Quercus garryana, commonly known as the Garry oak or Oregon white oak, is a deciduous tree or shrub belonging to the beech or Fagaceae taxonomic family (USDA 2018). It is native to the Pacific Coast of North America from Los Angeles County, CA at its southern extend and reaching up into British Columbia. It is more common to the west of the Cascade Range, but populations are scattered to the east as well (Gucker 2007). This species can be found in a variety of habitats--wetlands, mountains, valleys, grasslands, woodlands, and closed-canopy forests. Significant Oregon white oak habitat and populations have been lost primarily due to fire suppression, altered land use, habitat destruction, and introduced non-native species/invasive species. For example, numbers in the Willamette Valley are currently at about 15% of their pre-European abundance, and in some areas of Q. garryana’s range, habitat loss may be as high as 95% (Gucker 2007).
There are three varieties of Q. garryana. The tree variety can grow to a height of 20-30 meters. The shrub varieties, Breweri and Semota, grow to be around 5 meters high. Differentiation of the shrubs can be deciphered by the velvety underside of Breweri leaves versus Semota’s more felt-like foliage (Flora of North America 2018). Oregon white oak has a deep taproot along with lateral roots (Gucker 2007). The branches commonly have multiple leaves growing out of a single node. The leaves are shiny dark green above and pale green below, with three or four rounded lobes per side. This angiosperm has small green flowers growing downward in catkins. The mature bark of the Oregon white oak is grayish brown and is furrowed in a checkered pattern.
Quercus garryana has monoecious flowers with 6 petals and sepals which are evenly spaced around the reproductive organs. They have 6-10 stamens and one pistil per flower, are wind pollinated, and produce an acorn when fertilized (Giblin 2018). Acorns are at an extremely high risk of desiccation and predation unless buried. Such burial is often facilitated by animals such as Douglas squirrels and Steller’s jays, with some of the caches inevitably being forgotten. This gives the acorn an increased chance of survival. Acorns readily germinate in warm moist weather with no need for a catalyst such as fire or cold (Gucker 2007).
Oregon white oak acorns are a major food source for many animals and insects living in the area, while the oaks themselves provide food, shelter, nesting material, and many other vital ecological services for a great many species, a number of which are at risk or endangered (Gucker 2007). Q. garryana’s ability to thrive in different soils and in rocky areas with different climates makes it an important feature in diverse ecosystems and a vital constant across environments.
Oregon white oak sprout dimensions on cut or burned sites in the 2nd and 3rd posttreatment years
Oregon white oak mortality and
density on early, late-, and twice-burned sites
This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available (e.g. [40,62,63,64,101]).
Aboveground description: Oregon white oak is a deciduous tree or sometimes a shrub. Growth form can be affected by regional and site conditions. Oregon white oak may be 30 to 100 feet (8-30 m) tall with a solitary trunk or up to 20 feet (5 m) tall with many trunks [40,62,63,64]. In tree form, Oregon white oak's DBH is typically 24 to 40 inches (61-100 cm), although a DBH of 97 inches (250 cm) was reported in a review [102]. Oregon white oak trunks have thick, furrowed, scaly bark [63,110]. A short, crooked, and sometimes creeping form is described in rocky habitats with shallow soils [60,110]. At high-elevation sites in eastern Oregon and Washington, a "shrubby" growth form is typical [59]. A shrub form is also noted from the southernmost populations [102]. Thilenius [139] described "forest-form" and "savannah-form" trees in Willamette Valley. Forest-form trees were fairly tall with ascending branches near the crown and a DBH often less than 24 inches (60 cm). These trees grew in closed-canopy woodlands with nearly 1,045 trees/ha. Savannah-form trees had DBH measurements often exceeding 3 feet (1 m), massive branches, and spreading crowns. These trees grew in open woodlands with 17 trees/ha.
Leaves are moderately to deeply lobed and measure up to 6 inches (15 cm) long. Generally there are 3 to 7 pinnate lobes. Margins are entire or with 2 to 3 teeth [40,59,63,110]. Occasionally, trees produce a second set of summer leaves [60]. Male flowers are catkins that are produced on the current year's growth [63]. Female flowers are solitary or in clusters and appear in the leaf axils of new twigs [59]. Oregon white oak produces large acorns that measure 0.8 to 1.2 inches (2-3 cm) long and mature in a single growing season [40,106]. Five hundred years is the estimated Oregon white oak lifespan [102]. Growth rates evaluated in an 80-year-old Oregon white oak-Douglas-fir stand in Oregon State's McDonald-Dunn Forest decreased by over half after the first 20 years of life. Overtopping by Douglas-fir may have affected growth [82].
Belowground description: Oregon white oak produces a central taproot and many lateral roots in the top 12 inches (30 cm) of soil [60]. Roots have ecto- and endomycorrhizal associations [100,152].
Root systems of 27 Oregon white oak trees from 1.3 to 60.7 feet (0.4-18.5 m) tall and 3 to 95 years old were excavated from coarse-textured glacial outwash soils in Fort Lewis, Washington. Soils were 75% to 85% gravel at the C horizon (30 to <80 inches (70-<200 cm)). Total taproot length for seedlings (x=7 years), small trees (x=22 years), and large trees (x=93 years) was 38 inches (96 cm), 79.9 inches (203 cm), and 80.3 inches (204 cm), respectively. Taproots grew horizontally for at least part of their length and were highly bent once they reached the C horizon. Just one large tree had a taproot extending beyond 68.9 inches (175 cm) deep. Taproot dominance decreased with plant age. Seedlings and small trees have primary taproots and small-diameter lateral roots. Large tree taproots were tapered, and the shallow lateral roots were extensive and large [31].
Varieties and hybrids: Brewer's oak is a spreading, clonal shrub up to 20 feet (5 m) tall with smooth bark. Leaves are 1 to 4 inches (3-9 cm) long, and acorns are less than 1 inch (3 cm) long [40,62,101,106]. Quercus garryana var. garryana is a tree that may reach 70 feet (20 m) tall with large leaves that measure 3 to 5.5 inches (7-14 cm) long [40,62]. The description of Q. g. var. semota is much like that of Brewer's oak, but acorns are typically larger [40,101]. Epling's oak, Howell's oak, and Q. à subconvexa are described in [101]. Brewer's oak. © Michael Charters www.calflora.netOregon white oak is native to western North America. It occurs from Vancouver Island, British Columbia (49 °N latitude), to southern California (34 °N latitude) [102,128]. Oregon white oak occurs primarily west of the Cascade Range but populations are scattered east of the Cascade Range [63,64].
Distribution of varieties: Brewer's oak is found in the Siskiyou region of California and Oregon and may occur in the northern Sierra Nevada. The most widely distributed variety is Q. g. var. garryana, which occupies habitats from British Columbia south to possibly Los Angeles County. In the southernmost reaches, Q. g. var. garryana is restricted to riparian sites. Quercus garryana var. semota occupies western slopes of the Sierra Nevada and northern slopes of the Tehachapi Mountains, and reaches its northern limit in southern Oregon [40]. Flora of North America provides a distributional map of Oregon white oak and its varieties.
Past and present distributions: Oregon white oak habitat loss is reported throughout its range. A 1998 Pacific Northwest Ecosystem Consortium cited in [69] indicated that Oregon white oak woodlands and savannahs in the Willamette Valley of Oregon have declined to less than 15% of their pre-European settlement extent. In British Columbia, comparisons of early survey records and current occurrence reports indicate that Oregon white oak habitat loss has exceeded 95%. Habitat loss is primarily a result of European settlers that suppressed fires, altered land use, and introduced nonnative species and heavy grazing [87].
In Oregon white oak's easternmost distributions, habitat protection and Oregon white oak conservation alternatives may be limited. Slightly more than 83% of Oregon white oak habitat is privately owned, and none is under permanent protection in southeastern Oregon and/or eastern California [130].
Fire adaptations: Oregon white oak is a fire-resistant species; typically, saplings over 10 feet (3 m) tall resist even top-kill. Mortality from fire is rare, and root crown sprouts are common following top-kill in even the smallest size classes [134,135,148,149]. Mature tree bark is sufficient to withstand surface fires in open conditions [2]. If top-killed, Oregon white oak rapidly sprouts from the root crown and/or roots [2,3,4,120,134]. Acorns in the canopy survive low-severity fires, but scorched acorns on the ground have reduced germination [135]. Animal dispersal of acorns (see Seed dispersal and Importance to Livestock and Wildlife) onto burned sites is likely.
FIRE REGIMES: The persistence of Oregon white oak communities is dependent on periodic fire. Native Americans maintained open Oregon white oak stands through frequent fall burning. The loss of Oregon white oak-dominated habitats to conifer-dominated forests is in large part the result of increased fire-return intervals since European settlement and the subsequent elimination of Native American burning.
Historical fire-return intervals: Numerous researchers have suggested that Oregon white oak woodlands and savannahs burned frequently based on the fire adaptations of woodland species and the susceptibility of later successional conifer species. Because pre-European fires were fueled by gasses and forbs, they were "flashy and of low duration" and did not normally scar trees, making fire regime reconstruction difficult. However, a fire-return interval of 5 to 10 years likely would have restricted conifer encroachment [1,2]. Dry, hot sites occupied by Oregon white oak in Washington's Wenatchee National Forest burned in low-severity fires at intervals "judged to be in the 5 to 30 year range" [85]. White [158] reports that Oregon white oak in Oregon's Klamath Mountains is adapted to a 3- to 20-year fire-return interval.
Past fire frequencies were estimated at 4.5, 7.5, and 13.3 years for the presettlement (before 1875), settlement (1875-1897), and postsettlement (1898-1940) periods, respectively, in the Bull Creek Watershed of California's Humboldt Redwoods State Park. Basal sprouts and fire-scarred stumps in old growth redwood-Douglas-fir forests were used to determine fire frequency. When watershed zones were used to estimate fire frequency, estimates were approximately twice that reported for the entire study area for all time periods, suggesting spatial variability in fire frequencies [132]. The fire cycle increased dramatically after 1905 in a 5,745-acre (2,325 ha), mixed-conifer forest with Oregon white oak in California's Shasta-Trinity National Forest. From 1628 to 1995, 184 fire years were recorded. Fires burned primarily in the mid-summer or fall. The pre-European fire cycle of 19 years increased to 238 years after 1905. A large increase in young Douglas-firs coincided with fire exclusion [138].
Native American burning: The most extensively studied Oregon white oak communities burned by Native Americans are those in the Willamette Valley, which were probably burned annually or nearly annually. The Willamette Valley has been described as the most intensely fire-managed environment in the aboriginal Northwest [18]. Based on ethnohistorical evidence (ethnographic and archeological, published and unpublished sources) the Native people of the Willamette Valley burned grasslands and Oregon white oak savannahs nearly every year in low-severity late summer or early fall fires. The earliest recorded fire date for Native burning was 2 July, and the latest was 20 October. Likely sites in Oregon white oak woodlands were burned only after acorns were collected [17,19]. The frequency of Native American fires in Oregon white oak communities is difficult to determine, and annual burning is not considered likely by Agee [2]. Fires in the Willamette Valley served several purposes, most related to maintaining food sources of mule deer, tarweed (Madia spp.) seeds, and insects. Large-scale burning in the Willamette Valley was eliminated when the Kalapuya, Umpqua, and Tahelma people were sent to the Grande Ronde Reservation in 1855 [17,19].
Several additional references provide strong evidence of frequent Native American burning in Oregon white oak habitats. For additional information on evidence of burning and potential reasons for burning, see [84,93] (California), [78] (southwestern Oregon), [83] (southwestern Washington), and [147] (British Columbia).
From historical and current written accounts, maps, and aerial photos, researchers compared Willamette Valley vegetation in 1853 to that in 1969. Much of what was Oregon white oak savannahs became dense woodlands, and areas that were oak woodlands became Douglas-fir forests. Changes occurred with decreased fire frequency and European settlement [68]. Findings were similar from aerial photos and data collected in past surveys of the valley's Monmouth Township. In 1850 approximately 8% of the township was closed-canopy Oregon white oak woodlands, and 50% was open Oregon white oak savannahs. In 1955, closed-canopy Oregon white oak woodlands increased to 24% of the township [51,52].
Decreased fire frequency: Changes in stand density and composition, chiefly due to the encroachment of Douglas-fir, are common in Oregon white oak communities since fire exclusion.
Researchers have extensively studied Oregon white oak woodlands in California [134,135,136] and have summarized changes in all aspects of historic and current woodland FIRE REGIMES. Since the mid-1800s the management and composition of these woodlands have changed substantially. With the elimination of frequent Native American burning, Douglas-fir encroachment ensued. Nonnative grasses, which dry earlier than native herbs, were introduced with European settlement. Although earlier-curing fuels occur in Oregon white oak communities, fires continue to burn predominantly in the summer or early fall, like in the early 1800s. Fire frequency is much reduced from the historic annual or nearly annual frequency. Fire size historically ranged from 20 to 200 acres (10-100 ha) and presently averages less than 20 acres (10 ha). The spatial complexity of fuels was low historically due to nearly uniform herbaceous vegetation in the understory of Oregon white oak woodlands. The encroachment of Douglas-fir has increased vertical fuel loads. Short fire-return intervals and a lack of heavy fuels supported lower severity fires than occur presently. Historically, surface fires and only occasional torching occurred in Oregon white oak communities; currently, however, torching is more common, and crown fires are possible with extreme fire weather conditions [137].
Rapid invasion of oak (Quercus spp.) woodlands by Douglas-fir began in the early 1940s in Annadel State Park. Researchers found that Douglas-fir establishment paralleled increased oak density and canopy closure, which coincided with fire exclusion in the Park [13]. For a more detailed summary of this study, see Succession to coniferous forest. In the Fox Hollow Research Area in Willamette Valley, researchers found that forest structure and composition changed considerably from the 1800s to the mid-1970s. Prior to 1850 warm dry ponderosa pine- and Oregon white oak-dominated sites had estimated tree densities of 70/ha. The same sites in the mid-1970s supported an estimated 1,179 trees/ha. Douglas-fir dominated the seedling layer (74%). Researchers attributed changes in forest structure and composition largely to decreased fire frequency [27].
Oregon white oak and Douglas-fir establishment on Rocky Point, Vancouver Island, was facilitated through fire exclusion. Tree ring analyses and fire scar data from relatively undisturbed prairies, Oregon white oak woodlands, and coniferous forests allowed researchers to reconstruct stand composition and structure. Oregon white oak establishment began on prairies in 1850 and peaked in 1890. Minor Douglas-fir establishment began in 1890. From 1950 on, recruitment was almost exclusively by coniferous species. Researchers found that there were significantly (P<0.001) fewer Oregon white oak seedlings on plots with a coniferous overstory than those without. There were few saplings, indicating that seedlings were eventually unsuccessful. Browsing, nonnative grasses (orchardgrass, colonial bentgrass, and sweet vernalgrass (Anthoxanthum odoratum)), or climate change may have affected sapling development. A search for fire-scarred trees revealed no scarring fire since about 1850 [45].
Additional factors to Oregon white oak declines: Fire exclusion was not the only factor associated with changes and declines in Oregon white oak communities. Past silvicultural management decisions also affected Oregon white oak. See Silviculture management for a discussion of other factors affecting Oregon white oak declines.
The following table provides fire return intervals for plant communities and ecosystems where Oregon white oak is important. Find fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
Community or Ecosystem Dominant Species Fire Return Interval Range (years) grand fir Abies grandis 35-200 [7] California chaparral Adenostoma and/or Arctostaphylos spp. <35 to <100 [107] cheatgrass Bromus tectorum 109,157] California montane chaparral Ceanothus and/or Arctostaphylos spp. 50-100 western juniper Juniperus occidentalis 20-70 pinyon-juniper Pinus-Juniperus spp. <35 [107] Pacific ponderosa pine* Pinus ponderosa var. ponderosa 1-47 [7] mountain grasslands Pseudoroegneria spicata 3-40 (x=10) [6,7] coastal Douglas-fir* Pseudotsuga menziesii var. menziesii 40-240 [7,99,117] Pacific coast mixed evergreen Pseudotsuga menziesii var. menziesii-Lithocarpus densiflorus-Arbutus menziesii <35-130 [7,23] California oakwoods Quercus spp. <35 Oregon white oak Quercus garryana 3-30 [1,2,85,132] California black oak Quercus kelloggii 5-30 [107] interior live oak Quercus wislizenii <35 [7] redwood Sequoia sempervirens 5-200 [7,39,132] western redcedar-western hemlock Thuja plicata-Tsuga heterophylla >200 [7] *fire return interval varies widely; trends in variation are noted in the species reviewThe use of fire in Oregon white oak habitats is often complicated by their proximity to urban areas, associated nonnative, rare, or sensitive plant and wildlife species, and understory fuel composition. Appropriate fire use requires clearly defined management goals.
General challenges: There are numerous factors to consider when using fire to manage Oregon white oak habitats. Urban areas near Oregon white oak communities affect the timing and control of fire [3]. Nonnative, sensitive, and rare plant or wildlife species also need consideration. Many rare plants [20] and vulnerable, threatened, or endangered butterflies [50] are associated with Oregon white oak communities on Vancouver Island. In addition to the needs of rare and/or sensitive species are the unique needs of wildlife species in Oregon white oak habitats. For instance, acorn woodpeckers use large-sized trees for granaries [69], and wild turkeys in Washington's southern Klickitat County use Oregon white oak and Oregon white oak-ponderosa pine communities as brood habitat and Douglas-fir habitats for roosting. These studies suggest that stand structure and diversity at various scales may affect wildlife habitat suitability. See Importance to Livestock and Wildlife for more on Oregon white oak habitat characteristics that attract wildlife.
Nonnative species: Reintroduction of fire in Oregon white oak communities is often complicated by the presence of nonnative species and their response to fire [3]. The response of nonnative species is variable and likely affected by fire timing and severity. In Oregon white oak woodlands of Redwood National Park's Bald Hills, the most heavily grazed community (Oregon white oak/bristly dogstail grass) had the highest percentage of nonnative species, and the most recently burned community (Oregon white oak/common snowberry) had the highest percentage of native species [136]. On Vancouver Island's Cowichan Garry Oak Reserve, burning and mowing increased the cover of dominant nonnative grasses. Sites were evaluated in the first or second posttreatment year. Native plant recruitment on treated sites was limited by propagule dispersal, and sites lacking native species may require seeding [88].
In western Oregon, many nonnative species including thistles (Cirsium spp.), Scotch broom, purple foxglove (Digitalis purpurea), St Johnswort (Hypericum perforatum), English holly (Ilex aquifolium), Himalayan blackberry (Rubus discolor), and evergreen blackberry (R. laciniatus) were more frequent following canopy release. Of the 8 nonnative species studied, all but English ivy (Hedera helix) were more frequent on thinned or clearcut logged sites than control sites [49].
In the Cowichan Garry Oak Reserve, the prefire diversity affected the level of invasibility of Oregon white oak savannahs. Low-diversity savannah plots had more invading species and more Scotch broom and thistles present after fire than did high-diversity plots. Plots burned twice, once in July and again in October, and maximum soil surface temperatures during the fires ranged from 170 to 415 °F (74-213 °C). Invasibility was determined by seeding native species that were absent from most treated plots. Seeded species did not establish in unburned plots, and in burned plots the survival of seeded species increased with decreased species richness. Recruitment of Scotch broom and thistles that were not seeded into plots was significantly (P<0.0001) greater in low-diversity than in high-diversity burned plots. Postfire Scotch broom cover increased by 250% in low-diversity plots [86].
Increases in Scotch broom following fire may be related to soil heating. In greenhouse studies, Scotch broom stem density was significantly greater in heat treated soils. All other associated species were negatively impacted by ash and heat. Study findings are summarized in the table below. Heat did not affect Oregon white oak seedling survival, cover, or height. For more on the effects of heat and ash on Oregon white oak, see Acorn survival and emergence [113]. Additional information on Scotch broom and its heat scarified seed is available.
Stem density/container of Oregon white oak associated species and Scotch broom grown in heat and ash treated soils Treatment All associated species Scotch broomstem density
AshFuels: Composition of the understory vegetation and litter can affect fire behavior and thus prescribed fire procedures in Oregon white oak vegetation. In mixed Oregon white oak-Douglas-fir stands in Annadel State Park, grasses were lacking. With Oregon white oak and Douglas-fir litter as the primary surface fuel, fire carries only under the driest conditions [57].
Presence of Scotch broom may increase fire severity in Oregon white oak stands. Prescribed fires in Fort Lewis, Washington, plant communities with mature Scotch broom produced higher soil surface temperatures than those in Idaho fescue prairies, Oregon white oak woodlands, or on sites with newly established Scotch broom populations [149]. In the same area, Thysell and Carey [141] noted that sites with a dense understory of Oregon white oak, Douglas-fir, and Scotch broom may produce more "damaging" fires than oak savannah sites. Mature Scotch broom may provide ladder fuels into Oregon white oak crowns. In the study area, researchers observed mature fire-killed Oregon white oak, although not commonly [141].
Restoration fire management: Fire frequency and fire distribution can likely be manipulated to manage or maintain prairies, savannahs, mixed woodlands or a combination of these types. With the removal of Native American burning practices in the Willamette Valley, Oregon white oak savannahs quickly succeeded to closed-canopy Oregon white oak woodlands, and Oregon white oak woodlands became Douglas-fir-dominated forests [51,52,68]. On Vancouver Island, Oregon white oak and Douglas-fir establishment in prairies occurred after Native American burning ceased [45]. In Redwood National Park, prescribed fires produced high mortality of young Douglas-fir trees less than 10 feet (3 m) tall. To limit the succession of Oregon white oak woodlands to Douglas-fir-dominated forests, a fire-return interval of 10 years or less, a time less than that required for Douglas-fir to reach 10 feet (3 m), is needed [134].Dry prairies, wooded slopes, rocky bluffs, and montane coniferous forests all provide Oregon white oak habitat [40,63,101].
Climate: Oregon white oak's westernmost habitats experience more mild, maritime climates than those farther east. Throughout Oregon white oak's range, low January temperatures typically range from 13 to 50 °F (-11 to 10 °C), and high July temperatures are often 60 to 84 °F (16-29 °C). Summer droughts are moderate to extreme, and annual precipitation ranges from 10 to 100 inches (250-2,500 mm). Oregon white oak trees are somewhat resistant to snow and ice damage [102].
California: Warm summers, freezing winter temperatures, and annual precipitation ranges of 20 to 50 inches (510-1,300 mm) are reported in Oregon white oak habitats in California [106].
Oregon: Oregon white oak woodlands in central Oregon occupy sites receiving 12 to 59 inches (300-1,500 mm) of precipitation/year [154]. In southwestern Oregon, the Oregon white oak-Douglas-fir/blue wildrye vegetation type receives an average of 46 inches (1,160 mm) of precipitation/year and 5.5 inches (140 mm) in the dry season from May to September. Oregon white oak/birchleaf mountain-mahogany vegetation receives the least average amount of dry season precipitation1.6 inches (40 mm)/dry season [116].
The climate is mild in the Willamette Valley. Annual precipitation averages about 40 inches (1,000 mm), and most comes from November to May. Snow is rarely present for more than a few weeks. From June to September, conditions are dry. Winter temperatures rarely drop below 15 °F (-9.4 °C), and summer temperatures average 70 °F (21 °C). Mean spring and fall temperatures average 50 °F (10 °C) and 54 °F (12 °C), respectively [52,139]. One-year-old Oregon white oak stems collected from mature trees near Corvallis, Oregon, had a freezing resistance, defined as the lowest temperature at which no injury was sustained, of -4 °F (-20 °C). The freezing resistance of buds was 5 °F (-15 °C) [122].
Washington: In Washington's Wenatchee National Forest, Oregon white oak woodlands occupy some of the hottest and driest areas, where less than 20 inches (500 mm) of precipitation/year is common [85].
British Columbia: The climate in Oregon white oak habitats of British Columbia is described as maritime to submaritime, dry summer, cool mesothermal. Characteristic of this climate is an average temperature in the warmest month of less than 72 °F (22 °C), and less than 1.2 inches (30 mm) of precipitation in the driest summer month [73]. On southern Vancouver Island, Oregon white oak habitats receive 24 to 47 inches (600-1,200 mm) of precipitation per year [119].
Elevation:Elevation tolerances for Oregon white oak and varieties
Elevation (feet)
Variety, if applicable California Entire range 1,000-5,000 [62,101,106] 0-3,900 [128], up to 7,500 in southernmost range [102] Brewer's oak 2,000-6,200 [62,101] 2,000-6,200 [40,106] Q. g. var. garryana 980-5,900 [62] 0-5,900 [40,62] Q. g. var. semota 2,500-5,000 [101] 2,500-5,900 [40,101]Soils: Oregon white oak occurs on a variety of soils ranging from dry to very moist and poorly to rapidly draining. Gravelly and heavy clay substrates are tolerated [102,106,128].
In Castle Crags State Park, the Oregon white oak/cheatgrass plant association occurs on cobbly alluvial soils [133]. In the northern California Coast Ranges, Oregon white oak occurs on well-drained, slightly acidic loams [67]. Nutrients in the top 3 feet (1 m) of soil from Oregon white oak and Brewer's oak woodlands in California's Humboldt and Shasta counties is provided in [33].
Oregon white oak woodlands in the Willamette Valley occur on well-drained, moderately deep, acidic soils of igneous, alluvial, or sedimentary origin [139]. Quercus garryana var. garryana in southwestern Oregon grew on serpentine and nonserpentine alluvial soils; however, the site with the greatest concentrations of serpentine elements also supported Brewer's oak. Soil fertility was lower but Oregon white oak ectomycorrhizal diversity was higher on serpentine than alluvial soils [100].
In British Columbia, Oregon white oak is indicative of very dry (moisture deficit 3.5-5 months of year) to moderately dry soils (moisture deficit 1.5-3.5 months) [73]. On southern Vancouver Island, Oregon white oak habitats have Sombric Brunisol soils with deep, dark surface horizons and bedrock layers at 20- to 30-inch (40-80 cm) depths [119].
Many wildlife species utilize Oregon white oak as a food source and for cover, perching, nest material, and nest sites [92]. In a 1940 review, Van Dersal [153] indicates that ring-necked pheasants, band-tailed pigeons, ruffed grouse, gray sapsuckers, California woodpeckers, Lewis's woodpeckers, American black bears, mule deer, dusky-footed woodrats, and Douglas ground squirrels utilize Oregon white oak. Van Dersal's list is not exhaustive.
Variable Oregon white oak acorn production (see Seed production) may have affected findings in short-term usage studies.
Cattle: Cases of cattle being poisoned by Oregon white oak are often related to other extenuating circumstances. In southern Oregon, 30 of 117 steers became ill when grazing in Oregon white oak woodlands and savannahs. Calves were observed feeding under Oregon white oak trees where acorns were likely abundant because of an earlier severe storm. Green acorns likely made cattle ill. Weather events that dislodge an abundance of acorns, a lack of more palatable forage, and/or young grazing animals are often associated with reports of oak poisoning in cattle [71].
Domestic sheep: Domestic sheep grazing on Mt Hood appeared to prefer Oregon white oak acorns (Coville 1898, cited in [30]).
Deer: Oregon white oak provides habitat and food for young and old white-tailed and mule deer. The oak-Pacific madrone cover type was used most frequently (33%) by 11 white-tailed deer fawns. Fawns averaged 5.7 days old when collared and were monitored during the summer in Oregon's lower northern Umpqua River Watershed. Male fawns used the type more than female fawns [115]. In the Klickitat Basin of Washington, McCorquodale [97] found that 66 radio-collared, migratory Columbian black-tailed deer preferred (P<0.05) winter habitats with an overstory dominated or codominated by Oregon white oak. Preference was determined by use versus availability. The lack of snow, abundance of forage, availability of acorns, and associated shrubs and arboreal lichens likely affected preference [97].
In the William L. Finley National Wildlife Refuge, Oregon white oak acorns made up 9% to 93% of the weight of 4 Columbian black-tailed deer stomachs [26]. Brewer's oak receives heavy to moderate mule deer use and makes up a bulk of fall mule deer diets in California's western Glenn County [123].
Large mammals: The stomachs of mountain lions collected in the winter from Oregon's western Cascade Range did not contain Oregon white oak, but researchers noted that Oregon white oak was recovered from mountain lions collected at other times of the year. Whether or not Oregon white oak consumption was purposeful or incidental was not reported [142].
Small mammals: A variety of small mammals utilize Oregon white oak habitats and feed on Oregon white oak acorns and/or seedlings. In Oregon white oak-dominated sites in Fort Lewis, Washington, the most abundant small mammals, listed in order of decreasing abundance, were deer mice, vagrant shrews, Trowbridge's shrews, and creeping voles [159]. Oregon white oak woodlands are also important habitat for western gray squirrels in Fort Lewis. High-use stands had 34% Oregon white oak and 53% Douglas-fir in the overstory. Low-use stands had 53% Oregon white oak and 43% Douglas-fir in the canopy. Use was lower in stands with high Scotch broom abundance. Researchers observed western gray squirrels digging and foraging for Oregon white oak acorns from November to March and gathering and burying acorns in August and September [121].
Oregon white oak was found 11 times in 63 dusky-footed woodrat nests near Corvallis, Oregon [34]. In the William L. Finley National Wildlife Refuge, small mammals took 61% of the Oregon white oak acorns available in savannahs and 96% in closed-canopy woodlands [26]. In west-central Willamette Valley, 3 of 23 marked Oregon white oak seedlings died from taproot severing by pocket gophers [61]. An additional discussion of small mammals that feed on Oregon white oak acorns and disperse acorns is provided in Seed dispersal.
Game birds: Wild turkeys are common in Oregon white oak habitats of Oregon and Washington. Of 2,288 wild turkeys located in southern Wasco County, Oregon, 18.6% were in Oregon white oak, 15.2% in ponderosa pine-Oregon white oak, and 18.2% in ponderosa pine-Douglas-fir-Oregon white oak stands. Use of these habitats occurred year-round [28]. In Washington's Klickitat County, 4 wild turkey broods were monitored using radio transmitters from mid-May to early July. Broods used Oregon white oak and ponderosa pine-Oregon white oak habitats more than expected based on their availability (P<0.05). Douglas-fir forests and nonforested habitats were used less than expected. Oregon white oak and ponderosa pine-Oregon white oak communities supported a diverse understory, which likely provided escape cover, and many open areas with insects and herbaceous foods [90].
Other birds: Numerous studies suggest that Oregon white oak communities provide important breeding, nesting, and foraging sites. In 5 Oregon white oak stands in western Oregon, the Shannon-Weaver avian diversity was 2.46 to 3.13, depending on the season. The researcher noted that these levels of diversity were greater than those reported for many other forest communities [5]. In south-central Washington, bird abundance was high in study sites dominated by a mixture of small Oregon white oak and ponderosa pine trees and in pure Oregon white oak stands [91]. Species richness was greater in Oregon white oak woodlands than in any age class of Douglas-fir forests in the Cascade Range of south-central Washington (Manuwal 1991, cited in [91]). In northwestern Humboldt County, California, Oregon white oak acorns made up the bulk of band-tailed pigeon's fall diet [66].
In mixed Douglas-fir-hardwood forests of western Oregon, researchers observed 140 Oregon white oak trees with excavated cavities, indicating use by cavity-nesting birds in the area [21]. Oregon white oak woodlands in south-central Washington provided important nesting habitat for Nashville warblers [91]. Large-sized Oregon white oak trees are important to acorn woodpeckers in Benton County, Oregon. Granaries were located in areas where Oregon white oak basal area averaged 50.1 m²/ha, and the DBH of surrounding Oregon white oak trees averaged 25.5 inches (64.7 cm). Large tree conservation may be important in managing acorn woodpeckers [69].
Of 17 bird species surveyed in fragmented Oregon white oak woodlands on Vancouver Island, 2 species, the brown-headed cowbird and chipping sparrow, favored Oregon white oak woodlands over Douglas-fir forests. The size of many bird populations was related to patch size and human population densities, suggesting that protection of woodlands and forests from urbanization is important to bird management [38].
In the Willamette Valley, researchers found more breeding neotropical migrants in Oregon white oak woodlands than in coniferous forests. Western wood-pewee, Lazuli bunting, and Cassin's vireo were not found regularly in coniferous forests. Acorn woodpeckers, downy woodpeckers, white-breasted nuthatches, black-capped chickadees, northern flickers, and Bewick's wrens are cavity-nesting species, and large-diameter open-grown Oregon white oak trees provided more cavities than did Douglas-fir forests. White-breasted nuthatches were negatively correlated (R = -0.65) with increasing Douglas-fir cover, and populations are in decline in the Willamette Valley. Researchers indicate that "conservation of Oregon white oak habitats is critical to the maintenance of populations of several avian species in the Willamette Valley" [53]. An additional discussion of birds that feed on Oregon white oak acorns and often disperse acorns is provided in Seed dispersal.
Amphibians and reptiles: Many amphibians and reptiles occur in Oregon white oak meadows in the Georgia Depression of British Columbia. The "rarely observed" sharp-tailed snake has a distribution closely resembling Oregon white oak's, and sharp-tailed snake persistence may depend on Oregon white oak habitat conservation [103].
Palatability/nutritional value: Oregon white oak is considered good to fair browse for deer, poor to "useless" for cattle, domestic sheep and goats, and "useless" for horses [123]. In a review, Van Dersal [153] reports that Oregon white oak protein levels are similar to those in alfalfa (Medicago sativa). Oregon white oak leaves collected from lower crowns in Humboldt County, California, averaged 11.4% protein in the dry season (June-October) and 12% in the wet season (November-July). Acid soluble lignin concentrations averaged 15.1% and 21.1% in the dry and wet seasons, respectively. Total sugar concentrations were very similar in the dry (4.6%) and wet seasons (4.5%) [76]. Oregon white oak acorns collected from sites near Weaverville, California, were 3% protein, 3.4% fat, 9.1% fiber, 52.5% nitrogen-free extract, and 1.4% ash [160].
Cover value: Oregon white oak trees and shrubs provide important cover and shade for livestock and wildlife. This topic has been addressed briefly in Importance to Livestock and Wildlife.
forest chaparral with Brewer's oak and "scrubby" Oregon white oak
Bald Hills woodlands with tree-form Oregon white oak in the North Coast Ranges [25]
Oregon oak woodland in Coast Ranges
mixed north slope cismontane woodland in the valleys and lower slopes of the Klamath and North
Coast ranges [65]
Oregon white oak woodland vegetation type in north coast areas [161]
Oregon white oak/common snowberry (Symphoricarpos albus) in Bald
Hills of Redwood National Park
Oregon white oak/Columbian larkspur (Delphinium trolliifolium) in draws and
on moist sites in Redwood National Park's Bald Hills [135,136]
Oregon white oak/orchardgrass (Dactylis glomerata) in Bald Hills of Redwood National Park
Oregon white oak/bristly dogstail grass (Cynosurus echinatus) in heavily
grazed areas in Redwood National Park's Bald Hills [135,136]
Oregon white oak/cheatgrass (Bromus tectorum) plant association in
Shasta County's Castle Crags State Park [133]
Oak brush vegetation in Kern, Tulare, Butte and Shasta counties, dominated by
Q. g. var. semota [65]
Douglas-fir (Pseudotsuga menziesii)-Oregon white oak/poison-oak-western sword fern
((Toxicodendron diversilobum-Polystichum munitum) in the interior valleys of the Umpqua River basin [127]
Douglas-fir-Oregon white oak/poison-oak on the Tiller Ranger District in the southern
Cascade Range [11]
Oregon white oak-Douglas-fir/sheep fescue (Festuca ovina)
Oregon white oak-Douglas-fir/blue wildrye (Elymus glaucus) in the Umpqua and/or Rogue
river watersheds [116]
Oregon ash (Fraxinus latifolia)-Oregon white oak/common snowberry on the Muddy Creek floodplain in
northwestern Oregon's Finley Wildlife Refuge [96]
Oregon white oak-Pacific madrone (Arbutus menziesii)/poison-oak/bristly dogstail
grass
Oregon white oak-Oregon ash/sweetbriar rose/common rush (Rosa eglanteria/Juncus effusus) within the
interior valleys of the Umpqua
River basin [127]
Oregon white oak/California hazelnut (Corylus cornuta var. californica)/western sword fern
on mesic sites in the Willamette Valley
Oregon white oak/sweet cherry (Prunus avium)/common snowberry in the Willamette
Valley [139]
Oregon white oak-birchleaf mountain-mahogany (Cercocarpus montanus var. glaber)
in the Umpqua and/or Rogue river watersheds [116]
Oregon white oak/Scotch broom/creeping bentgrass (Cytisus scoparius/Agrostis stolonifera)
in the Myrtle Island Research Natural Area [140]
Oregon white oak/Saskatoon serviceberry (Amelanchier alnifolia)/common snowberry in
the Willamette Valley [139]
Oregon white oak/poison-oak/medusahead (Taeniatherum caput-medusae)-bristly dogstail
grass
Oregon white oak/poison-oak/bristly dogstail grass
Oregon white oak/poison-oak/orchardgrass
within the Interior Valleys of the Umpqua River Basin [127]
Oregon white oak/poison-oak on xeric sites in the Willamette Valley [139]
Oregon white oak/woods strawberry (Fragaria vesca) on Tiller and Steamboat Ranger Districts in
the southern Cascade Range [11]
Oregon white oak/California brome (Bromus carinatus)
Oregon white oak/bristly dogstail grass in the Umpqua and/or Rogue River watersheds [116]
westside oak woodlands and dry Douglas-fir forests in the Willamette
Valley, Puget lowlands, and Klamath Mountains
ponderosa pine (Pinus ponderosa) forests and woodlands on eastern
slopes of the Cascade Range in eastern Oregon and Washington [22]
Oregon white oak/beaked hazelnut (Corylus cornuta)-common snowberry
Oregon white oak/bluebunch wheatgrass (Pseudoroegneria spicata)
Oregon white oak/pinegrass-elk sedge (Calamagrostis rubescens-Carex geyeri) in
the Wenatchee National Forest [85]
Oregon white oak/hollyleaved barberry (Mahonia aquifolium) [35,36]
Oregon white oak/oceanspray (Holodiscus discolor) [74]
Oregon white oak/pink honeysuckle (Lonicera hispidula)
Oregon white oak/large camas (Camassia leichtlinii)
Oregon white oak/miner's lettuce (Claytonia perfoliata) [35,36]
Oregon white oak/broadleaf stonecrop (Sedum spathulifolium)
Oregon white oak/common chickweed (Stellaria media) [74]
Oregon white oak/dicranum moss-shortspur seablush (Dicranum scoparium-Plectritis congesta)
Oregon white oak/rhacomitrium-Wallace's spikemoss (Rhacomitrium canescens-Selaginella wallacei)
Oregon white oak/Sierra pea (Lathyrus nevadensis)
Oregon white oak/California brome
Oregon white oak/blue wildrye
Oregon white oak/long-stolon sedge (Carex inops)
Oregon white oak/Alaska oniongrass (Melica subulata) [35,36]
Oregon white oak/ripgut brome (Bromus diandrus ssp. rigidus)
Oregon white oak/poverty brome (B. sterilis) [74]
Epling's oak/poison-oak
Epling's oak/spreading hedgeparsley (Torilis arvensis)
Epling's oak/California fescue (Festuca californica) on Bennett
Mountain in Sonoma County [145]
Conservation:
There is considerable concern about the future of Oregon white oak habitats. Recent and rapid losses
of habitat have prompted the need for the protection, recovery, and restoration
of Oregon white oak woodlands and savannahs. According to Agee [2] "without
prescriptive treatment, up to 50% of threatened oak woodlands could be beyond
help by the year 2010," and the "window of opportunity narrows every
year".
Oregon white oak ecosystem conservation is necessary for the protection of associated
species and culturally important historical sites. Many plant and animal species at
risk of local or global extinction are associated with Oregon white oak communities. Lists of these species are
presented in [42]. Because Oregon white oak is often an indicator of culturally
important sites in western Washington [131], the loss of these
communities could also mean a loss of artifacts, historical evidence, as well as an
appreciation or understanding of the practices of Native people.
Conservation of Oregon white oak vegetation is difficult for several reasons. Scott
and others [125] report that only a very small portion of Oregon white oak's geographic distribution is
currently protected. In British Columbia, 40% to 76% of the understory species in
Oregon white oak communities
are nonnative and make up 59% to 82% of the understory cover (Erickson 1996
and Roemer 1995, cited in [94]). Establishing a reference condition,
often the first step to restoration, is challenging without native flora [94].
However, many sources address Oregon white oak management and conservation.
Harrington and Devine [56] provide guidelines for
releasing Oregon white oak from overtopping conifers. They include information on stand selection,
release types, treatment season, and concerns or problems with associated nonnative species. Guidelines for
Oregon white oak woodland preservation and management in Washington that include
future land use practices, prescribed fire, and selective harvest are described
in [80]. Information on determining management goals,
considering ecosystem structure and function, reevaluating management effects, identifying tradeoffs,
and setting management priorities in Oregon white oak woodlands is provided in [151].
Climate change:
Using existing relationships between the distributions of oak species, the prevailing climates
within these distributions, and 3 general climate change models, researchers
suggest that predicted changes in climate will not significantly impact the
distribution of oaks in California [95].
Diseases/pests:
Diseases affecting Oregon white oak in California are identified and
described in [111].
Silviculture management:
Decreased fire frequencies in Oregon white oak habitats are not solely
responsible for declines in Oregon white oak. Past silvicultural management
decisions also contributed to declines.
In a study conducted near Oregon State College in the Willamette Valley,
researchers designed several treatments to increase conifer production on Oregon
white oak-dominated sites. Researchers indicated that Oregon white oak "stands
were poor producers of forest products because of exceptionally
slow growth". Treatments to increase productivity of Oregon white
oak-dominated woodlands included clearcutting, burning, planting to pasture, underplanting with Douglas-fir, thinning and underplanting to Douglas-fir, and
clearcutting and planting to Douglas-fir [54]. Similar management goals are reported in the 1950s from northwestern California.
In a 1955 paper, Roy [120] indicated that hardwood sprouts following logging or fire
are "pernicious" and "capture ground area which otherwise
could be used to grow conifers". He also suggests that "treatments
may be necessary to obtain adequate stocking of desired conifers".
Guidelines for herbicides use to control Oregon white oak
in reforestation and/or timber production efforts are provided in [156].
Native people of the western United States utilized Oregon white oak; acorns were often an important food source. Salish groups of the Puget Sound ate Oregon white oak acorns after bitter tannins were removed through soaking. They also used Oregon white oak bark in treatments for tuberculosis and other ailments [110,146]. Since Oregon white oak provided important foods to early inhabitants, Storm [131] indicates that mature Oregon white oak stands can be used to find culturally important sites in western Washington. In northern California, Native people considered Oregon white oak acorns sweet and palatable [58]. In Mendocino County, California, acorns made up a large portion of Native people's diets. Male tribe members beat acorns from the tree, and women collected them in baskets. Acorns were dried, ground into meal, and made into bread or soup [24].
Oregon white oak is an attractive landscape plant in the Pacific Northwest. The hardiness, branching pattern, and white bark of Oregon white oak and Brewer's oak are appealing characteristics [75].
Wood Products: Oregon white oak wood is strong, hard, and close grained. In the past it was used for ships, wagons, and railroad ties [106]. Characteristics of Oregon white oak as a fuelwood are provided in [55]. Today Oregon white oak is used to make furniture, flooring, veneer, boxes, crates, pallets, and caskets [102]. Oregon white oak has been used for fence posts [106]. Additional information regarding the decay resistance of Oregon white oak is available in [124]. For more on the uses, characteristics, and properties of Oregon white oak wood and factors that may affect these characteristics, see [82,104].
Seedlings: Seedlings on burned sites are reported in several fire studies [2,3,4,114]. It is unclear whether seedlings were from on-site sources or from caches made on recently burned sites. Researchers in Redwood National Park found that acorns in the canopy were unaffected by low-severity prescribed fire, but scorched or charred acorns on the ground had germination percentages nearly half that of unburned acorns [135]. There is some evidence that time since fire may affect Oregon white oak acorn production. For more information, see Seed production.
Oregon white oak sprout. © Br Alfred Brousseau,Oregon white oak seedling emergence may be related to fire severity, substrate, and/or canopy coverage. Seedlings were most common on high-severity burned sites in the Oak Patch Natural Area Preserve, suggesting that severely burned microsites are important to seedling regeneration [2,3,4]. On burned sites in Fort Lewis, Washington, Oregon white oak seedling emergence was high in soils with char and low in ash substrates; however, seedling mass was greatest in ash. Seedling densities were also affected by canopy composition [114].
More complete summaries of the studies identified in Oregon white oak sprout and/or seedling regeneration are presented below.
Oregon white oak reproduces sexually through acorn production [32,135] and asexually through root, root crown, and epicormic sprouting. Root and/or root crown sprouts are common following fire or cutting [102,134]. Epicormic sprouts occur following disturbance and canopy release [32]. Oregon white oak seedlings can sprout following shoot mortality [41,61].
Pollination: Oregon white oak flowers are wind pollinated.
Breeding system: Oregon white oak is monoecious [62]. An Oregon white oak genetics study in British Columbia revealed outcrossing rates near 100%, but levels of "correlated mating", described as siblings of a common mother sharing a common father, were significant (P≤0.05) [118].
Seed production: Acorn production by Oregon white oak is variable. Studies indicate that stand density, light availability, tree age, and time since fire may affect production. Irregular acorn production is reported by many [106,135,160]. In California, Wolf [160] observed heavy acorn production by Brewer's oak and Q. g. var. semota in some years and practically none in others. In the Bald Hills of Redwood National Park, researchers evaluated Oregon white oak acorn production for 5 years. Production was moderate to heavy 1 year. No acorns were produced in another year. Light and light to moderate crops were reported for 2 years and 1 year, respectively [135].
Possible factors affecting production: Studies suggest that Oregon white oak acorn production increases with increased sunlight, but that variable production is commonplace. On Oregon's William L. Finley National Wildlife Refuge, production was 602 kg/ha in 1976, 131 kg/ha in 1977, and 0 kg/ha in 1978. In producing years nearly 40% more acorns were produced in savannahs than in closed-canopy woodlands, but these differences were not significant (P>0.05). A search for acorns in the rest of the Willamette Valley during the nonproducing year revealed low acorn production throughout the Willamette Valley [26]. Acorn production increased following the removal of Douglas-fir canopy trees in western Washington. Neighboring Douglas-fir trees within a full radius and a half radius of the study tree's height were removed. In posttreatment years 2 and 4, when acorn crops were greatest, production was significantly greater (P<0.05) for full and half release treatments than for control trees. Increased sunlight appeared to increase acorn production, because those crown portions receiving direct sunlight had the most acorns. Epicormic branches that appeared following canopy release produced acorns 5 years after sprouting [32].
Oregon white oak acorn production varied with tree age and time since fire in western Washington and Oregon. A single season of production by 248 trees, 11 to over 300 years old, on 60 sites was evaluated. Acorn production was estimated visually using a method based on a 1 to 4 scale developed by Graves [48]. Nonproducing trees produced no acorns. Light producing trees had acorns that were visible only after very close examination. Moderate producers had readily visible acorns, but the entire tree was not covered. Heavy producers had acorns covering the entire tree and limbs that sagged with acorn weight. Nearly 50% of the trees produced no acorns; 34% produced light crops and 19% produced moderate crops. No trees produced heavy crops. Production was greatest for trees at least 60 years old, growing with little "competition" on well-watered, well-drained sites. Researchers assessed competition levels through stand basal area, individual tree shape, and crown contact. Trees less than 20 years old did not produce acorns, but production increased with age until trees were nearly 80 years old, when production leveled off. The oldest tree (>300 years) produced no acorns. On sites that burned 1 year earlier, 71% of trees were nonproducing. On sites unburned for 20 years and sites burned 2 to 4 years earlier, 48% of trees were nonproducing. Sites burned 6 to 10 years earlier had 18% non- and 41% moderate producing trees, respectively [108].
Seed predation: While seed production is variable, seed predation is ubiquitous. Fallen acorns are quickly cached, consumed, or infected by wildlife and insects. In central Oregon, insect larva were common in fallen acorns [154]. In Oregon white oak savannahs and woodlands on the William L. Finley National Wildlife Refuge, 80% of acorns were removed by 25 November in 1976, and 99% were removed by 3 November in the following year [26]. In Metchosin on Vancouver Island, acorn predation was highest in areas with moderate to high tree, extensive shrub, and low herbaceous cover. Predation was lowest in habitats with high herbaceous and low to moderate shrub and tree cover [41]. The substantial utilization of Oregon white oak acorns is also discussed in Seed banking and Importance to Livestock and Wildlife.
Seed dispersal: Oregon white oak acorns are dispersed by many agents; dispersal distance is often greatest through active transport by birds and shortest through passive movement by gravity. In central Oregon, 41 of 116 painted acorns were located in the spring. The maximum dispersal distance of these acorns, likely the result of gravity and rolling, was 21.8 feet (6.65 m) from the trunk. Most acorns were found beneath the canopy. In the same area, Douglas's squirrels, western gray squirrels, blue jays, Steller's jays, and Lewis's woodpeckers dispersed acorns. Douglas's squirrels carried acorns approximately 30 feet (8 m) before burying them. On 2 occasions blue jays transported acorns almost 1,000 feet (300 m) before consuming the acorns. Steller's jays typically carried acorns 1,000 to 1,300 feet (300-400 m) into conifer-dominated sites. Sometimes acorns were dropped, other times consumed. Lewis's woodpeckers often transported acorns 100 to 200 feet (30-50 m) into Oregon white oak- or western juniper (Juniperus occidentalis)-dominated habitats before dropping or consuming them [154].
Populations of Oregon white oak near Yale, British Columbia, are nearly 100 miles (200 km) from the main distribution of the species on Vancouver Island. After assessing all possible sources for this disjunct population, Glendenning [46] suggested that long-distance acorn dispersal by band-tailed pigeons was most likely.
Seed banking: Long term seed survival in the soil is unlikely, as Oregon white oak seed is viable for just 1 year [102]. The potential for seed predation and desiccation is high without burial [41]. On southern Vancouver Island, 53% to 100% of acorns on the soil surface were removed. Of those acorns that survived predation on the soil surface, most dried out and died. Mortality of acorns buried under litter or in soil was less than 17% in all but one habitat [41].
Numerous wildlife species cache and bury Oregon white oak acorns. Unrecovered caches are likely an important source of Oregon white oak germination. On southern Vancouver Island, researchers found that Steller's jays transported and hid acorns singly in scattered locations. Of 151 acorns, 68% were buried under moss or litter, and 24% were buried in the soil. Emergence was significantly greater (P<0.05) for buried acorns than for those left on the surface. Nearly half of Steller's jay hoards were in habitats characterized as small clumps of overlapping Oregon white oak, Pacific madrone, and Douglas-fir canopies, conifer sapling patches within Oregon white oak stands, or in riparian areas. However, when 2,700 acorns were planted in all available habitats, emergence was greatest in those habitats chosen less often by Steller's jays [43]. In central Oregon, Douglas's squirrels were observed burying Oregon white oak acorns about 0.8 inch (2 cm) deep [154]. Western gray squirrels in Fort Lewis, Washington, gathered and buried Oregon white oak acorns in August and September. Acorns were buried separately under or near the source tree [121]. Pennoyer [34] found Oregon white oak acorns 11 times in a total of 63 dusky-footed woodrat nests near Corvallis, Oregon. Nest material may offer protection from desiccation, and acorns may germinate if not recovered.
Germination: Oregon white oak seed germinates readily given warm, moist conditions, and stratification is unnecessary [16,102,105]. Germination is limited by predation, desiccation (see Seed Banking), and fire (see Fire Effects).
Germination is hypogeal and typically complete in 2 to 5 weeks. Germination of Oregon white oak acorns in loam soils maintained at 86 °F (30 °C) during the day and 70 °F (21 °C) at night was 77% to 100% [16].
Seedling establishment/growth: There is conflicting information among studies regarding the conditions most conducive to Oregon white oak seedling recruitment. Even on the same site, conditions beneficial for germination are often not conducive to seedling growth, and conditions favorable to seedling establishment are different from those benefiting sapling growth.
Sites with increased light availability had more Oregon white oak seedlings than did those with less light in west-central Willamette Valley. Seedlings, defined as multistemmed plants that lacked a single dominant stem, were dense and occupied patches of up to 1 acre (0.5 ha) in size in open sites harvested 15 to 25 years ago. Seedlings and saplings were sparsely scattered on unharvested sites. Seedlings were smaller and grew more slowly than saplings, defined as those plants with a single dominant stem. Seedling growth averaged 1.8 inches (4.6 cm)/year), and sapling growth averaged 6.2 inches (15.7 cm)/year. Seedlings had multiple stems, and this morphology persisted for up to 20 years. Researchers observed seedlings with 21-year-old taproots and 9-year-old aboveground stems, indicating that dieback and sprouting occurred multiple times before seedlings transitioned into saplings. Seedling taproots averaged 22.2 inches (56.3 cm) long, and taproot diameter averaged 0.5 inch (1.2 cm) at 0.8 inch (2 cm) depths. Taproots grew an average of 2.9 inches (7.3 cm)/year, and growth generally increased with penetration depth. Over 3.5 years, 3 of 23 marked seedlings died from taproot severing by pocket gophers. Seedling and saplings were rarely browsed [61].
In Metchosin, seedling mortality was not associated with overstory vegetation, but acorn survival was positively associated with dense herbaceous cover and low shrub and tree cover (see Seed predation). Habitats favoring acorn survival and germination were poor habitats for seedling survival. Shade did not encourage or reduce seedling growth, and browsed seedlings sprouted. The majority of seedling mortality was the result of desiccation and was concentrated on south-facing slopes. However, researchers noted that many seedlings survived dry conditions [41]. Rapid taproot development likely helps Oregon white oak seedlings tolerate xeric conditions [61,102]. In central Oregon, a study of age structure and climate data indicated that Oregon white oak regeneration was favored during dry periods in mixed Douglas-fir-ponderosa pine-Oregon white oak forests [154].
A study in Fort Lewis, Washington, suggested that shade was beneficial to Oregon white oak seedling growth. Seedlings from acorns collected in Fort Lewis, Washington, and grown in greenhouse conditions were later moved to either full sun or shade (50% full sun) conditions in an outdoor nursery. At 1 year old, seedlings were transplanted on a Fort Lewis prairie site dominated by Idaho fescue (Festuca idahoensis) and colonial bentgrass (Agrostis capillaris). Most seedlings transplanted in September died, but most planted in early November, mid-January, and early March survived. Seedlings grown in outdoor nursery shade were damaged in full sun conditions in the prairie. At the end of the first field growing season, shoot mortality was 11% in the shade and 85% in the sun, regardless of the nursery growing conditions. Shoot mortality was considered a result of moisture stress, and yellowing and browning appeared first in the full sun area. Shoot mortality is not equivalent to seedling mortality, and a number of seedlings with dead shoots had live roots and root crown buds [105].
When sites with low and high historical grazing intensities in northern California's Coast Ranges were compared, researchers found that Oregon white oak seedling density was greater (33.5 seedlings/100 m²) on high- than on low-intensity (19.1 seedlings/100 m²) grazed sites. However, sapling density was slightly (9.3 saplings/100 m²) higher on high-intensity than on low-intensity (10.8 seedlings/100 m²) grazed sites. Researchers suggested that herbivore removal of surrounding vegetation may encourage Oregon white oak seedling development, but grazers may negatively affect Oregon white oak sapling growth [67].
Vegetative regeneration: Oregon white oak produces epicormic, root, and root crown sprouts [41,61,102,134]. Root crown sprouts are common following aboveground stem mortality [102]. Oregon white oak seedlings sprout following shoot mortality that may or may not be the result of a disturbance [41,61]. Epicormic sprouts occur following disturbance and canopy release [32]. The abundance and "vigor" of sprouts typically increases with increased parent plant size [102].
Oregon white oak is considered a pioneer and a disturbance "climax" species. It is often the first invader on prairies, but without periodic disturbance it is replaced by conifers. However, site conditions can affect the persistence and successional status of Oregon white oak. On very dry sites, Oregon white oak may dominate without disturbance [102,128]. On the Wenatchee National Forest, Oregon white oak occurs in dry areas with gravelly, stony soils. Here is it both a pioneer and a climax species, since coniferous species, primarily Douglas-fir and ponderosa pine, do not regenerate well. Stands with Douglas-fir and ponderosa pine emerging above the Oregon white oak canopy occur only on the most "favorable" sites [85].
Shade tolerance: Mature Oregon white oaks are not considered shade tolerant. However, developmental stage affects shade tolerance, and presumably shade tolerance decreases with age. In a study of Oregon white oak seedlings in Metchosin, researchers found that seedling mortality was not affected by overstory vegetation and that shade intolerance developed sometime after the seedling stage [41]. A study conducted in Fort Lewis, Washington, suggested shade was beneficial to Oregon white oak seedling growth [105].
While growth of Oregon white oak seedlings may be unaffected or favored by shade, tree growth in shade is often restricted. Following the removal of Douglas-fir canopy trees in western Washington, Oregon white oak in the "suppressed" midstory responded rapidly with increased growth, epicormic branching, and acorn production. Treatments involved the removal of Douglas-fir within a full radius and a half radius of the study tree's height. Oregon white oak DBH growth was significantly greater on 3-year-old (P=0.003) and 5-year-old (P<0.001) treated sites. Epicormic branching in the first and second posttreatment years averaged 9.3 new branches in full-radius plots, 7.1 in half-radius plots, and 1.2 in control plots [32].
Succession to coniferous forest: Conditions fostering the transition from Oregon white oak woodlands to coniferous forests are well described in a study in California's Sonoma Mountains. In Annadel State Park, researchers analyzed mixed Oregon white oak-Douglas-fir stands. Oregon white oak trees were consistently older than Douglas-fir trees, indicating recent conifer invasion. Although Douglas-fir regeneration had occurred since 1910, researchers noted 2 establishment "surges". The first, in the early 1940s, corresponded to improved fire detection and suppression through technological advancements and the utilization of prison inmates as firefighters. A second Douglas-fir establishment flush occurred in the early 1970s, when the Park was established, livestock were removed, and a Douglas-fir seed source was available due to the 1940s establishment. Prior to the practice of excluding fire in the early 1900s, Annadel State Park experienced widespread frequent fires. Researchers indicated that Douglas-fir establishment coincided with increased Oregon white oak density and canopy closure, which coincided with fire regime changes in the Park [13].
The scientific name of Oregon white oak is Quercus garryana Dougl. (Fagaceae) [40,62,64,70]. As
the common name suggests, Oregon white oak belongs to
the white oak subgenus (Lepidobalanus) [143].
Infrataxa:
Quercus garryana var. breweri (Engelm.) Jepson [70], Brewer's oak
Quercus garryana var. garryana
Quercus garryana var. semota (Jepson) [47,70], Oregon white oak
Hybrids:
Quercus ÃÂ eplingii C. H. Muller [47,62,101,106,144], Epling's oak
(Oregon white oak ÃÂ blue oak (Q. douglasii))
Quercus ÃÂ howelii Tucker [101,143,144], Howell's oak
(Oregon white oak ÃÂ Nuttall's scrub oak (Q. dumosa))
Quercus ÃÂ subconvexa Tucker [40,62,101,143,144]
(Oregon white oak ÃÂ leather oak (Q. durata))
Brewer's oak hybridizes with deer oak (Q. sadleriana) [62,144].
Quercus garryana var. garryana hybridizes with scrub oak (Q. berberidifolia) [62]
and valley oak (Q. lobata) [62,144]. There may be introgression of Q. garryana var. semota and valley oak
in isolated locations of distribution overlap [40].
According to Govaerts and Frodin [47], Q. ÃÂ subconvexa and Howell's oak describe the same
hybrid―Oregon white oak ÃÂ Nuttall's scrub oak.
Quercus garryana is an oak tree species of the Pacific Northwest, with a range stretching from southern California to southwestern British Columbia.[3] It is commonly known as the Oregon white oak or Oregon oak or, in Canada, the Garry oak. It grows from sea level to an altitude of 690 feet (210 metres) in the northern part of its range, and from 980 to 5,900 ft (300 to 1,800 m) in the south of the range in California.[4] The eponymous Nicholas Garry was deputy governor of the Hudson's Bay Company.
Quercus garryana is typically of medium height, growing slowly to around 80 feet (24 metres) and occasionally as high as 100 ft (30 m), or in shrub form to 10 to 15 ft (3.0 to 4.6 m) tall. The trunks grow to 3 feet (0.91 m) thick, exceptionally 5 ft (2 m). The bark is gray and fissured.[5] It has the characteristic oval profile of other oaks when solitary, but is also known to grow in groves close enough together that crowns may form a canopy. The leaves are deciduous, 2–6 inches (5.1–15 cm) long and 1–3 inches broad, with 3–7 deep lobes on each side, darker green on top and finely haired below.[5] The flowers are catkins, the fruit a small acorn[a] 3⁄4–1 inch (rarely 1 1⁄2 inches) long and 1⁄2–3⁄4 inch broad, with shallow, scaly cups. Its fall color is unspectacular, with many trees turning plain brown. Other individuals may have subtle mixtures of brown, green and yellow, or in less common cases a fairly bright 'peas and corn' effect.
The Oregon white oak is commonly found in the Willamette Valley hosting the mistletoe Phoradendron flavescens.[5] It is also commonly found hosting galls created by wasps in the family Cynipidae. 'Oak apples', green or yellow ball of up to 5 cm in size, are the most spectacular.[7] They are attached to the undersides of leaves. One common species responsible for these galls is Cynips maculipennis. Other species create galls on stems and leaves. Shapes vary from spheres to mushroom-shaped to pencil-shaped.
Individual specimens can grow to around 500 years in age, such as those on Sauvie Island near Portland, Oregon.[5]
David Douglas discovered the species in the 1820s and named it after Nicholas Garry, who was deputy governor of the Hudson's Bay Company from 1822 to 1835 and a supporter of Douglas.[5]
There are three varieties:
In Oregon, the tree grows on the west side of the Cascade Range, primarily in the Willamette, Umpqua and Rogue River valleys, and along the Columbia River Gorge, as well as in canyons adjacent to the gorge.[9][10]
In California, the garryana variety grows in the foothills of the Siskiyou and Klamath Mountains, the Coast Ranges of Northern California, and of the west slope of the Cascades. The semota variety grows in the Sierra Nevada and Coast Ranges as far south as Los Angeles County.[8]
In Washington, the tree grows on the west side of the Cascade Range, particularly in the Puget Sound lowlands, the northeastern Olympic Peninsula, Whidbey Island, the Chehalis river valley, and the San Juan Islands. It also grows in the foothills of the southeastern Cascades and along the Columbia River Gorge.[9][10]
In British Columbia, the Garry oak grows on the Gulf Islands and southeastern Vancouver Island, from west of Victoria along the east side of the island up to the Campbell River area. There are also small populations along the Fraser River on the British Columbia mainland.[4] The northernmost population of Garry oak can be found just below 50°N on Savary Island, in the northern stretches of the Strait of Georgia.[11] The Garry oak is the only oak native to British Columbia, and one of only two oaks (along with the bur oak) native to western Canada.[12]
It is a drought-tolerant tree. Older specimens are often affected by heart rot.[5]
The acorns are consumed by wildlife and livestock.[6] David Douglas recorded that bears consumed them.[13]
In British Columbia, the Garry oak can be infested by three nonnative insects: the jumping gall wasp Neuroterus saltatorius, the oak leaf phylloxeran, and the gypsy moth.[4]
While the invasive plant disease commonly called sudden oak death attacks other Pacific Coast native oaks, it has not yet been found on the Oregon white oak. Most oak hosts of this disease are in the red oak group, while Oregon white oak is in the white oak group.[14]
Oregon white oak is the only native oak species in British Columbia, Washington, and northern Oregon. In these areas, oak woodlands are seral, or early-successional; they depend on disturbance to avoid being overtaken by Douglas-fir (Pseudotsuga menziesii). The disturbance allowing oak to persist in an area that would otherwise succeed to coniferous forest was primarily fire. Natural wildfires are relatively common in the drier portions of the Pacific Northwest where Oregon white oak is found, but fire suppression has made such events much less common. In addition, early settlers' records, soil surveys, and tribal histories indicate that deliberate burning was widely practiced by the indigenous people of these areas. Fire perpetuated the grasslands that produced food sources such as camas, chocolate lily, bracken fern, and oak; and that provided grazing and easy hunting for deer and elk. Mature Oregon white oaks are fire-resistant, and so would not be severely harmed by grass fires of low intensity. Such fires prevented Douglas-fir and most other conifer seedlings from becoming established, allowing bunch grass prairie and oak woodland to persist. Fire also kept oak woodlands on drier soils free of a shrub understory. Wetter oak woodlands historically had a substantial shrub understory, primarily snowberry.[15]
Oregon white oak woodlands in British Columbia and Washington are critical habitats for a number of species that are rare or extirpated in these areas, plant, animal, and bryophyte:[15][16][17]
Quercus garryana woodlands create a landscape mosaic of grassland, savanna, woodland, and closed-canopy forest. This mosaic of varied habitats, in turn, allows many more species to live in this area than would be possible in coniferous forest alone. Parks Canada states that Garry oak woodlands support more species of plants than any other terrestrial ecosystem in British Columbia.[18] It grows in a variety of soil types, for instance, rocky outcrops, glacial gravelly outwash, deep grassland soils, and seasonally flooded riparian areas.[15][16]
The Donation Land Claim Act of 1850 encouraged settlement of Washington and Oregon by the United States and marked the beginning of the end of regular burning by native peoples of the area.[15]: Perdue The arrival of Europeans also reduced the number of natural fires that took place in Oregon white oak habitat. With fire suppression and conversion to agriculture, oak woodlands and bunch grass prairies were invaded by Douglas-fir, Oregon ash (Fraxinus latifolia), and imported pasture grasses. Oaks were logged to clear land for pasture, and for firewood and fence posts. Livestock grazing trampled and consumed oak seedlings. By the 1990s, more than half the Oregon white oak woodland habitat in the South Puget Sound area of Washington was gone.[15] On Vancouver Island, more than 90% was gone,[16] and on Whidbey Island up to 99% of native understory Oregon white oak habitat is gone.[19] Remaining Oregon white oak woodlands are threatened by urbanization, conversion to Douglas-fir woodland, and invasion by shrubs, both native and nonnative (Scotch broom Cytisus scoparius, sweetbriar rose Rosa eglanteria, snowberry Symphoricarpos albus, Indian plum Oemleria cerasiformis, poison-oak Toxicodendron diversilobum, English holly Ilex aquifolium, bird cherry Prunus avens).[10] Conversely, oak groves in wetter areas that historically had closed canopies of large trees are becoming crowded with young oaks that grow thin and spindly, due to lack of fires that would clear out seedlings.[15]
Chionodes petalumensis caterpillars feed on oak leaves, including those of Quercus garryana[20] and valley oak (Q. lobata).[21]
Oregon white oaks and their ecosystems are the focus of conservation efforts, including communities such as Tacoma, Washington, where an Oak Tree Park has been established; Oak Bay, British Columbia, which is named after the tree; and Corvallis, Oregon, which has protected the oak savannah remnants around Bald Hill.[22] Oak Harbor, Washington, named after the tree[23] and home to Smith Park that contains a dense grove of mature Garry Oak trees, is actively pursuing conservation of the city's namesake tree with the formation of the Oak Harbor Garry Oak Society.[24][25][26]
In Southwest Washington, significant acreages of Oregon white oaks are preserved in the Scatter Creek Wildlife Area, in sites such as the Scatter Creek Unit, which contain some of the few remaining areas of south Puget Sound prairie.[27]
In Oak Bay, British Columbia, a fine of up to $10,000 may be issued for each Garry oak tree cut or damaged.[28]
The mildly sweet (but perhaps unpalatable) acorns are edible, ideally after leaching.[6][29] The bitterness of the toxic tannic acid would likely prevent anyone from eating enough to become ill.[29] Native Americans ate the acorns raw and roasted, also using them to make a kind of flour.[5]
The hardwood is hard and heavily ring-porous. It has distinctive growth rings and prominent rays. Heartwood can be a deep chocolate brown color and sapwood will vary from golden brown to nearly white. This makes it particularly attractive to woodworkers, however it can be difficult to use in woodworking without experiencing warping and cracking.[30] Although it was popularly used around the turn of the 20th century,[5] historically, the tree has not been regarded as having significant commercial value and is frequently destroyed as land is cleared for development. The wood is suitable for making fence posts. With similar qualities to those of other white oaks, the wood has been used experimentally in Oregon for creating casks in which to age wine. In Washington, it has been used for aging single malt whiskey since the 2010s.[31][32] Oregon white oak barrels are said to give the product "burnt sugar notes, marshmallow sweetness, and a light floral character that showcases the best of the Garry oak".[33] When used as firewood, Oregon white oak produces 28 million British thermal units per cord (2.3 MWh/m3) burned.[34]
Footnotes
Citations
Quercus garryana is an oak tree species of the Pacific Northwest, with a range stretching from southern California to southwestern British Columbia. It is commonly known as the Oregon white oak or Oregon oak or, in Canada, the Garry oak. It grows from sea level to an altitude of 690 feet (210 metres) in the northern part of its range, and from 980 to 5,900 ft (300 to 1,800 m) in the south of the range in California. The eponymous Nicholas Garry was deputy governor of the Hudson's Bay Company.
