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Ecology and Current Distribution of Common Oaks in the Pacific Northwest

Dave Vesely, Pacific Wildlife Research, Corvallis, Oregon.

Oregon white oak has, by far, the most extensive distribution of any Quercus species across the Pacific Northwest. However two other oaks, Canyon live oak and black oak are common in southwest Oregon and the Klamath region of California. The following information on these three species has been collected from Burns and Honkala¹ , where further details about the life histories of these trees can be found.
¹ Burns, R.M. and B.H. Honkala. 1990. Silvics of North America, Vol. 2, Hardwoods. Washington DC: U.S.D.A. Forest Service Agriculture Handbook 654.

Canyon Live Oak (Quercus crysolepsis)

^* Geographic Range: In southern Oregon, canyon live oak grows on the interior side of the Coast Ranges and on the lower slopes of the Cascade Range. Its range extends southward through the Klamath Mountains and the Sierra Nevada to Baja, Mexico. Isolated populations occur in Nevada and Arizona.

^* Soils and Topography: In southwest Oregon, Canyon live oak usually grows on steep, shallow, rocky, infertile soils having little soil development. Where soils are deeper, the species usually occurs as a sub-dominant component of the forest canopy or as a shrub. Canyon live oak grows at elevations of 1,600 to 5,000 ft in southwestern Oregon. As it's name implies, Canyon live oak is often the dominant tree in steep, rocky canyons.

^* Plant Communities: In southwestern Oregon, canyon live oak is primarily associated with Douglas-fir, tanoak, giant chinkapin (Castanopsis chrysophylla), and Pacific madrone (Arbutus menziesii) in the mixed evergreen forests. Canyon live oak is less tolerant of shade than its associates in the mixed evergreen forests of the Siskiyou region, but is more tolerant than Pacific madrone. Canyon live oak occurs as an early successional shrub or tree, but is soon outgrown by its associates and eliminated from a stand. On drier, more open sites, it persists in the climax forest as a subordinate tree and shrub. Only on very rocky, canyon walls does it occur as a dominant in the climax forest.

^* Reproduction and Growth: Canyon live oak trees do not usually begin producing flowers until they are 15-20 years old. Flowering usually occurs in May or June. Acorn production is somewhat irregular; good crops tend to occur at 2-3 year intervals. Acorns mature in one season and fall to the ground in October. Canyon live oak also regenerates from sprouts that appear from dormant buds when the tree is injured or burned. Sprout growth can be rapid-growth of more than 3 ft in one year has been measured. Saplings and mature trees grow slowly.

^* Other Notes: Canyon live oak was used historically for farm implements, shipbuilding, furniture, and fuel. One of it's common names, maul oak, came from its use as handles for splitting mauls.

Oregon White Oak (Quercus garryanna)

^* Geographic Range: At it's northernmost extent, Oregon white oak occurs on Vancouver Island, isolated populations in the Frasier Valley, British Columbia and on islands in Puget Sound. The species is common along the Columbia River Gorge and in interior valleys of western Oregon. In California, Oregon white oak occurs in the Klamath region, interior Coast Range, and localized populations in the southern Sierras.

^* Soils and Topography: Oregon white oak grows on a wide range of soil series, but is outgrown by faster growing trees on good sites. The species can survive on seasonally-flooded clay soils, as well as xeric sites-conditions to which its competitors are poorly adapted. Oregon white oak typically occurs on flood plains, terraces, and gentle slopes.

^* Plant Communities: Oregon white oak occurs as scattered trees in savanna communities and in pure or mixed-species closed canopy woodlands. The Oregon Natural Heritage Information Center has identified nine native plant associations in the state that are dominated by Oregon white oak. Pacific madrone (Arbutus menziesii), western serviceberry (Amelanchier alnifolia), ponderosa pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii), and grand fir (Abies grandis) are among the most common tree species that co-occur with Oregon white oak. Poison-oak (Rhus diversiloba) and common snowberry (Symphoricarpos albus) are perhaps the most characteristic shrubs of Oregon white oak habitats. Oregon white oak is typically a seral species that only maintains dominance over competing trees through the action of natural disturbance, usually fire. Several characteristics of white oaks (low amount of resin, thick bark, capability to withstand injuries) allow the species to survive on fire-prone landscapes where other species are unable to become established. The vast expanses of oak savanna that were perpetuated by annual burning conducted by American Indian tribes largely have transitioned into dense, closed canopy woodlands or converted to agricultural uses since European settlement. In the absence of fire, Oregon white oak woodlands will eventually become dominated by tree species that are faster growing or more shade tolerant such as Douglas-fir, grand fir, and bigleaf maple. Oregon white oak can occur as a climax species on droughty sites or where natural fire is frequent.

^* Reproduction and Growth: Oregon white oak flowers between March-June, depending upon latitude and elevation. Acorns mature in one season and drop between late August and November. Annual acorn production is irregular. In the Willamette Valley, one heavy acorn crop was estimated to be 1,550-lbs/per ac. Acorns germinate soon after coming into contact with the ground. Oregon white oak also regenerate from sprouts that arise from dormant buds at the base of the tree or on exposed roots. The species usually grows slowly in both height and diameter. Measurements taken from cut stumps across widely separated locations indicate that 16 to 20 rings per inch are typical, although much faster growth has been measured at some sites.

^* Other Notes: Like other western oaks, Oregon white oak is not widely utilized for commercial purposes because of the uncertain supply of oak logs for mills and the species' slow growth. It has been used in limited production flooring and cabinet stock. Oregon white oak has proven to have exceptional properties for the manufacture of wine barrels.

California Black Oak (Quercus kelloggii)

^* Geographic Range: California black oak is most common in the northern Coast Range of California and along the west side of the southern Cascades and Sierra Mountains. The species is locally common in southwestern Oregon. Northernmost populations occur near Eugene, Oregon.

^* Soils and Topography: The species requires well-drained sites for good growth. Coarse- and medium-textured soils provide the most suitable conditions; the species is rarely found on clay soils. California black oak occurs across a wide range of topographic positions: from flat, valley floors having gravel soils to high, montane ridges. The species can withstand high moisture stress and thrive on sites too dry for most other tree species.

^* Plant Communities: California black oak usually occurs as a component of hardwood stands or mixed hardwood-conifer forests. More than 20 different tree species and 30 shrubs are known to co-occur on sites with California black oak. Some of the most commonly associated species are ponderosa pine (Pinus ponderosa), knobcone pine (Pinus attenuata),California white fir (Abies concolor var. lowiana), bigcone Douglas-fir (Pseudotsuga macrocarpa), tanoak (Lithocarpus densiflorus), Pacific madrone, and Oregon white oak. California black oak typically occurs as a dominant or co-dominant tree in even-age forests that result from a stand replacement fire. The species rarely occurs in forest understories.

^* Reproduction and Growth: California black oak flowers from mid-March to mid-May depending on local conditions. Acorns mature in the second year. Trees typically don't produce any acorns until they are at least 30 years old and don't yield abundantly until they are more than 80 years old. The magnitude of the acorn crop varies greatly from year-to-year. Depending on the location of the stand, abundant crops may occur every 2-3 years, or as infrequently as one out of every eight years. Most regeneration occurs from vegetative sprouts that originate from the stump of a tree that was cut or burned. Sprouts can grow more than 7 ft in height in four years following cutting. Saplings can grow faster than most other tree species that co-occur on the same sites, including conifers, and dominate a stand for many years. One study found that 100-year old California black oaks average 72 ft in height.

^* Other Notes: During the late-1800's, shipbuilders along the northern California Coast manufactured ship keels and ribs from California black oaks having forked stems of certain dimensions. Today, California black oaks are utilized for pallets, industrial lumber, and fuelwood.

Oregon white oak acorns can rapidly grow a long tap root during its first year of growth. Connie Harrington, US Forest Service.

California black oak can be most easily distinguished by its 3-tooth, bristle-tipped leaves from Oregon white oaks, which have smooth-lobed leaves. Raven OKeefe.

Wildflowers such as this Brodiaea coronaria can provide a colorful spring display in savanna-type habitats and open woodlands. Lynda Boyer, Heritage Seedlings.

Current Distribution

Oregon white oak distribution map:

Canyon live oak distribution map:

California black oak distribution map:

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