Lithocarpus densiflorus



INTRODUCTORY



           
 

                  Dwarf tanoak (left) and the typical variety of tanoak (right). Photos by Br. Alfred Brousseau, St Mary's College.

AUTHORSHIP AND CITATION:
Fryer, Janet L. 2008. Lithocarpus densiflorus. 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:
LITDEN

NRCS PLANT CODE [236]:
LIDE3
LIDED2
LIDEE

COMMON NAMES:
tanoak
tanbark oak
dwarf tanoak

TAXONOMY:
The scientific name of tanoak is Lithocarpus densiflorus (Hook. & Arn.) Reh. (Fagaceae). Varieties are [54,71,95,113]:

Lithocarpus densiflorus var. densiflorus, typical variety of tanoak
Lithocarpus densiflorus var. echinoides (R. Br.) Abrams, dwarf tanoak

It is unclear if the 2 varieties differ genetically or if the small stature of dwarf tanoak is due to unproductive site conditions (see Site Characteristics). Ecology literature does not usually distinguish between the 2 infrataxa. This review notes where the varieties are differentiated in the literature by referring to them as either the "typical variety" or "dwarf tanoak." "Tanoak" refers to the species.

The Lithocarpus genus is transitional between chestnuts (Castanea spp.) and true oaks (Quercus spp.), with flowers like chestnuts and fruits similar to those of true oaks. There are hundreds of Lithocarpus species in Asia, but tanoak is the only North American member of the genus [6,71,154,191,232,233].

SYNONYMS:
Notholithocarpus densiflorus (Hook. & Arn.) Manos, C.H. Cannon & S. Oh [229]
Pasania densiflora (Hook. & Arn.) Oerst [44]
Quercus densiflora Hook. & Arn. [38,103]

LIFE FORM:
Tree-shrub

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
Information on state-level protection status of plants in the United States is available at NatureServe.

DISTRIBUTION AND OCCURRENCE

SPECIES: Lithocarpus densiflorus
GENERAL DISTRIBUTION:
Tanoak is native and endemic to southern Oregon and California. Along the Pacific Coast it ranges from Reedsport, Oregon, near the Umpqua River south almost to Santa Barbara, California. It is most common just above the redwood (Sequoia sempervirens) zone in coastal locations. Inland, tanoak ranges east to the Siskiyou and Klamath mountains, then has scattered occurrences from the lower slopes of Mt Shasta in California south through the Cascade Range and Sierra Nevada to Mariposa County [20,54,137,154,224,229]. On inland sites, tanoak is most common in Yuba and Butte counties, California [154]. The US Geological Survey provides a distributional map of tanoak.

Varieties: The typical variety of tanoak is distributed from Douglas County, Oregon, south along the Pacific Coast to Santa Barbara County, California, and east through the Siskiyou and Klamath mountains to Yuba County, California [54,229]. Large tanoaks are occasionally reported in the Sierra Nevada [118,127], which lies outside the distributional range usually described for the typical variety [54]. Dwarf tanoak has a scattered distribution from Coos County, southwestern Oregon, south through the Cascade Range and Sierra Nevada to Mariposa County, California, and east to the Siskiyou and Klamath mountains [54,189]. Flora of North America provides a distributional map of tanoak's varieties.

HABITAT TYPES AND PLANT COMMUNITIES:
Tanoak is a major species in and above mixed-evergreen and redwood forests along the Pacific Coast [16,20,54,57,170,190,201,235,251,251]. Its distribution may extend upward as far as the red fir (Abies magnifica) zone [95]. Mixed-evergreen forests where tanoak is dominant usually have a coast Douglas-fir (Pseudotsuga menziesii var. menziesii) overstory, while tanoak dominates the subcanopy or shrub layer [28,34,37,85,99,138]. Less frequently, tanoak is the overstory dominant in a hardwood phase of the mixed-evergreen type. A large component (10-60% canopy or subcanopy cover) of tanoak, Pacific madrone (Arbutus menziesii), and/or canyon live oak (Quercus chrysolepis) is required to meet most definitions of mixed-evergreen old growth [27,60,203,203,252]. Where tanoak dominated the subcanopy or shrub layer before stand-replacing disturbances such as fire, it usually assumes overstory dominance afterward [34], so tanoak is also important in seral forests (see Successional Status for further details). Pacific madrone is the most common hardwood associated with tanoak. For lists of tree, shrub, and herbaceous species associated with tanoak, see these sources: [151,189,224].

Tanoak mixed-evergreen forest is a major hardwood type along the southern Oregon coast and in the Siskiyou and Klamath mountains. Tanoak forests are usually a seral type maintained by frequent fire or logging, although tanoak communities also occur on sites that cannot support Douglas-fir and/or other conifers [57]. Tanoak forms its own series (>50% cover) in the Siskiyou Mountains. The tanoak series is dominated in seral stages by Douglas-fir; but tanoak is the climax dominant, so Douglas-fir is omitted from the series name [18,20]. A vegetation survey of the tanoak Siskiyou Mountains series showed tanoak dominated the canopy on only 5% of plots. Tanoak sprouts resulting from past fires dominated the subcanopy, and Douglas-fir dominated the overstory. The shrub layer had 14% to 36% cover, some of which was tanoak [20].

Dwarf tanoak is common to dominant on upland brushfields in the Siskiyou and Klamath mountains. It may be locally dominant elsewhere [72,73,224].

Tanoak is usually not a dominant species in the Sierra Nevada (for example, [77,226]), although it may be locally common [226].

Tanoak is an associated species in many forest types including Port-Orford-cedar (Chamaecyparis lawsoniana) [204,257], white fir (Abies concolor) [17,248], Oregon white oak (Q. garryana) [205], knobcone pine (Pinus attenuata) [41], canyon live oak [139,164,231], coast live oak (Q. agrifolia) [31,51], Monterey pine (P. radiata) [209], and Sierra Nevada mixed conifer. It is infrequent in Pacific ponderosa pine (P. ponderosa var. ponderosa) and Jeffrey pine forests (P. jeffreyi), which are generally too dry to support tanoak [105,142,226,234].

Vegetation typings describing tanoak-dominated communities are listed below.

Oregon and California: Oregon: California

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Lithocarpus densiflorus

 

Charles Webber © California Academy of Sciences

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 (for example, [54,95]).

Tanoak grows as a tree or shrub. The typical variety is a medium-sized tree, usually attaining 65- to 80-foot (20-24 m) heights [54,95,165,224]. Dwarf tanoak is a shrub, usually less than 10 feet (3 m) tall [54,95]. In the typical variety, trees in the subcanopy usually have narrow crowns [6,54,95,154], while open-grown trees have broad, rounded crowns [224]. The champion tanoak grows near Ophir, Oregon. It is 144 feet (43.9 m) tall, 23 feet (7.0 m) in circumference, and 54 feet (16 m) in spread [9]. Tanoak boles are generally long and straight [224]. Shaded trunks typically self-prune [165,224], so they are often clear of branches for 30 to 80 feet (9-24 m). Trunks may be crooked in dense stands [224]. Mature trunks range from 0.5 to 2.5 feet (0.2-0.8 m) in diameter [165,224], with a large burl at the trunk base. The burl grows outward and downward, so portions of it are nearly always buried in mineral soil [2,115]. The bark of mature trees is usually 1 to 3 inches (3-8 cm) thick, occasionally 4 to 5 inches (10-13 cm) thick [189]. Branches are ascending, with densely tomentose twigs [54]. Leaves are sclerophyllous and evergreen, reaching 1 to 5.5 inches (3-14 cm) in length. First-year leaves are densely covered with trichomes, while older leaves are nearly glabrous and have a thick wax coating on the upper surface [54,125,224]. The flowers are spiky catkins. Pistillate and staminate catkins may be on the same or separate stalks [6,54,95,154]. The 3-inch (8 cm)-long pistillate flowers can be so numerous that they hide the foliage; hence the specific epithet densiflorus [140,224]. The fruit is an acorn—a type of nut—ranging from 0.8 to 1.3 inches (2-3 cm) long [6,54,95,154]. Acorns are usually borne singly but may occurs in clusters of 2 to 4 [6,54,95,154,154]. Mature tanoaks have deep taproots and an extensive network of lateral and surface roots [224].

Stand and age class structure: A survey of old-growth redwood-Douglas-fir forest of Big Basin Redwoods State Park, California, found understory tanoaks averaged 20 inches (40 cm) in DBH [99]. Tanoak snag density can vary greatly, depending upon site characteristics and disturbance history. The Big Basin Redwoods State survey showed tanoak comprised the majority of snags and downed trees [99] (see Successional Status for further details). However, a survey of a Douglas-fir-tanoak forest on the Six Rivers National Forest, California, found the majority of snags were Douglas-firs (59%), not tanoaks (2%). Most tanoak snags were small (x=14 inches (36 cm) DBH) [110]. See Habitat Types and Plant Communities for further descriptions of stand structure of tanoak-dominated forests.

Across tanoak's range, mean age of tanoaks in unlogged stands is about 180 years, with typical ages of mature trees ranging from 80 to 300 years (review by [189]). Tanoak reaches a maximum age of about 400 years [109]. Overstory conifers are usually older than subcanopy tanoaks. Douglas-firs in old-growth mixed-evergreen forests on the Klamath National Forest, California, for example, were 250 to 520 years old [252].

Models— Several researchers provide height-diameter equations for tanoak and other southern Oregon trees [66,132]. Hann and Paine [81,171] give equations for predicting tanoak crown width. Hann and Wang [83] provide equations for predicting tanoak mortality rates in the mixed-conifer zone of southwestern Oregon.

RAUNKIAER [181] LIFE FORM:
Phanerophyte
Chamaephyte

REGENERATION PROCESSES:
Tanoak regenerates from acorns and sprouts. Sprouting is more common than seedling establishment [152,153].

Pollination and breeding system: Tanoak is wind pollinated and monoecious [224].

Seed production: Tanoak's prodigious flower production usually results in good seed crops. Tanoak is a masting species [78]. Acorn production varies across years [80], but no western oak species produces acorn crops as reliably as tanoak (reviews by [140,191]). Tanoak burl sprouts may first produce acorns at 5 years of age, with maximum production beginning at age 30 to 40 [6,54,95,153,154,224]. Tanoak acorns mature in their second year [153,154]. Open-grown tanoaks tend to produce heavier crops than trees in shade [153]. Complete acorn crop failure is rare, although drought or frost may result in a scanty crop [224]. A "veteran tanoak" 30 inches (76 cm) in DBH produced an estimated mean of 1,000 pounds (454 kg) of acorns yearly. Annual number of acorns/tree can range from 3,900 to 110,000 (review by [154]). Mean annual production of tanoaks between 18 and 24 inches (46-61 cm) in DBH is estimated at 3,900 to 4,600 acorns [224]. A 24-year study on a productive northern California site found tanoak seed production was more consistent than that of associated California black oaks (Quercus kelloggii) and Pacific madrones. Tanoak production was mostly light [145,147]. Tanoak acorn production in a heavy seed year ranged from 220,000 to 420,000 sound acorns/ha [140].

Tanoak crop production over 24 years on the Challenge Experimental Forest, California [145]
Category* Number of acorn crops
very light to light 9
medium to heavy 4
*very light: few acorns on <25% of trees; light: few acorns on >25% of trees; medium: many acorns on 25-50% of trees; heavy: many acorns on >50% of trees.

Seed dispersal: Tanoak acorns are large and heavy, so they generally fall and remain beneath the parent tree unless dispersed by animals [224]. Acorn-predatory rodents and birds disperse tanoak acorns [106,120]. In terms of regeneration, western gray squirrels, western scrub-jays, and Steller's jays are the most important animal dispersers because they bury the acorns in shallow caches [120].

Seed banking: Acorn-caching animals build up a transient tanoak seedbank. Because animal-cached tanoak acorns are shallowly buried, cached acorns not retrieved by their hiders have a greater chance of establishing than unburied or deeply buried acorns [131,140]. Tanoak acorns on the soil surface usually die from frost, heat, or desiccation, and deeply-buried acorns do not germinate [152,154]. A Marin County, California, study on Mt Tamalpais found western gray squirrels preferred burying tanoak acorns in the mixed-evergreen forest cover rather than open annual grassland [120], where desiccation is more likely.

Acorn depletion: A number of bird, mammal, and insect species consume tanoak acorns (see Importance to Wildlife and Livestock), so acorn predation is usually heavy. Referring to tanoak, McDonald [154] reported that "although it fairly rains acorns in the fall of a bumper seed year, few remain by spring". Studies in Oregon and northern California found over 99% of tanoak acorns were consumed (Thornburgh 1994, personal communication in [154]), [224]. Filbert weevils and filbertworms may destroy ≥50% of the year's crop (review by [224]). Masting helps ensure tanoak seedling establishment in heavy seed crop years [152].

Germination: Tanoak acorns are not dormant [154,189], and shade does not hinder germination [224]. In the laboratory, acorn soundness varied from 48% to 79% [154,159,222]. The first and last acorns to fall are generally unsound [154]. Germination is hypogeal [189]. Litter or duff provides the best seedbed [152,165], although tanoak also establishes in mineral soil [189]. On riparian sites in Oregon, tanoak established mostly in duff (90% of total seedlings found). Eight percent of tanoak seedlings established in mineral soil, and 2% emerged from a decayed wood seedbed [158]. In the laboratory, tanoak acorns required an average of 22 days after sowing for seedling emergence [159].

Seedling establishment: Tanoak germinants establish readily in shade [154,224]. A conifer understory provides an "ideal environment for reproduction" [224]. On group-selection sites on the Challenge Experimental Forest, California, more tanoak seedlings established in the smallest group-selection openings (30-foot-wide (9 m) openings) than in 60-foot (20 m) and 90-foot (30 m) openings. Tanoak numbers (seedlings and sprouts combined) were 1111, 544, and 550 trees from smallest to largest openings, respectively. A small majority of tanoak seedlings established the first year after harvest, but a similar number of seedlings established in postharvest years 2, 3, and 4 [147]. Tappeiner and others [152,222] found seedling establishment was limited on open, disturbed sites such as burns and clearcuts due to high acorn predation. On clearcuts in Oregon, seed predation from chipmunks and deer mice approached 99%. For tanoak seedlings that established, first-year survival was high (79-94%), and seedling establishment was not associated with percent canopy cover or soil moisture content (P=0.05). The rodent populations spiked after clearcutting, and the researchers concluded that acorn predation, not lack of shade or low soil moisture content, limited tanoak seedling establishment on the open sites [222].

Even with favorable conditions, only a small percentage of tanoak acorns establish as seedlings [165]. Tappeiner and others [224] reported an establishment rate of 1 seedling:156 sound tanoak acorns. Despite the low proportion of seedlings:acorns, tanoak seedlings are not rare. Bolsinger [30] reported tanoak seedlings on all plots surveyed across northern California. Seedlings are not as common as sprouts, however, and sprouts generally account for tanoak's dominance on many sites [152,153].

Vegetative regeneration: Tanoak sprouts from the burl after fire, cutting, or other top-killing events [48,49,50,119,133,144]. It is a strong sprouter, usually dominating the overstory where it was a subcanopy or shrub-layer dominant before top-kill. Bolsinger [30] wrote that tanoak "regenerates too well", with tanoak sprouts usually overtopping conifer seedlings (see Other Management Considerations). Sprouts generally grow best in full sunlight [30,154]. Tanoak seedlings develop a thickened root crown early in development, so even seedlings may sprout after top-kill by fire or other disturbance. On a California site, for example, 7-day-old tanoak seedlings top-killed by frost produced 3 to 7 sprouts/seedling. Two months after the frost, 80% of the frost-damaged tanoak seedlings had sprouted. Seedling food-storage capacity of the stem base increases as the root crown thickens and develops into a burl, increasing likelihood of sprout survival and growth after top-kill [153]. The root crowns have expanded enough to be classified as burls by the time seedlings are 1 or 2 years old, and burls are "fully developed" by about 5 years of age [152,224].

Tanoak sprout die-back is common even without fire, browsing, or other damage. McDonald and Tappeiner [153] noted that on the Challenge Experimental Forest, some tanoak seedlings died back to the burl for "no apparent reason", then sprouted [153]. The original seedling stem typically dies back by 6 to 12 years of age, with the new "seedling-sprouts" growing a stouter stem than the original [224]. Tanoak dies back and sprouts from the burl at least 3 to 5 times by age 60, even when top-killing events are not apparent. Burl buds divide as the burl enlarges, so the number of subsurface buds increases as tanoaks age [153]. One large tanoak stump supported about 1,400 buds (review by [153]). Open-grown tanoaks tend to produce more sprouts/burl than tanoaks in shade [153]. The sprouts can be very dense after logging or fire, often forming extensive stands [152]. Tanoak densities of "tens of thousands of stems per acre" are reported on harvested sites in northern California [30].

Tanoak surface roots may develop burls, which in turn produce sprouts [224]. As of 2008, no information was available on the relative importance of root sprouting in tanoak regeneration.

Growth:
Sprouts— Tanoak sprouts usually grow rapidly for the first few years after top-kill [89,224]. Tanoak sprout heights of 12 feet (4 m) are reported after 3 growing seasons in Douglas-fir-tanoak-Pacific madrone forests near the Pacific Coast [119]. After an initial spurt, however, tanoak sprout growth usually slows [224,224]. A mean growth rate of 2 feet (0.6 m)/year is reported for 15- to 20-year-old sprouts (review by [224]). Light increases sprout growth rate. In southwestern Oregon, tanoak coppice sprouts on clearcut and broadcast-burned Douglas-fir/tanoak plots were thinned to 25%, 50%, and 100% (unthinned control) relative tanoak cover in postfire year 2. Relative growth rates of tanoak sprouts were fastest on plots with 25% relative tanoak cover and least on the unthinned control [86,89]. Ten years after clearcutting on a productive site in Yuba County, California, tanoak sprouts averaged 19 feet (5.8 m) in height, and sprout clumps averaged 10 feet (3 m) in width [140,143]. Also in northern California, the number of tanoak sprout clumps dropped greatly between the 1st and 2nd years after top-kill but remained stable from postdisturbance years 2 through 6. Over 6 years, the number of tanoak sprouts/clump declined, with remaining sprouts growing rapidly [188,189].

Tanoak sprout development after fire or logging in Trinity County, California [188,189]
Time since disturbance Height (feet) of tallest sprout in clump Crown diameter (feet) of sprout clump Sprouts/clump
  mean range mean range mean range
1 year 2.4 0.7-5.6 2.6 0.6-7.4 16 1-162
2 years 5.2 2.2-8.3 6.2 2.9-11.5 27 7-79
3 years 6.8 2.2-10.3 7.0 3.4-12.1 12 4-25
4 years 7.9 2.3-11.3 8.4 3.4-14.3 10 4-25
5 years 9.3 2.7-13.6 9.9 4.8-15.2 10 4-25
6 years 10.3 3.5-14.7 10.3 5.0-15.6 9 1-25

On small clearcuts on the Challenge Experimental Forest, tanoak abundance increased over 5 postharvest years [146].

Tanoak regeneration (mostly sprouts and a few seedlings) on clearcuts on the Challenge Experimental Forest [146]
  Frequency (%) Density (trees/acre) Cover (feet²/acre) Height (feet)
postharvest year 1 1 210 90 1.4
postharvest year 2 22 233 217 2.6
postharvest year 3 17 183 217 2.0
postharvest year 4 17 217 783 4.8
postharvest year 5 25 350 900 4.9

Tanoaks originating from sprouts accumulate basal area rapidly. Coverages of 100 feet²/acre are reported 9 years after top-kill, and 160 to 260 feet²/acre coverage is noted for sprout-originated stands aged 50 years or more [165].

Seedlings— Tanoak seedlings generally grow more slowly than sprouts, but seedling growth rates are variable. Heights of 2 to 8 inches (5-20 cm) are reported for first-year seedlings [165]. Most growth occurs in the roots, with root length several times more than shoot length in 1-year-old seedlings [152]. Lengths of 24 inches (61 cm) are reported for first-year tanoak seedling roots (review by [189]). In a review, Roy [189] reported rapid height growth of first-year seedlings (x=5.2 inches (13 cm)), but only "moderate" growth in later years. In northern California, tanoak seedlings averaged 4.3 feet (1.3 m) in height after 10 years, with "pronounced" dieback. Tanoak stands starting from acorns develop differently than sprout-originated stands, which are usually even-aged. Tanoak seedlings typically establish in conifer/hardwood understories, with only a few tanoak seedlings establishing each year. Seedlings remain small for long periods, and an unevenaged understory or subcanopy results [149,152].

Tanoak is generally regarded as slow growing after the sapling stage [6]. However, Roy [189] notes in a review that knowledge of growth rates beyond the seedling and sapling stages is limited because growth rates of only a few larger tanoaks have been measured. One study found 48-year-old tanoaks averaged 35 feet in height (10 m) and 10 inches (25 cm) in diameter. Eighty- to 128-year-old tanoaks ranged from 14 to 18 inches (35-45 cm) in diameter, and 150- to 250-year-old tanoaks ranged from 20 to 60 inches (50-150 cm) in diameter [217].

Growth models: Harrington and others [92,221] present equations for predicting rates of increase in tanoak sprout clump height, crown area, leaf area, and biomass by stump size and time since top-kill. Their model is based on tanoak growth on logged or burned sites in southwestern Oregon, where 40- to 50-year-old sprout clumps averaged 15 inches (37 cm) in diameter 5 to 6 years after top-kill [221]. Tappeiner [220] presents rates of clump diameter growth and crown cover increases based on data collected on the Siskiyou National Forest, Oregon. Hann and Larsen [82] provide equations for predicting tanoak bole diameter growth over 5 years.

SITE CHARACTERISTICS:
Tanoak requires relatively high moisture levels and mild temperatures, restricting it from xeric or cold sites [20,152,224]. The typical variety occurs only where moisture is available from the atmosphere and/or soil [152], (review by [154]). On unproductive sites and in the southern portion of its range, the typical variety is mostly restricted to riparian zones, shady, sheltered habitats, and north slopes [152,189].

Dwarf tanoak is most common on unproductive sites but grows on some productive sites [151]. It occurs on a wide range of soil types including ultramafic soils. Soils are typically moist. Dwarf tanoak may form extensive cover in the Sierra Nevada, with clumps assuming flattened growth from winter snow compression [224].

Tanoak is an indicator of productive sites in southwestern Oregon [152]. Tanoak site index equations are available [177].

Aspect and elevation: On Oregon's Coast Ranges, the tanoak series occurs on relatively deep soils and low elevations and is not restricted by aspect [16]. Inland, tanoak is most common on north aspects [20]. In the Klamath Mountains of Oregon, the tanoak series occurs on moist, north-facing slopes with fine-textured soils [16]. On moist, north-facing slopes of the Sierra Nevada, tanoak sometimes occurs on thin, dry soils that cannot support conifers, but it is usually displaced by Pacific madrone and drought-tolerant oaks on such soils [152,189]. McDonald and Tappeiner [152] report that tanoak attains best development from 500 to 3,000 feet (152-915 m) on north- and east-facing slopes in the North Coast Ranges, from 2,400 to 4,700 feet (580-1,525 m) on west-facing slopes in California's Central Coast Ranges, and from 1,900 to 5,000 feet (580-1,525 m) in the Sierra Nevada.

Across their distributions, the typical variety of tanoak occurs from sea level to 7,500 feet (0-1,500 m) elevation [54], and dwarf tanoak occurs from 180 to 670 feet (600-2,200 m) [54,95]. The tanoak series occupies midelevation slopes between ponderosa pine and Douglas-fir forest below and white fir above, averaging 3,100 feet (945 m) in elevation [16,20].

Tanoak elevational ranges by region

Region Elevation
southwestern Oregon 140-5,000 feet (42-1,524 m), x=2,400 feet (750 m)
Klamath Mountains 200-3,800 feet (61-1,200 m), x=2,394 feet (730 m) [15]
northern Sierra Nevada 1,900-4,000 feet (580-1,220 m)
southern Sierra Nevada 3,000-5,000 feet (915-1,525 m) [152]

Climate: Tanoak is best adapted to a mediterranean climate modified by cool-moist coastal air currents [152,224]. Mean annual precipitation across tanoak's distribution ranges from 40.16 to 100 inches (1,020-2,540 mm), with rainy winters and dry summers and falls [224]. Productive tanoak sites are humid, with plentiful moisture from soil, rain, fog, low clouds, and/or high humidity [152], (review by [154]). However, in redwood forests of coastal Monterey County, California, tanoak attains greatest abundance and largest size on mesic sites above the fog zone [32].

Soils supporting tanoak are typically deep and well drained [152,189,224]. Soil depth on tanoak plots in the Siskiyou Mountains averaged 39 inches (97 cm): slightly deeper than average for the region [20]. Tanoak requires moister soils than most associated hardwoods. Its abundance decreases with decreasing soil moisture, especially on well-drained, granitic soils [20]. Tanoak grows in many soil textures and parent materials [224]. Common parent materials include sandstone, mudstone, and schist [20]. Atzet and Wheeler [17] report it on "all types of parent rock" in the Siskiyou Mountains [17], being most common on gabbro- and diorite-derived soils [189,249]. It is least common on ultramafic soils [19,20]. The tanoak/California coffeeberry series occurs on serpentine soils in the Siskiyou Mountains [20], however, and dwarf tanoak also grows on serpentine soils there [189,249].

SUCCESSIONAL STATUS:
Tanoak is shade tolerant when young [1,16,23] and can persist in shade as a mature tree. Tanoak also tolerates full sunlight, so it can be either a pioneer after fire or other top-killing disturbance or a subcanopy component in old-growth forests [20,165,189,224]. Sprouts tolerate full sunlight better than seedlings. Once seedlings establish, however, shade slows their growth [154]. Most rapid growth occurs with top light [224] when there is a conifer canopy, so tanoak is well adapted to a subcanopy position. Sudden exposure to full sunlight causes leaf scorch and crown die-back [165], a significant loss for a species with large, evergreen leaves [224]. Tanoak responds well to canopy release, however, after new leaves develop [141,165,189].

McDonald and Tappeiner [152] describe succession in tanoak forests as "complex" due to interactive effects of fire, logging, and high geological and topographical diversity. Because tanoak sprouts, it may dominate burned or logged mixed-evergreen forests within 1 to 8 postdisturbance years [152,256]. Tanoak can form dense, sometimes nearly pure stands in early succession but is typically overtopped by conifers decades later, often becoming dominant in the subcanopy [8,85,152,256]. Conifers regain dominance about 70 years after logging on mixed-evergreen sites in northern California [256]. Most of the conifer/tanoak types are in late succession due to fire exclusion, favoring tanoak over less shade-tolerant species (see Fire regimes). Tanoak was more abundant, for example, under dense than open canopies in mixed-conifer forest near Downieville, California [1]. Atzet and others report tanoak as a late-seral species on mesic to moist sites in the Klamath Mountains [16,85] and in redwood forests along the Pacific Coast [20]. Subcanopy tanoak may eventually grow into the conifer overstory in the long absence of disturbance [20].

Tanoak usually reaches greatest coverage in old growth [27,60,203,203,252]. On the Klamath National Forest, California, tanoak dominated the subcanopy of an unlogged old-growth Douglas-fir forest (51% cover and 100% frequency). It was still dominant but less abundant on unsalvaged, 20-year-old burns (40% cover and 100% frequency) and salvage-logged, 20-year-old burn edges (22% cover and 70% frequency) [85].

Fire is a common disturbance in tanoak-dominated communities. Atzet [15] found fire caused 74% of all disturbances in plots in the Klamath Mountains, with human-caused disturbances other than fire comprising 17%, disease comprising 4%, and wind comprising 2% of all disturbances. Large tanoaks damaged by fire or other disturbance may topple in wind or ice storms, allowing canopy-gap succession in mature and old-growth forests. In Big Basin Redwoods State Park, downed tanoaks comprised the majority of fallen trees (55%), although the canopy gaps resulting from tanoak fall were much smaller than those created after Douglas-fir or redwood fall [99]. Tanoak filled twice as many canopy gaps as it formed [100]. Hunter and others [100] predicted tanoak would become increasingly dominant without surface fires, but would not become a canopy dominant as long as surface fires occurred at intervals frequent enough to promote less shade-tolerant species.

Tanoak encroachment into annual grasslands is slow. A Mt Tamalpais study suggests that tanoak seedling establishment on annual grassland is dispersal-limited because acorn-caching animals prefer areas with forest cover to open grassland as cache sites. However, some tanoak acorns were cached in annual grassland, which may translate to significant tanoak encroachment in the long term [121]. Tanoak seedlings growing in annual grassland had established beneath nurse Douglas-fir saplings, which were also encroaching into the grassland [122].

Tanoak may encroach into oak savannas. Griffin [75] noted tanoak seedling establishment in valley oak-interior live oak (Q. lobata-Q. wislizenii) savanna in the Santa Lucia Mountains of northern California.

SEASONAL DEVELOPMENT:
Tanoak has an extended flowering period, from spring through summer (April-August). It may reflower in autumn [54,224], (review by [154]). Heaviest flowering occurs from June through August [224]. Leaves persist for 3 to 4 years [224], with leaf fall coinciding with acorn drop. Acorns disperse from mid-September to mid-November (review by [154]), [224]. On the Challenge Experimental Forest, tanoak acorns began falling in early September and stopped falling on 15 November. Peak acorn drop was on 20 October, when there were warm, dry, northeasterly winds [145]. Acorns usually germinate in spring but may germinate in fall if temperatures remain warm and rainfall is plentiful [189,224]. On low-elevation sites on the Trinity River Watershed, tanoak vegetative buds opened in mid-April, and leaves expanded in late May [224].

FIRE ECOLOGY

SPECIES: Lithocarpus densiflorus
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: Tanoak sprouts from the burl after top-kill by fire [13,16,50,76,114]. Postfire establishment from onsite [144] and animal-dispersed [131,140,245] acorns is also possible, although such establishment is not well documented.

Fire regimes: Plant communities where tanoak dominated or was an important component of the vegetation historically experienced mostly mixed-severity fires [2,5] that occurred in summer or early fall [215,239]. Native Americans increased fire frequency in tanoak ecosystems with frequent underburning. Frequent fires, set after acorn collection, killed acorn-predatory insects such as the filbert weevil [10] and reduced the shrub understory, which interfered with acorn collection [172]. Fire regime information below is arranged by forest type and region.

Mixed-evergreen forests: Agee [2] characterizes mixed-evergreen forests as having a "complex fire disturbance history". Fire severity is mixed [2]. Mean historic fire-return intervals in mixed-evergreen forest clustered around 15 to 35 years but ranged from 3 to more than 70 years (reviews by [2,98]). Interior stands had the shortest mean fire-return intervals, around 20 years, while coastal areas averaged 60 years between fires. Size and severity of presettlement fires varied across time at the landscape level (review by [98]). Mean annual area burned in presettlement Douglas-fir/hardwood forests of Oregon was 732,000 acres (296,000 ha). Within the mixed-severity matrix, a high percentage of the landscape was historically burned by surface fires. Because of postfire sprouting of tanoak and other hardwoods, frequent surface fires created a 2- or 3-layered subcanopy. The waxy leaves of tanoak and other subcanopy sclerophylls fueled fires that were sometimes intense and carried flames into the conifer overstory, creating severely-burned patches of land that were generally smaller than surrounding patches of underburned land (review by [2]). See Fuels for more information on live and dead tanoak fuels.

On cool, moist sites typical of the North Coast Ranges of Oregon, where tanoak reaches its northernmost distribution, old-growth Douglas-fir forests with a tanoak component probably had long-return intervals of mixed-severity and stand-replacement crown fires. Large fires occurred over these areas in the past, but narrowing down their return intervals is difficult. Agee and Edmonds [5] state that "our knowledge of old-growth forest establishment dates is so weak as to preclude firm hypotheses about disturbance pulses of the presettlement past". Atzet and Wheeler [16] suggest that fire-return intervals were longer, and fires more severe, in the North Coast Ranges compared to inland Douglas-fir sites. In California's North Coast Ranges, fire frequencies have decreased since the 1950s, but fire size has increased greatly [215].

Inland, dry-mesic Douglas-fir/tanoak forests historically experienced moderate-return interval, mixed-severity fires. In a review, Agee [4] noted that mean historic fire-return intervals decrease from about 90 to 150 years in Douglas-fir forests of coastal Oregon to about every 50 years for inland sites in the North Coast Ranges and 20 years in the eastern Siskiyou Mountains.

Siskiyou Mountains: Mixed-evergreen forests of the Siskiyou and Klamath mountains are drier than those on the coast, with shorter historic fire-return intervals. Fires were of low and mixed severity, with fire-return intervals getting longer and fires more severe with increasing elevation [3,136]. Mixed-severity fires in the Siskiyou Mountains tanoak series historically burned "large portions" of the landscape. In a review, Lininger [136] stated that patches of severe fire historically accounted for 10% to 20% of total area burned by mixed-severity fires. Severe fire was most common on steep slopes [136]. Atzet and Wheeler [16] estimate a 20-year fire-return interval in the western Siskiyou Mountains of Oregon. Data from fire-scarred stumps of logged Douglas-firs and white firs and permanent photography points showed that a low-elevation (3,900 feet (1,200 m)), mixed-evergreen Douglas-fir/dwarf Oregon-grape forest with a tanoak component had an historic mean fire-return interval of 16 years from 1854 to 1915. Fire-scarred Douglas-fir stumps on south-facing slopes registered a shorter mean of 12 years from 1850 to 1920. A high-elevation (4,300-5,900 feet (1,300-1,800 m)), mixed white fir-tanoak-oak (Quercus spp.)/herb forest in Oregon Caves National Monument had an historic mean fire-return interval of 37 years from 1650 to 1930. Neither site had experienced fire from 1921 to 1988 (the year of study): the longest fire-free interval in 300 years [3].

Klamath Mountains: Fire-return intervals were historically somewhat shorter in the Klamath Mountains than in the Siskiyou Mountains. A fire history study of a mixed conifer-hardwood forest on Whiskeytown National Recreation Area, California, found presettlement fire-return intervals averaged 1.3 years from 1663 to 1849. Most fires occurred late in or after the growing season. Fires became less frequent around 1850, when Native American ignitions ceased. Above-average precipitation during the settlement period probably worked in concert with social changes to reduce fire frequency. Fires during the fire exclusion period (past 1924) were significantly larger than those during the presettlement and settlement periods (P<0.05) [62]. A fire history study on 3 Douglas-fir/tanoak-Pacific madrone sites on the Klamath National Forest had similar findings. There were no significant differences between either sites or presettlement and settlement period fire-return intervals. However, mean fire-return interval of the fire exclusion period was significantly different from those of the presettlement and settlement periods, with intervals between fires increasing greatly around the turn of the twentieth century (P=0.010) [252].

Means and ranges of fire-return intervals on 3 sites on the Klamath National Forest, California [252]
Location and period Time interval Mean (years) Range (years)
Site 1
Presettlement 1745-1849 17.3 5-41
Settlement 1849-1894 15.0 8-26
Fire exclusion 1894-1987 46.5 43-50
Site 2
Presettlement 1742-1855 10.3 5-18
Settlement 1855-1901 9.2 7-12
Fire exclusion 1901-1987 28.7 18-45
Site 3
Presettlement 1752-1849 13.9 7-25
Settlement 1849-1913 16.0 5-25
Fire exclusion 1913-1987 37.0 3-71

Fire-return intervals were historically longer in mid- to upper-montane Douglas-fir/tanoak forests with a white fir component, and severe fire covered more of the landscape than at low-montane elevations. Dwarf tanoak may dominate mid-montane Klamath Mountain sites that experience frequent, stand-replacement fires [201]. In an inventory taken after the Megram Wildfire, which occurred in 1999 on the Six Rivers National Forest after a 1996 blowndown, the tanoak series had 2nd highest frequency of burned acres (24%), with the white fir series 1st (50%) and the red fir series 3rd (9%), roughly reflecting relative abundance of each type on the landscape. Fire in the tanoak series was mostly moderate severity, with 26% to 70% tree mortality (all species). Some areas had thinning and/or fuel reduction treatments before the wildfire. Fire severities were generally highest in blowdown areas where large woody fuels were removed with no follow-up fuel reduction, untreated blowdown areas, and "early-mature" seral stands. Across sites, fire severity was reduced by slash piling alone but not slash piling followed by pile burning. Piling and burning did reduce fire severity in the upper one-third of slope positions, however. Failure of pile burning to reduce fire severity in other positions was not explained in the study results. Slash piling followed by pile burning and then understory burning was the most successful in reducing fire hazard [111].

Redwood forests with a tanoak subcanopy historically had widely ranging but mostly short fire-return intervals. In a review, Arno and Allison-Bunnell [13] reported fire-return intervals ranging from 5 to 25 years before 1850. Finney and Martin [53] used fire scars on redwoods and Bishop pines (Pinus muricata) to study fire-return intervals at Salt Point State Park, California, where tanoak is an important component of the redwood forest. Presettlement fire-return intervals ranged from 3.6 to 35.2 years (x=13.8), with a period of significantly longer fire-return intervals in the 17th century (x=16.8-year intervals, P=0.05). Fires were most frequent on south-facing slopes [53]. Fire-return intervals tended to shorten during the settlement period and increase during the postsettlement period compared to presettlement times. In Redwood National Park, California, fire history studies found mean fire-return intervals of 13.3 years for the presettlement period (before 1876), 16 years for the settlement period (1875-1897), and 4.5 years for the postsettlement period (1989-1940) [213].

Fire histories of redwood forests to the south are less well studied. Generally, historic fire-return intervals shortened with increasing Douglas-fir cover and southern latitude [241]. In Marin County, Finney [52] found fire-return intervals ranged from <2 to 7.5 years from 1600 to 1850. Native American-set fires probably increased fire frequency, keeping most fires on the forest floor. A series of crown fires, probably larger in extent than fires of the past, began in 1980 after decades of fire exclusion [52]. Native Americans probably set understory fires frequently in presettlement redwood forests of the Santa Cruz Mountains. Presettlement Native American population in the Santa Cruz Mountains was relatively dense, probably ranging from 1 to 3 persons/km². Some suggest a pre-Columbian mean fire-return interval of 8 to 10 years in the Santa Cruz Mountains due to frequent Native American-set fires. Crown fires occurred about every 135 years (review by [46]).

Tanoak may persist in the subcanopies of redwood forests indefinitely, and periodic fire may not be required to maintain tanoak in redwood ecosystems [240].

Sierra Nevada mixed conifer: In the lower montane zone of the Sierra Nevada where tanoak occurs, the historic fire regime was mixed-severity, dry-season fires of mostly low to moderate severity. Patchy, stand-replacement fires were most common on north-facing slopes and during extended droughts. Although most fires occurred in summer or late summer, some occurred in spring, early summer, and even winter [239]. A fire history study on Blodgett Forest Research Station in the north-central Sierra Nevada found most fire scars were in latewood, so fires were historically common in early fall. The mixed-conifer forest had a tanoak component [206].

Other: Fire-return intervals in other ecosystems where tanoak is an associated species vary from medium to short. Port-Orford-cedar occurs on moist, lowland sites that historically burned less frequently than drier upland types. Zobel and others [258] found fire-return intervals of 45 and 148 years on a Port-Orford-cedar site in southwestern Oregon.

Historic fire regimes in canyon live oak forests and woodlands were characterized by mixed-severity fires [12,173] and relatively frequent, low- to moderate-severity surface fires of short- to medium-length fire-return intervals [200,201]. Arno [12] and Paysen and others [173] characterize the fire regime in the canyon live oak cover type [139] as mixed severity with a frequency of <35 years [173].

There is little fire history research in Monterey pine forests. Fires were probably of mixed severity, with patches of severe fire required for Monterey pine regeneration. A study near Santa Cruz, California, found fire-return intervals ranged from 11.2 to 20.1 years in a Monterey pine forest with tanoaks [209].

Changes in fire regime: Contemporary fires in the Siskiyou and Klamath mountains are still of mixed severity at the landscape level. However, there is a trend towards larger fires, with more total area experiencing severe fire, compared to historic fire sizes and severities [247]. Since the 1980s, most large fires in Oregon have occurred in the southwestern portion of the state, where Douglas-fir/tanoak is the dominant low-elevation forest type [2]. Agee and Edmonds [5] state that greater fuel continuity due to fire exclusion and slash on clearcuts are partial causes of the current regime of increasingly large and severe fires. In 1987, for example, a widespread lightning storm in southern Oregon ignited over 600 fires, forming the Klamath Fire Complex. Nineteen of the wildfires burned over 1,000 acres (400 ha) each. Total area burned by all fires in the complex was around 200,000 acres (100,000 ha) (review by [5]), [167]. Fire severity was 59% low, 29% moderate, and 12% high [167]. In the 1987 Hayfork Fire Complex on the Shasta-Trinity National Forest, crown fire (>50% of crown consumed) burned 5% of the landscape. Twenty-five percent of the landscape was >50% scorched; 32% was 10% to 50% scorched; and 38% was <10% scorched (Weatherspoon and Skinner, unpublished document cited in [2], review by [5]).

        Agee and Edmonds [5] concluded in 1992 that without fire hazard reduction, the trend toward large, increasingly severe fires would continue. The 12 July 2002 Biscuit Fire was more extensive than any other recorded fire in the conterminous United States (as of 2008). It began as a fire complex that merged into one large fire, burning nearly 500,000 acres (200,000 ha) in southwestern Oregon and northwestern California. The fire was of mixed severity [21,22,33,182], burning mostly in Douglas-fir/tanoak and tanoak forests [21,22] (see Plant Response to Fire for more information about tanoak response on the Biscuit Burn).

Analyzing patterns of large-acreage fires (6,200-130,000 acres (2,500-50,600 ha)) in the Klamath and Siskiyou mountains of southern Oregon and northern California, Alexander and others [7] found mixed-severity fire at the landscape level. Severe crown fire was most common on south- and west-facing slopes (P=0.003). In the 2001 Quartz Fire in the Siskiyou Mountains of Oregon, high-elevation sites (approximately 6,070 feet

                      The Biscuit Fire in Douglas-fir/tanoak. Photo compliments of Wildlandfire.com.

(1,850 m)) with large-diameter trees (approximately 47 inches (120 cm) DHB) were most likely to experience low- and moderate-severity surface fire (P=0.018). There was no significant relationship between slope and fire severity. In the 1999 Big Bar Fire Complex in the Klamath Mountains of northern California, however, gentle slopes were likely to burn at moderate severity, with probability of either low- or high-severity fire increasing with increased slope (P=0.020). Fire severity and tree DBH were not significantly associated [7].

In mixed-evergreen forests, fire exclusion may not increase fire severity on all sites or in all stages of succession. In fire history studies of Douglas-fir-tanoak forests on the Klamath National Forest, Odion and others [167] found a trend toward large fires (>3,700 acres (1,500 ha)) in recent decades compared to fire sizes before the 1970s, which averaged around 1,000 acres (500 ha). In the Klamath Fire Complex, fire was generally most severe in shrubland and open forest and lowest in multiaged, closed-canopy forests. In closed-canopy forests, fire severity was lower where fire had been excluded since 1920 compared to sites that had burned since 1920. The authors concluded that fuel loads in the closed-canopy, mixed-evergreen forests had decreased, not built up, in the long absence of fire. Fuel build-up did occur in open forests and plantations, however [167].

See Sudden oak death disease in the Fuels section below for information on possible changes in fire regimes and fuel loads in tanoak ecosystems due to heavy sudden oak death infection.

The following table provides fire regime information that may be relevant to tanoak.

Fire regime information on vegetation communities in which tanoak may occur. For each community, fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Models [130]. These vegetation models were developed by local experts using available literature, local data, and/or expert opinion as documented in the PDF file linked from the name of each Potential Natural Vegetation Group listed below. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.
Pacific Northwest California Southwest Great Basin Northern Rockies
Northern Great Plains Great Lakes Northeast South-central US Southern Appalachians
Southeast        
Pacific Northwest
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northwest Woodland
Oregon white oak-ponderosa pine Replacement 16% 125 100 300
Mixed 2% 900 50  
Surface or low 81% 25 5 30
Pine savannah (ultramafic) Replacement 7% 200 100 300
Surface or low 93% 15 10 20
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
Oregon white oak Replacement 3% 275    
Mixed 19% 50    
Surface or low 78% 12.5    
Northwest Forested
Sitka spruce-western hemlock Replacement 100% 700 300 >1,000
Oregon coastal tanoak Replacement 10% 250    
Mixed 90% 28 15 40
Dry ponderosa pine (mesic) Replacement 5% 125    
Mixed 13% 50    
Surface or low 82% 8    
Douglas-fir-western hemlock (dry mesic) Replacement 25% 300 250 500
Mixed 75% 100 50 150
Douglas-fir-western hemlock (wet mesic) Replacement 71% 400    
Mixed 29% >1,000    
Mixed conifer (southwestern Oregon) Replacement 4% 400    
Mixed 29% 50    
Surface or low 67% 22    
California mixed evergreen (northern California) Replacement 6% 150 100 200
Mixed 29% 33 15 50
Surface or low 64% 15 5 30
Red fir Replacement 20% 400 150 400
Mixed 80% 100 80 130
California
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
California Shrubland
Montane chaparral Replacement 34% 95    
Mixed 66% 50    
California Woodland
California oak woodlands Replacement 8% 120    
Mixed 2% 500    
Surface or low 91% 10    
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
California Forested
California mixed evergreen Replacement 10% 140 65 700
Mixed 58% 25 10 33
Surface or low 32% 45 7  
Coast redwood Replacement 2% ≥1,000    
Surface or low 98% 20    
Mixed conifer (North Slopes) Replacement 5% 250    
Mixed 7% 200    
Surface or low 88% 15 10 40
Mixed conifer (South Slopes) Replacement 4% 200    
Mixed 16% 50    
Surface or low 80% 10    
Jeffrey pine Replacement 9% 250    
Mixed 17% 130    
Surface or low 74% 30    
Interior white fir (northeastern California) Replacement 47% 145    
Mixed 32% 210    
Surface or low 21% 325    
Red fir-white fir Replacement 13% 200 125 500
Mixed 36% 70    
Surface or low 51% 50 15 50
Red fir-western white pine Replacement 16% 250    
Mixed 65% 60 25 80
Surface or low 19% 200    
*Fire Severities
Replacement: Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed: Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low: Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [84,129].

Fuels: Tanoak grows in some of the most productive temperate forests of the world, so total litter production in tanoak ecosystems is very great. Litter may decompose rapidly in the moist environments typical of tanoak sites [16,215]. In a review, Stuart and Stephens [215] report that in Douglas-fir/tanoak forests, Douglas-fir and tanoak litterfalls decompose to 5% of their original dry weights in 7 and 9 years, respectively. Tanoak litter output may outpace rates of decomposition on productive sites, however. Franklin [57] reported slow decomposition of tanoak litter along the Oregon coast. Considering understory woody species in the tanoak series of southwestern Oregon, where tanoak dominates the subcanopy and Douglas-fir the canopy, Atzet and others [20] stated "their high capacity for producing biomass...is a major management problem". Litter cover may be as much as 98% in redwood-tanoak forests [17].

Tanoak sprouts can create heavy live fuel loads. Biomass of live understory fuels on a ponderosa pine plantation near Challenge, California, was 91 Mg/ha. The plantation was established to replace ponderosa pines killed after a wildfire. Tanoak sprouts dominated the mixed-shrub understory, which was completely closed and excluded most herbaceous species [34]. On coastal and inland redwood/Douglas-fir/tanoak sites in California, annual litterfall (all species) ranged from 3,120 to 4,690 kg/ha; 9% of the litterfall was from tanoak. Based on estimated litter decay rates, equilibrium litter-layer load was projected at 7,760 to 14,500 kg/ha. Decay rates were higher than those reported for southwestern Oregon Douglas-fir or Sierran mixed-conifer forests. Litter load data were lacking for other redwood sites at the time of the study, and the researchers caution that their results apply only to their study sites. They call for further research on patterns of litter accumulation and decay in redwood/Douglas-fir/tanoak types [176].

Tanoak is intolerant of heavy snow loads and decayed trees are not windfirm, so tanoak breakage from heavy snow and/or high winds can create heavy loads of downed woody debris (review by [215]), [224]. White and others [248] provide information on snag density and downed woody debris loads in a white fir/tanoak/prince's pine forest of southern Oregon. Ohmann and Waddell [168] provide mean volumes of large, downed woody debris on mixed-conifer-hardwood forests of southwestern Oregon by successional stage.

Flammability: Sclerophyllous species such as tanoak are highly flammable. The leaves have a high proportion of resin, oil, wax, and other flammable materials. Among sclerophyllous species, tanoak leaves are more flammable than leaves of associated hardwoods. When tanoak stands are dense, the subcanopy creates a horizontally continuous, highly flammable layer of ladder fuels. Even without continuous fuels, dry tanoak leaves can fuel long flames when they burn in the subcanopy (reviews by [143,215]).

Sudden oak death disease may increase fuel loads and alter fire regimes in areas of heavy infection. Increased dead fuel loads, more open canopies, and changes in fuel moisture, understory composition and postfire successional pathways can follow tanoak mortality from sudden oak death disease, which is caused by a water mold (Phytophthora ramorum) [46]. (See the discussion in Damaging agents for details of the disease.) Tanoak mortality and dieback may increase fire hazard. Dead and downed woody fuels in areas with high infection rates can increase fire intensity, severity, and crown fire potential [134,155,162], (review by [215]). Condeso and Meentemeyer [43] speculate that in Sonoma County, California, fire exclusion may have increased oak woodland density relative to historic conditions, creating conditions favorable to rapid spread of sudden oak death disease. As of this writing (2008), studies are underway to assess potential impacts of sudden oak death disease on fuel loads and the fire ecology of tanoak and western oaks [46,134]. Fire may not control Phytophthora ramorum. On an infected site in Marin County, infected tanoaks and coast live oaks were cut and the area burned under prescription to test fire effects on Phytophthora ramorum. Tanoak stumps sprouted, but 90% of sprouts growing from infected stumps had sudden oak death disease [134]. The website Monitoring Sudden Oak Death provides updates on ongoing studies testing sudden oak death Phytophthora ramorum's response to fire and/or fungicides.

Models: Many models are available to help estimate tanoak fuel loads. See the following sources for estimating tanoak's total aboveground biomass: [202,218,228], crown mass: [202,218], crown area: [237], and stem, bark, and branch masses: [202,218]. See Growth models for predicting rates of tanoak sprout growth after fire.

Fuels management studies: A few studies provide results from fuel reduction treatments using thinning and/or prescribed burning in mixed-conifer forests with a tanoak component. Knapp and others [126] compare fuel reduction and fire behavior of early-season (June) and late-season (September-October) prescribed fires in mixed-conifer forest in Sequoia National Park. Stephens and Moghaddas [207,208] discuss results of a Blodgett Forest Research Station fuels reduction study using crown thinning and thinning from below followed by mechanical treatment (mastication of understory trees), mechanical treatment followed by prescribed fire, prescribed fire alone, and a no-treatment control. They discuss benefits of retaining some coarse woody debris and creating snags with prescribed fire for wildlife benefit, and describe treatment impacts to forest structure [207].

POSTFIRE REGENERATION STRATEGY (adapted from [211]):
Tree with adventitious buds, a sprouting burl, and/or root suckers
Tall shrub, adventitious buds and/or a sprouting burl
Small shrub, adventitious buds and/or a sprouting burl
Crown residual colonizer (on site, initial community)
Initial off-site colonizer (off site, initial community)
Secondary colonizer (on-site or off-site seed sources)


FIRE EFFECTS

SPECIES: Lithocarpus densiflorus

 
  Tanoak sprouts. Photo courtesy of Lynn Watson.
IMMEDIATE FIRE EFFECT ON PLANT:
With its flammable leaves and successional position in the understory or subcanopy, tanoak is adapted to catch fire easily. Small trees usually burn back to the burl. Tanoak seedlings and saplings are typically top-killed by even low-severity surface fire [2,13,16,76]. Large trees usually survive moderate-severity fire [4], bearing fire scars afterward. Even tanoaks with thick bark (1-5 inches (3-10 cm)) typically sustain bole damage from fire [224]. Fire scars may extend 4 to 10 feet (1-3 m) up the trunk (review by [189]),[224]. Severe fire generally top-kills mature tanoaks and may kill small trees [4,76,115,118,127,224]. Severe surface fire occasionally kills large trees [189,224].

Tanoak burls are usually at least partially buried in mineral soil and survive most surface and crown fires. Surface fire may kill the burls of seedlings and saplings [118,127], but the burls of large tanoaks typically survive even severe fires [2,115,247] that completely consume litter and duff surrounding the burls [2,115].

Fire generally kills tanoak acorns in litter or duff [73].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
Wind or ice storms may topple fire-damaged tanoaks [99,189].

PLANT RESPONSE TO FIRE:
Tanoak sprouts from the burl after top-kill by fire [13,16,50,76,115]. Even seedlings may sprout after fire [153]. Postfire sprout survivorship is high. McDonald and Tappeiner [153] report that "nearly all" tanoak burls sprout after fire, and "rarely do all the sprouts die". Because tanoak is a strong sprouter, very frequent fire promotes tanoak dominance over that of conifers [57]. Burls of large, rapidly-growing tanoaks tend to produce rapidly-growing sprouts after top-kill. Debris around the burl, or thick burl bark on old stumps, reduces the number of sprouts. Large burls may initially support hundreds of sprouts, but 60% to 90% of tanoak sprouts typically die by age 20, so the number of sprouts/burl declines over time [153].

Seedlings are not as common on burns as sprouts [144], but postfire seedling establishment is ecologically important. It provides opportunities for tanoak to colonize new sites and increases genetic diversity on burns where tanoak clones are numerous [131]. Animal caches [131,140] and on-site, surviving parent tanoaks [144] are likely seed sources for postfire tanoak seedling establishment. Studies documenting establishment and mortality rates of tanoak seedlings on burns are few. Rodents cache tanoak acorns on new burns [245] but prefer caching acorns on sites that provide more cover [120], so postfire rodent caching may not be important in the first few postfire years. After that, rodents may increase acorn caching as tanoak and other sprouting woody plants provide increasingly better hiding cover on burns. As of 2008, studies documenting Steller's jay or western scrub-jay dispersal of tanoak acorns onto burns were lacking.

Sprouting is the primary method of postfire tanoak regeneration, and tanoak sprouts are usually abundant on a newly-burned site where tanoak was present before fire. Griffin [76] and Agee [4] noted tanoak sprouts in the Ventana Wilderness, California, 10 months after the stand-replacing Marble Cone Fire. Tanoak cover and density have generally increased as a result of fire exclusion [18]. Extensive, pure tanoak stands are common in northwestern California, resulting from fire and/or logging that occurred in the mid-1900s (Thornburgh 1994, personal communication in [154]). Broadcast burning in clearcuts where tanoak was present before harvest can produce a dense tanoak stand [153]. Nineteen years after clearcutting and broadcast burning of a mixed-conifer forest on the Challenge Experimental Forest, McDonald [144] reported that tanoak stump sprouts were "scattered throughout and, where present, outgrew all other vegetation". Sprouts numbered up to 100/burl. Tanoak seedlings were few and tended to grow where a mature tanoak grew before logging [144]. See Roy's [188,189] study in Growth for further information on growth rate and development of tanoak sprouts after fire or logging.

Arno and Allison-Bunnell [13] stated that in redwood-Douglas-fir forests, frequent burning "physiologically stresses" subcanopy tanoaks. Historically, frequent surface fires may have kept growth of tanoaks and other sprouting hardwoods low, creating relatively open understories [13,18].

In mixed-evergreen conifer/hardwood forests, relative postfire abundance of tanoak depends upon fire severity and availability of conifer seed sources. Fires severe enough to kill overstory conifers and eliminate conifer seed sources generally favor tanoak over conifers [196]. Agee [2] reviews postfire successional trajectories that tanoak has followed. Following "intense fire" in Douglas-fir/tanoak stands, either species may dominate the stand, or they may codominate. If tanoak dominates, it usually shades out and excludes Douglas-fir until the tanoak canopy begins to break up, about 60 years after fire. When many Douglas-fir seedlings establish early in postfire succession, Douglas-fir can attain dominance after 15 to 30 postfire years, growing more quickly than tanoak sprouts after that (see Growth). Tanoak may codominate or dominate the stand in late postfire succession, when the Douglas-fir stand begins to break up. Successive, stand-replacement fires may push Douglas-fir/tanoak succession towards a stand dominated by tanoak and other hardwoods [2]. Frost and Sweeny [61] describe similar successional pathways for Douglas-fir/tanoak stands in the Siskiyou Mountains:

Studies conducted after the Hayfork Fire Complex and the Biscuit Fire illustrate the effects of unprecidentedly large wildfires (see Changes in fire regime) and show how tanoak responds to such wildfires. See Silvicultural management and postfire succession for a discussion of effects of and tanoak response to the Hayfork Fire Complex.

The Biscuit Fire was of mixed severity [182,247], with about 30% of the area lightly burned, 26% moderately burned, and 44% severely burned [183,247]. Douglas-fir/tanoak was the predominant cover type burned: 65% of the total burn area, or 204,800 acres (82,900 ha). Thirty-three percent of Douglas-fir types burned at moderate or high severity. Tanoak was the dominant hardwood cover type burned: 63% of the total hardwood area ((76,500 acres) (31,000 ha)) [183]. The Burned Area Emergency Response (BAER) team found fire severity in the tanoak cover type was mostly very low and low severity; less than 15% was classified as moderate or high severity [183]. Prefire size of tanoaks was mostly mature trees (32% of all tanoaks present), with few pole-sized trees and almost no saplings and seedlings [22]. Tanoaks sprouted soon after the wildfire passed [136,247]. Surveys taken in August and September 2002—before the fire had gone out in some areas—showed tanoak sprouts throughout the Douglas-fir/tanoak and tanoak cover types, including severely burned areas [247]. A portion of Biscuit Fire burned through permanent plots on experimental Douglas-fir/tanoak units. Fire histories show an 80- to 110-year fire-return interval, mixed-severity fire regime for the experimental sites. On experimental plots, fire was most severe in a) plantations of 5-year-old Douglas-firs; b) 5-year-old plantations of mixed, early-seral conifers; and c) mature, thinned stands that had not been treated with postthinning prescribed fire [33,183]. On thinned-only plots, severe surface fire consumed the "extensive" fine woody fuels left from thinning and the 5-year-old canopy of hardwood sprouts (mostly tanoak) [183]. Douglas-fir mortality, measured in postfire month 22, was nearly 100% on plantation and thinned-only plots, and tanoak abundance was greatly reduced from prefire levels. Tanoak frequency on the 5-year-old plantations dropped from 80% in 1998, 4 years before the fire, to 20% at postfire month 22. Fire severity and tree mortality were least in mature stands that had been thinned and underburned 1 year before the Biscuit Fire. About 98% of trees on thinned, underburned plots had bole damage, but tree mortality at postfire month 22 was only 2% [33]. Sparse fuels completely stopped fire spread into one thinned, underburned plot [183]. Using a fire behavior model, Raymond and Peterson [182] projected that thinned-only treatments reduced canopy and ladder fuels but the potential for crown fire did not change in thinned stands not subsequently treated with prescribed fire because thinning increased surface fuels. Projected fire intensity and flame lengths were greatest on those stands; and in fact, the wildfire reached into the tanoak subcanopy and crowned, substantiating their modeled findings. Stands that were thinned and underburned before the Biscuit Fire had reduced canopy, ladder, and surface fuels compared to thinned-only sites; so surface fire intensity was less, and potential for crown behavior was reduced. Consequently, the Biscuit Fire did not crown in thinned and underburned stands [182,183]. About 350,000 acres (140,000 ha) of the Douglas-fir/tanoak type burned at severities high enough that the conifer overstory was reduced by at least half. Sessions and others [196] caution that without management intervention, hardwoods and shrubs in general—and tanoak in particular—are likely to dominate postfire succession for decades in areas where conifer seed sources were greatly reduced by wildfire, especially if reburns occur before early-seral conifers become large enough to resist fire damage.

Fire effects and postfire response models: Scanlon and Valachovic [195] compared FARSITE, a fire behavior model, predictions of fire behavior and postfire over- and understory damage after the Canoe Fire in Redwoods State Park to a postfire inventory of fire damage. Redwood-Douglas-fir/tanoak stands were modeled and inventoried. FARSITE successfully projected fire perimeter advance and flame lengths, but predicted and actual fireline intensities were poorly correlated. Prefire fuel load data would have increased ability of FARSITE to predict fire intensity [195].

Kobziar and others [127] conducted fall prescribed burning in a mixed-conifer forest on the Blodgett Forest Research Station to develop models for predicting tree mortality based upon tree diameter, percentage crown volume scorch, scorch height, and fuel consumption. Tanoak was mainly represented in the shrub layer. Mortality of small tanoaks was significantly higher than mortality of 6 associated overstory tree species (P=0.05). The fire killed the only large tanoak present on study plots. Models presented in this study can be used to predict tree density reductions from prescribed fire in Sierran mixed-conifer forests [127].

Mortality of tanoak on the Blodgett Experimental Forest, California [127]
DBH (cm) Mortality (%)
2.5-25 38.03 (SD=32.94)
25-51 0.00
51-76 size class not represented in the stand
>76 100 (n=1)

See Growth models for information on predicting rates of postfire development of tanoak sprouts.

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Spring and fall prescribed fires on the Challenge Experimental Forest significantly reduced tanoak density and frequency in postfire year 2 compared to pretreatment levels. Treatments compared effects of fire season and fuel loads on 3 mixed-conifer-hardwood sites, although tanoak was only present on the Challenge site. Early and late spring burning resulted in greatest tanoak reduction (P<0.05), followed by early and late fall fires (P<0.1). The Research Project Summary of Kauffman and Martin's [114,116,117,118] study provides survivorship and pre- and postfire density and frequency information for tanoak and associated species, and discusses management implications of the study results.

Tanoak sprouts may facilitate conifer seedling establishment on severely burned and other harsh sites [197]. See Other Management Considerations for details.

Silvicultural management and postfire succession: Management activities such as logging and site preparation can alter postfire successional pathways and influence relative composition of hardwoods, including tanoak, in mixed-evergreen forests. In 1994, Weatherspoon and Skinner [244] studied the effects of prefire management on wildfire behavior and damage to the overstory (crown scorch) after the 1987 Hayfork Fire Complex. Study sites were in Douglas-fir-tanoak-Pacific madrone types logged before the wildfire. They found that on sites next to clearcuts, fire behavior and fire effects were greatly influenced by prefire management of the clearcuts. Overstory trees adjacent to clearcuts where slash was not removed after harvest were more likely to sustain crown damage compared to trees near clearcuts that were either machine-piled or broadcast burned after harvest. Management of nearby stands also affected fire damage in plantations, with plantation trees adjacent to uncut stands or partially cut stands with logging damage incurring more crown scorch than trees next to either piled or broadcast-burned sites. Plantation trees next to partially cut stands without postharvest treatment had greatest damage. Conifer plantations with high grass and forb cover and/or at low elevation had significantly more crown scorch compared to plantations with high cover of tanoak and other hardwoods and/or those at high elevation (P<0.001) [244].

A study on the Klamath National Forest, California, was conducted to determine how silvicultural treatments influenced postfire species composition on Douglas-fir/tanoak/deerbrush (Ceanothus integerrimus) sites 2 years after the Hotelling Fire and on Douglas-fir/tanoak-canyon live oak sites 12 years after the Hog Fire. The 2 sites supported both seral and old-growth forests prior to wildfire. The wildfires removed 100% of the woody plant cover of both seral and old-growth forests. Treatments were: 1) logging and plantation planting 10 to 20 years prior to wildfire, 2) postfire salvage logging, site preparation, and plantation planting, and 3) an unlogged, unplanted control. The study found that the 12-year-old Hog Burn had more shrub and hardwood cover than the 2-year-old Hotelling Burn (P<0.001). Treatment effects were not yet discernible on the Hotelling Burn. On the Hog Burn, unsalvaged sites had more cover of forbs and shrubs than salvaged sites (P=0.006 and P<0.001 for forbs and shrubs, respectively). Cover of hardwoods (including tanoak) and shrubs was greater on salvaged than unsalvaged sites (P=0.007 and P=0.003 for hardwoods and shrubs, respectively). Postfire coverage of tanoak alone was not provided. Old-growth sites had greater postfire cover of hardwoods and conifers, and less forb coverage, than seral sites (P=0.0041, P<0.001, and P<0.001 for hardwoods, conifers, and forbs, respectively). There were no significant differences in vegetation cover between planted and unplanted sites. The researchers predicted that tanoak and other hardwoods would continue to dominate salvaged sites for decades, probably interfering with growth of young Douglas-firs. They recommend frequent understory burning of mixed-evergreen forests to reduce the likelihood of stand-replacement burns such as the Hotelling and Hog fires [214].

FIRE MANAGEMENT CONSIDERATIONS:
More than a hundred years of fire exclusion have greatly altered successional pathways of mixed-evergreen and redwood/tanoak forests. Tanoak is not threatened with decline by large wildfires like the Biscuit Fire and Hayfork Fire Complex. Many authorities predict tanoak increases under a regime of wildfires that are larger and more severe than those recorded in the past [2,61,144,196]. It is the conifer overstory that is at risk from such wildfires. In a satellite-imagery study of forests managed under the Northwest Forest Plan from 1994 to 2003, Moeur and others [160] found that "fire is the most stochastic factor, yet arguably the most important influence on the future condition of the older forest system in the Plan area, at least in the dry provinces". Douglas-fir/tanoak forests in the Siskiyou and Klamath mountains lie directly within the dry-province region. The researchers note that past management practices—especially fire exclusion and logging practices that greatly reduced the hardwood component of forest—and climate change have worked in concert to greatly increase susceptibility of old, dry-mesic forest types such as Douglas-fir/tanoak to large wildfires. In the Klamath Mountains, the majority of old forests lie within current-fire-condition classes mapped as having missed at least one fire-return interval, with an associated buildup of fuels. Such highly at-risk forests would benefit from restoration activities such as thinning and broadcast underburning. They conclude that in the "fire-prone ecosystems most at risk, the possibility of major loss of older forests cannot be ignored". Moeur and others cautioned that the scale of information used in the analysis was coarse, and call for further studies to increase understanding of the relationships between fire management and management of forest composition and structure [160].

Researchers recommend frequent prescribed surface fires to reduce fire hazard in mixed-evergreen forests and mixed-conifer forests with a tanoak component [5,18,40,214]. Agee and Edmonds [5] caution that site preparation and underburning must occur over large areas to be effective. A 1st fire in an area where fire has long been excluded consumes many fuels, but small-diameter trees killed by prescribed fire create new dead fuels. They recommend a 2nd fire within 10 years of the 1st to reduce fire hazard and open the understory. Collins and others [40] provide thinning and fire prescriptions used to reduce basal area of overstory trees and understory plant density on the Blodgett Forest Research Station. Treatment stands were in a mixed conifer-hardwood forest with tanoaks in the overstory [40].

Fuel mastication translocates dead and live tanoak and other midstory fuels to the forest floor, increasing loading of dead woody surface fuels. On mixed-evergreen forest study sites in southwestern Oregon and northern California, mastication of live tanoak, Pacific madrone, and manzanita (Arctostaphylos spp.) understories significantly increased 1- and 10-hour time-lag fuels and total woody fuel loads compared to untreated sites (P<0.001). Across sites, surface fuel depth did not predict surface fuel loads (R²=0.24, P=0.22), probably due to differences in machinery and operator experience. The researchers were therefore unable to develop a model predicting total fuel loading after mastication, and called for further modeling research to predict how mastication affects fuel loads in mixed-evergreen forests [112].

As of 2008, little research had been conducted on interactive effects of sudden oak death disease and fire (see Other Management Considerations and the Sudden oak death disease section of Fuels). Therefore, tanoak decline and fuel increases resulting from the disease are not incorporated into tanoak growth and fuel models presented in this review. Research on how sudden oak death disease affects all aspects of tanoak biology—including biomass production, die-back and mortality, and response to fire—and modification of existing models will be needed if sudden oak death disease further decimates tanoak populations.

MANAGEMENT CONSIDERATIONS

SPECIES: Lithocarpus densiflorus
IMPORTANCE TO WILDLIFE AND LIVESTOCK:
Wildlife Tanoak provides habitat and food for a variety of forest-dwelling mammals and birds [18,20,165,189]. As a consistent acorn producer (reviews by [140,191]), tanoak acorns may be especially important when oak acorn crops are scant. Studies in northern California showed that abundance of 12 bird, 7 mammal, and 5 salamander species increased with increasing tanoak canopy volume. Northern flying squirrels, Allen's chipmunks, and dusky-footed woodrats were especially dependent on tanoak mast and/or nesting cover [165,180]. Mule deer consume tanoak browse and acorns [192]. Chipmunks, squirrels, and northern raccoons also eat tanoak acorns [189,192,224]. In addition to the acorns, the ectomycorrhizal fungi infecting tanoaks are important foods for northern flying squirrels [34]. Many bird species consume tanoak acorns [224] including the acorn woodpecker [78,186,189,238], Steller's jay, and varied thrush [80]. Chickadees and other gleaning birds forage on tanoak [29].

Ralph and others [179] provide inventories of breeding birds and small mammals using Douglas-fir/tanoak habitat in southwestern Oregon and northwestern California. Rosenberg and Raphael [187] provide a survey of vertebrates using Douglas-fir/tanoak habitat on the Six Rivers, Klamath, and Shasta-Trinity National Forests, California. Welsh and Lindi [246] give an inventory of herptiles using Douglas-fir/tanoak habitats in Oregon and northern California.

Young tanoaks may tolerate browsing better, or are selected less often, than associated oaks. In the Santa Lucia Mountains, tanoak seedlings were "heavily browsed" by mule deer. Despite that, tanoak seedlings were growing faster and showing better survivorship than valley oak and interior live oak seedlings [75].

Species of concern: Young- [56] and old-growth Douglas-fir-tanoak and redwood-Douglas-fir-tanoak forests provide favorable habitat for northern spotted owls [102]. A well-developed tanoak or mixed-hardwood subcanopy is an important structural component of both northern spotted owl habitats [128] and those of their main prey, dusky-footed woodrats [230]. Subcanopy structure open enough to allow development of large overstory trees is optimal for northern spotted owls. Dense subcanopies reduce northern spotted owl habitat quality due to reduced hunting success and increased mortality of small-diameter conifer stems, which cannot serve as northern spotted owl nest snags. Canopy gaps increase northern spotted owl habitat quality in dense forests. Thinning and/or prescribed fire may be required for northern spotted owl management in some conifer/tanoak habitats [227]. Studies of redwood-Douglas-fir/tanoak habitat in Humboldt and Del Norte counties, California, showed seral forests with basal areas of 23 to 69 m²/ha gave best reproductive success for northern spotted owls. Such stand structure also tends to increase dusky-footed woodrat populations [230]. Northern spotted owls may use tanoaks for resting and hiding cover. A northern spotted owl in Mendocino County was observed using a tanoak branch fork as a cache site for rodent carcasses [102]. Although they nest in tanoak ecosystems, northern spotted owls do not usually select tanoaks as nest trees [94,227,230]. Dusky-footed woodrats, however, may preferentially select tanoak canopies or downed logs as denning and/or nesting sites [165,180]. California spotted owls use ponderosa pine/hardwood and mixed-conifer/hardwood forests with a tanoak component for nesting habitat [36,79,242]. See the FEIS review of spotted owl for further information on managing forests as spotted owl habitat.

Marbled murrelets use redwood/Douglas-fir/tanoak habitat for nesting [199]. Mixed-evergreen forests with tanoak provide habitat for fishers [254,255]. Rosenberg and Raphael [187] identified fishers, ringtails, spotted owls, sharp-shinned hawks, blue grouse, pileated woodpeckers, and Pacific giant salamanders as species of potential concern due to vulnerability of Douglas-fir/tanoak forests on the Six Rivers, Klamath, and Shasta-Trinity National Forests, California, to fragmentation.

Livestock readily consume tanoak acorns, although browse use is variable. Cattle, domestic goats, and domestic and feral pigs eat the acorns [192,224].

Palatability/nutritional value: Palatability of tanoak browse may vary with phenological stage and availability of more palatable browse. Trichomes on twigs and young leaves are distasteful [192,224] and easily inhaled during foraging [224]. Cattle may selectively browse mature leaves [124], which are not tomentose. On the Blodgett Forest Research Station, tanoak was the most preferred browse of cattle, comprising 8% to 39% of the total cattle summer diet [124]. In general, tanoak browse is rated palatable to mule deer and unpalatable to cattle and domestic horses, sheep, and goats [192].

Tanoak acorns have a high fat content [224] and are palatable to cattle and a number of wildlife species [224]. They are rated highly palatable to mule deer [192]. Wolf [253] provides a nutritional analysis of tanoak acorns.

Cover value: Tanoak provides hiding, thermal, and nesting cover for many mammal and bird species [18,20]. For example, band-tailed pigeons in Humboldt County, California, used tanoaks for nesting cover. Overall stand structure of the Oregon white oak-Pacific madrone-tanoak forest was dense [67]. Other information on wildlife use of tanoak cover is provided in Importance to Wildlife and Livestock.

VALUE FOR REHABILITATION OF DISTURBED SITES:
Tanoaks provide watershed protection and are valuable wildlife trees [20], but they are usually left to reproduce naturally on restoration sites. Tanoak is difficult regenerate artificially. McDonald and others review nursery practices for propagating tanoak [154] and provide information on techniques that may improve establishment rates of artificial tanoak regeneration [153], but conclude that "how to achieve consistent and reliable seedling growth remains a mystery" [154].

OTHER USES:
Tanoak wood is used for lumber and a variety of other hardwood products. Tanoak's leaf and twig trichomes shed when disturbed. They irritate skin and are easily inhaled, making it unpleasant to log in tanoak forests [6,152,165,180].

Tanoak's common name comes from the past use of tannin, extracted from tanoak bark, for tanning saddle and other heavy leathers. In the early twentieth century, tanoak was so heavily harvested for its tannin that some managers expressed concern for its eventual elimination (reviews by [154,189]), [172,253].

Native Americans preferred tanoak acorns over those of all western oak species for food [38,156,189,224]. After leaching the acorns, they ground tanoak acorns and used the meal in breads, porridges, and puddings [38,189]. The Costanoan used a tanoak bark infusion as a wash for facial sores and to tighten loose teeth (review by [54]).

OTHER MANAGEMENT CONSIDERATIONS:
Tanoak is the most common hardwood in Douglas-fir, redwood, and Port-Orford-cedar timber stands of southwestern Oregon and northwestern California [189]. Its management is confounded by its importance as a wildlife tree and its interference with growth of timber trees [189,224].

Tanoak can slow overall growth rates of young seral conifers [48,49,87,104,148,178,223]. A study in southwestern Oregon, for example, found competition with tanoak sprouts for light and water reduced Douglas-fir sapling growth [87,88]. Complete removal of tanoak sprouts maximized Douglas-fir growth, while removal of 50% or more of the tanoak sprouts produced a productive, mixed-conifer-hardwood stand [89]. A study on the Challenge Experimental Forest found tanoak outcompeted ponderosa pine seedlings for space, and that reducing tanoak density increased ponderosa pine seedling growth rate [169]. Atzet and others [20] recommend controlling tanoak sprouts soon after fire or logging on timber sites. They write "the time and energy required to shift the dominance in favor of the crop tree species increases significantly with delays". They emphasize that unit boundaries and sizes, site preparation, cutting prescriptions, and timely postharvest or postfire planting can all be modified to minimize growth of tanoak and sprouting shrubs, reducing the need for chemical control [18,20]. Historically, surface fires may have helped keep cover of tanoak and other hardwoods low, so frequent preharvest underburning may reduce the need for postharvest tanoak control [18].

Despite its ability to outcompete conifers, tanoak is an important part of mixed-conifer-hardwood ecosystems, providing species and structural diversity and wildlife food. Extreme reduction or elimination of tanoak by chemical or other means may actually slow conifer establishment [157,197] by removing shade protection, which can facilitate conifer seedling establishment on some sites. A survey of severely burned Douglas-fir/tanoak sites in the Klamath and Siskiyou mountains showed conifer seedling abundance was positively associated with cover of sprouting hardwoods and shrubs [197]. On an Oregon clearcut, Douglas-fir and white fir established beneath tanoak sprout clumps. Light intensity was reduced under tanoak, but was "sufficient" for conifer growth. Soil moisture content was generally higher under tanoak than in the open. The researcher concluded that on hot southwestern aspects and other harsh sites, clumps of tanoak and other sprouting hardwood species provide nurse sites for conifer seedlings, but the hardwoods would probably slow conifer growth in later growth stages [157].

Control:
Chemical control— Researchers at Oregon State University's Forest Research Laboratory found picloram + triclopyr spraying gave 90% to 100% tanoak control for 2 years; 2,4-D (water carrier), glyphosate, or triclopyr gave 60% to 90% control; and 2,4-D (oil carrier) or picloram + 2,4-D gave 25% to 60% control [42]. Trials in coastal northern California found painting newly-harvested tanoak stumps with 2,4-D in October gave nearly 100% control of tanoak sprouts for 3 years [119]. Tappeiner and others [224] provide an in-depth analysis of chemical treatments used to control tanoak sprouts on Douglas-fir/tanoak timber sites in Oregon.

Slashing— Hobbs [96] reviews strategies for manual control of tanoak including effects of various timings, frequencies, and intensities of slashing. McDonald and Fiddler [149,150] analyze manual and chemical treatments successfully used to control tanoak on a medium-productive Douglas-fir plantation on the Six Rivers National Forest.

Damaging agents: Tanoaks are windfirm and fairly resistant to insect and fungal attacks until fire or other injury damages the bole. Several root- and stem-rotting fungi may infest injured tanoaks. Of these, Armillaria mellea generally causes greatest damage. Several insects feed on tanoak, but their damage is usually minor. California oakworms (Phryganidia californica) may cause local defoliations [224]. Until the mid-1990s, tanoak was relatively disease-free. Since then, the forest disease sudden oak death has become an extremely serious threat to tanoak [35].

Tanoak is more susceptible to damage and death from Phytophthora ramorum, the fungus-like water mold causing sudden oak death disease, than any other known North American plant. Moist, mixed-evergreen and redwood/tanoak forests are the water mold's primary habitat in North America [11,35,64,184,241]. Phytophthora ramorum infection is nearly always fatal to tanoaks, although mature trees may take several years to die [11,241]. All sizes and ages of tanoak are susceptible to leaf, branch, bole, bark, and/or root infection [35]. Sudden oak death disease has caused extensive mortality of tanoaks in Oregon and coastal California [35,43,55,63,166]. Tanoaks in large, continuous forests may be more susceptible to infection than tanoaks in fragmented forests, where spread of the water mold's spores is apparently more limited [43]. Field monitoring in Marin County, California, showed a progression of total infection rates (tanoak + all oak species) of 39.0% in 2000 to 62.4% in 2003, with a consummate rise in mortality from 3.8% to 9.4% [35]. Fuel loads may increase as a result of mortality from sudden oak death disease.

Phytophthora ramorum is apparently nonnative, although its geographic origin is uncertain [184]. Based on genetic studies that showed a "limited gene pool" for North American Phytophthora ramorum populations compared to European populations, Garbelotto and others [64] speculate that the water mold is "an introduced organism, but its actual origin and global genetic structure remain unknown."

The water mold's life cycle is complex, involving tanoaks and red oaks (Erythrobalanus) as primary hosts and many potential intermediate plant hosts, most of which are native. Some intermediate hosts show symptoms of infection and some do not. The California Oak Mortality Task Force [35] website provides lists of known intermediate hosts—including frequently associated species such as California bay (Umbellularia californica), redwood, toyon (Heteromeles arbutifolia), and Pacific rhododendron (Rhododendron macrophyllum)—and information on forest sanitation practices that may reduce sudden oak death disease spread. For further information, see these sources: [55,63,212]. The website Monitoring Sudden Oak Death provides county and regional maps of infestations in California. The Pacific Southwest Region of the US Department of Agriculture, Forest Service, provides annual monitoring updates on their Forest Pest Conditions website. Fungicides for controlling Phytophthora ramorum are being investigated. Prescribed burning in Marin County did not control Phytophthora ramorum (see Sudden oak death disease); however, further studies on possible control of Phytophthora ramorum with fire were ongoing in 2008. Federal and State agencies in Oregon are testing a clearcut-and-burn treatment for infected sites in southwestern Oregon [64]. Treatment results were not available as of 2008.

Actual methods of Phytophthora ramorum spore dissemination were not documented as of 2008. Suspected mechanisms include wind, water, soil, sap-sucking insects and other animal vectors, and transported firewood [11,45,65]. Bark beetles often attack infected trees [155], but they are apparently secondary agents, not sudden oak death vectors [65].

Sudden oak death disease reduces habitat quality for wildlife species, such as the acorn woodpecker, the oak titmouse, and the dusky-footed woodrat, that depend on tanoaks and oaks for food and/or cover. Regression models predict population declines for tanoak- and oak-dependent bird species where tanoak and oak populations decline as a result sudden oak death disease [161].

Lithocarpus densiflorus: REFERENCES


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