Index of Species Information

SPECIES:  Juglans californica

Introductory

SPECIES: Juglans californica
AUTHORSHIP AND CITATION : Esser, Lora. 1993. Juglans californica. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].
ABBREVIATION : JUGCAL SYNONYMS : NO-ENTRY SCS PLANT CODE : JUCA COMMON NAMES : southern California walnut California walnut California black walnut southern California black walnut TAXONOMY : The currently accepted scientific name for California black walnut is Juglans californica S. Watson [19,25,37]. There are two varieties: J. c. var. californica (southern california black walnut) and J. c. var. hindsii Jepson (northern California black wanut). California black walnut hybridizes readily with black walnut (J. nigra) and English walnut (J. regia). LIFE FORM : Tree FEDERAL LEGAL STATUS : None [37] OTHER STATUS : Southern California walnut woodland is severely threatened by urbanization. The Nature Conservancy, in cooperation with the state of California, is giving high priority to aquiring vegetative/habitat data on the woodland. They list it as one of California's rare and imperiled natural communities [1,5].


DISTRIBUTION AND OCCURRENCE

SPECIES: Juglans californica
GENERAL DISTRIBUTION : Southern California walnut is endemic to California [10]. The current distribution of southern California walnut-dominated forests and woodlands is limited to the Santa Clarita River drainage in the vicinity of Sulphur Mountain, small stands in the Simi Hills and Santa Susana Mountains, the north slope of the Santa Monica Mountains, and the San Jose, Puente, and Chino hills. The best remaining stands are in the San Jose Hills [8]. Outside of this range, southern California walnut occurs in Santa Barbara, western San Bernardino, and northern San Diego counties [25]. It is conspicuously absent from the coastal foothills of the Santa Ana Mountains, San Diego County [33]. Southern california walnut is cultivated in Hawaii [38]. ECOSYSTEMS : FRES28 Western hardwoods FRES34 Chaparral - mountain shrub STATES : CA HI BLM PHYSIOGRAPHIC REGIONS : 3 Southern Pacific Border 7 Lower Basin and Range KUCHLER PLANT ASSOCIATIONS : K030 California oakwoods K033 Chaparral K035 Coastal sagebrush SAF COVER TYPES : 246 California black oak 248 Knobcone pine 249 Canyon live oak 250 Blue oak - Digger pine 255 California coast live oak SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : Southern California walnut woodland may be monospecific or mixed. Coast live oak (Quercus agrifolia) frequently codominants in the walnut woodland [13]. Between Santa Barbara and Orange counties, southern California walnut is locally dominant or codominant in the coast live oak phase of oak woodland [1,8]. Narrow, isolated stands of southern California walnut sometimes occur in chaparral [29]. Occasionally, southern California walnut is found in coastal sage scrub [9]. Classifications naming southern California walnut as a dominant or indicator species are as follows: Community ecology and distribution of California hardwood forests and woodlands [1] Californian evergreen forest and woodland [5] Oak woodland [8] Vegetation types of the San Gabriel Mountains [9] Demographic structure of California black walnut (Juglans californica; Juglandaceae) woodlands in southern California [13] An introduction to the plant communities of the Santa Ana and San Jacinto Mountains [33]. Associated species not previously mentioned include arroyo willow (Salix lasiolepis), California sycamore (Platanus racemosa), white alder (Alnus rhombifolia), California bay (Umbellularia californica), laurel sumac (Malosma laurina), sugar sumac (Rhus ovata), toyon (Heteromeles arbutifolia), Mexican elder (Sambucus mexicana), redberry (Rhamnus crocea), coffeeberry (R. californica), hollyleaf cherry (Prunus ilicifolia), birchleaf mountain-mahogany (Cercocarpus betuloides), California scrub oak (Quercus dumosa), poison-oak (Toxicodendron diversilobum), spiny ceanothus (Ceanothus spinosus), bigpod ceanothus (C. megacarpus), California sagebrush (Artemisia californica), California buckwheat (Eriogonum fasciculatum), black sage (Salvia mellifera), fuschia-flower gooseberry (Ribes speciosum), brome (Bromus spp.), wild oat (Avena fatua), sweetscented bedstraw (Galium triflorum), rape mustard (Brassica rapa), wildrye (Elymus spp.), and Mexican whorled milkweed (Asclepias fascicularis) [9,13,14,18,24,28].

MANAGEMENT CONSIDERATIONS

SPECIES: Juglans californica
IMPORTANCE TO LIVESTOCK AND WILDLIFE : Southern California walnut forests and woodlands provide favorable habitat for a number of vertebrates and invertebrates. A 2-year survey in a southern California walnut woodland in the San Jose Hills found 29 species of diurnal birds [25]. Many rodents, including California ground squirrels and western gray squirrels, eat the nuts [11,25]. The nuts are rarely eaten by deer [25]. PALATABILITY : NO-ENTRY NUTRITIONAL VALUE : NO-ENTRY COVER VALUE : Larger southern California walnut trees provide excellent cover for deer, nesting birds, and rodents [25]. Raptors such as owls use the upper reaches of trees as roosts and nesting places. California ground squirrels dig burrows at the bases of old trees [25]. VALUE FOR REHABILITATION OF DISTURBED SITES : Southern California walnut has been successfully planted for erosion control on road slopes with deep soil at elevations below 3,500 feet (1,066 m). Best growth is achieved in partial shade [11]. In Los Angeles County, southern California walnut was planted in brush wattles during construction of a road fill. Trees reached heights of 12 feet (3.7 m) in 10 years [11]. OTHER USES AND VALUES : Humans eat the nuts of southern California walnut, but the nuts are not grown commercially [25]. Chumash Indians ate the walnuts and used the nutshells for dice. They used the bark for making baskets [31]. Southern California walnut is suitable for ornamental landscaping and is widely planted in urban forestry projects [11,13]. OTHER MANAGEMENT CONSIDERATIONS : Southern California walnut communities are in decline [5,10]. Threats include urban and rural development, overgrazing, and increased recreational use of walnut woodlands [14,25]. In Aliso Creek, Chino Hills State Park, cattle grazing initiated dry conditions, which were worsened by a 5-year drought. The resulting very dry environment hindered survival of walnut seedlings [14]. Grazing has been the principal economic activity in California walnut forests and woodlands for 200 years. The species composition of the southern California walnut woodland understory in the Puente and San Jose hills is attributed to overgrazing by cattle [25]. Pathogens: Southern California walnut is highly susceptible to crown (Phytophthora spp.) rots. Walnuts planted in soil infested with P. citricola and flooded for 48 hours biweekly showed reduced growth and high rates of mortality [17]. In the San Jose Hills, southern California walnut develop heart rot between 20 to 30 years of age. Portions of the trunk and older limbs subsequently become infested with termites and wood-boring beetles. Older multistemmed trees often have some stems that are healthy, some with heart rot, and others that are dead [25].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Juglans californica
GENERAL BOTANICAL CHARACTERISTICS : Southern California walnut is a native, deciduous tree that grows from 20 to 49 feet (6-15 m) tall [15,21]. It varies considerably in morphology according to the age of the tree and site characteristics. Trees in savanna woodland tend to have multiple trunks which grow outward from a ring at the base, giving younger trees the appearance of "V"-shaped shrubs. Trees in more dense stands tend to be single-stemmed and taller [13,25]. The strongly scented trunk is blackish brown and becomes deeply furrowed with age [15]. The root system is extensive, often with a deep taproot [11]. The leaves are 1.5 to 3 inches (3.5-7.5 cm) long [15]. Southern California walnut trees live to be about 100 years old [11]. Southern California walnut is monoecious [15,21]. Slender staminate catkins develop on the wood of the previous year. Pistillate flowers are borne singly or in clusters in short terminal spikes on the current year's growth [4]. The globose fruit is contained in an indehiscent husk or shell that does not open at maturity [4,15]. RAUNKIAER LIFE FORM : Phanerophyte REGENERATION PROCESSES : Sexual reproduction: Southern California walnut produces seed at 5 to 8 years of age [4]. Variations in precipitation from year to year can affect fruit production and seedling establishment. In drought years little or no fruit is produced [13]. Seeds do not have a dormancy period and usually germinate within 4 weeks of dispersal [4,13]. In the spring in the San Jose Hills, densities of 4,742 seedlings per acre (2,000/ha) have been reported [25]. The western gray squirrel may be an important dispersal agent for walnut seed [25]. Vegetative reproduction: Southern California walnut sprouts from the root crown and trunk following cutting or burning [25,29]. SITE CHARACTERISTICS : Southern California walnut occurs in a mediterranean climate, characterized by mild, wet winters and hot, dry summers [12]. Trees generally occur on mesic sites such as north slopes, creekbeds, canyon bottoms, and alluvial terraces [5,19,25]. Trees grow best in deep, alluvial soils with high water-holding capacity. Soils are high in clay content [10,25]. At California State Polytechnic University, soils beneath walnut forests are 3.3 feet (1 m) deep [25]. Elevation: Although southern California walnut has been successfully planted at elevations up to 3,500 feet (1,066 m), it usually occurs from 500 to 2,500 feet (150-760 m) elevation [1,25]. SUCCESSIONAL STATUS : NO-ENTRY SEASONAL DEVELOPMENT : Southern California walnut leaves appear in January and February, with all trees in full leaf by March [25]. Trees on warmer or drier sites develop leaves several weeks earlier than those in cooler, more mesic locations. Flowering begins about the same time as leaf production, with fruits developing to full size during spring. By late summer fruits have matured. Fruit abscission begins in October and November, but some fruits remain on the tree throughout winter [25].

FIRE ECOLOGY

SPECIES: Juglans californica
FIRE ECOLOGY OR ADAPTATIONS : Southern California walnut has large woody platforms at the soil surface. The platforms shield the meristematic tissue beneath them from fire. After fire, sprouts surround the platforms, resulting in multiple trunks [25]. According to Quinn [25], the basal platforms are an adaptation to fire similar to the lignotuber. Most southern California walnut woodlands are subject to periodic fires. Fire is an annual possibility in most locations, where dead annual grasses are present beneath and between the trees during the summer fire season [25]. POSTFIRE REGENERATION STRATEGY : Tree with adventitious-bud root crown/soboliferous species root sucker

FIRE EFFECTS

SPECIES: Juglans californica
IMMEDIATE FIRE EFFECT ON PLANT : Southern California walnut trees are top-killed by most fires [25]. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : NO-ENTRY PLANT RESPONSE TO FIRE : Southern California walnut recovers well from fire. It sprouts vigorously from the trunk and root crown when top-killed by fire, but does not produce seedlings, an indication that most seeds are killed by fire [11]. In Los Angeles County, 10-year-old southern California walnuts were severely burned. Sprouts from the root crowns reached 5 feet (1.5 m) during postfire year 1 [11]. Southern California walnut was sprouting from the root crown 3 years and 8 months after a fire in Big Sycamore Canyon, Ventura County, in the fall of 1973 [29]. Several hundred trees were burned in July 1989 at California State Polytechnic University. One year after fire there was no evidence of dead trees, even though most of the branches and stems had been top-killed. Almost all of the trees sprouted from the root crown within 6 weeks of the fire [25]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : In plant communities near urban areas, the overstory of oak and walnut is a special resource that managers usually protect from fire. However, the understory of these forests can be burned during cool weather to eliminate accumulated ground fuels and produce a shaded fuelbreak [28]. Quinn [25] suggested that prescribed fires of low intensity, at intervals of several years, be tested for their effects on southern California walnut communities.

REFERENCES

SPECIES: Juglans californica
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Endangered plant communities of southern California: Proceedings, 15th annual symposium; 1989 October 28; Fullerton, CA. Special Publication No. 3. Claremont, CA: Southern California Botanists: 80-97. [21321] 4. Brinkman, Kenneth A. 1974. Juglans L. walnut. In: Schopmeyer, C. S., ed. Seeds of woody plants in the United States. Agric. Handb. 450. Washington, DC: U.S. Department of Agriculture, Forest Service: 454-459. [7684] 5. Brown, David E. 1982. Californian evergreen forest and woodland. In: Brown, David E., ed. Biotic communities of the American Southwest--United States and Mexico. Desert Plants. 4(1-4): 66-69. [8887] 6. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905] 7. 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] 8. Griffin, James R. 1977. Oak woodland. In: Barbour, Michael G.; Malor, Jack, eds. Terrestrial vegetation of California. New York: John Wiley and Sons: 383-415. [7217] 9. Hanes, Ted L. 1976. Vegetation types of the San Gabriel Mountians. In: Latting, June, ed. Symposium proceedings: plant communities of southern California; 1974 May 4; Fullerton, CA. Special Publication No. 2. Berkeley, CA: California Native Plant Society: 65-76. [4227] 10. Holstein, Glen. 1984. California riparian forests: deciduous islands in an evergreen sea. In: Warner, Richard E.; Hendrix, Kathleen M., eds. California riparian systems: Ecology, conservation, and productive management: Proceedings of a conference; 1981 September 17-19; Davis, CA. Berkeley, CA: University of California Press: 2-22. [5830] 11. Horton, Jerome S. 1949. Trees and shrubs for erosion control of southern California mountains. Berkeley, CA: U.S. Department of Agriculture, Forest Service, California [Pacific Southwest] Forest and Range Experiment Station; California Department of Natural Resources, Division of Forestry. 72 p. [10689] 12. Johnson, Donald Lee. 1977. The late quaternary climate of coastal California: evidence for an ice age refugium. Quaternary Research. 8: 154-179. [7455] 13. Keeley, Jon E. 1990. Demographic structure of California black walnut (Juglans californica: Juglandaceae) woodlands in southern California. Madrono. 37(4): 237-248. [13767] 14. Keller, Terry. 1993. Riparian zone plant ecology and hydrology in Aliso Creek, Chino Hills State Park, southern California. In: Keeley, Jon E., ed. Interface between ecology and land development in California: Proceedings of the symposium; 1992 May 1-2; Los Angeles, CA. Los Angeles, CA: The Southern California Academy of Sciences: 137-141. [21702] 15. Krochmal, Arnold; Krochmal, Connie. 1982. Uncultivated nuts of the United States. Agriculture Information Bulletin 450. Washington, DC: U.S. Department of Agriculture, Forest Service. 89 p. [1377] 16. 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] 17. Matheron, M. E.; Mircetich, S. M. 1985. Relative resistance of different rootstocks of English walnut to six Phytophthora spp. that cause root and crown rot in orchard trees. Plant Disease. 69(12): 1039-1041. [11544] 18. McDonald, Philip M. 1990. Pseudotsuga macrocarpa (Vasey) Mayr bigcone Douglas-fir. In: Burns, Russell M.; Honkala, Barbara H., technical coordinators. Silvics of North America. Volume 1. Conifers. Agric. Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest Service: 520-526. [13412] 19. McGrananhan, Gale H.; Hansen, John; Shaw, Douglas V. 1988. Inter- and intraspecific variation in California black walnuts. Journal of the American Society of Horticultural Science. 113(5): 760-765. [21777] 20. Moriarty, David J.; Farris, Richard E.; Stanton, Patricia A. 1985. Effects of fire on a coastal sage scrub bird community. Southwestern Naturalist. 30(3): 452-453. [6150] 21. Munz, Philip A. 1973. A California flora and supplement. Berkeley, CA: University of California Press. 1905 p. [6155] 22. Pancheco, Alex A. 1987. Some implications of public involvement in hardwood management. In: Plumb, Timothy R.; Pillsbury, Norman H., technical coordinators. Proceedings of the symposium on multiple-use management of California's hardwood resources; 1986 November 12-14; San Luis Obispo, CA. Gen. Tech. Rep. PSW-100. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station: 144-147. [5369] 23. Patey, Katherine J.; Wishner, Carl; Gibson, Joseph G. 1991. Tapo Canyon Creek riparian habitat restoration plan. Restoration & Management Notes. 9(1): 47-48. [15454] 24. Perala, C.; Hoover, D. A. 1990. Hand-removal of exotics and planting of natives key to restoration of riparian forest understory. Restoration & Management Notes. 8(2): 118. [13791] 25. Quinn, Ronald D. 1990. The status of walnut forests and woodlands (Juglans californica) in southern California. In: Schoenherr, Allan A., ed. Endangered plant communities of southern California: Proceedings, 15th annual symposium; 1989 October 28; Fullerton, CA. Special Publication No. 3. Claremont, CA: Southern California Botanists: 42-54. [21319] 26. Radtke, Klaus. 1978. Wildland plantings & urban forestry: Native and exotic 1911-1977. Los Angeles, CA: County of Los Angeles Department of Forester and Fire Warden, Forestry Division. 134 p. In cooperation with: U.S. Department of Agriculture, Forest Service, Forestry Research, Chaparral R & D Program. [20562] 27. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p. [2843] 28. Riggan, Philip J.; Franklin, Scott; Brass, James A. 1986. Fire and chaparral management at the chaparral/urban interface. Fremontia. 14(3): 28-30. [18368] 29. 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] 30. Stickney, Peter F. 1989. Seral origin of species originating in northern Rocky Mountain forests. Unpublished draft on file at: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT; RWU 4403 files. 7 p. [20090] 31. Timbrook, Jan. 1990. Ethnobotany of Chumash Indians, California, based on collections by John P. Harrington. Economic Botany. 44(2): 236-253. [13777] 32. 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] 33. Vogl, Richard J. 1976. An introduction to the plant communities of the Santa Ana and San Jacinto Mountains. In: Latting, June, ed. Symposium proceedings: plant communities of southern California; 1974 May 4; Fullerton, CA. Special Publication No. 2. Berkeley, CA: California Native Plant Society: 77-98. [4230] 34. Vogl, Richard J. 1977. Fire frequency and site degradation. In: Mooney, Harold A.; Conrad, C. Eugene, technical coordinators. Proc. of the symp. on 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: 193-201. [4843] 35. Warter, Janet K. 1976. Late Pleistocene plant communities - evidence from the Rancho La Brea tar pits. In: Latting, June, ed. Symposium proceedings: plant communities of southern California; 1974 May 4; Fullerton, CA. Special Publication No. 2. Berkeley, CA: California Native Plant Society: 32-39. [4219] 36. Hickman, James C., ed. 1993. The Jepson manual: Higher plants of California. Berkeley, CA: University of California Press. 1400 p. [21992] 37. U.S. Department of the Interior, Fish and Wildlife Service. 2013. Endangered Species Program, [Online]. Available: http://www.fws.gov/endangered/. [86564] 38. St. John, Harold. 1973. List and summary of the flowering plants in the Hawaiian islands. Hong Kong: Cathay Press Limited. 519 p. [25354]


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