This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available (e.g., [88,101,103,245]).
Canyon live oak is one of the most morphologically variable oaks in North America [61]. It is a spreading, perennial, sclerophyllous evergreen [61,88,100] that ranges from less than 15 feet to 100 feet (5-30 m) tall and up to 10.7 feet (3.3 m) DBH [88,101,168,179]. Its growth form varies depending on the site [34]. It grows as a shrub and may form dense thickets on mountain slopes and ridgetops, and it grows as a tree in sheltered, moist canyons [43,52,133,150,219]. Its size generally increases with soil depth [161]. In open areas the crown is dense, wide-spreading, and reaches nearly to the ground. In closed stands the crown is smaller in diameter and concentrated in the top half of the tree [179].
Canyon live oak is a thin-barked tree for its size [144,148]. The bark is smooth to flaky. It is fissured in small stems and more deeply furrowed in large stems [88,143,179]. Twigs are 1 to 2 mm in diameter. They are densely pubescent when young and become smooth with age [61,143]. Leaves are thick, leathery, oblong and 0.5 to 4.0 inch (1.3-10.0 cm) long. Leaf margins are usually spiny in young trees and smooth in old trees, although both leaf types are often present on the same tree [6,88,101,143,179]. Canyon live oak begins to produce flowers at approximately 20 years of age [219]. Male flowers are in catkins 2 to 4 inches (5-10 cm) long. Female flowers are solitary or in sparsely-flowered spikes [37,117,219]. Acorns are ellipsoidal, 1 to 3 inches (2.5-7.6 cm) long, and 0.5 to 1.3 inches (1.3-3.3 cm) wide. They are 1-seeded, or rarely 2-seeded, and occur singly or in clusters of 2 to 5 [37,61,88,143,179,219].
Canyon live oak has a deep and extensive root system [89,93,219]. Road cuts have exposed roots up to 24 feet (7.3 m) deep [87]. In coarse soils canyon live oak has a pronounced taproot, whereas in rocky areas the roots are shallow and spreading [219]. Canyon live oak supports ectomycorrhizal fungi that enhance growth of Douglas-fir seedlings in southwest Oregon and northern California forests [7,38]. Canyon live oak is long lived: it may survive for up to 300 years [93,141,168,179,219].
Fire adaptations: Canyon live oak sprouts from the root crown and/or bole after top-kill by fire [47,133,141,144,168,172,198]. Canyon live oak may also sprout from the branches after fire [93]. Seedlings may establish from off-site seed sources or from crown-stored acorns if the parent is not top-killed [213].
FIRE REGIMES: Canyon live oak grows in a wide variety of plant communities, all of which are subject to periodic or frequent fire [53]. Information below describes FIRE REGIMES in plant communities where canyon live oak is most common.
Canyon live oak forest and/or woodland: Pure stands of canyon live oak generally occur within a major vegetation type (e.g., mixed-evergreen forest, mixed-conifer forest, chaparral), each of which has a distinct relationship with fire. Canyon live oak forests and woodlands, therefore, are highly influenced by the fire regimes of surrounding communities. Historic FIRE REGIMES in canyon live oak forests and woodlands were characterized by relatively frequent, low- to moderate-severity surface fires with short- to medium-length fire-return intervals [197,199]. Fires occurred mainly in the summer and fall and were medium to large in size [199]. Arno [12] and Paysen and others [169] characterize the fire regime in the Society of American Foresters canyon live oak cover type [133] as mixed severity with a frequency of <35 years [12,169]. Skinner and others [199], however, indicate that historic fire regime reconstruction in canyon live oak forests is problematic due to decay around fire scars. Fire regime information, therefore, is often based on tree ring analyses of surrounding conifer forest communities where fire scars are preserved [199].
Canyon live oak stands with high stem density and abundant ground fuels are susceptible to wildfire [171]. Canyon live oak commonly grows, however, on steep, xeric, rocky sites with little understory vegetation. Fires are relatively infrequent on these sites due to sparse and discontinuous surface fuels [168,169,180,197,199,216]. On very steep slopes, fire is carried by the fuels that accumulate in draws and on the upslope side of canyon live oak trees [199]. Griffin [80] indicates that when they are dense, canyon live oak crowns can carry a fire even when there is little flammable litter on the ground. Stands of large canyon live oaks in deep, moist canyons are somewhat protected from fire. Low-severity surface fires are typical on these sites [80,199].
Mixed-evergreen forest: Mixed-evergreen forests of southern Oregon and northwestern California, where canyon live oak is an important subcanopy species, historically experienced mixed-severity fires [1,209,216]. Sources of ignition included lightning and Native Americans [25]. Mean historic fire-return intervals in mixed-evergreen forest clustered around 15 to 35 years but ranged from 3 to more than 70 years [2,3,131,199,209,216,246]. Mixed-evergreen forests of the Siskiyou and Klamath mountains are drier than those on the coast, with historically shorter fire-return intervals. Fires were of low and mixed severity, with fire-return intervals getting longer with increasing elevation [2,128]. Atzet and Wheeler [13] estimate a 20-year fire-return interval for the Siskiyou Mountains of Oregon. Size and severity of presettlement fires varied across time at the landscape level (review by [96]). Relatively frequent fires prevented fuels from accumulating, thus moderating fire severity in many cases [48]. Surface fires were more common than crown fires [209]. The waxy leaves of canyon live oak and other sclerophylls in the subcanopy, however, fueled fires that were sometimes intense and carried into the conifer overstory. Severely-burned patches of land were generally smaller than surrounding patches of underburned land (review by [1]).
Contemporary fires in mixed-evergreen forests are larger, with more total area experiencing severe fire, compared to historic fire sizes and severities [209,242]. Mean fire-return intervals are longer than intervals before fire exclusion [209,216]. In a fire history study on the Klamath National Forest, Wills and Stuart [246] found no significant differences in presettlement fire-return intervals among 3 Douglas-fir/tanoak-Pacific madrone sites; however, mean fire-return interval of the fire exclusion period was significantly different from those of the presettlement and settlement periods, with intervals between fires increasing greatly around the turn of the twentieth century (P=0.010).
Means and ranges of fire-return intervals on 3 sites on the Klamath National Forest, California [246] Location Time interval Mean (years) Range (years) Site 1 Presettlement 1745-1849 17.3 5-41 Settlement 1849-1894 15.0 8-26 Fire exclusion 1894-1987 46.5 43-50 Site 2 Presettlement 1742-1855 10.3 5-18 Settlement 1855-1901 9.2 7-12 Fire exclusion 1901-1987 28.7 18-45 Site 3 Presettlement 1752-1849 13.9 7-25 Settlement 1849-1913 16.0 5-25 Fire exclusion 1913-1987 37.0 3-71Mixed-conifer forest: Historic ignition sources in mixed-conifer forests included both lightning and Native Americans [166,167,235,238]. The historic fire regime in mixed-conifer forests was characterized by frequent, low- to moderate-severity surface fires [44,102,152,213,238]. Large, severe fires were infrequent in presettlement mixed-conifer forests of Oregon and California [109,153], although crown fires affecting small areas were probably common (review by [238]). In the lower montane zone of the Sierra Nevada, patchy, stand-replacement fires were most common on north-facing slopes and during extended droughts [226]. Historic fire-return intervals in mixed-conifer forests ranged from approximately 3 to 30 years [45,102,131,163,213,226,235]. In giant sequoia groves in the Sierra Nevada, Swetnam and others [211] reported mean fire-return intervals of 5 to 10 years and a maximum fire-return interval of 20 years. Throughout the mixed-conifer zone, mean fire-return intervals varied with site: more mesic and/or sheltered sites burned less often than more xeric and/or exposed sites. Frequent fires prevented accumulation of surface fuels and maintained an open, park-like forest structure (review by [238]).
As a result of fire exclusion since the early 1900s, fires in mixed-conifer forests are now less frequent, larger, and more severe [44,60,153,167,197,238]. The large size and high severity of modern-day fires is related, in part, to greater fuel accumulation during longer fire-free intervals compared to presettlement times. Because small fires are generally suppressed, very large fires are more likely to occur during severe fire weather, such as Santa Ana Winds and heat waves [145]. Canyon live oak mortality is likely to be greatest on steep slopes where dense stands of canyon live oak often occur [152].
Many mixed-conifer forests in the Sierra San Pedro Mártir in northern Baja California still experience an unmanaged fire regime. The fire regime there is characterized by moderate- to high-severity surface fires that create open, park-like stands of mature trees. Fires may be as large as 12,000 acres (5,000 ha) with a relatively long (~50 year) fire-return interval that results from the gradual buildup of litter and shrub cover. Lightning strikes are the primary source of ignition. Fire severity is often high in stands on steep slopes, where canyon live oak is likely to grow, and in stands with a dense subcanopy of canyon live oak and greenleaf manzanita [145,154].
Bigcone Douglas-fir-canyon live oak forest: Bigcone Douglas-fir-canyon live oak forests generally occur on steep, rocky slopes and in moist ravines where fire is infrequent [20,152]. Historically, low-severity fires occurred in high-elevation bigcone Douglas-fir-canyon live oak forests approximately once every decade, while low-elevation forests burned 1 or 2 times each century [105]. These forests, however, often occur within large expanses of chaparral and are therefore also influenced by chaparral FIRE REGIMES [153,203]. Canyon live oak can act as a buffer against the spread of severe chaparral fires due to the nonflammable nature of tree-sized canyon live oaks (relative to adjacent chaparral vegetation) [151,152] and the limited accumulation of understory fuels in dense canyon live oak stands [139]. Although stand-replacement fires are rare in bigcone Douglas-fir-canyon live oak forests [153], strong Santa Ana Winds may drive severe chaparral fires into bigcone Douglas-fir-canyon live oak stands, resulting in stand conversion to canyon live oak woodland [139,141,152]. Large, stand-replacement fires have become more common in bigcone Douglas-fir-canyon live oak forests since fire exclusion [153,203]. Bigcone Douglas-fir can sprout from the bole after a moderate-severity surface fire [139]. After a stand-replacement fire, it commonly takes 40 to 70 years for bigcone Douglas-fir to grow through a 16- to 30- foot (5-9 m) canyon live oak canopy [141].
Oak woodland: Throughout its range, canyon live oak is a component of a variety of oak woodland communities. Historically, these communities were maintained by very frequent, low-severity surface fires [22,92,138,199,226]. Fire-return intervals around 8 to 10 years have been reported for both California black oak and blue oak forests and woodlands [22,138]. A century of fire exclusion has led to encroachment by conifers, reducing the extent of many oak woodlands [22,92,167].
Chaparral: FIRE REGIMES in California chaparral communities are variable [106]. Stand flammability and fire severity generally increase with time since burning due to the buildup of shrub cover and dead fuels [131,149]. Most chaparral becomes extremely flammable within 30 to 60 years after the previous fire [146]. Fires in mature chaparral are generally high-severity, fast-moving crown fires [19,41,131,231] that can exceed 30,000 Btus/second/foot and flame lengths of over 50 feet (15 m) [131]. Stand-replacement crown fires are common, especially under dry, windy conditions. Shrub fuels burn readily once ignited [169]. In a typical chaparral fire, all aboveground biomass is consumed except for the largest stems due to horizontal and vertical continuity of stands (review by [149]).
Most estimates of historic fire-return intervals in California chaparral range from 20 to 60 years [41,90,131,250], although fire-return intervals at high elevations and on northerly aspects range from 50 to 100 years [169]. In montane chaparral in the northern Sierra Nevada, the mean fire-return interval was 28 years prior to fire exclusion in the late 1800s and early 1900s, with a range of 16 to 60 years [50,158]. High-severity fires were typical, with most shrubs being top-killed [50].
Some argue that large chaparral fires are an artifact of decades of fire exclusion, which has resulted in a heavy buildup of fuels [27,55,149]. In a review, however, Keeley [105] states that historically, the majority of the landscape in southern California burned in large, Santa Ana Wind-driven fires that occurred 1 to several times each century. Fire frequency in southern California chaparral was historically greatest in the summer due to dry fuels and the high frequency of lightning storms. These fires were relatively small and may have acted as fuel breaks against larger fires. This mixed-severity fire regime perpetuated a patchy mosaic of age classes in chaparral stands [41,152]. In his review, Keeley states that fire suppression has not effectively excluded fire from southern California chaparral and, although fire size has decreased due to habitat fragmentation, large fires are a natural part of the chaparral fire regime [105].
The following table provides fire regime information that may be relevant to canyon live oak. 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".
Fire regime information on vegetation communities in which canyon live oak may occur. For each community, fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Models [123]. These vegetation models were developed by local experts using available literature, local data, and/or expert opinion as documented in the .PDF file linked from the name of each Potential Natural Vegetation Group listed below. Cells are blank where information is not available in the Rapid Assessment Vegetation Model. Pacific Northwest California Southwest Great Basin Pacific Northwest Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics Percent of fires Mean intervalCanyon live oak occurs on a wide variety of sites ranging from canyon bottoms to ridgetops [6,133]. It grows under more variable conditions than any other oak in California [6]. It is commonly found on steep, rocky, exposed ridges, rock crevices, and canyon slopes [43,81,133,140,148,179]. Canyon live oak also grows in riparian areas [180,229,241,247], sheltered coves, and deep, moist, shady ravines and canyons [23,27,43,79,88,101,179]. It forms extensive, often pure stands on many of these sites [91,133,148].
Elevation: Canyon live oak is most common at middle elevations [161,196,249], but can occur between 300 and 9,000 feet (90-2,700 m) across its range [41,61,88,101,103,133,219,245].
Elevational ranges of canyon live oak Location Elevation Arizona 5,500-7,000 feet (1,700-2,100 m) [103] California 300-9,000 feet (90-2,700 m) [41,88,133,219] Nevada 5,500-6,600 feet (1,700-2,000 m) [101] Oregon 1,600-5,000 feet (488-1,525 m) [219] Sonora and Baja California, Mexico <6,600 feet (2,000 m) [245]Soils: Canyon live oak grows in a wide variety of soils [168,219]. It reaches its greatest size in deep, rich soils in canyon bottoms [168,179]. It also grows on rocky, shallow, infertile soils [112,148,219] but assumes a small, often shrubby growth form on these sites [133,168]. Canyon live oak grows on sedimentary, metasedimentary, and granitic parent materials [219]. It has been documented on serpentine soils in California [230,240], although it may only survive on serpentine if its roots extend into adjacent, nonserpentine soils [86].
Moisture: Moisture conditions vary in communities where canyon live oak is present. Canyon live oak grows in locations that receive as little as 6 inches (150 mm) and as much as 110 inches (2,790 mm) of annual precipitation [219]. Canyon live oak is well adapted to arid conditions [168,188]. It has deep roots that access deep sources of water during summer drought [89]. Its leathery, evergreen leaves have thick epidermal walls and a waxy cuticle that minimize water loss [98,168]. Knops and Koenig [111] describe canyon live oak as a "drought evader" that limits its growth during the dry season.
Temperature: Mean temperatures in the northern portion of canyon live oak's range are 68 to 74 °F (20-23 °C) in the summer and 37 to 41 °F (3-5 °C) in the winter. In the southern portion of its range, average temperatures are 70 to 77 °F (21-25 °C) in the summer and 41 to 45 °F (5-7 °C) in the winter. The frost-free period ranges from 160 to 230 days across its range [219].
Canyon live oak has limited food value for livestock. Although its leaves are reportedly eaten by domestic sheep, goats, and cattle in California [132], Sampson and Jespersen [189] consider it "useless" for cattle, domestic sheep, goats, and horses. Canyon live oak is a valuable food source, however, for many species of wildlife. Deer feed on canyon live oak foliage and twigs throughout the year in California and Arizona [11,93,121,126,127,186,189]. Evergreen oaks provide a dependable food source for deer and other wildlife through the winter [224]. Sprouting oaks, including canyon live oak, provide browse for wildlife following wildfires [212,251].
Canyon live oak acorns are a primary food source for acorn woodpeckers [82,119]. The acorns are also an important food source for western scrub jays, Steller's jays, band-tailed pigeons, wild turkeys, mountain quail, ground squirrels, western gray squirrels, woodrats, common crows, gophers, American black bears, and mule deer [95,107,115,210,219].
Palatability/nutritional value: Palatability of canyon live oak foliage is generally low [189], although it is considered highly palatable to Columbian black-tailed deer (Orr 1937, cited in [224]). Crude protein content of canyon live oak browse varies from 4.1% to 11.6% depending on the season and location [24,26,126,189,212]. Protein content is higher in canyon live oak leaves than in stems [212]. Fat content ranges from 2.4% to 8.7%, and fiber content ranges from 12.7% to 32.4% [24,126]. Additional nutritional information is provided by Bean and Saubel [24] and Lawrence and Biswell [126].
Canyon live oak acorns are highly palatable to many birds and mammals [95,107,115,219]. In a nutritional study, protein content of canyon live oak acorns was 3.9%, carbohydrate content was 12.6%, lipid content was 16.7%, and energy content was 11.39 kJ/g [114]. American black bears may prefer canyon live oak acorns over interior live oak acorns because canyon live oak acorns have a lower concentration of tannins (Fleck and Layne 1990, cited in [210]).
Cover value: Canyon live oak provides cover for many species of mammals, birds, reptiles, amphibians, and invertebrates. The type and quality of cover provided by canyon live oak is determined in large part by its growth form. Shrubby thickets provide readily available browse and can serve as good hiding or nesting cover for many small birds and mammals. Large trees provide perching, nesting, resting, and foraging sites for numerous species of birds and provide shade and cover for both large and small mammals [189].
Mammals: Canyon live oak forest and woodlands provide habitat for a variety of large mammals including American black bears, deer, coyotes, mountain lions, bobcats, and American badgers [72,161] and small mammals including red tree voles [66], deer mice, white-footed mice, pinyon mice, California pocket mice, California voles, Botta's pocket gophers, and broad-footed mice [32].
Birds: A variety of birds forage in canyon live oak forests and woodlands. In Kern County, California, foraging birds include Nuttall's woodpeckers, acorn woodpeckers, white-breasted nuthatches, plain titmice, black-headed grosbeaks, and Baltimore orioles [29,156]. California spotted owls use a variety of habitats where canyon live oak is common, including canyon live oak forest, mixed-conifer forest, mixed-evergreen forest, riparian hardwood forest, and oak woodlands [33,65,83,161,201,229,238]. In the southern Coast Ranges of California, canyon live oak was the dominant tree at 91% of the sites below 3,600 feet (1,100 m) elevation where California spotted owls were found [70]. On the Sierra National Forest and in Sequoia National Park, California, canyon live oak, interior live oak, and California black oak were most commonly used for California spotted owl nests in foothill riparian and oak woodland habitats. Nesting platforms were found in living canyon live oak trees at a mean height of 47.5 feet (14.5 m). Canyon live oak nest trees were larger than the average canyon live oak tree size: nest trees averaged 18.4 inches (47 cm) in diameter compared to the average diameter of 10.4 inches (26.4 cm). Mean nest tree height was 55 feet (17 m). All of the nests found in canyon live oak trees were platform structures that were likely abandoned squirrel, raptor, or raven nests. The use of platforms allows for California spotted owl reproduction in woodland habitats where trees are not large enough to support cavity nests [201].
Reptiles and amphibians: Hollows and cavities in oak trunks are used for nesting and shelter by a variety of herptiles. Several species of reptiles and amphibians are associated with canyon live oak stands in southern California, particularly on mesic, north-facing slopes. These include San Bernardino Mountain kingsnakes, San Gabriel Mountain slender salamanders, large-blotched salamanders, black-bellied slender salamanders, California slender salamanders, Gilbert's skinks, yellow-blotched salamanders, foothill yellow-legged frogs, western fence lizards, and southern alligator lizards. Many of these are Sensitive Species or Species of Conservation Concern in California [30,31,32,33,204].
Invertebrates: A variety of invertebrates are found in canyon live oak forests [160]. For information on insects found in a canyon live oak forest on the San Bernardino National Forest and the effects of prescribed burning on invertebrate abundance, see the Research Project Summary of Narog and others's [159,160,161] study.
Canyon live oak occurs in pure, often extensive stands throughout its range
[91,133,148]. In California, canyon live oak forest covers an estimated 344,000 acres
(139,000 ha), and canyon live oak woodland covers an estimated 777,000 acres
(314,000 ha). Canyon live oak is also a component of many plant communities and is reportedly found,
although sometimes sparingly, in nearly every forest type
in California [34]. Several of the plant communities where canyon
live oak is a dominant or common species are described below.
Mixed evergreen:
Canyon live oak is a dominant subcanopy species in mixed-evergreen forests in
the mountains of southern Oregon and California [20,21,25,42,67,79,85,130,191,194]. A canyon live
oak phase of mixed-evergreen forest occurs in shady canyons and on steep,
north-facing slopes [79]. For information on tree, shrub,
and herbaceous species associated with canyon live oak in mixed-evergreen
forests, see these sources: [4,8,36,63,168].
Mixed conifer:
Canyon live oak is a hardwood associate in mixed-conifer forests
in southwest Oregon, California, and
northern Baja California [148,153,154,234]. For information on species associated
with canyon live oak in mixed-conifer forests, see these sources: [60,153,164,219,220].
Canyon live oak is also a subcanopy component
of giant sequoia (Sequoiadendron giganteum) forests in the Sierra Nevada [108,167,237] and upland redwood
(Sequoia sempervirens) forests in northern coastal California [97,193].
Bigcone Douglas-fir-canyon live oak:
Canyon live oak is codominant with bigcone Douglas-fir (Pseudotsuga
macrocarpa) on mesic, steep, north-facing slopes and in ravines in southern
California, often within a matrix of chaparral vegetation [20,36,43,90,94,139,141,148,219].
Mixed hardwood and oak woodland:
Canyon live oak is an important component of mixed hardwood forests and oak (Quercus
spp.) woodlands throughout California [82,92,99,196,219,244]. It grows in California black oak
(Q. kelloggii) woodlands in southwestern Oregon and California [42,43,63,99,234,252].
Canyon live oak grows with scrub oak (Q.
dumosa) and island oak (Q. tomentella) on Santa Catalina Island
[165] and is a component of blue oak (Q. douglasii)
woodlands in California foothills [18,20,21,40,162,168]. It is also associated with Oregon white oak
(Q. garryana) [99,202], interior live oak (Q. wislizeni), coast live
oak (Q. agrifolia), and valley oak (Q. lobata) [43,59,82,90,168].
Chaparral:
Canyon live oak is common in montane and mixed-chaparral communities in the foothills and mountains of
southwestern Oregon, California, and northern Baja California [19,63,64,75,110,132,152,219,226,227].
It also occurs in chaparral communities in
Arizona [47,219].
Other:
Canyon live oak is also commonly associated with Coulter pine (Pinus coulteri) on xeric sites
within or adjacent to chaparral in central and southern California [20,62,153,219,248]
and northern Baja California [150]. Canyon live oak is associated
with cypress (Cupressus spp.) groves throughout California [219] and with bristlecone fir
(Abies bracteata) forests in the Santa Lucia Mountains of Monterey County, California [91,196,214].
It is common in the understory of singleleaf pinyon (Pinus
monophylla) woodlands in southern California [152,228,232,233] and
Parry pinyon (P. quadrifolia) forests in northern Baja California [150].
Canyon live oak is listed as a dominant species in the
following vegetation classifications:
Prolific sprouting in canyon live oak can hinder reestablishment of conifer
timber species after harvesting [217]. An
experiment conducted in the Siskiyou Mountains of southwestern Oregon
illustrated the negative impact of sprouting canyon live oak and greenleaf
manzanita on Douglas-fir seedling growth and survival. The negative impacts
increased with increasing sprout cover [217,218]. Control measures are therefore necessary
where the silvicultural goal is to maintain conifer stands after cutting [217]. There
is little information, however, on effective methods of sprout control in canyon
live oak [140]. Canyon live oak is
generally resistant to or only lightly injured by herbicides [207]. In a mixed
conifer-hardwood forest near Yreka, California, the effectiveness of herbicides and manual
cutting in controlling canyon live oak sprouts were tested following site
preparation by cutting and burning. The 3 herbicides tested in this study were
"erratic" in their effectiveness. Cutting was effective initially, but sprouts
resumed growth quickly [140]. In a separate study, Hobbs and Wearstler
[89] also found manual cutting of canyon live oak was an ineffective control
method. Additional information on the use and effects of herbicides on canyon live oak is provided
in these sources: [54,73,76,236].
General information on diseases in canyon live oak and other California oaks is provided
by Raabe [181]. Canyon live oak is less susceptible to the oak wilt pathogen Ceratocystis
fagacearum than the deciduous red or black oaks (subgenus Erythrobalanus) in California. In an
inoculation experiment, canyon live oak was the least susceptible to oak wilt
out of 7 species tested. Where canyon live oak grows in association with
California black oak, however, it may be more
susceptible to oak wilt [10]. Canyon live oak is a host of Phytophthora ramorum, the pathogen that
causes sudden oak death disease in tanoak and many species of oak (Quercus
spp.) in California and Oregon [174,185].
Canyon live oak acorns were eaten by Native Americans in the Sierra Nevada and southern California [9,24,51,253]. Because canyon live oak often grows in steep and inaccessible locations, the acorns may have been used less than acorns from other California oaks [49,51]. Canyon live oak acorns may be bitter or possibly poisonous when raw [6,49,51]. The meal from canyon live oak acorns may require more washing than the acorn meal from other oak species [51].
Canyon live oak wood is the highest quality of all western oaks [221]. The wood is particularly hard and is sometimes referred to as "rock oak" or "maul oak". It has been used for axles, tool handles, mauls, wagon tongues, plow beams, ship frames, and wheels [124,161,187]. Wedges made from canyon live oak were used to split redwood into railroad ties [127]. Today, its commercial value is limited by the small quantities available [161,221].
Canyon live oak is an attractive landscaping tree [93,120,219] and an important source of firewood in southern California [184,239].
Canyon live oak generally remains on a site after a fire, regardless of the fire severity, due to its ability to establish from sprouts or from acorns [80].
Sprouting: Canyon live oak regenerates by sprouting from the root crown or bole after it is damaged or top-killed by fire [47,133,141,144,172,198]. Canyon live oak can sprout within weeks after a fire [168], advancing regeneration and helping to maintain canyon live oak cover [133]. Top-killed canyon live oak exhibit a particularly strong sprouting response. Following the Stanislaus Complex Fires, 100% of top-killed canyon live oak trees sprouted from the root crown, compared to sprouting in 36% of trees that were not top-killed [183]. Within 18 months of the November 1975 Village Fire on the Angeles National Forest, southern California, 90% of top-killed canyon live oak trees had sprouted [176]. Sprouting also occurs when canyon live oak is only slightly damaged by fire [148]. Sprouting may be triggered when sufficient cambial and/or crown damage disrupts the production of growth-regulating hormones that normally inhibit sprouting of dormant buds [183].
Canyon live oak may sprout in the same season it is burned. Within 1 month of the August, 1977 Marble Cone Fire in Monterey County, California, top-killed canyon live oak trees were sprouting "vigorously" from the base of charred trunks. By November of that year, many of the sprouts were several feet tall [80]. Within 3 months of a July, 1960 wildfire on the San Dimas Experimental Forest in southern California, 56% of canyon live oak trees were sprouting. Within 4.5 months, 66% were sprouting [175]. Sprouting response was strongest at low elevation.
Effect of elevation on sprouting in canyon live oak 4.5 months after wildfire in southern California [175] Elevation (feet) % Sprouting 2,100 73 4,100 60Seeds and/or seedlings: In some cases, canyon live oak establishes from soil-stored acorns after fire [213]. Because canyon live oak acorns are generally destroyed by fire [93], however, seedling establishment is more likely from off-site seed sources or from crown-stored acorns that survive the fire. The Marble Cone Fire crowned in portions of the summit forest area and changed to a surface fire as it burned downhill into the slope forest area. Following the fire, canyon live oak regenerated from both sprouts and acorns in both forest areas [213].
Constancy (%) of canyon live oak before and after the 1977 Marble Cone Fire [213] Summit forest (crown fire) Slope forest (surface fire) Prefire Postfire Prefire Postfire Sprouts 60 100 20 100 Seedlings 0 100 0 100Canyon live oak seedling density increased moderately following a low-severity prescribed fire in a Jeffrey pine (Pinus jeffreyi)-California black oak forest in Cuyamaca Rancho State Park, California. Canyon live oak sapling density decreased significantly on burned plots (P<0.02) [135]. For further information, see the Research Project Summary of Martin and Lathrop's [125,135] study.
Repeated burning: Repeated burning favors the shrubby growth form of canyon live oak [148]. Canyon live oak woodland can convert to chaparral with repeated burning. In the absence of fire, the chaparral may revert back to canyon live oak woodland when canyon live oak basal sprouts become tall enough (approximately 15 feet (4.6 m)) to shade out chaparral shrubs [133]. Fire-free intervals of 50 to 100 years may be required for the development of tree-sized canyon live oaks [151]. In general, oaks (Quercus spp.) die if they are burned too frequently [180].
Delayed mortality: The full effect of fire on canyon live oak may not be apparent for several months, or even years, following burning. Heat-injured canyon live oak trees may not die until 8 years after a fire [159]. The Village Fire burned through a dense stand of 6-to 12-inch (15-31 cm) DBH canyon live oak. On most trees, initial damage was apparently restricted to charring at the bottom 1 to 5 feet (0.3-1.5 m) of the trunk and leaf kill of one-third to two-thirds of the crown. Within 18 months, however, all trees 3 inches (7.6 cm) DBH or smaller were top-killed. Mortality from crown damage developed more slowly in larger trees. At 18 months, at least 55% of the larger trees seemed alive, even though most appeared girdled at the base. During the next 18 months, however, approximately 50% of these trees died [176].
Percent of living canyon live oak crowns 18 and 36 months after fire on the Angeles National Forest, California [176] Tree DBH (inches) 0-3 3-6 6-12 % live crown after 18 months 0 24 74 % live crown after 36 months 0 15 46Following prescribed burning in a canyon live oak forest on the San Bernardino National Forest, canyon live oak mortality increased 4% to 5% between postfire years 2 and 6 [171]. For further information on this study, see the Research Project Summary of Narog and others's [159,160,161] study.
Canyon live oak regenerates from acorns and by sprouting from the bole and/or root crown [80,133,144,176].
Pollination: Canyon live oak is wind pollinated [118,219].
Breeding system: Canyon live oak is monoecious [37,219]. Male and female flowers are scattered throughout the crown, which helps to prevent self-fertilization [219].
Seed production: The minimum seed-bearing age in canyon live oak is 20 years [37]. Canyon live oak is a "prolific" seed producer at irregular intervals [179]. Some trees apparently produce acorns every year [219]. Acorn production was highest in canyon live oak out of 5 oak species studied on the Hastings Natural History Reservation in central coastal California. Canyon live oak produced consistently good acorn crops over the 7-year study period [46].
Canyon live oak acorn production varies among years, populations, and individual trees [46,115]. Open-grown trees can produce large acorn crops: up to 400 pounds (180 kg) of acorns per tree have been reported [249]. There are approximately 150 acorns/lb [155], although many acorns are not viable [141]. Trees in sprout clumps tend to produce fewer acorns than larger, single-stemmed trees [219]. In a study of acorn production in the Central Coast Ranges, variation in weather parameters explained 63% of variation in canyon live oak acorn production (P<0.01). High amounts of rainfall had a positive influence in both years of acorn development, while cool temperatures during the first year of acorn development reduced acorn production [116,117]. Mast fruiting may increase pollination and/or satiate acorn predators [118]. Canyon live oak masts approximately every 2 to 6 years [113,219].
Seed dispersal: Canyon live oak acorns are large and usually fall a short distance from the tree [141]. On steep canyon slopes, acorns may roll downhill a long distance [219]. Small mammals and birds that cache canyon live oak acorns are also effective dispersal agents [118,219].
Seed banking: Seed banking in canyon live oak is unlikely because the acorns, lacking a dormant phase, often germinate soon after falling from the tree [37,107]. Some acorns, however, are likely stored in the soil by acorn-caching animals.
Germination: Germination in canyon live oak starts later in the growing season and continues longer than associated oak species [137]. Germination is hypogeal. Canyon live oak acorns germinate best in moist soil covered with leaf litter. Few uncovered acorns germinate [219]. Under greenhouse conditions, canyon live oak acorns planted in peat and loam in deep boxes and covered with 1 inch (2.5 cm) of "firmed" soil germinated in about 60 days [120]. Acorns can germinate in dense shade [219].
Germination rates in canyon live oak vary from 5% to 75% [120,142,155,206]. In a greenhouse experiment, 35% germination occurred after 2 years of storage [177]. In a separate experiment, 50% germination occurred after 35 days at 55 to 68 °F (13-20 °C) with no stratification [137]. Canyon live oak acorns germinate well at temperatures ranging from 41 to 48 °F (5-9 °C) [137]. Cold stratification enhances germination [178,219], although some acorns germinate readily without treatment [104,136]. Canyon live oak may germinate successfully from planted acorns without added water [206].
Seedling establishment/growth: Seedling growth is relatively slow in canyon live oak [141,215]. Seedlings grow best in shade [141,219]. Seedling abundance is high in "favorable years" [93]. Seedlings can be very dense and evenly distributed in canyon live oak stands [219]. In California, there is concern that some oak species are declining due to lack of regeneration. Seedling and sapling density data, however, suggest that canyon live oak does not have a regeneration problem in juvenile size classes. Seedlings were found on 94% of the canyon live oak vegetation type sampled throughout California. Saplings were found on 81% of this type [34]. In the southern Sierra Nevada, canyon live oak seedlings were present in 75% of oak woodland plots sampled, and saplings were present in 48% of plots [200]. In a bigcone Douglas-fir-canyon live oak community in the San Bernardino Mountains, California, canyon live oak density averaged 365 seedlings/ha [141].
Limited data suggest that seedling survival may be high in canyon live oak. In an experiment in the southern California Coast Ranges, 16 germinating canyon live oak acorns were planted in cleared plots. Seedling survival was 94% after 1 year and 69% after 2 years [78]. Recruitment of pole-sized trees may be poor, however. A size-class analysis of canyon live oak in the San Jacinto Mountains of southern California showed high seedling abundance relative to the number of older trees [190]. This difference may or may not signify poor recruitment of canyon live oak into older age classes on some sites. Further research on canyon live oak recruitment beyond the sapling stage is needed.
Vegetative regeneration: Canyon live oak sprouts from the bole or root crown after fire [47,133,141,144,172,198] or other disturbances [53,89,183,195,219]. In recently disturbed stands, sprouting results in a high density of small-diameter (1.1- to 14-inch (2.8-35 cm)) canyon live oak stems [141]. Seedlings may sprout following top-killing disturbance [133]. Sprouts may reach 1 to 3 feet (0.5-1 m) during the first year of growth. Young, "vigorous" plants sprout readily, although large trees produce more and taller sprouts than small trees. Over time, growth is concentrated in a few dominant sprouts, and the total number of sprouts per clump decreases [219].
Canyon live oak sprouts after harvesting but may not require disturbance to sprout. On Skinner Ridge in the San Bernardino Mountains, canyon live oak sprouted in both thinned and control plots. Most trees that showed a strong root crown sprouting response showed a weak bole sprouting response, and vice versa. Root crown sprouting was generally greater than bole sprouting, as shown in the table below [172].
Sprouting response of canyon live oak in thinned and control plots, San Bernardino Mountains, California [172] Plots thinned in 1984 Plots thinned in 1985 Control plots Prethin stems/ha 3,144 2,919 3,247 Postthin residual stems/ha 1,341 1,742 3,247 Percent sprouting 62% 67% 53% Mean bole sprouts/tree 21.45 24.47 23.61 Mean root crown sprouts/tree 88.53 39.52 28.89In the eastern Siskiyou Mountains of southwest Oregon, canyon live oak produced more sprouts after clearcutting than after thinning. Sprouts emerged within 3 weeks of cutting. Canyon live oak produced up to 100 sprouts/root crown: more than either tanoak or Pacific madrone. After the first year, canyon live oak sprouts formed dense, overlapping clumps averaging 3.3 feet (1 m) in height [89].
Sprouting response (stems/ha) in canyon live oak after clearcutting and thinning in the eastern Siskiyou Mountains, Oregon [89] Clearcut Thinned Control Pretreatment 24,092 22,486 29,405 Immediately after treatment 0 19,768 29,405 Posttreatment year 1 553,009 157,957 33,359Canyon live oak is shade tolerant and long lived [17,133,143,179,215,219]. These attributes enable canyon live oak to persist in a variety of late seral and climax communities including old-growth mixed-evergreen, mixed-conifer, and hardwood forests [35,85,219].
Canyon live oak is also an important component of many early seral communities, primarily because of rapid, prolific sprouting that enables it to grow much faster after disturbance than conifers that reproduce only by seed [28,168]. Canyon live oak is an early-successional tree or shrub on favorable sites in mixed-evergreen forests in the northern portion of its range [219]. It is a common pioneer species in thinned and clearcut forests in Oregon [38], northwestern California [134], and southern California [53]. On the Klamath National Forest in northern California, canyon live oak increased in abundance from the interior to the edge of burned and salvaged forest stands [85]. In some areas, vigorous, shade-tolerant sprouters such as canyon live oak slow the development of coniferous forest by interfering with conifer regeneration [63,89].
The ability of canyon live oak to assume multiple growth forms allows it to dominate early-seral, late-seral, and climax stages in some communities. Bigcone Douglas-fir-canyon live oak forests in southern California, for example, are converted to canyon live oak woodland under a regime of frequent fires. In the absence of fire, bigcone Douglas-fir slowly grows above canyon live oak, although canyon live oak remains a community dominant (review by [139]), [141].
