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:
https://www.fs.usda.gov/database/feis/plants/tree/jugcal/all.html [].
ABBREVIATION:
JUGCAL
SYNONYMS:
Juglans californica S. Watson var. californica
NRCS PLANT CODE:
JUCA
COMMON NAMES:
southern California walnut
California walnut
California black walnut
southern California black walnut
TAXONOMY:
The scientific name of southern California walnut is Juglans californica
S. Watson [19,25,37]. Southern California 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 - gray 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 southern California 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].
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:
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].
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].
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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