Quercus garryana



INTRODUCTORY


 

N. Dechaine, Mt Tolmic Fire-August 2005

AUTHORSHIP AND CITATION:
Gucker, Corey L. 2007. Quercus garryana. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

FEIS ABBREVIATION:
QUEGAR
QUEGARB
QUEGARG
QUEGARS

NRCS PLANT CODE [150]:
QUGA4
QUGAB
QUGAG2
QUGAS

COMMON NAMES:
Oregon white oak
Garry oak
Oregon oak

TAXONOMY:
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 eplingii C. H. Muller [47,62,101,106,144], Epling's oak (Oregon white oak blue oak (Q. douglasii))
Quercus howelii Tucker [101,143,144], Howell's oak (Oregon white oak Nuttall's scrub oak (Q. dumosa))
Quercus subconvexa Tucker [40,62,101,143,144] (Oregon white oak 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. subconvexa and Howell's oak describe the same hybridOregon white oak Nuttall's scrub oak.

SYNONYMS:
Quercus garryana var. fruticosa (Engelm.) Govaerts [47]
    =Q. g. var. breweri [70]

LIFE FORM:
Tree-shrub

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
Information on state-level protected status of plants in the United States is available at Plants Database.

DISTRIBUTION AND OCCURRENCE

SPECIES: Quercus garryana
GENERAL DISTRIBUTION:
Oregon 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].

ECOSYSTEMS [44]:
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES27 Redwood
FRES28 Western hardwoods
FRES34 Chaparral-mountain shrub
FRES35 Pinyon-juniper
FRES36 Mountain grasslands

STATES/PROVINCES: (key to state/province abbreviations)
UNITED STATES

CA OR WA

CANADA
BC

BLM PHYSIOGRAPHIC REGIONS [15]:
1 Northern Pacific Border
2 Cascade Mountains
3 Southern Pacific Border
4 Sierra Mountains
5 Columbia Plateau

KUCHLER [77] PLANT ASSOCIATIONS:
K002 Cedar-hemlock-Douglas-fir forest
K005 Mixed conifer forest
K006 Redwood forest
K007 Red fir forest
K009 Pine-cypress forest
K010 Ponderosa shrub forest
K011 Western ponderosa forest
K012 Douglas-fir forest
K014 Grand fir-Douglas-fir forest
K024 Juniper steppe woodland
K025 Alder-ash forest
K026 Oregon oakwoods
K028 Mosaic of K002 and K026
K029 California mixed evergreen forest
K030 California oakwoods
K033 Chaparral
K034 Montane chaparral
K050 Fescue-wheatgrass
K051 Wheatgrass-bluegrass

SAF COVER TYPES [37]:
207 Red fir
210 Interior Douglas-fir
211 White fir
213 Grand fir
220 Rocky Mountain juniper
221 Red alder
229 Pacific Douglas-fir
230 Douglas-fir-western hemlock
231 Port-Orford-cedar
232 Redwood
233 Oregon white oak
234 Douglas-fir-tanoak-Pacific madrone
238 Western juniper
243 Sierra Nevada mixed conifer
244 Pacific ponderosa pine-Douglas-fir
245 Pacific ponderosa pine
246 California black oak
248 Knobcone pine
249 Canyon live oak
250 Blue oak-foothills pine
255 California coast live oak

SRM (RANGELAND) COVER TYPES [126]:
101 Bluebunch wheatgrass
109 Ponderosa pine shrubland
110 Ponderosa pine-grassland
201 Blue oak woodland
202 Coast live oak woodland
203 Riparian woodland
207 Scrub oak mixed chaparral
208 Ceanothus mixed chaparral
209 Montane shrubland
412 Juniper-pinyon woodland
416 True mountain-mahogany
421 Chokecherry-serviceberry-rose
422 Riparian

HABITAT TYPES AND PLANT COMMUNITIES:
Oregon white oak is a dominant species in the following vegetation types and plant communities:

California: Oregon: Oregon and Washington:

Washington: British Columbia: Epling's oak is a dominant species in the following vegetation types of California:

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Quercus garryana

GENERAL BOTANICAL CHARACTERISTICS:
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. subconvexa are described in [101].
Brewer's oak. Michael Charters www.calflora.net

RAUNKIAER [112] LIFE FORM:
Geophyte
Phanerophyte

REGENERATION PROCESSES:
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 m) on high- than on low-intensity (19.1 seedlings/100 m) grazed sites. However, sapling density was slightly (9.3 saplings/100 m) higher on high-intensity than on low-intensity (10.8 seedlings/100 m) 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].

SITE CHARACTERISTICS:
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].

SUCCESSIONAL STATUS:
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].

SEASONAL DEVELOPMENT:
Oregon white oak flowers are produced with leaves in the spring (April-June) [63,101,110]. In the southern and northern part of Oregon white oak's range, flowers may appear as early as March and as late as June, respectively. Acorns require a single growing season to mature and ripen from August to November [102]. Flowering in Oregon white oak varieties is similar; most flower in the spring. However, Brewer's oak flowering may be slightly delayed compared to Q. g. var. garryana and Q. g. var. semota [40].

FIRE ECOLOGY

SPECIES: Quercus garryana
FIRE ECOLOGY OR ADAPTATIONS:
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. For further information, see the FEIS review of the dominant species listed below.

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 <10 [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 review

POSTFIRE REGENERATION STRATEGY [129]:
Tree with adventitious bud/root crown/soboliferous species root sucker
Geophyte, growing points deep in soil
Initial off-site colonizer (off-site, initial community)
Secondary colonizer (on-site or off-site seed sources)

FIRE EFFECTS

SPECIES: Quercus garryana
IMMEDIATE FIRE EFFECT ON PLANT:
Oregon white oak mortality is rare following fire. The bark on mature trees is sufficient to withstand cambial kill from fire in open woodlands [2]. There are 2 reports of saplings over 10 feet (3 m) tall resisting top-kill in low-severity fires [135,148]. However, Thysell and Carey [141] observed fire-killed mature Oregon white oaks, although rarely, after a severe fire fueled by a dense understory of Oregon white oak, Douglas-fir, and Scotch broom in Fort Lewis, Washington.

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
No additional information is available on this topic.

PLANT RESPONSE TO FIRE:
Sprouts: When top-killed, Oregon white oak sprouts from the roots or root crown [2,3,4,120,134]. Abundance or "intensity" of sprouting may be affected by tree age, tree diameter, crown scorch, and/or fire severity. Following a fire in Redwood National Park, Sugihara and Reed [134] reported sprouts produced 7 to 10 feet (2-3 m) away from the parent stem. They noted that sprouting was more "intense" from 40-year-old than 70-year-old trees. After cutting and burning in California's Humboldt and Trinity counties, sprout clump diameter, number of sprouts/clump, and sprout height increased with increased parent tree diameter [120]. Following prescribed fires in Fort Lewis, Washington, the crown scorch of sprouting Oregon white oak was significantly (P<0.001) greater than that of nonsprouting Oregon white oak [114]. Two years after a prescribed fire in Washington's Oak Patch Natural Area Preserve, Oregon white oak sprouts were concentrated on sites that burned at low severity [2,3,4].

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,
Saint Mary's College.

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.

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Generally, Oregon white oak is not killed by fire, and often sprouts and seedlings occur on burned sites. However, for a fire-adapted species seen as a candidate for recovery through fire use, there are relatively few fire effects studies. The Comprehensive fire effects study described in this section provides the most in-depth analysis of Oregon white oak regeneration following fire available to date (2007). The study provides information on acorn survival and emergence, sprout production, and stand structure in communities with a nonnative species component. Nonnative species are common in Oregon white oak habitats, and understanding fire effects in communities with nonnative species is important to the future management of this species. See Nonnative species for more information.

Prescribed fires in oak woodlands in the Bald Hills of Redwood National Park top-killed Oregon white oak trees that were less than 10 feet (3 m) tall. Fires were low-severity backing and head fires that spread at 0.6 to 0.9 m/minute, had an average flame height of 1 foot (0.3 m) and a maximum height of 3.9 feet (1.2 m). At the time of burning, relative humidity averaged 55%, air temperature averaged 66 F (19 C), and winds ranged from 0 to 3.2 km/hour. Of the 20 closely-monitored Oregon white oak trees, all less than 10 feet (3 m) tall were top-killed and sprouting "vigorously from the base" 10 months following the fire. Trees 10 feet (3 m) or taller showed little damage or sprouting. Researchers noted some scarring by this fire. Acorns collected from the ground and from the canopy on unburned sites had germination percentages of 99.2% and 100%, respectively. On burned sites, 52.6% of acorns collected from the ground germinated, and 100% of the acorns from the canopy germinated [135].

Nearly all burned Brewer's oak shrubs sprouted in burned chaparral vegetation in the lower Kern River Watershed of the Sequoia National Forest. The fire burned in July in "ancient" stands that had not burned for at least 90 years prior to this fire and in "mature" stands that had not burned for 50 or 60 years before the July fire. In ancient and mature stands, 94.2% and 99% of Brewer's oak sprouted in the first postfire year [72].

Sprout production measured as clump diameter, number of sprouts/clump, and height of sprouts increased with increased diameter of the parent tree on 2- and 3-year-old burned or clearcut sites in California's Humboldt and Trinity counties. Burned and logged sites were analyzed together, so differences between fire and logging on spout production are not discernable. Both sprout height and sprout clump diameter increased with increased time since treatment, while the number of sprouts/clump decreased with increasing time since treatment. Study findings are summarized in the table below [120]:

Oregon white oak sprout dimensions on cut or burned sites in the 2nd and 3rd posttreatment years

Time since treatment (years) Sample size Height of tallest sprout in a clump (feet) Crown diameter of sprouting clump (feet) Number of sprouts/clump
mean range mean range mean range
2 50 6.6 4.4-11.2 6.8 2.9-12.3 18 1-57
3 49 9.2 6.1-12.8 8.2 3.5-12.3 10 1-25

Sugihara and Reed [134], through studies of regeneration following prescribed fires in Redwood National Park, observed and summarized several regeneration phenomena. They found that sprouting is "more intense" from 40-year-old than 70-year-old Oregon white oak trees. Sprouts grow rapidly and may reach 3 feet (1 m) in a single year. Seedlings, however, may take 10 years or more to reach 3 feet (1 m) tall. Sprouts may occur 7 to 10 feet (2-3 m) from the base of the parent tree, producing increased Oregon white oak coverage on burned sites. Researchers also found that fires can stimulate basal sprouting without top-killing stems [134].

On 2-year-old prescribed-burned sites in the Oak Patch Natural Area Preserve, Oregon white oak seedlings were more common on high-severity burned sites, and sprouts were concentrated on low-severity burned sites. Seedlings occurred on areas where logs had burned and soil carbon and nitrogen concentrations were low. Seedlings were associated with species characteristic of very disturbed areas, such as stinking willie (Senecio jacobaea), common velvetgrass (Holcus lanatus), and fireweed (Chamerion angustifolium). Oregon white oak sprouts were associated with native species such as baldhip rose (Rosa gymnocarpa), Saskatoon serviceberry, salal (Gaultheria shallon), and cascara (Rhamnus purshiana). Findings suggest that seedling regeneration may depend on severely burned microsites. However, these conditions often produce habitats for nonnative species, too [2,3,4]. For additional information on the effects of fire on nonnative species in Oregon white oak communities, see Nonnative species.

There was no damage to mature trees following spring or fall fires in Fort Lewis, Washington. Fire effects were evaluated in the first postfire year on sites that burned every 3 to 5 years. Temperatures ranged from 50 to 70 F (10-20 C), relative humidity levels were 20% to 50%, and wind speeds were less than 5 km/hour at the time of burning. Nearly all top-killed Oregon white oak sprouted. Only 3 clumps of 5 to 10 stems that were less than 3 feet (1 m) tall and 2 trees with a DBH of 2 to 4 inches (5-10 cm) were killed. Mature trees were undamaged, and top-kill was concentrated in stems that were less than 3 feet (1 m) tall and 0.8 inch (2 cm) in diameter [148,149].

Comprehensive fire effects study: Numerous aspects of Oregon white oak regeneration were evaluated on early (February-April), late (August-October), and twice- (2 early or late-season fires within 6 years) burned woodland and conifer fringe stands in Fort Lewis, Washington. There were 4 early, 4 late-, and 3 twice-burned sites, and time since fire ranged from 1 to 6 years. The basal area in unburned areas averaged 18.1 m/ha.

Stand structure: Relative percent reductions in stem basal area from prescribed fire were similar for Oregon white oak, Douglas-fir, and ponderosa pine. However, small and medium size classes of Oregon white oak and medium to large size classes of Douglas-fir and ponderosa pine contributed most to basal area reductions. Small, medium, and large size classes were defined as 0.04 to 4 inch (0.1-10 cm), 4 to 20 inch (10.1-50 cm), and >20 inch (50 cm) DBH, respectively. Twice-burned had the greatest reductions in Oregon white oak basal area and density. Single-fire sites accounted for the majority of Douglas-fir and ponderosa pine densities and basal area. Results suggest that frequent fires (at least 3 in 10 years) create oak savannahs, and less than 2 fires/decade produce dense Oregon white-oak and/or mixed sapling thickets. Study findings are summarized in the table below [113,114].

Oregon white oak mortality and density on early, late-, and twice-burned sites

Early Late Twice
Density reductions
(m/ha)
0.7 0.6 2.1
Mortality
(stems/ha)
94 91 523

Regeneration: Sprouts outnumbered seedlings 4:1 on burned sites. Thirty-nine percent of 874 burned Oregon white oak that were breast height or taller sprouted. Sprout production increased with decreased basal area and increased crown scorch produced by the fire. Sprouting was related to tree size, too. The average DBH of sprouting Oregon white oak was about 4 inches (9 cm) less than nonsprouting Oregon white oak (P<0.001). Heights of sprouting trees were approximately 11 feet (3.5 m) less than that of nonsprouting Oregon white oak (P<0.001), and the crown scorch of sprouting Oregon white oak was nearly double that of nonsprouting Oregon white oak (P<0.001). Overall, large trees with minimal scorch, growing in areas with little to no change in stand basal area, produced few sprouts [113,114].

There were Oregon white oak seedlings on 7 of the 11 burned sites. Just 3% of Oregon white oak seedlings were found in open conditions (beyond tree canopies). Seedling density was lowest under Oregon white oak canopies and highest beneath Douglas-fir (P=0.057). Most Oregon white oak seedling regeneration (>75%) occurred under the canopy of Douglas-fir trees with a DBH of 20 inches (50 cm) or more [113,114]. The importance of Douglas-fir in Oregon white oak seedling emergence may affect management decisions in mixed conifer-Oregon white oak forests.

Acorn survival and emergence: In Fort Lewis, Washington, researchers conducted experiments on the survival, germination, and establishment of Oregon white oak acorns in the field and in the greenhouse. In 1999 no acorns were left on the soil surface after 75 days. In 2000, seeds were buried and predation decreased. Of those surviving acorns, emergence was significantly greater (P=0.022) in soils with char than in ash or unburned areas. However, Oregon white oak seedling mass was greatest when grown in ash. In greenhouse studies, acorn survival and growth were compared in soils treated with ash and heat before planting. Survival, cover, and height of seedlings from acorns planted in ash were significantly lower than in soils without ash. Heat did not affect Oregon white oak seedling survival, cover, or height. Study results are summarized in the table below. In an additional greenhouse study, researchers found that Scotch broom stem density was significantly greater on heat-treated soils, a finding that complicates fire management in Oregon white oak habitats. For additional information regarding management challenges in Oregon white oak habitats with nonnative species, see Fire Management Considerations [113,114].

Survival, cover, and height of Oregon white oak seedlings grown in heat and ash treated soils
Treatment Survival (%) Cover (%) Height (cm)
Ash
(surficial 2 cm dry ash from Oregon white oak logs)
20a 4.2a 1.2a
No ash 36.5b 7.1b 2.4b
Heat
(60 C for 10 minute, prior to planting)
28 6.4 1.6
No heat 28.5 4.9 2
Averages with different letters within survival, cover, and height columns are significantly different (P<0.001, P<0.007, and P<0.001, respectively).

FIRE MANAGEMENT CONSIDERATIONS:
The 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 broom
 

stem density

Ash
(surficial 2 cm dry ash from Oregon white oak logs)
8.5a 4.0a
No ash 49.5b 10.5b
Heat
(60 C for 10 minute, prior to planting)
33.5a 11.0a
No heat 49.5b 3.5b
Averages for ash and heat treatments within the all competitor column are significantly different (P<0.001 and P<0.006), respectively. Ash and heat treatments for Scotch broom are also significantly different (P<0.01 and P<0.001), respectively.

Fuels: 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].

MANAGEMENT CONSIDERATIONS

SPECIES: Quercus garryana
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
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 m/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.

VALUE FOR REHABILITATION OF DISTURBED SITES:
No information is available on this topic.

OTHER USES:
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].

OTHER MANAGEMENT CONSIDERATIONS:
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].

There are regression equations useful for predicting Oregon white oak height in Oregon. Larsen and Hann [79] provide equations for predicting Oregon white oak height in southwestern Oregon using DBH, basal area, or site indices as the independent variables. Equations to predict height using DBH of Oregon white oak trees in west-central Willamette Valley are given in [155].

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