This species reportedly hybridizes with Quercus kelloggii and Q . wislizenii .
The Mahuna used Quercus agrifolia medicinally to heal the bleeding navel of a newborn (D. E. Moerman 1986).
Number of trees in DBH1 class (cm)
Vigor of trees in DBH2 class (cm)
Coast live oak is a native, drought-resistant, evergreen tree, ranging in height from 19 to 82 feet (6-25 m) and in diameter from 1 to 4 feet (0.3-1.2 m) [70,129]. The bark of young trees is smooth. With age, it develops deep furrows, ridges, and a thickness of about 8 to 9% of bole or branch diameter [70,129]. The inner bark and cork layers are thick [43,129]. Open-grown crowns are broad and dense, with foliage often reaching the ground [70]. In open areas trunks are usually 4 to 8 feet (1.2-2.8 m) tall; at this height, primary branches originate and grow horizontally. Trees in dense stands generally have irregular crowns and few lower branches. In closed stands trunks may be branchless up to 20 feet (6.2 m) high, where several branches extend diagonally upward [129]. Coast live oak stands are typically from 40 to 110 years old. Individual trees may live over 250 years [43,129].
The root system consists of a deep taproot that is usually nonfunctional in large trees [35,128]. Several deep main roots may tap groundwater if present within approximately 36 feet (11 m) of the soil surface [31,35,128]. Coast live oak develops extensive horizontal root branches and surface-feeding roots [18,35,128]. Tree roots in southwestern California are associated with mycorrhizae that aid in water uptake during the dry season. A network consisting of roots from 3 coast live oak trees and their and associated mycorrhizae covered a 50- Ã 13-foot (15- Ã 4-m) area of the soil profile that reached through weathered granite through to bedrock. Roots in clay soils were not infected with mycorrhizae [18].
Fire adaptations: Coast live oak is exceptionally fire resistant, more so than other California oak species. Adaptations to fire include evergreen leaves, thick bark, and sprouting ability. Evergreen leaves allow coast live oak to allocate greater amounts of energy to recovery from fire than to replacing the entire crown annually. Evergreens are often better able to conserve nutrients than deciduous species, and are favored in fire-prone environments [102]. Coast live oak bark is the thickest among California oaks; it is mainly composed of live inner bark with little dead outer tissue [128,129,130]. Oaks are more likely to be damaged by fall fire than earlier fires [129]. Because of mortality among small-diameter trees, frequent fire limits coast live oak invasion of grasslands [104].
Coast live oaks sprout from the main trunk and upper crown even after severe burning [37,130]. When trees are top-killed, they sprout from the root crown [43]. Vigorous sprouting is supported by food reserves stored in the extensive root system [35]. Sprouting from the root crown often occurs during the first 2 months after top-kill, but some charred trees do not sprout for 2 to 3 years [122,129]. Scorched trees retaining live vascular cambial tissue sprout from the bole and from scaffold and smaller surviving branches. A few scorched trees may produce root crown as well as epicormic sprouts [37]. Prefire crown volume is generally recovered, or nearly so, in about 8 to 10 postfire years [37,129].
Roots are protected from fire by an outer corky layer and soil. Coast live oak roots generally suffer little direct heat damage except to feeder roots near the soil surface [128]. Acorns on the soil surface are killed by low-severity fire, while animal-buried acorns usually survive moderate-severity fire, sometimes allowing high rates of postfire establishment [42,89]. Severe fire may kill even buried acorns, and complete removal of shrubs by fire may reduce coast live oak seedling survival [28,42,118]. By caching acorns in burned areas burned areas, which are preferred caching sites, scrub jays may facilitate postfire establishment of coast live oak seedlings [115].
Fire regimes: Fire frequency largely defines the extent of coastal sage scrub, chaparral, and oak woodland; in these habitats decreasing fire frequency tends to favor the development of coast live oak. Conversely, where coast live oak occurs in mixed evergreen forests (or where coast Douglas-fir is invading oak woodlands), frequent fire favors coast live oak and other seral species. One study of vegetation dynamics in coastal sage scrub, chaparral, and oak woodland near Santa Barbara found that without fire or livestock grazing, coastal sage scrub was replaced by coast live oak woodland at a rate of 0.3% annually. Grassland to coastal sage scrub transition occurred at a rate of 0.69% per year, and oak woodland reverted to grassland at a rate of 0.08% per year. On burned areas without livestock grazing or on unburned sites with livestock grazing, rates of transition of grassland to coastal scrub and coastal scrub to oak woodland were lower and the rate of oak woodland reversion to grassland was higher [29].
Oak woodlands: Analysis of oak pollen (primarily that of coast live oak) records showed that oak woodlands remained stable for up to 4 centuries before major European-American settlement (approximately 1470 to 1870). Coinciding with a decrease in fire frequency between 1870 and 1985, percent oak pollen increased to its highest level in 560 years. The 2-fold increase in oak pollen reflected both increase in oak density and in area occupied [104]. Coast live oak woodlands may experience an increase in shrub cover in the absence of frequent fire or heavy grazing, but there are also reports of oak savannas and adjacent grasslands that, without fire for 50 years, have not had a noticeable increase in shrub cover. Sites without shrub increase are generally south facing and/or on shallow soils [66]. Generally, grass is present in open stands, while closed stands have up to 5 inches (12.7 cm) of oak litter [129].
Riparian forests: Coast live oak associates in riparian areas include white alder, California sycamore, and Fremont cottonwood, all of which are sprout after fire. Severe fire was apparently historically rare in these habitats. Currently most fire is accidental and of high severity, causing relatively high rates of top-kill and basal sprouting of coast lie oak and associated tree species [10,42].
Mixed evergreen forests: Where coast live oak occurs in mixed evergreen forests of coast Douglas-fir, tanoak, and Pacific madrone, historic fire return intervals were less than 35 years, with fires generally occurring between late August and November after termination of radial growth [5,24]. In many of these stands fire ceased in the early to mid-1900s, and there has been a concomitant increase in coast Douglas-fir density. Bowcutt [19] states that coast Douglas-fir increase in coast live oak woodlands may indicate that such stands, when coast Douglas-fir was not present, represented "a disclimax created by native people through burning." A study of fire frequency and coast Douglas-fir establishment on Point Reyes Peninsula, where coast live oak occurs with California bay, showed coast Douglas-fir establishment greatly accelerated with cessation of fire in the early 1900s. Fire history of 2 such sites is provided below; only 1 fire scar was observed after 1945 [24]:
Period analyzed Number of intervals Mean fire interval (years, with standard deviations) Range of intervals (years) Weibull mean (50% exceedance) probability interval (years) 5% to 95% probability interval (years) Site 1 1820 to 1905 11 7.7 (5.0) 1 to 17 6.9 1.3 to 17.6 Site 2 1825 to 1918 11 8.5 (5.3) 3 to 18 7.8 2.1 to 16.0Chaparral and coastal sage scrub: Prior to settlement, chaparral communities in which coast live oak grows in a shrubby, shorter form had mean fire intervals of 10 to 30 years [121]. With land use conversion and urbanization, fire frequency has decreased. In the Santa Monica Mountains, chaparral sites dominated by California sagebrush, California brittlebrush (Encelia californica), coastal buckwheat (Eriogonum cinereum), purple sage, and black sage (Salvia mellifera) (with 11 to 19% cover of coast live oak) had fires in 1903, 1945 and 1978. A similar site with 5.2% coast live oak cover had fire in 1903 and 1978 [93]. In most chaparral and coastal scrub areas, FIRE REGIMES are entirely anthropogenic, and with urbanization, steep slopes, containment difficultly, and erosion potential, fire's current use is limited [42,68]. The absence of fire, particularly in coastal sage scrub, has allowed coast live oak to increase in density and area. On sites in the Monterey Bay area with fire exclusion for over 70 years, coast live oak has increased significantly (p<0.001) from 2 to 5.5% between 1976 and 2000. Where coast live oak has developed, understory density and diversity have declined dramatically [155].
Fire intervals: Greenlee and Langenheim [63] described FIRE REGIMES of different coast live oak associated communities in the Monterrey Bay area between aboriginal time and present. Their results, presented below, show the remarkable decline in fire frequency in the recent era (1929 was chosen to demarcate the recent fire regime because of restrictions that were put in place against burning). "Probable mean fire interval" refers to estimates of fire intervals that are derived from historical or very limited physical evidence.
Fire regime Vegetation where burning concentrated Vegetation where burning incidental Recorded or calculated mean fire intervals (years) Probable mean fire intervals (years) Lightning Prairies 1-15 Coastal sage 1-15 Chaparral 10-30 Oak woodland 10-30 Mixed evergreen 15-30 Redwood forest 135 Aboriginal (until approximately 1792) Prairies 1-2 Coastal sage 1-2 Chaparral 18-21 Oak woodland 1-2 Mixed evergreen 50-75 Redwood forest 17-82 Spanish (1792 to 1848) Prairies 1-15 Coastal sage 1-15 Chaparral 19-21 Oak woodland 2-30 Mixed evergreen 50-75 Redwood forest 82 European-American (1847 to 1929) Prairies 20-30 Coastal sage 20-30 Chaparral 10-27 Oak woodland 50-75 Mixed evergreen 7-29 Redwood forest 20-50 Recent (1929 to present) Prairies 20-30 Coastal sage 155 Chaparral 155 Oak woodland 225 Mixed evergreen 215 Redwood forest 130Fire return intervals for plant communities and ecosystems in which coast live oak occurs are presented below. Find further 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".
Community or Ecosystem Dominant Species Fire Return Interval Range (years) California chaparral Adenostoma and/or Arctostaphylos spp. coastal sagebrush Artemisia californica California steppe Festuca-Danthonia spp. 121] Pacific ponderosa pine* Pinus ponderosa var. ponderosa 1-47 [159] coastal Douglas-fir* Pseudotsuga menziesii var. menziesii 40-240 [5,110,135] California mixed evergreen P. m. var. m.-Lithocarpus densiflorus-Arbutus menziesii California oakwoods Quercus spp. coast live oak Q. agrifolia 2-75 [63] canyon live oak Q. chrysolepis blue oak-foothills pine Q. douglasii-Pinus sabiniana Oregon white oak Q. garryana 5] California black oak Q. kelloggii 5-30 [121] interior live oak Q. wislizenii 5] *Fire return interval varies widely; trends in variation are noted in the species summary.Coast live oak occurs in a mediterranean climate characterized by mild, wet winters and hot, dry summers. Climatic extremes are modified near the coast, where trees receive more precipitation than inland populations [43]. Trees generally occur on mesic sites such as north slopes, alluvial terraces, canyon bottoms, or upper streambanks [23,46,101]. Coast live oak's preference for mesic sites is most pronounced in the southern part of its range [106]. Coast live oak may grow where it can access groundwater, but most individuals have extensive shallow root networks [79].
Low-elevation coastal populations of coast live oak generally grow in loam, while higher-elevation coastal populations are associated with shaley clay-loam soil. Inland populations are found on sandy soil, while those in southern California islands grow in clay or clayey loam [34,43]. Coast live oak tolerates serpentine soils [53]. Coast live oak is often associated with depositional environments, deeper soils, and higher organic matter. Coast live oak occurs on soils ranging from silts and clays to weathered granite [18,47].
Elevations of coast live oak populations range from sea level to 3,000 feet (914 m) in central and northern California and from sea level to 5,000 feet (1,524 m) in southern California [70,79,129]. Coast live oak occurs at slightly higher elevations in Baja California. On the coastal side of the Sierra Juarez coast live oak grows below 4,260 (1,300 m), and on western slopes of Sierra San Pedro Martir, elevations range from 3,930 to 5,580 (1,200-1,700 m) [106].
Coast live oak seedlings and saplings less than 3 inches (7.6 cm) in diameter may be top-killed by low- to moderate-severity fire, and severe fire kills trees of this size [46,122,128,129,151]. Because of vascular cambium protection, mature trees have high fire survival rates, even with crown fire. Heavily charred bark has a checkered appearance and frequently exfoliates, but damage typically extends only 0.5 to 0.8 inch (1.3-1.9 cm) into the bark. If cambium death occurs in large trees it is typically in small scars at the base [129]. Trees greater than 6 to 8 inches (15.2 to 20.3 cm) in diameter resist top-kill [122,129]. Saplings 2 to 6 inches (5.1-152 cm) in diameter are top-killed by severe fire. An "extremely hot" crown fire on the San Bernardino National Forest caused only 4% coast live oak mortality. Ninety percent of the oaks less than 3 inches (7.6 cm) in diameter were top-killed, and 2% were killed. Of trees greater than 6 inches (15.2 cm) in diameter, the trunks and crowns of all but 5% survived the fire without top-kill (the 5% includes 3% that were top-killed and 2% killed) [128].
For small-diameter trees, mortality as a result of low- to moderate-severity fire depends on tree height and location with respect to other tree crowns. Fire mortality of Engelmann oak and coast live oak (in a woodland with herbaceous and coastal sage scrub species in the understory) was studied for trees less than 3.9 inches (10 cm) in diameter: of 1,214 small trees surveyed, 531 survived 5 years after fire. Mortality was similar for each species: 56% for coast live oak and 59% for Engelmann oak. Mortality was 50% among trees 11.8 to 15.7 inches (30-40 cm) tall, 30% among those 29.3 to 78.7 inches (1-2 m) tall, and 10% among trees taller than 78.7 inches (2 m). In gaps between tree canopies mortality was significantly lower (p<0.0001). Coast live oak mortality was 40% in gaps and 59% under canopies [89] .Generally mortality of coast live oak is greater when there is a considerable shrub understory or when trees are adjacent to chaparral. Coast live oak in the Santa Monica Mountains was killed in large numbers when a hot chaparral fire burned into the oak woodland [141].
Coast live oak woodlands are some of the most important habitats to wildlife in California [57]. These communities are preferred habitat for black bear and black-tailed deer. In chaparral areas where shrubs predominate, coast live oak stands with an understory of mixed shrubs and forbs are critical to black-tailed deer [131]. Coast live oak provides browse for black-tailed deer and various rodents and lagomorphs [140]. Feral pigs and pocket gophers eat the roots, and black bear, feral pig, black-tailed deer, rodents, and various upland game and nongame birds consume the acorns heavily [123,140]. Coast live oak litter provides excellent hunting opportunities for insectivorous vagrant and ornate shrews [131]. Cattle eat coast live oak sprouts [124]. Most livestock do not readily browse mature foliage, although domestic goats eat it year-round [62]. Livestock readily consume the acorns [140].
Coast live oak communities support a number of bird species including the federally endangered least Bell's vireo and least tern [87,117]. Acorns of coast live oak are of particular value to acorn feeders, as they are retained on tree for up to 8 months [32]. Acorn-dependent birds include the acorn woodpecker, yellow-billed magpie, and scrub jay [64,88]. Acorns comprise over 50% of diets of the acorn woodpecker and scrub jay in fall and winter [88].
Palatability/nutritional value: Nutritional information on coast live oak foliage is sparse. One study found the protein content of leaves was 4.6% in December. Springtime protein levels were not determined; however, protein content of interior live oak, a closely related species, was 17.6% in May [15]. Coast live oak acorns are 6.26% protein, 16.7% fat, and 54.7% carbohydrate [6]. The palatability of coast live oak foliage has been rated useless for cattle and horses, poor to useless for domestic sheep, and fair to poor for black-tailed deer [140].
Cover value: Western sycamore/coast live oak communities in the South Coast Ranges provide wintering grounds for 32 species of birds, at a density of approximately 251 birds per acre (620/ha) [51]. An estimated 41% of owl territories in southern California are interior and coast live oak/bigcone Douglas-fir forests. Owls are benefited by fire in adjacent chaparral, which increases prey populations [160]. Red-shouldered hawks rely heavily on coast live oak woodlands in southern California but adapt to urban woodlands as well [16].
Several cavity-nesting birds use coast live oak for nesting. In a Santa Barbara County study, western bluebird and ash-throated flycatcher were the most common nest occupants. Bewick's wren, oak titmouse, tree swallow, and violet-green sparrow also use coast live oak cavities [113].
Mesic coast live oak woodlands with shrub understories have adequate
regeneration, while xeric woodlands are
likely to have limited recruitment [30]. Thus, northern coastal populations of this tree are
generally stable, but the species is in decline
in southern California [112,143].
Coast live oak regeneration in xeric sites can be improved by reducing grazing intensity or
protecting individual seedlings from livestock [32,64,123,124]. Other threats to this oak
include urban and rural development, increased recreational
use of oak woodlands, and cutting trees for firewood [129,143].
Some coast live oak woodlands were cleared to increase forage for domestic
livestock, but since the early 1970s, urban and residential development have had
a much larger impact [1]. Coast live oak populations in Baja California were not
as heavily logged as in California, as natural gas and propane were available
when human populations in the area expanded. Here heavy grazing around population centers
has been the
primary anthropogenic limitation on recruitment [107]. Presence of honey-fungus (Armillaria
mellea) in the soils of sites now bereft of coast live or other oaks is a
good indicator of oak dominance in the past [22].
Diseases: The most serious threat to coast live oak, other red
oaks, and related non-oak species in the beech family is sudden oak death
disease. The primary pathogen response for sudden oak death is the
fungus-like water mold Phytophora ramorum.
Previously described only as a greenhouse pathogen from northern Europe, its
origins are uncertain [55,103,136]. Another pathogen, Hypoxylon
thouarsianum, is associated with the disease as a secondary fungus.
Mature coast live oak are highly susceptible to sudden oak death, which can
kill apparently healthy trees within a few weeks to several years. Sudden oak
death disease has reached epidemic proportions in California and southwestern Oregon
and is particularly virulent on California's central coast, where coast live
oak is the dominant red oak species [103,136]. For example, coast live oak on 2
sites in Marin County showed infection rates of 35% in 2000 and 38% in 2001,
and 16% in 2002 and 19% in 2001, respectively. Coast live oak mortality at the
2 sites rose from 8 to 15% and 6 to 8% during that time. About 1/3rd of coast
live oak on the 2 sites showed evidence of infection.
Etiology of sudden oak death is unclear as of this
writing (2002). Bark and ambrosia
beetles (Scolytidae) are associated with infected trees and may be vectors for
the fungal pathogens [103] Coast live oak on moist sites may be more vulnerable
to Phytophora ramorum infection than trees on drier sites [150]. Ability of
infected trees to overcome the disease is unknown
[103]. Besides species in the oak family, a variety native woody plant species
serve as alternate hosts for Phytophora ramorum (i.e., Rhododenron
spp., huckleberries (Vaccinium spp.), and manzanitas). Although currently
isolated to 2 west coast states, seedling inoculum trials suggest that some
eastern red oak species may be even more susceptible to sudden oak death than
coast live and related California red oaks [136]. Standard fungicide
treatments (e.g., metalaxyl, cupper sulfate, and phosphoric acid) have shown
positive control of Phytophora ramorum in preliminary tests. Fungicides
may provide Phytophora ramorum control in urban settings and protect
small groups of wildland trees, but are not likely to be practical in large
wildland settings [78]. Information on how sudden oak death
is transmitted [40], diagnosed [136], and can be monitored [78] is available.
Coast and interior live oaks are susceptible to oak drippy-nut disease, which
develops after wasps, acorn weevils, or other acorn feeders puncture acorns and allow
the bacteria Erwinia quercina to develop within [17]. Diplodia quercina, a
fungal pathogen that grows hyphae through wounds, may cause dieback of large branches
of coast live oak, valley oak, and California black oak. "Twigblight" in coast and
interior live oaks is caused by the fungal pathogens Cryptocline
cinerescens and Discula quercina; dieback may range from a few twigs to the
entire crown [69]. Epidemics of oak wilt disease, caused by the pathogen Ceratocystis
fagacearum, have occurred among
Texas oaks in urban forests and in live oak (Q. virginiana) savannas; coast and interior live oaks
are more resistant [4]. Watering during summer may cause root rot as a result of Armillaria
mellea infection or crown rot as a result of Phytophthora spp.
infection [69].
Coast live oak is used as an urban ornamental tree [26]. Native Americans planted coast live oaks to harvest the acorns as food. Coast live oak may have expanded its range into interior live oak habitats of northern California when coast live oak acorns were planted inland [137].
Wood Products: Coast live oak wood is primarily used for fuel [129] and can be managed for firewood production. Coast live oak is a good candidate for coppice management, as it sprouts vigorously from cut stumps. Few studies have been conducted on coast live oak response to thinning. Coast live oak stands on 4 sites on the central and southern California coastline responded to thinning with significantly greater basal area compared to unthinned stands [126].
Some commercial charcoal is made from coast live oak wood. The wood is hard, heavy, and fine-grained, but it is unsuitable for lumber because it cracks easily and warps badly [129].
Coast live oak sprouts from the bole, branches, and /or root crown after fire damage. Mature trees with live branches generally sprout from the branches. Trees with damaged branches sprout from the bole, which is better protected from fire by its thicker bark [37,130]. Seedlings and saplings are generally top-killed, and sprout from the root crown after fire [43,151]. Coast live oak recovers rapidly from moderate-severity fire. Severely burned crowns, trunks, and root crowns may require several years to sprout. If sprouting occurs within several postfire months, basal sprouts can be 2 to 3 feet (0.6-0.91 m) tall in 2 years, and crown density can be 80 to 100% of prefire levels within 10 years [88,130]. The most common fire damage to the trunk is a basal wound resulting in potential cambium death. Wounds less than a few inches in size may eventually heal with no accompanying heart rot, but larger wounds are susceptible to fungal and bacterial pathogens and insect infestation [138].
Light-severity surface fire has little effect on mature coast live oak. An October prescribed fire in northern San Luis Obispo-southern Monterey counties varied from light to moderate severity. The fire had no effect on postfire coast live oak canopy coverage, measured at postfire year 1. Six percent of the canopy was singed. No mature trees died, and the number of coast live oak snags was unchanged [151,158].
Saplings and seedlings generally recover quickly from light- to moderate-severity fire. For the fall prescribed fire in southern Monterey and northern San Luis Obispo counties, 22 percent of coast live oak saplings were killed. Survival was best for saplings with light fuel loads within 3.3 feet (1 m) of their stems. The remaining 78% of saplings were top-killed and had root crown sprouts by the next fall. Average number of sprouts was 6.4 (+1.2 SE) per sapling. Average length of the longest sprout was 24.1 inches (61.2 cm) (+4.1 inches (10 cm) SE) [151].
Recovery of coast live oak following severe fire on the San Bernardino National Forest showed patterns typical of the species. Mortality and top-kill rates were highest among the smallest size classes. Basal sprouting was common in smaller size classes and crown sprouting (or crown sprouting in addition to basal sprouting) was more common among larger size classes. Sprouting and mortality rates were observed after 5 years on 0.64-acre (0.25 ha) transects; rates are summarized below by size class [128]:
Tree diameter (inches) Number of charred trees Dead (%) Basal sprouts only (%) Basal and crown sprouts (%) Crown sprouts only (%) 0-3 90 2 88 1 9 3-6 54 11 26 28 35 6-12 65 1 5 52 42 12-18 24 0 0 62 38 18+ 22 4 5 50 41Coast live oak experiences severe fire in riparian habitats. After the high-severity Wheeler Fire near Ojai, California, coast live oak, white alder, and California sycamore all sprouted. Most burnt tree trunks remained after fire until storms the following winter, when some were uprooted. Six of 19 coast live oak boles blew down in winter. Sprouting rates were 7% for white alder, 83% for California sycamore, and 70% for coast live oak. Basal sprouting of coast live oak was positively correlated (p<0.001) with tree size [42].
Regeneration from acorns following fire is variable, depending on fire severity and site characteristics. Acorn survival is high in low- to moderate-severity fire, particularly when acorns have been cached by animals. Acorn survival in severe fire is low, and postfire seedling recruitment is slower. Following a severe fire in Ventura County, burned sites supported no coast live oak germinants the following spring, while adjacent unburned areas produced new seedlings [42]. Fire in an Engelmann oak/coast live oak stand in southern California had positive effects on coast live oak seedling establishment. In the 2 years preceding fire there was no establishment; in 5 postfire years 1,118 oak seedlings established, of which 1,025 were coast live oak. Establishment was greatest under the outer edges of canopies, particularly for coast live oak [89].
Breeding system: Oaks (Quercus spp.) are monoecious with staminate flowers in naked aments and solitary or clustered pistillate flowers [145]. Genetic studies using biochemical and molecular markers show that coast live oak is the least diverse of all California oaks in the subgenus Erythrobalanus. This suggests that coast live oak populations are highly outcrossing, and most genetic diversity is among, rather than within, populations [44].
Pollination: Coast live oaks are wind pollinated [32,44].
Seed production: Coast live oak is the only black oak in California whose acorns develop in 1 year [21,129]. Acorns are 1.0 to 1.5 inches (2.5-3.8 cm) long and 0.4 to 0.6 inch (1.0-1.5 cm) wide [70,129]. Coast live oak à California black oak hybrids' acorns mature in 2 years [114]. Information on the age of sexual maturity and age of maximum production of acorns is lacking [32].
Acorn production is variable within and among years, but coast live oak is productive relative to other California oak species. Acorn production over a 5-year period was observed for canyon live oak, coast live oak, valley oak, blue oak, and California black oak. Canyon live oak was most productive, and coast live oak was 2nd most productive [32]. Crop failure is frequent, and large crops may occur in consecutive years but no more frequently than expected by chance. In low acorn years, acorns can be absent on up to 90% of trees: this occurred in valley oak, coast live oak, blue oak stands observed in Santa Barbara, San Luis Obispo, and San Benito counties [57].
Though crop size is variable, it is often synchronized across oak populations and species. Synchronization is more common among California oak species whose acorns mature in the same year, but it also can occur among species with different acorn maturation times [32,81,83]. Synchronization may be detectable on areas as large as 190 to 390 square miles (500-1000 km2) [81]. Observation of acorn production cycles among canyon live oak, coast live oak, valley oak, blue oak, and California black oak in the Santa Lucia Mountains of central California found no species-specific patterns in acorn production. The 5 oaks were observed over 12 years; at only 2 of 60 date/year combinations (3.3% of sample dates) was there no acorn production from any species. Coast live oak, however, had crop failures (acorns per tree averaging less than 1) 50% of the time [84].
Several nonmutually exclusive hypotheses seek to explain the variability and synchronicity of California oak acorn crop sizes. This may be an adaptation to seed predation as high acorn production years have incomplete seed consumption and allow leftover seed to establish [84]. Synchronicity over large geographic areas may also be because the areas experience similar environmental conditions [83]. One study found that acorn crops for coast live oak and canyon live oak were larger when the previous 1 and 2 years had more rain [82]. Another 5-year study found no correlation between crop size and 14 weather variables [32].
Seed dispersal: Coast live oak retains its acorns longer than other California oaks. Most of its acorns are dropped in fall, but some remain attached to trees until spring. This adaptation reduces seed loss to birds and small mammals such as squirrels, magpies, and scrub jays; in small crop years 100% of the crop may be consumed [32,115]. Though seed predation may be high, it also provides a means of seed dispersal. Seed-caching animals such as the scrub jay and California ground squirrel are important to species survival, as acorns buried by these animals are more likely to develop into seedlings than acorns that have not been cached [28,32]. Scrub jays cache about 5,000 acorns each year over an average home range of about 6.2 acres (2.5 ha), effectively seedling at a rate of 800 acorns per acre (2,000 per ha). Though 95% of cached acorns are found and eaten, remaining acorns have high germination and survival rates because they are typically cached about 0.4 inch (1 cm) below the soil surface [100]. Scrub jays prefer burned sites for acorn caching [115].
Acorn-feeding insects damage coast live oak seed. Weevil and moth larvae on the Santa Rosa Plateau Ecological Reserve preferred coast live oak acorns to those of Engelmann oak, and researchers concluded that coast live oak acorns provided a more nutritious diet. Although damage inflicted to individual acorns appeared slight, the ability of insect-damaged acorns to germinate and establish is poorly understood. Further studies are required to determine the impact of insect damage to coast live oak establishment [52].
Seed banking: Little information is available regarding coast live oak seed banks, but, because coast live oak acorns have no dormancy requirement, it is reasonable to assume that seed banks are small.
Germination: Coast live oak acorns have no dormancy requirement and germinate 15 to 50 days after falling [25,64,108]. Germination is slower than other California oaks; this limits coast live oak establishment on dry sites [95]. Griffin [64] found 100% viability of acorns collected in the Carmel Valley, while Mirov and Kraebel [108] reported 73% germination of acorns collected in Berkeley. Fifty percent germination after 18 days of 55 to 68 degrees Fahrenheit (13-20 °C) controlled climate without stratification has also been reported [96]. Acorns with low moisture content show higher rates of germination and produce taller seedlings than do acorns with high moisture content, but unviable seed is not a serious problem for this species [75,115].
Seedling establishment/growth: Seedling top-growth is slow under natural conditions, with early development concentrated on rapid, early root growth [96]. Lateral root growth of 9.8 inches (25 cm) in 6 months has been observed under moist controlled conditions [27]. In the field, coast live oak taproot elongation of approximately 28 inches (70 cm) in 2 months has been noted [39]. Under ideal nursery conditions, coast live oak seedlings have attained heights of 5 to 8 feet (15.2-24.4 m) in 2 years [144].
Acorn predation strongly limits establishment in small crop years, but seedling survival rates are also low [115]. At sites in the Central and South Coast ranges, current sapling-to-tree ratios are 1:3 or lower [112]. Common causes of mortality include herbivory and livestock trampling and inadequate moisture [32,115,123]. Mortality results from aboveground or root herbivory by domestic livestock, black-tailed deer, pocket gophers, grasshoppers, cutworms, and feral pigs [32,48,64,123,149,153].
Coast live oak appears to be more susceptible to browsing damage than other California oaks while in the seedling stage, but shows better ability to sprout after herbivory damage incurred in the sapling stage [64,111,127]. Coast live oak seedlings are particularly vulnerable to browsing damage because some insect and mammalian browsers prefer coast live oak seedlings over seedlings of associated oaks [48].
Coast live oak is more susceptible to drought than other California oaks. In experimental soils wherein subsurface moisture was controlled and dried while leaving a moist surface horizon, coast live oak did not increase lateral root production when the vertical root tip died in dry soil. In contrast, blue oak and valley oak both responded to the treatment with increased lateral growth; these morphological differences are consistent with the species' different ranges [27].
Because of drought and herbivory's deleterious effects on seedling survival, recruitment is best among germinants growing in shade, where herbivory protection and water availability are higher [157]. Recruitment among rock outcrops is relatively common as this offers some protection from large browsers [66]. Common nurse plants are California heathgoldenrod (Ericameria ericoides), chamise, coyote bush (Baccharis pilularis), purple sage (Salvia leucophylla), orange bush monkeyflower (Diplacus aurantiacus ssp. aurantiacus), chamisso bush lupine (Lupinus chamissonis), California sagebrush (Artemisia californica) and poison-oak (Toxicodendron diversilobum) [28,118]. Eighty percent of seedlings found on sites in the Santa Ynez Valley of Santa Barbara County were growing under purple sage or California sagebrush. Another 15% grew under mature coast live oak. Mortality due to herbivory was considerably higher among seedlings under parent trees [28]. Establishment is generally greater in coastal sage scrub than in other types of chaparral [30]. A study of coast live oak seedling establishment, with and without nurse shrubs and cages for protection, found that acorns planted in the open had higher germination but lower 1-year survival. Between 1 and 2 years of age, nurse shrubs had no effect on seedling survival, but cages continued to have a positive effect by reducing black-tailed deer browsing [118]. Another study of coast live oak establishment at 2 sites in central California showed strong association of seedlings with shrubs. Shrub cover was 30%, but 80% of coast live oak seedlings were under canopies. In 2 years of monitored growth, survivorship was 0% in open areas and 31% under shrubs. Seedlings in the open were grazed more, but drought also increased stress. Mortality related to moisture and temperature stress was 17% under shrubs and 63% in the open. The authors noted that differential dispersal might also increase recruitment under shrubs [28].
Asexual regeneration: Coast live oak sprouts from the root crown and/or trunk following cutting or burning [37,43,126,128,130].
Ecologists refer to changes in the grassland, chaparral, and oak woodland mosaic of California as "non-directional fluctuations" rather than succession [12]. Coast live oak may be considered seral or climax depending on habitat, but it is tolerant of shade throughout its life [129]. Where their ranges overlap, deciduous trees such as blue oak and California black oak are seral to coast live oak [13]. However, because deer and cattle prefer coast live oak, it is gradually replaced by California bay in some areas of coastal northern California where the 2 species codominate [99]. In mixed evergreen forest that is burned or logged, a coast live oak phase is seral to the climax evergreen deciduous and conifer forest. However, on steep slopes or poor sites within this habitat type, coast live oak represents a topographic or edaphic climax [7]. Succession on coastal dunes at Asilomar State Park on the Monterey Peninsula includes an early stage of beach wormwood (Artemisia pycnocephala) and/or California heathgoldenrod on slopes; the next sere includes dense shrub (coyote bush, seaside woollysunflower (Eriophyllum stoechadifolium), California coffeeberry (Rhamnus californica), poison-oak, and Pacific dewberry (Rubus vitifolius)) development with coast live oak and/or gray pine in the overstory. If fire frequency and deer numbers are low, coast live oak replaces gray pine [9]. In the San Francisco Bay area light browsing allows coyote bush to invade grasslands, and coyote bush subsequently facilitates coast live oak woodland development [139]. In the absence of disturbance, coyote bush brushland almost always gives way to coast live oak and California bay, as coyote bush seedlings do not develop beneath their own canopies [161].
Recruitment of most oaks in California has declined, with some species not regenerating rapidly enough to maintain current density. There is much debate about the causes of change and size of decline, but it appears that recruitment patterns are dependent on both species and locality [11]. Overall coast live oak and interior live oak are recruiting at higher rates than the deciduous oaks of the region; this may be because of pocket gophers' preference for the roots of deciduous oaks over those of live oaks [66]. Generally, coast live oak woodlands with shrub understories have stable population structures, and more xeric woodlands with herbaceous understories are likely to be recruitment limited [30].
The currently accepted scientific name of coast live oak is Quercus agrifolia
Nee. (Fagaceae). Two varieties of coast live oak are recognized [70,76]:
Quercus agrifolia Nee var. agrifolia
Quercus agrifolia Nee var. oxyadenia (Torr.) J.T. Howell
Coast live oak is classified in the
red oak subgenus (Erythrobalanus)
[7,65,67,92,114].
Several hybrids between coast live oak and other red oak
species have been documented [20,70]. Quercus a. var. oxyadenia ÃÂ California black oak (Q. kelloggii) hybrids, known as
Q. ÃÂ ganderi C.B. Wolf, occur in San Diego County [20]. California black oak also hybridizes with the typical variety
of coast live oak (Q. a. var. agrifolia). This cross, known as Q. ÃÂ chasei McMinn, is found in Monterey and
Santa Cruz counties. Hybrids between interior live oak (Q. wislizenii) and
the typical variety of coast live oak are known
in many areas in northern California. Coast live oak also hybridizes with Nuttall's scrub oak (Q. dumosa)
and Shreve oak (Q. parvula var. shrevii)
[44,114]. All these oak species show evidence of introgression
with one another [44].
There is some uncertainty about the degree of introgression between interior
and coast live oaks. Brophy and Parnell [20] note that limited hybridization has occurred
but the 2 species remain relatively distinct. Dodd and others [45] estimate that in the northern part of
interior and coast live oaks' ranges, where hybridization is greatest, up to 60%
of coast live oak may show signs of introgression.
Coast live oak is favored for use in rehabilitation projects throughout its range. It is used in watershed improvement, restoration, and wildlife habitat rehabilitation projects [59,74,124].
Artificial regeneration of coast live oak is typically from acorn plantings or transplanting seedlings and saplings. The Oak Habitat Restoration Project in Walnut Creek has had good success with direct plantings of coast live oak acorns. About 1 in 3 acorns established as seedlings, and survivorship of 1st-year seedlings has been about 60%. Kraetsch [85] provides techniques for artificial regeneration of coast live oak from acorns. In the Sepulveda Wildlife Reserve of Los Angeles County, nursery seedlings were planted for slope stabilization and wildlife habitat improvement. Survival of these seedlings was between 40 and 75% over 3 years [119]. Transplants along the Santa Margarita River in San Diego County have also shown good survival [134]. In eastern Ventura County, coast live oak was planted to help restore the ecotone between saltbush (Atriplex spp.), black sage, and annual grassland communities [120]. Recommendations for nursery propagation of coast live oak are 36 to 41 degrees Fahrenheit (2.5-5 °C) acorn storage, germination in wet vermiculite, and planting in tar paper tubes filled with 25% topsoil, 25% organic matter, and 50% sand. Burger and others [26] also recommend transferring seedlings to glass houses after 0.8 inch (2 cm) of aboveground growth. Root fragments seldom host both ecto- and endomycorrhizae; inoculating with both types is generally detrimental [50].
Transplanting older trees has been successful. Planting saplings, rather than seedlings, may be indicated if herbivory pressure is expected to be high. Studies show that while coast live oak mortality from herbivory can be great, saplings are resistant to browsing damage [48,111,127]. Large coast live oak trees slated for removal because of roadway or other construction have been successfully transplanted onto favorable sites using heavy equipment [36]. Dagit and Downer [38] provide information on transplanting mature trees.
Coast live oak is also established by acorn plantings. In the Berkeley Hills, seedlings grown from locally collected acorns had 75% survival in their 1st year. Seedlings were hand-watered twice during summer because of drought [133]. Seedling survival is enhanced by weeding competitors, providing protection against herbivores and acorn predators with above- and belowground wire caging, and providing microsite shading. Acorns are collected from local oaks in late fall. Planting density recommendations and other cultivation methods have been detailed [115,144].
Quercus agrifolia, the California live oak,[3] or coast live oak, is a highly variable, often evergreen oak tree, a type of live oak, native to the California Floristic Province. It may be shrubby, depending on age and growing location, but is generally a medium-sized tree.[4] It grows west of the Sierra Nevada mountain range from Mendocino County, California, south to northern Baja California in Mexico.[5] It is classified in the red oak section of oaks (Quercus sect. Lobatae).[6]
This species is commonly sympatric with canyon live oak (Q. chrysolepis), and the two may be hard to distinguish because their spinose leaves are superficially similar.
Coast live oak typically has a much-branched trunk and reaches a mature height of 10–25 metres (33–82 feet). Some specimens may attain an age exceeding 1,000 years. Examples of this include the Grand Oak of Cherry Valley, California,[7] the Encino Oak Tree, which died in the 1990s (part of the stump has been preserved)[8] and the Pechanga Great Oak.[9]
The trunk, particularly for older individuals, may be highly contorted, massive and gnarled. The crown is broadly rounded and dense, especially when aged 20 to 70 years; in later life the trunk and branches are more well defined and the leaf density lower.[6] The oldest specimens might exceed 6 m (20 ft) in trunk circumference and 30 m (100 ft) in height.[9][10]
The leaves are dark green, oval, often convex in shape, 2–7 centimetres (3⁄4–2+3⁄4 inches) long and 1–4 cm (1⁄2–1+1⁄2 in) broad; the leaf margin is spiny-toothed (spinose), with sharp thistly fibers that extend from the lateral leaf veins. The outer layers of leaves are designed for maximum solar absorption, containing two to three layers of photosynthetic cells.[6]
These outer leaves are deemed to be small in size to more efficiently re-radiate the heat gained from solar capture. Shaded leaves are generally broader and thinner, having only a single layer of photosynthetic cells. The convex leaf shape may be useful for interior leaves which depend on capturing reflected light scattered in random directions from the outer canopy.[6]
The flowers are produced in early-to-mid spring; the male flowers are pendulous catkins 5–10 cm (2–4 in) long, the female flowers inconspicuous, less than 0.5 cm (1⁄4 in) long, with 1–3 clustered together. The fruit is a slender reddish brown acorn 2–3.5 cm (3⁄4–1+1⁄2 in) long and 1–1.5 cm (3⁄8–5⁄8 in) broad, with the basal quarter enclosed in a cupule; unusually for a red oak, the acorns mature about 7–8 months after pollination (most red oak acorns take 18 months to mature).[6]
Coast live oak, Sonoma County
Acorns and leaves
There are two varieties of Quercus agrifolia:
Several hybrids between coast live oak and other red oak species have been documented. Hybrids with interior live oak (Q. wislizenii) are known in many areas in northern California. Coast live oak also hybridizes with Shreve oak (Q. parvula var. shrevei). All these oak species show evidence of introgression with one another.
In naming the species, Née compared it to a species illustrated in Leonard Plukenet's Phytographia under the descriptive name "Ilex folio agrifolii americana, forte agria, vel aquifolia glandifera" which Plukenet had compared, in his Almagestum botanicum, to Luigi Anguillara's Agrifolia glandifera, the noun 'Agrifolia' being a Medieval Latin form of 'Aquifolium' meaning a holly or holly-leaved oak, and related to the Modern Italian 'Agrifoglio,' meaning 'holly.'[11][12][13]
Normally the tree is found on well-drained soils of coastal hills and plains, often near year-round or perennial streams. It may be found in several natural communities including coast live oak woodland, Engelmann oak woodland, valley oak woodland and both northern and southern mixed evergreen forests. While normally found within 100 kilometers (62 miles) of the Pacific Ocean at elevations less than 700 m (2,300 ft), in southern California it occasionally occurs at up to 1,500 m (4,900 ft) in elevation.
It is the only California native oak that thrives in the coastal environment, although it is rare on the immediate shore; it enjoys the mild winter and summer climate afforded by ocean proximity, and it is somewhat tolerant of aerosol-borne sea salt. The coastal fog supplies relief from the rainless California summer heat.
It is the dominant overstory plant of the coast live oak woodland habitat, often joined by California bay laurel and California buckeye north of Big Sur. Associated understory plants include toyon, various manzanitas and western poison-oak.
The California oak moth (Phryganidia californica) caterpillar subsists entirely on living and fallen leaves of the Coast Live Oak. In 8–10 year cycles, the caterpillar will appear in sufficient abundance to denude healthy trees. The trees recover, and botanists speculate that the species provide mutual benefit, possibly in the form of fertilizer for the oak.[14] The coast live oak is also the only known foodplant of Chionodes vanduzeei caterpillars.
Live oak trees, among other western oaks, are also known to support acorn woodpeckers, which store their acorns in tree trunks and remove them when they want to eat. [15]
The pollen of the coast live oak is a severe allergen. Pollination occurs in spring.[16]
At least twelve distinct cultures of Native Americans are known to have consumed the acorns as a dietary staple. The seeds were ground into meal, which after being washed was boiled into mush or baked in ashes to make bread.[17] In the 18th century, Spaniards in the San Fernando Valley used the wood for charcoal to fire kilns in making adobe. Later this form of charcoal would be utilized in the baking, gunpowder and electric power industries.
In the 18th and 19th centuries shipbuilders sought out the odd angular branches to make special joints. Pioneers moving west would harvest small amounts for making farm implements and wagon wheels, but the greatest impact was the wholesale clearing of oak woodlands to erect sprawling cities such as San Diego and San Francisco. The irregular shape often let the tree escape widespread harvest for building timbers, and also led the early settlers to endow the coast live oak with mystical qualities. Its stateliness has made it a subject of historical landscape painters throughout California modern history since the mid-19th century.
Coast live oak has also become a common addition to western US landscaping. It is however sensitive to changes in grading and drainage; in particular, it is important to respect the root crown level and avoid adding soil near the trunk when construction or landscaping occurs.
Also, if incorporating it into a landscaping scheme with artificial irrigation, it is important to avoid regular watering within the oak's drip line (canopy), since wet soil in the summer increases infection rates by soil-borne Phytophthora diseases like sudden oak death.[18]
The coast live oak, especially in its Spanish forms encino or encina, encinitas "little oaks", and encinal "oak grove", gave its name to seven land grants across California and to many communities and geographic features. These include Rancho Los Encinos, the Los Angeles community of Encino, Encinitas near San Diego, and Encinal del Temescal, now the city of Oakland.[19]
Paso Robles (fully 'El Paso de Robles' or 'Pass of the Oaks') also refers to the ubiquitous live oaks in the region as a geographical place name.
Quercus agrifolia, the California live oak, or coast live oak, is a highly variable, often evergreen oak tree, a type of live oak, native to the California Floristic Province. It may be shrubby, depending on age and growing location, but is generally a medium-sized tree. It grows west of the Sierra Nevada mountain range from Mendocino County, California, south to northern Baja California in Mexico. It is classified in the red oak section of oaks (Quercus sect. Lobatae).
This species is commonly sympatric with canyon live oak (Q. chrysolepis), and the two may be hard to distinguish because their spinose leaves are superficially similar.
