Common Name: Encina

General Information

Quercus agrifolia is an evergreen shrub or a tree growing 6 - 25 metres tall. Open grown trees have a broad, dense crown, branching from around 2 metres from the ground, whilst in closed stands the bole can be 6 metres tall before branching. The bole can be 30 - 120cm in diameter[, ]
The tree is harvested from the wild for local use as a food, medicine and source of materials. Wild stands are sometimes managed for the production of firewood, as well as the commercial production of charcoal.[, ]. The tree is used in land rehabilitation projects within its native range and is also often grown as an ornamental.
Although Quercus agrifolia faces threats in certain localities, especially from human development and sudden oak death, it covers a wide range and has not experienced a significant decline, nor is it believed to face future rapid decline. 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 - western California, Baja California.

Habitat

A dominant tree, forming open groves of great extent in valleys and on not too dry slopes in woods; also co-dominant in walnut woodland and mixed evergreen forest; and found as a shrub on coastal sand dunes; at elevations to 1,500 metres[, , ].

Properties

Conservation Status	Least Concern
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	15.00 m
Growth Rate	Slow
Pollinators	Wind
Cultivation Status	Ornamental, Semi-cultivated, Wild

Cultivation Details

Quercus agrifolia is not very cold-hardy, tolerating temperatures falling to around -8°c when dormant. It grows in a mediterranean climate, characterized by mild, wet winters and hot, dry summers. It generally adapts well to maritime climates, though will often not fruit well unless the summers are hot[, , ]. Trees fruited very heavily at Kew Gardens, London (hardiness zone 7 - 8) in the hot summer of 1989[].
Prefers a good deep fertile loam which can be on the stiff side[, ]. Plants are lime tolerant[]. Young plants tolerate reasonable levels of side shade[]. Tolerates moderate exposure, surviving well but being somewhat stunted[]. Established plants are moderately drought resistant[].
Seedlings soon develop a taproot and become intolerant of root disturbance, they should be planted into their permanent positions whilst young[]. As trees grow older, the taproot usually becomes non-functional, the tree developing an extensive system of surface roots[].
Native Americans used to plant the seeds of this tree in favoured positions so that they could harvested the acorns for food. The tree is planted as an ornamental, often being used as a street tree or in parks etc[].
A slow-growing but long-lived tree in the wild, with trees more than 250 years old[, ].
The tree flowers on new growth produced in spring, the seed ripening in its first year[, ].
The bark of mature trees is thick and can protect the tree from moderate fires, though severe fires will usually kill top growth[].
Trees can resprout from the trunk and/or root crown if they are felled or top-killed by fire[].
This is the dominant tree in California's southern and central coastal oak woodlands, and populates the chaparral phase of the southern oak woodland as a shrub[].
The bark of immature trees is smooth and develops deep ridges with age, with branches often reaching the ground in areas lacking grazing. Providing some of the most important habitats for many insects, birds and mammals in California, Quercus agrifolia also feeds many birds and rodents with its acorns, and provides a critical source of food for Black-tailed Deer with its foliage[]
Hybridizes freely with other members of the genus[].
This species reportedly hybridizes with Quercus kelloggii and Quercus wislizenii[].
Mature Quercus agrifolia are very susceptible to sudden oak death, which can wipe out an initially healthy tree within a few weeks to several years. In California the disease has reached "epidemic proportions" and there is particular risk on California's central coast[].
This species is notably resistant to honey fungus[, ].

Edible Uses

Seed - cooked[, , , , ]. The seed is 15 - 35mm long and 10 15mm wide[]. It is used as a staple food by several native North American tribes[]. It can be dried, ground into a powder and used as a thickening in stews etc or mixed with cereals for making bread. The seed is up to 40mm long and 20m wide[, ], contains bitter tannins.
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[, ].

A decoction of the chipped bark has been used as a wash on skin sores[].

Agroforestry Uses:

Quercus agrifolia aids in the control of erosion by stabilizing soil on slopes, and is favoured for use in rehabilitation projects including watershed improvement and wildlife habitat restoration. It is also an important element in landscaping[].

Other Uses

The leaves of most species in this genus are more or less rich in tannins. A mulch of the partially decayed leaves can be placed around vulnerable plants in order to repel slugs, snails, grubs etc, and these will in time break down to add humus and nutrients to the soil. Fresh leaves should be used with caution, however, since as these decay they utilize some of the nitrogen in the soil and thus can 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 and is also used by many cultures to make ink[, ].
The bark of oak trees is also usually rich in tannins and can be used as a dyestuff and for waterproofing rope[, ].

The seed cups are used as buttons[].

The wood is fine-grained, hard, very heavy but also very brittle. It is not exploited commercially because it cracks easily and warps badly[1050.
The wood is highly valued as a fuel and is used to make a good quality charcoal[, , , ]. Wild stands are sometimes managed for the production of firewood, as well as the commercial production of charcoal.[, ].

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.