Common Name: Californian Black Oak

General Information

Quercus kelloggii is a deciduous tree with a broad, rounded crown; it usually grows up to 25 metres tall, occasionally reaching 36 metres or more. The straight, cylindrical bole is usually 30 - 140cm in diameter, exceptionally to 200cm; when growing in forest conditions it can be free of branches for up to 12 metres. At the higher elevations of its range, or on dry, infertile sites, the plant often becomes scrubby[].
Long used as a staple food by native N. Americans, the acorns are still harvested in quantity and are a potential commercial crop[]
Although Quercus kelloggii faces competition from more shade-tolerant trees in some areas due to fire suppression, and could face pressure in the future from harvesting for lumber and other wood products, this species currently seems to be secure when examining its entire range. The plant is classified as 'Least Concern' in the IUCN Red List of Threatened Species(2013)[].

Known Hazards

All parts of the plant contain tannins. Whilst tannins are found in many foods, and have a range of medicinal uses. They are usually only present in low concentrations. In some foods made from oaks (particularly the seeds), the tannin content can be quite high unless the food is treated to reduce tannin content.
Tannins are only of low toxicity and, because of their bitter taste and astringency, are unlikely to be eaten in large quantities. However, if they are taken in excess, they can cause stomach pains; constipation followed by bloody diarrhoea: excessive thirst; and excessive urination[].

Botanical References

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Range

South-western N. America - southwestern Oregon, California

Habitat

Found in a variety of forest habitats, growing on clay or gravelly soils in hills and mountains; at elevations below 2,500 metres[, , ]. Sometimes forms groves of considerable extent in coniferous forests[].

Properties

Conservation Status	Least Concern
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Deciduous Tree
Height	20.00 m
Pollinators	Wind
Cultivation Status	Ornamental, Semi-cultivated, Wild

Cultivation Details

Quercus kelloggii grows in the mainly mediterranean climate of southwestern N. America, with wet, mild winters and hot, dry summers. Most of the annual precipitation (around 80 - 90%) falls from November to April. The mean annual precipitation ranges from 300 - 3,000mm, with up to 80% of total precipitation falling as snow. Summer temperatures can reach 39°c, with winter lows down to -20°c[]. The plant usually grows well in areas with cooler summers, but then often does not fruit well[].
Grows best in a sunny position[], though young plants tolerate reasonable levels of side shade[]. Requires a well-drained soil[]. Prefers a good deep fertile loam, though it can also tolerate shallow, rocky soils[, , ]. Tolerates moderate exposure, surviving well but being somewhat stunted[]. Established plants are highly drought tolerant[].
California black oak was profoundly important to local Native American tribes. The acorns were a tribal food staple and many villages were located near the oak groves. The acorns were a primary source of tribal wealth and a much-desired trade item for desert tribes without ready access to acorns. Oak woodlands were managed as orchards on many sites - the trees were pruned, and stands thinned and burned to enhance acorn production[].
California Black Oak acorns are still gathered by people of many different tribes in California and southern Oregon and known as the most edible of the oak acorns in the region. Although not currently so utilized, the acorns are a potential source for commercial food production[].
A very ornamental plant, often grown as a shade tree[].
The tree flowers on new growth produced in spring, the seed taking two summers to ripen[].
Seedlings soon develop a taproot and become intolerant of root disturbance, they should be planted into their permanent positions whilst young[].
The tree sprouts freely from the base if it is cut down or is top-killed by fire[]. Fire is important habitat factor that promotes the growth of this species at the expense of others, especially conifers - it resprouts freely before the conifers can become re-established, allowing it to become the climax tree in the area[].
Hybridizes freely with other members of the genus[]. It hybridizes in the wild with Quercus agrifolia and Quercus wislizenii[].
California Black Oak is particularly susceptible to fungi, especially heart rot of the bole and large limbs due to the pathogens Inonotus dryophila and Laetiporus sulphureus. Older trees, if infected, are often reduced to shells, and by the time a stand is 85 years old the proportion of infected trees begins to increase rapidly, growing to almost 40% infected at 110 years. However, there is not evidence that these pathogens are currently causing significant damage to the species[].
This species is notably resistant to honey fungus[, ].

Edible Uses

Seed - cooked[, , ].Used as a staple food by several native North American Indian tribes[]. A bitter taste prior to leaching[]. The seed is considered to have a superior taste and a pudding-like texture when cooked, it can be mixed with other oak meals in order to improve meal flavour and texture[]. The seed is 21 - 34mm long and 14 - 22mm wide[, ].
The seed is usually cooked before eating, though it can also be eaten raw. It can be eaten whole, though it is more commonly dried, then ground into a powder and used as a thickening in stews etc or mixed with cereals for making bread.
In some species, especially many of those classified as 'white oaks', the seeds are low in tannins and have a more or less sweet and agreeable flavour. The seed of most species, however, have a very bitter flavour, due especially to the presence of tannins. In these species there are various processes that can remove or at least reduce the amount of these bitter substances (although other water-soluble substances, including some minerals, will also be removed).
Tannins are water-soluble and therefore the easiest way to remove or reduce tannin levels is by soaking in water. A few different methods are listed:-
A traditional method of preparing the seed was to bury it in boggy ground overwinter and allow the wet soil to gradually leach the tannins. The germinating seed was dug up in the spring when it would have lost most of its astringency and bitterness.
Another method was to wrap the seeds in a cloth bag and place them in a stream for several weeks.
Drying the seed and grinding it to a powder before soaking speeds up the process. The fastest method is to use hot water, by cooking the powder and changing the water several times until the cooking water is no longer bitter. Alternatively, you can use cold water (which is reported to produce the best quality flour). In this case, you soak the powdered seed in cold water for 12 - 24 hours then discard the water. Repeat this process for a number of times until the soak water is no longer bitter.

The roasted seed of many Quercus species has been used as a coffee substitute.

Medicinal

Quercus (oak) species are used in the traditional medicine of many cultures, being valued especially for their tannins. Various parts of the plant can be used, most frequently it is the leaves, bark, seeds, seed cups or the galls that are produced as a result of insect damage. A decoction or infusion is astringent, antibacterial, antifungal, antiseptic, styptic and haemostatic. It is taken internally to treat conditions such as acute diarrhea, dysentery and haemorrhages. Externally, it is used as a mouthwash to treat toothache or gum problems and is applied topically as a wash on cuts, burns, various skin problems, haemorrhoids and oral, genital and anal mucosa inflammation[]. Extracts of the plant can be added to ointments and used for the healing of cuts[, ].

Black oak flour that has gone mouldy in storage has been used to treat boils and sores[].

Agroforestry Uses:

Within its native range, the tree is used for wildlife habitat restoration, and its well-established roots reduce erosion and protect watersheds. Mature trees are windfirm[].

Other Uses

The leaves of most species in this genus are more or less rich in tannins. A mulch of the leaves can be placed around vulnerable plants in order to repel slugs, snails, grubs etc. Fresh leaves should be used with caution, since these can utilize some of the nitrogen in the soil and this inhibit plant growth[, ].

Oak galls are excrescences that are sometimes produced in great numbers on the tree and are caused by the activity of the larvae of different insects. The insects live inside these galls, obtaining their nutrient therein. When the insect pupates and leaves, the gall can be used as a rich source of tannin, that can also be used as a dyestuff[]. The galls have been used as a dark dye for the hair[].
A black dye can be made from the bark[].

Acorn meal has been used to mend cracks in clay pots[].

Young shoots, produced after a tree has been top-killed, are used in basketry[].

The wood is coarse-grained, heavy, hard, strong, very brittle, not very durable. It is of little economic importance, but is occasionally used for fence posts and as a fuel[, ].
Since the 1960s, several mills in northern California have commercially produced lumber from Quercus kelloggii, more than half of which is of the highest grade. The wood is strong, with a light reddish-brown colour and ascetically pleasing grain patterns. It is used for making furniture, panelling, cabinets, shipping pallets, industrial flooring and other valuable products, while scraps from the mills are used for packaged firewood, mulch and livestock bedding[, ].
The wood is a good fuel, burning well with a lot of heat[, ].

Propagation

Seed - it quickly loses viability if it is allowed to dry out. It can be stored moist and cool overwinter but is best sown as soon as it is ripe in an outdoor seed bed, though it must be protected from mice, squirrels etc. Small quantities of seed can be sown in deep pots in a cold frame. Plants produce a deep taproot and need to be planted out into their permanent positions as soon as possible, in fact seed sown in situ will produce the best trees[]. Trees should not be left in a nursery bed for more than 2 growing seasons without being moved or they will transplant very badly.