Common Name: Tanbark Oak

General Information

Notholithocarpus densiflorus is an evergreen shrub or a tree that sometimes is no more than 3 metres tall, more usually grows up to 20 metres tall, exceptionally reaching 45 metres. Trees growing in the subcanopy usually have narrow crowns, while open-grown trees have broad, rounded crowns. The bole is usually straight and cylindrical, though occasionally is crooked; when grown in forest conditions it can be free of branches for 9 - 24 metres and 20 - 80cm in diameter. Mature trees have deep taproots and an extensive network of lateral and surface roots[, ].
The tree is harvested from the wild for local use as a food, medicine and source of materials. The tree has been harvested on a commercial basis for its wood and also for the tannins in its bark. It is sometimes grown as an ornamental.

Known Hazards

The tree's leaf and twig trichomes shed when disturbed. They irritate the skin and are easily inhaled, making it unpleasant to log in tanoak forests[].

Botanical References

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Range

Southwestern N. America - southern Oregon and California.

Habitat

Mixed evergreen forest and redwood forest, open conifer forest, margins of woods, on slopes and dry slopes; at elevations up to 2,200 metres[, ]. Fertile mountain slopes[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	10.00 m
Growth Rate	Slow
Cultivation Status	Ornamental, Wild

Cultivation Details

Notholithocarpus densiflorus is a moderately cold-hardy tree, tolerating occasional temperatures down to around -15°c when dormant. It grows best in areas with to a mediterranean climate modified by cool-moist coastal air currents. It grows in a region where the mean annual precipitation ranges from 1,020 - 2,540mm, with rainy winters and dry summers and autumns. Productive tanoak sites are humid, with plentiful moisture from soil, rain, fog, low clouds, and/or high humidity.
Both young and older trees are shade tolerant; they also grow well in full sun[]. Prefers a deep fertile soil with medium drainage[], growing in the wild on a variety of soil types[, ].
A slow-growing tree in the wild, living up to 300 - 350 years old[].
Plants usually flower in the spring and sometimes again in the autumn[]. The seeds take two seasons to ripen[]. Prolific crops are usually produced every other year in the wild[].
The mean annual production of trees with boles between 45 - 60cm in diameter is estimated at 3,900 - 4,600 acorns. 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. Tanoak acorn production in a heavy seed year ranged from 220,000 - 420,000 sound acorns per hectare[].
Tanoak seedlings quickly develop a burl at the base of the trunk from which they can resprout if damaged. The burl is already partly effective within a few days of germination and is fully developed within about 5 years[]. Young plants often die back to this burl for no apparent reason. The original seedling stem typically dies back by the time the plant is 6 - 12 years old, with the new stem being somewhat stouter stem than the original. The tree can die back and resprout from the burl at least 3 to 5 times by the age of 60, even when top-killing events are not apparent. The burl buds divide as the burl enlarges, so the number of subsurface buds increases as tanoaks age. One large tanoak stump supported about 1,400 buds. Open-grown tanoaks tend to produce more sprouts/burl than tanoaks in shade. The sprouts can be very dense after logging or fire, often forming extensive stands[].

Edible Uses

Seed - cooked[, ]. The seed was a staple food for several native North American Indian tribes[]. It contains bitter-tasting tannins and there are various ways of removing them. The fastest is by soaking the ground-up seed in hot water - if the water is changed at least once the tannins should be removed within 12 hours. Traditionally, the seeds were placed in a cloth bag and either buried in swampy ground or suspended in a running stream for a few months. Once the tannins have been removed, the seed is then dried, ground into a powder and can be used as a porridge or can be mixed with cereal flours in baking bread etc[, ]. It has a pleasant taste after it has been leached[]. The yellowish brown, globose to cylindric-tapered nut is 15 - 35mm long and wide[, , ].

The seed is valued for its oil[].

Medicinal

The bark is very astringent. An infusion is used as a wash for face sores[]. The infusion can also be held in the mouth to tighten loose teeth[].

Other Uses

The bark is exceedingly rich in tannin, yielding up to 29%[, , , ]. It has been used as a brown dye and also to preserve rope that is being used in water[, ].

The wood is hard, strong, close grained, brittle. It is not commercially important and is used mainly for fuel[, ].

Propagation

The seed is best sown as soon as it is ripe in the autumn in a cold frame[]. It needs to be protected from mice, squirrels and other seed eaters. The seed has a short viability but can be stored for a few months if kept cool and slightly damp - the salad compartment of a fridge is a good storage place. Germination takes place in the winter or early spring. When they are large enough to handle, prick the seedlings out into individual pots. If the plants are 15cm or more tall by the summer they can be planted out into their permanent positions. Give them a good weed-excluding mulch and some protection from the cold for their first couple of years outdoors. If growth is not sufficient then grow them on in the greenhouse for their first winter and plant them out into their permanent positions in late spring or early summer, after the last expected frosts.