Notholithocarpus densiflorus, commonly known as the tanoak or tanbark-oak, is a broadleaf tree in the family Fagaceae, and the type species of the genus Notholithocarpus. It is native to the far western United States, particularly Oregon and California. It ranges from 15–40 meters (49–131 feet) in height, with a trunk diameter of 60–190 centimeters (24–75 inches).
It can reach 40 meters (130 feet) tall in the California Coast Ranges, though 15–25 m (49–82 ft) is more usual,[2] and can have a trunk diameter of 60–190 centimeters (24–75 inches). The bark is fissured, and ranges from gray to brown.[2]
The leaves are alternate, 8–13 cm (3–5 in), with toothed margins and a hard, leathery texture,[2] and persist for three to four years. At first they are covered in dense orange-brown scurfy hairs on both sides, but those on the upper surface soon wear off; those on the under surface persist longer but eventually wear off too.
The seed is an acorn 2–3 cm (3⁄4–1+1⁄4 in) long and 2 cm in diameter, very similar to an oak acorn, but with a very hard, woody nut shell more like a hazel nut. The nut sits in a cup during its 18-month maturation; the outside surface of the cup is rough with short spines.[2] The nuts are produced in clusters of a few together on a single stem.
Currently, the largest known tanoak specimen is on private timberland near the town of Ophir, Oregon. It has a circumference of 7.9 m (26 ft), is about 2.51 m (8 ft 3 in) in diameter at breast height, and is 37 m (121 ft) tall with an average crown spread of 17 m (56 ft).[3]
N. densiflorus var. echinoides in Berkeley, California
Acorn of N. densiflorus
Members of populations in interior California (in the northern Sierra Nevada) and the Klamath Mountains into southwest Oregon are smaller, rarely exceeding 3 m (9 ft 10 in) in height and often shrubby, with smaller leaves, 4–7 cm (1+1⁄2–2+3⁄4 in) long; these are separated as "dwarf tanoak", Notholithocarpus densiflorus var. echinoides. The variety intergrades with the type in northwest California and southwest Oregon. Tanoak grows as a shrub on serpentine soils.
By 2008, the species was moved into a new genus, Notholithocarpus (from Lithocarpus), based on multiple lines of evidence.[4] It is most closely related to the north temperate oaks (Quercus) and not as closely related to the Asian tropical stone oaks (Lithocarpus, where it was previously placed), but instead is an example of convergent morphological evolution.
While related to oaks (as well as chestnuts), the name is written as 'tanoak' because it is not a true oak.[2]
It is native to the far western United States, found in southwest Oregon and in California as far south as the Transverse Ranges and east in the Sierra Nevada. It grows from sea level to elevations of 1,200 m (3,900 ft).[2]
Tanoak is shade tolerant and benefits from disturbances. It is susceptible to wildfire, wounds from which are exploited by rot fungi.[2] It one of the species most seriously affected by "sudden oak death" (Phytophthora ramorum), with high mortality reported over much of the species' range.[5]
Fine hairs on the young leaves and twigs discourage deer from eating them.[2] Various animals, including squirrels, deer and bears, eat the nuts.[2]
The nut kernel is very bitter, and is inedible for people without extensive leaching. Some California Native Americans prefer this nut to those of many oak acorns because it stores well due to the comparatively high tannin content. The Concow tribe call the nut hä’-hä (Konkow language).[6] The Hupa people use the acorns to make meal, from which they would make mush, bread, biscuits, pancakes, and cakes. They also roast the acorns and eat them.[7] Roasted, the seeds can be used as a coffee substitute.[8]
The name tanoak refers to its tannin-rich bark, a type of tanbark, used in the past for tanning leather before the use of modern synthetic tannins. By 1907, the use of tanoak for tannin was subsiding due to the scarcity of large tanoak trees. There were not enough trees around for a worthwhile economic return. By the early 1960s, there were only a few natural tannin operations left in California. The industry was beginning to switch to a synthetic alternative.[9] Tanoak tannin has been used as an astringent.[10]
A mulch made from the leaves of the plant can repel grubs and slugs.[8]
The wood is strong and sometimes used as lumber, but suitable trees are usually inaccessible. It is also used as firewood.[2]
Notholithocarpus densiflorus, commonly known as the tanoak or tanbark-oak, is a broadleaf tree in the family Fagaceae, and the type species of the genus Notholithocarpus. It is native to the far western United States, particularly Oregon and California. It ranges from 15–40 meters (49–131 feet) in height, with a trunk diameter of 60–190 centimeters (24–75 inches).
