Canyon live oak is a spreading, perennial, sclerophyllous evergreen ranging from less than 15 feet to 100 feet tall and up to 10.7 feet in diameter. It is one of the most morphologically variable oaks in North America and its growth form varies depending on the site. 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. Its size generally increases with soil depth. 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.
Canyon live oak is a thin-barked tree for its size. Its bark is smooth to flaky. It is fissured in small stems and more deeply furrowed in large stems. Twigs are 1 to 2 mm in diameter. They are densely pubescent when young and become smooth with age. Leaves are thick, leathery, oblong and 0.5 to 4.0 inch 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. Canyon live oak begins to produce flowers at approximately 20 years of age. Male flowers are in catkins 2 to 4 inches long. Female flowers are solitary or in sparsely-flowered spikes. Acorns are ellipsoidal, 1 to 3 inches long, and 0.5 to 1.3 inches wide. They are 1-seeded, or rarely 2-seeded, and occur singly or in clusters of 2 to 5.
Canyon live oak has a deep and extensive root system. Road cuts have exposed roots up to 24 feet deep. In coarse soils, canyon live oak has a pronounced taproot, whereas in rocky areas the roots are shallow and spreading. Canyon live oak is long lived: it may survive for up to 300 years.
Canyon live oak regenerates from acorns and by sprouting from the bole and/or root crown. Canyon live oak is wind pollinated and monoecious. Male and female flowers are scattered throughout the crown, which helps to prevent self-fertilization.
With the minimum seed-bearing age in canyon live oak at 20 years, upon maturity these trees prove themselves “prolific” seed producers at irregular intervals. Some trees apparently produce acorns every year. Acorn production was highest in canyon live oak out of five 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.
Canyon live oak acorn production varies among years, populations, and individual trees. Open-grown trees can produce large acorn crops: up to 400 pounds of acorns per tree have been reported. There are approximately 150 acorns/lb, although many acorns are not viable. Trees in sprout clumps tend to produce fewer acorns than larger, single-stemmed trees. 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. 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. Exceptionally high seed production fruiting may increase pollination and/or satiate acorn predators.
Canyon live oak acorns are large and usually fall a short distance from the tree. On steep canyon slopes, acorns may roll downhill a long distance. Small mammals and birds that cache canyon live oak acorns are also effective dispersal agents.
Seed banking in canyon live oak is unlikely because the acorns, lacking a dormant phase, often germinate soon after falling from the tree. Some acorns, however, are likely stored in the soil by acorn-caching animals.
Germination in canyon live oak starts later in the growing season and continues longer than associated oak species. Germination is hypogeal, that is, the embryonic seed leaves remain below ground. Canyon live oak acorns germinate best in moist soil covered with leaf litter. Few uncovered acorns germinate. Acorns can germinate in dense shade.
Germination rates in canyon live oak vary from 5 percent to 75 percent. Canyon live oak may germinate successfully from planted acorns without added water.
Seedling growth is relatively slow in canyon live oak. Seedlings grow best in shade. Seedlings can be very dense and evenly distributed in canyon live oak stands. 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 percent of the canyon live oak vegetation type sampled throughout California. Saplings were found on 81 percent of this type. In the southern Sierra Nevada, canyon live oak seedlings were present in 75 percent of oak woodland plots sampled, and saplings were present in 48 percent of plots. In a bigcone Douglas-fir-canyon live oak community in the San Bernardino Mountains, California, canyon live oak density averaged 365 seedlings per hectare.
Canyon live oak sprouts from the bole or root crown after fire or other disturbances]. In recently disturbed stands, sprouting results in a high density of small-diameter (1.1- to 14-inch) canyon live oak stems. Seedlings may sprout following top-killing disturbance. Sprouts may reach one to three feet 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.
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.
Canyon live oak grows in a wide variety of soils. It reaches its greatest size in deep, rich soils in canyon bottoms. It also grows on rocky, shallow, infertile soils but assumes a small, often shrubby growth form on these sites. Canyon live oak grows on sedimentary, metasedimentary, and granitic parent materials. It has been documented on soils derived from parent rock materials that have high levels of nickel, chromium, and magnesium and low levels of calcium, magnesium, and other nutritionally essential minerals that plants can uptake in a chemically available state in California, although it may only survive on such soils if its roots extend into adjacent more fertile soils.
Canyon live oak germinates in late winter or early spring. Germination occurs later at high elevations]. Flowering occurs between April and June, before or at the same time as leaf emergence.
Canyon live oak occurs in pure, often extensive stands throughout its range. In California, canyon live oak forest covers an estimated 344,000 acres, and canyon live oak woodland covers an estimated 777,000 acres. 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.
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.
Canyon live oak is a component of mixed hardwood forests and oak (Quercus spp.) woodlands, including blue oak (Q. douglasii) woodlands in California foothills.
Canyon live oak is common in montane and mixed-chaparral communities in the foothills and mountains of southwestern Oregon, California, and northern Baja California and the chaparral communities in Arizona.
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 and northern Baja California. Canyon live oak is associated with cypress (Cupressus spp.) groves throughout California and with bristlecone fir (Abies bracteata) forests in the Santa Lucia Mountains of Monterey County. It is common in the understory of singleleaf pinyon (Pinus monophylla) woodlands in southern California.