Lithocarpus densiflorus

Tanoak

Fagaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Magnoliophyta. Class - Magnoliopsida. Order - Fagales. Family - Fagaceae (Beach family). Genus -Lithocarpus. Species - Lithocarpus densiflorus (Hook. & Arn.)

Ecology: Tanoak grows as an evergreen tree or shrub. The typical variety is a medium-sized tree, usually attaining 20-24 m heights. Mature tanoaks have deep taproots and an extensive network of lateral and surface roots. Tanoak is shade tolerant when young 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. Sprouts tolerate full sunlight better than seedlings. Once seedlings establish, however, shade slows their growth. Most rapid growth occurs with top light when there is a conifer canopy, so tanoak is well adapted to a subcanopy position.

Identification

Shrubs or trees , to 20(-45) m. Bark gray or brown, smooth or deeply furrowed. Twigs densely yellowish tomentose. Leaf blade adaxially convex, to 60-120 mm, leathery to brittle, margins often revolute, regularly toothed, teeth prominent to obscure; surfaces abaxially prominently and densely woolly, often glabrate at maturity, revealing gray or bluish green waxy surface, veins often distally impressed. Fruits: cup scales subulate, spreading to strongly recurved, hooked; nut yellowish brown, globose to cylindric-tapered, to 15-35 mm, extremely hard, densely tomentose, eventually glabrate.

Threats

Pathogens: Tanoak is extremely susceptible to damage and death from Phytophthora ramorum, the fungus-like water mold causing sudden oak death disease.

Fire Effects: 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. Large trees usually survive moderate-severity fire, bearing fire scars afterward. Even tanoaks with thick bark (3-10 cm) typically sustain bole damage from fire. Fire scars may extend 1-3 m up the trunk. Severe fire generally top-kills mature tanoaks and may kill small trees. Tanoak sprouts from the burl after top-kill by fire. Even seedlings may sprout after fire...Seedlings are not as common on burns as sprouts, 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. Animal caches and on-site, surviving parent tanoaks are likely seed sources for postfire tanoak seedling establishment.

Reproduction

Tanoak is wind pollinated and monoecious...The flowers are spiky catkins. Pistillate and staminate catkins may be on the same or separate stalks.

Seed production - Tanoak is a masting species. Acorn production varies across years, but no western oak species produces acorn crops as reliably as tanoak. Tanoak burl sprouts may first produce acorns at 5 years of age, with maximum production beginning at age 30 to 40. Tanoak acorns mature in their second year. Open-grown tanoaks tend to produce heavier crops than trees in shade.

Seed dispersal - The fruit is an acorn - a type of nut - ranging from 2-3 cm long. Acorns are usually borne singly but may occurs in clusters of 2 to 4...Tanoak acorns are large and heavy, so they generally fall and remain beneath the parent tree unless dispersed by animals. Acorn-predatory rodents and birds disperse tanoak acorns. 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. S

Seedling establishment - Tanoak acorns are not dormant, and shade does not hinder germination.

Vegetative regeneration - Tanoak sprouts from the burl after fire, cutting, or other top-killing events. It is a strong sprouter, usually dominating the overstory where it was a subcanopy or shrub-layer dominant before top-kill.

Species Distribution

Citation

USFS Plant Database
Habeck, R. J. 1992. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

USDA Plants Database
USDA, NRCS. 201. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.

Flora of North America
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 19+ vols. New York and Oxford.