoot variability in Yucca Whipplei subsp.        percursa (Agavaceae). Madrono. 31(4): 197-202.  [5803] 14.  Doust, Jon L.; Doust, Lesley L. 1983. Parental strategy:  gender and        maternity in higher plants. BioScience. 33(3): 180-185.  [5805] 15.  Eyre, F. H., ed. 1980. Forest cover types of the United States and        Canada. Washington, DC: Society of American Foresters. 148 p.  [905] 16.  Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; [and others].        1977. Vegetation and environmental features of forest and range        ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of        Agriculture, Forest Service. 68 p.  [998] 17.  Haines, Lee. 1941. Variation in Yucca whipplei. Madrono. 6: 33-45.        [5763] 18.  Hoover, Doris Anne. 1973. Evidence from population studies for two        independent variation patterns in Yucca whipplei Torrey. Northridge, CA:        California State University, Northridge. 145 p. M.S. thesis.  [6076] 19.  Keeley, Jon E.; Keeley, Sterling C. 1981. Post-fire regeneration of        southern California chaparral. American Journal of Botany. 68(4):        524-530.  [4660] 20.  Keeley, Jon E.; Keeley, Sterling C. 1984. Postfire recovery of        California coastal sage scrub. American Midland Naturalist. 111(1):        105-117.  [5587] 21.  Keeley, Jon E.; Keeley, Sterling C.; Ikeda, Diane A. 1986. Seed        predation by yucca moths on semelparous, iteroparous, and vegetatively        reproducing subspecies of Yucca whipplei (Agavaceae). American Midland        Naturalist. 115(1): 1-9.  [5819] 22.  Keeley, Jon E.; Meyers, Adriene. 1985. Effect of heat on seed        germination of southwestern Yucca species. Southwestern Naturalist.        30(2): 303-304.  [5761] 23.  Keeley, Jon E.; Tufenkian, Dav. 1984. Garden comparison of germination        and seedling growth of Yucca whipplei subspecies (Agavaceae). Madrono.        31(1): 24-29.  [5801] 24.  Kirkpatrick, J. B.; Hutchinson, C. F. 1977. The community composition of        Californian coastal sage scrub. Vegetatio. 35(1): 21-33.  [5612] 25.  Kuchler, A. W. 1964. Manual to accompany the map of potential vegetation        of the conterminous United States. Special Publication No. 36. New York:        American Geographical Society. 77 p.  [1384] 26.  Lyon, L. Jack; Stickney, Peter F. 1976. Early vegetal succession        following large northern Rocky Mountain wildfires. In: Proceedings, Tall        Timbers fire ecology conference and Intermountain Fire Research Council        fire and land management symposium; 1974 October 8-10; Missoula, MT. No.        14. Tallahassee, FL: Tall Timbers Research Station: 355-373.  [1496] 27.  Malanson, George P.; O'Leary, John F. 1982. Post-fire regeneration        strategies of Californian coastal sage shrubs. Oecologia. 53: 355-358.        [3490] 28.  McKelvey, Susan Delano. 1938. Yuccas of the southwestern United States:        Part one. Jamaica Plains, MA: The Arnold Arboretum of Harvard        University. 147 p.  [3902] 29.  Mills, James N. 1986. Herbivores and early postfire succession in        southern California chaparral. Ecology. 67(6): 1637-1649.  [5405] 30.  Munz, Philip A. 1973. A California flora and supplement. Berkeley, CA:        University of California Press. 1905 p.  [6155] 31.  Munz, Philip A. 1974. A flora of southern California. Berkeley, CA:        University of California Press. 1086 p.  [4924] 32.  National Academy of Sciences. 1971. Atlas of nutritional data on United        States and Canadian feeds. Washington, DC: National Academy of Sciences.        772 p.  [1731] 33.  Paysen, Timothy E.; Derby, Jeanine A.; Black, Hugh, Jr.; [and others].        1980. A vegetation classification system applied to southern California.        Gen. Tech. Rep. PSW-45. Berkeley, CA: U.S. Department of Agriculture,        Forest Service, Pacific Southwest Forest and Range Experiment Station.        33 p.  [1849] 34.  Raunkiaer, C. 1934. The life forms of plants and statistical plant        geography. Oxford: Clarendon Press. 632 p.  [2843] 35.  Sauer, Jonathan D. 1977. Fire history, environmental patterns, and        species patterns in Santa Monica Mountain chaparral. In: Mooney, Harold        A.; Conrad, C. Eugene, technical coordinators. Proceedings of the symp.        of the environmental consequences of fire and fuel management in        Mediterranean ecosystems; 1977 August 1-5; Palo Alto, CA. Gen. Tech.        Rep. WO-3. Washington, DC: U.S. Department of Agriculture, Forest        Service: 383-386.  [4866] 36.  Simpson, Philip George. 1975. Anatomy and morphology of the Joshua tree        (Yucca brevifolia):  an arborescent monocot. Santa Barbara, CA:        University of California. 524 p. Dissertation.  [6280] 37.  Tratz, Wallace Michael. 1978. Postfire vegetational recovery,        productivity, and herbivore utilization of a chaparral-desert ecotone.        Los Angeles, CA: California State University. 133 p. Thesis.  [5495] 38.  Barry, W. James. 1984. Management and protection of riparian ecosystems        in the state park system. In: Warner, Richard E.; Hendrix, Kathleen M.,        eds. California riparian systems: Ecology, conservation, and productive        management. Berkeley, CA: University of California Press: 758-766.        [5873] 39.  U.S. Department of Agriculture, Soil Conservation Service. 1982.        National list of scientific plant names. Vol. 1. List of plant names.        SCS-TP-159. Washington, DC. 416 p.  [11573] 40.  Udovic, Daniel. 1981. Determinants of fruit set in Yucca whipplei:        reproductive expenditure vs. pollinator availability. Oecologia. 48(3):        389-399.  [5794] 41.  Udovic, Daniel. 1986. 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