Tanoak (Lithocarpus densiflorus), also called tanbark-oak, is an evergreen hardwood that, with other species in the genus, is considered a link between the chestnut, Castanea, and the oak, Quercus. Tanoak has flowers like the chestnut and acorns like the oak. This medium-sized tree grows best on the humid moist slopes of the seaward coastal ranges. It usually occurs in a complex mixture with conifers and other hardwoods, but often forms pure even-aged stands. The wood is hard, strong, and fine-grained. Tanoak is designated a commercial species in California. Current major uses are for fuel and pulp. The acorns are a valuable food source for many kinds of wildlife.
A disjunct stand slightly north of the Umpqua River in southwestern Oregon has been reported as the northernmost limit of tanoak’s natural range. The general northern limit of tanoak in the Coast Ranges, however, is farther south in the Coquille River drainage. Its eastern limit in Oregon extends from west of Roseburg to Grants Pass, and then southwesterly into the Applegate River drainage. Tanoak’s range stretches southward through the Coast Ranges in California to the Santa Ynez Mountains north and east of Santa Barbara, CA. The range also extends northeastward from the Humboldt Bay region to the lower slopes of Mount Shasta, then intermittently southward along the western slopes of the Sierra Nevada as far as Mariposa County. In the Sierra Nevada, tanoak is most common between the Feather and American Rivers.
Tanoak grows in a climate broadly classified as humid. Annual precipitation, however, is seasonal and varies from 1020 to 2540 min (40 to 100 in). Some precipitation is snow. Summer and early fall are dry and the winter rainy. From June through September rainfall totals less than 25 min (1 in) a month. In fact, precipitation during these months amounts to only 5 percent of the year’s total. Most of the precipitation-about 70 percent-falls between November and February.
Average mean daily temperatures range from 2° to 6° C (36° to 42° F) during January and 16° to 23° C (60° to 74° F) in July. The season free of killing frosts begins between March 8 and April 30 and ends between October 20 and November 20, varying in length between 160 and 249 days. Over a 30-year period the maximum temperature recorded at 183 in (600 ft) elevation in the center of tanoak’s area of maximum development was 45° C (113° F).
Soils and Topography
Tanoak grows well on a variety of soils developed from igneous, metamorphic, or sedimentary rocks, or sedimentary rock alluvium. It grows best on soils that are deep, well-drained, and loamy, sandy, or gravelly. Tanoak also grows on soils derived from serpentine, which are intermediate between the moist and dry extremes, but is limited to a shrubby form. It is seldom found on heavy clayey soils.
High-site soils for redwood (Sequoia sempervirens) or Douglas-fir (Pseudotsuga menziesii), such as the Hugo, Sheetiron, Josephine, Empire, Larabee, Sites, and Melbourne series, are also well suited for the growth of tanoak. These soils have been derived from either consolidated or soft sedimentary rocks. They are light grayish brown or light reddish brown to brown in color and are moderately to strongly acidic. Soil textures grade through gravelly loam, sand loam, fine sandy loam, loam, silt loam, to clay loam. Soil orders are mostly Inceptisols and Alfisols.
Besides growing well on deep soils, tanoak also thrives on stony and shallow soils that are less suitable for conifers. Yet tanoak requires more moisture than many other hardwoods. It will grow well on the shallow and stony soils of north slopes, for example, but will be supplanted by Pacific madrone (Arbutus menziesii), Oregon white oak Quercus garryana), or California black oak (Q. kelloggii) on the warmer, drier south slopes.
Throughout the Coast Ranges from the northern limit of tanoak’s distribution (lat. 43° 42° N.) to the Santa Lucia Mountains (lat. 35° 40°N.) tanoak grows from sea level to elevations of 1220 or 1525 in (4,000 or 5,000 ft). The terrain is rough, steep, and extremely dissected by both major streams and smaller drainages. In the Santa Ynez Mountains, at the southern limit of its range (lat. 34° 34° N.), tanoak grows at 730 to 1435 in (2,400 to 4,700 ft). In the northern Sierra Nevada, it grows between elevations of 580 and 1220 in (1,900 and 4,000 ft) and in the central Sierra Nevada between 915 and 1525 m (3,000 and 5,000 ft). At its southern limit in the Sierra Nevada, tanoak is found between 1525 to 1980 in (5,000 and 6,500 ft) near Signal Peak (lat. 37° 32° N.) in the Sierra National Forest (24).
Tanoak is most abundant and, in general, attains its largest sizes in Humboldt and Mendocino Counties, CA, between elevations of 150 to 915 in (500 to 3,000 ft) on northerly and easterly slopes and toward the summits of the seaward exposures of the Coast Ranges. In the southern Coast Ranges, tanoak is common in the Santa Cruz and Santa Lucia Mountains, particularly on the westerly slopes. And in the central Sierra Nevada, where the climate is less humid, it grows in valleys, coves, ravines, along streams, and on north slopes.
Associated Forest Cover
Tanoak grows within the life zones classified as the Canadian and Transition. It is the most abundant hardwood species in timber stands of the Coast Ranges of California and southwestern Oregon. Tanoak is a common component in the following forest cover types: Redwood (Society of American Foresters Type 232), Pacific Ponderosa Pine (Type 245), Pacific Ponderosa Pine-Douglas-Fir (Type 244), Sierra Nevada Mixed Conifer (Type 243), and California Coast Live Oak (Type 255). It is a particularly important component of Pacific Douglas-Fir (Type 229) and Douglas-Fir-Tanoak-Pacific Madrone (Type 234).
The principal body of tanoak is a broad band along the inland side of the redwood belt. Here tanoak sometimes forms almost pure stands (6). More often it is an understory tree with Douglas-fir or is a component of hardwood stands or mixed hardwood-conifer forests. The most common hardwood associated with tanoak is Pacific madrone. Other frequent hardwood associates include giant chinkapin (Castanopsis chrysophylla), canyon live oak (Quercus chrysolepis), California black oak Q. kelloggii), and California-laurel (Umbellularia californica). Tanoak is found most often with Douglas-fir and redwood. Other common conifer associates are California white fir (Abies concolor var. lowiana), Sitka spruce (Picea sitchensis), sugar pine (Pinus lambertiana), ponderosa pine (P. ponderosa var. ponderosa), California torreya (nutmeg) (Torreya californica), and western hemlock (Tsuga heterophyl1a).
A large variety of shrubs, forbs, grasses, sedges, and ferns are also associated with tanoak. Generally these plants are not abundant on forested land, but, with tanoak sprouts, often become aggressive on burned or cutover areas. Among the most common shrubs are blueblossom (Ceanothus thyrsiflorus), California hazel (Corylus cornuta var. californica), salal (Gaultheria shallon), Pacific bayberry (Myrica californica), Pacific rhododendron (Rhododendron macrophyllum), flowering currant (Ribes sanguineum), thimbleberry (Rubus parviflorus), western poison-oak (Toxicodendron diversilobum), and California huckleberry (Vaccinium ovatum).
Two smaller plants producing woody growth above ground are prince’s-pine (Chimaphila umbellata var. occidentalis) and Oregon grape (Berberis nervosa). Many forbs and grasses are plentiful in the tanoak range. Among the most important forbs are bull thistle (Cirsium vulgare), New Zealand fireweed (Erechtites arguta), Australian fireweed (E. minima), and western whipplea (Whipplea modesta). Common grass species include California brome (Bromus carinatus), soft chess (B. mollis), California fescue (Festuca californica), and California sweetgrass (Hierochloe occidentalis). Western swordfern (Polystichum munitum) and western bracken (Pteridium aquilinum var. pubescens) sometimes grow abundantly with tanoak. Sedges (Carex spp.) also are represented in some places.
The Indians in California’s North Coast Range obtained one of their principal foods from tanoak. In fact, the main fare of many Indian communities was salmon and tanoak acorns. The large acorns were ground, leached, and then prepared as a soup, cooked mush, or a kind of bread. After being leached, the acorns are said to have an agreeable acid taste. They also contain a comparatively large amount of oil. On this account, tanoak acorns were preferred by local Indians over all other kinds. Ground tanoak acorns have also been fed to chickens.
Tannin from tanoak bark has properties intermediate between chestnut tannin and the usual oak tannin of commerce. The extract from tanoak bark, however, furnishes the best tannage known for the production of heavy leathers. For example, it gives excellent plumping when used to tan sole or saddle leather. The superiority of tanoak bark extract is attributed to the presence of certain other acids, such as gallic and acetic, with the tannic acid. Tanoak tannin has also been used medicinally as an astringent.
One successful attempt to graft European chestnut (Castanea sativa) scions to tanoak stumps has been reported from southern Mendocino County.