Tanoak (Lithocarpus densiflorus): what the agencies record

This page reports what US federal publications say about one tree. It does not identify trees from descriptions or photos and does not say what should be done with any tree. The family overview, tree species in the agency records, explains the sources and holds the comparison table. A separate page covers sudden oak death, a disease the 1990 handbook chapter does not discuss.

At a glance

Item	What the source records
Scientific name	Lithocarpus densiflorus (Hook. & Arn.) Rehd., beech family (Silvics). USDA PLANTS lists it as Notholithocarpus densiflorus, symbol NODE3
Other name, Silvics	Tanbark-oak
Native status, USDA PLANTS	Native in the lower 48 states
Size, Silvics	Mature trees are generally 15.2 to 27.4 m (50 to 90 ft) tall; the largest diameter of record is 277 cm (109 in), on a tree near Kneeland, Humboldt County, California, 30.5 m (100 ft) tall with a crown spread of 23.2 m (76 ft)
Green weight of the wood, NRS-38	65 lb per cubic foot, without bark

Native range and climate

The Silvics of North America handbook (Agriculture Handbook 654, Volume 2, 1990) reports a disjunct stand slightly north of the Umpqua River in southwestern Oregon as the northernmost limit, with the general northern limit in the Coast Ranges farther south in the Coquille River drainage. The range runs south through the California Coast Ranges to the Santa Ynez Mountains north and east of Santa Barbara, and northeast from the Humboldt Bay region to the lower slopes of Mount Shasta, then intermittently south along the western slopes of the Sierra Nevada as far as Mariposa County. Tanoak is most abundant, and generally reaches its largest sizes, in Humboldt and Mendocino Counties, California.

The handbook classes the climate as humid but seasonal, with annual precipitation of 1,020 to 2,540 mm (40 to 100 in), about 70 percent of it falling between November and February and only 5 percent from June through September. Mean daily temperatures run from 2 to 6 degrees C (36 to 42 degrees F) in January to 16 to 23 degrees C (60 to 74 degrees F) in July. Elevation runs from sea level to 1,220 or 1,525 m (4,000 or 5,000 ft) in the Coast Ranges, and the handbook gives 580 to 1,220 m (1,900 to 4,000 ft) in the northern Sierra Nevada. It says tanoak grows best on deep, well-drained loamy, sandy or gravelly soils, is seldom found on heavy clays, and is limited to a shrubby form on serpentine soils. It calls tanoak the most abundant hardwood in the timber stands of the California Coast Ranges, usually found with Douglas-fir and redwood.

Acorns and seedlings

Silvics describes a monoecious tree with erect male catkins 5 to 10 cm (2 to 4 in) long, blooming mostly in June, July or August, and acorns that ripen in the second autumn and drop between September 20 and November 15. Acorns are 2.5 to 5.1 cm (1.0 to 2.0 in) long. The handbook calls tanoak a heavy seeder, with viable seed generally abundant after the 30th to 40th year and trees heavily laden almost every alternate year. One estimate puts a veteran tree 76 cm (30 in) in diameter at about 454 kg (1,000 lb) of acorns a year, over 110,000 acorns.

Insect larvae infested 51 percent of the acorns in one study, and the handbook says at least 38 animal species eat them. In one count, only one seedling grew from 156 sound acorns. Germination rates in a limited number of tests ran from 19 to 80 percent. Seedlings begin forming burls below ground at 1 to 2 years of age, and after 6 to 12 years the original stem dies and a new top replaces it, so seedlings become what the handbook calls seedling-sprouts.

Sprouting and growth

The handbook says tanoak reproduces prolifically by sprouts from woody buds under the bark at the base of the tree, mostly on burls below the groundline, after fire, logging, bark stripping or even a minor basal injury. As many as 1,400 sprouts were counted on one large stump, and in clearcuts sprouts reached 1.7 m (5.6 ft) in the first year and 4.1 m (13.6 ft) after 5 years. Tanoak is classed as tolerant of shade and, because it sprouts and seeds, is considered a climax species in Douglas-fir, redwood and mixed-conifer forests. Silvics notes that sprouts often provide severe competition to conifer seedlings.

Form varies: in dense conifer stands tanoaks develop one central axis and trunks clear for 9.1 to 24.4 m (30 to 80 ft), while in open stands they branch freely with short thick trunks. The handbook gives the tallest tree reported as 63.4 m (208 ft) and 137 cm (54 in) in diameter, in Monterey County. It says the age of tanoak is difficult to ascertain, and that trees 51 to 152 cm (20 to 60 in) in diameter were from 150 to 250 years old at one location. Sapwood is extremely thick, reaching 66 percent even on large trees, and leaves persist for 3 to 4 years. A shrubby variety, echinoides, grows near Mount Shasta, in the Trinity Alps, and through the Klamath and Siskiyou Mountains into southern Oregon.

Wood

The Wood Handbook (FPL-GTR-282, 2021) says the sapwood is light reddish brown when first cut and darkens until it is almost indistinguishable from the dark reddish brown heartwood. It calls the wood heavy and hard, with strength properties like those of eastern white oak except for compression perpendicular to grain, and says tanoak shrinks more than white oak and tends to collapse during drying. It describes the wood as quite susceptible to decay, with sapwood that takes preservatives easily, and names flooring, truck flooring and preservative-treated railroad crossties among its uses. Tanoak was also known as tanbark-oak because high-grade tannin was once obtained from its bark in commercial quantities.

Wood Handbook figure	Green	At 12% moisture content
Specific gravity (Table 5-3b)	0.58	Not published
Modulus of rupture, lbf per square inch (Table 5-3b)	10,500	Not published
Side hardness, lbf (Table 5-3b)	Not published	Not published

The green weight is in the NRS-38 table, the same figure used in the log weight calculator.

Damaging agents the handbook names

Fire. Silvics calls fire the principal enemy of individual trees. Ground and crown fires are sometimes fatal, but more often leave long vertical wounds 1.2 to 3.0 m (4 to 10 ft) up the trunk. Small-tree wounds often heal over, while on older trees fungi usually enter and the exposed wood rots. One study found saw log cull of 39 percent in cull trees and 13 percent across all trees.
Rots and leaf spot. Beefsteak fungus (a brown cubical rot), weeping conk (a white root rot) and Schizophyllum commune (a sap rot on injured areas) are named, with susceptibility to shoestring root disease and a commonly seen leaf spot caused by Ceuthocarpum conflictum.
Insects. Armored scales, a whitefly, a mealybug and other sap feeders are listed, and the handbook says damage is generally not economically significant. In 1957 the California oakworm completely destroyed that year's foliage on tanoaks at one site in Trinity County, a localized event. Twig girdlers and a false powderpost beetle prune and girdle twigs and small limbs.
Unexplained decline. Decline of sprout vigor was observed in mixed conifer-hardwood forests in the central Sierra Nevada, where affected clumps were only one-fifth as tall as unaffected clumps; the handbook says the reason was not known.
Browsing. Livestock avoid tanoak if better feed is available and mule deer rarely browse it; the new growth is protected by abundant stellate hairs.

The handbook says tanoak is relatively free from insect attacks and fungal diseases until injured by fire. For who takes reports of regulated pests, see reporting a pest in the United States, and pests and diseases by country sets out which ones agencies regulate.