COMMON OAK: CHARACTERISTICS, HABITAT, DISTRIBUTION, CULTIVATION - BIOLOGY - 2024

The common oak (Quercus robur) is an arboreal species of great size and natural slow growth of the European continent. Oak trees are large deciduous trees belonging to the Fagaceae family that live for more than 800 years.

Adult specimens can reach 45-50 m in height, with a particularly short, thick, sloping or sinuous trunk and a very leafy crown. The large deciduous leaves have an elliptical shape and lobed margins of a light green, dark green or red-brown color depending on each stage of development.

Quercus robur. Source: Ilme Parik

Like all monoecious species, it has male and female flowers on the same trunk. Male flowers arranged in long hanging clusters or catkins of yellowish tones, and small female ones in groups of 2-3 units of whitish tone.

The common oak adapts to various types of soil and continental climates. However, it prefers humid but well-drained soils, with a clay-loam texture and a high content of organic matter.

Its distribution is located from the north of Spain to the south of the Scandinavian countries, and from the United Kingdom to the countries of Eastern Europe. In fact, it is frequently located in the Ural Mountains, at altitudinal levels from sea level to 1,800 meters above sea level.

This forest species is of great importance from an ecological and economic point of view. It is used as a regenerator of silvicultural environments, the high quality wood is used in construction and navigation, as well as in tannery, artisanal medicine and nutritional supplement.

General characteristics

Root

Deep root system with a main root that during the first stages of growth reaches 1-2 m deep. From 8-10 years, the development of the secondary root system of wide lateral extension begins.

Trunk

The straight and cylindrical trunk 2 m wide, reaches up to 40 m in height with a wide and oval crown. The bark is smooth and grayish in color when young, and deeply cracked and dark gray in color when adult.

Leaves

The alternately arranged deciduous leaves are oblong or spatulate, 5-20 cm long by 2-10 cm wide. It is wider towards the upper third, with small apricots at the base and a lobed margin with small pointed teeth.

The coloring of the leaves is dark green on the upper side and slightly yellowish on the underside. During the autumn they acquire various reddish tones as the leaflets dry out.

The leaves have a small petiole 2-7 mm long, being smaller than the petiole of the Quercus petreae species (sessile oak), with which it is regularly confused.

Quercus robur male flowers. Source: AnRo0002

flowers

The common oak is a monoecious plant with male and female flowers with well marked morphological differences. The male flowers appear as small hanging catkins of a yellowish-green color.

The female ones appear in small glabrous axes in groups of 2-3 units attached to a long peduncle from the upper leaves. Flowering occurs in mid-spring, between the months of March and May.

Fruit

The fruit is an ovoid acorn 3-4 cm long with a reddish-brown color, lacks streaks and its dome is platiform in appearance. It is attached to the branches by a long peduncle, inside a seed that matures from spring to summer is located.

In Quercus robur, acorns have a bitter and astringent taste due to their high tannin content. Other species have developed acorns with a sweet and pleasant taste that constitute the food base of various wild animal species.

Fruits of Quercus robur. Source: Photo: Bff / Wikimedia Commons

Taxonomy

- Kingdom: Plantae.

- Subkingdom: Tracheobionta.

- Division: Magnoliophyta.

- Class: Magnoliopsida.

- Subclass: Hamamelidae.

- Order: Fagales.

- Family: Fagaceae.

- Genus: Quercus.

- Subgenus: Quercus.

- Section: Quercus.

- Species: Quercus robur L.

Subspecies

Taxonomically described three subspecies:

- Quercus robur subsp. robur, distributed throughout the eastern region of the Iberian Peninsula, reaching the western limits of Galicia.

- Quercus robur subsp. broteroana Schwarz, located in northern Portugal and northwestern Spain. The lobes of its leaves are shallower, the upper surface bright and the domes larger (15-23 mm).

- Q. robur subsp. Estremadurensis (Schwarz) Camus, located from north-central Portugal, to the western region of the Sierra Morena. Its thin, lustrous leaves with secondary veining lack intercalary veins.

Etymology

- Quercus: the name of the genus comes from the Latin «quercus» which means oak, the sacred tree of the god Jupiter.

- robur: the specific adjective derives from the Latin «robur, roboris» in references to very hard woods with great vigor, heavy and robust.

Quercus robur leaves. Source: Daniel Capilla

Habitat and distribution

The common oak grows preferably on loose, acidic and well-developed soils, although it tolerates compact, slow-draining soils. It lives in regions with a temperate climate, requires full sun exposure in the early stages of growth and is susceptible to summer drought.

It is located at altitude levels up to 1,800 meters above sea level, on deep soils, in humid or oceanic climate conditions. It requires soils free of lime and with some humidity, it is resistant to low temperatures, but it does not tolerate drought.

It grows wild forming extensive forests, both alone and in association with species such as Fagus sylvatica or common beech. As well as with oak forests of the Quercus pirenaica or Quercus petraea species, with whom it is usually easily hybridized.

It is distributed throughout much of Europe, the Caucasian region, and East Asia. In the Iberian Peninsula it is located in the northwestern region bordering Portugal, Galicia, Asturias, Cantabria, the Basque Country and Navarra, up to Cáceres and Salamanca.

In the same way, it is distributed by León, Palencia, Huesca, La Rioja and Catalonia. In addition, it forms small forests in some mountainous regions of the interior, being cultivated for years in the Casa de Campo in Madrid.

Quercus robur during the fall. Source: AnRo0002

Cultivation and care

- Spread

The common oak reproduces through fresh seeds obtained from its acorns. The use of old or dry seeds is not recommended, since they substantially lose their germination percentage when dehydrated.

The most appropriate is to use seeds from native plantations, adapted to the edaphoclimatic conditions of the area where the new plantation will be established. Oak seeds require a scarification process, which allows hydration of the germ and favors its germination.

In the same way, it is suggested to subject the seeds to a stratification process by applying natural or artificial cold. In a natural way, the seeds are kept exposed to the low winter temperatures for three months before starting sowing.

Artificially, the seeds wrapped in a vermiculite substrate are kept refrigerated at 6ºC for three months. Later they are sown in polyethylene bags with a fertile substrate and constant humidity until they sprout.

The establishment of the definitive plantations is carried out on soils with good moisture retention, but well drained. Likewise, high ambient humidity is desirable, since very dry summers have a negative influence on the development of the plantation.

On the other hand, this species resists summer climates, even occasional frosts below -15 ºC average temperature. Temperatures that oscillate between 18-20 ºC are favorable for their growth, mainly in the juvenile development phase.

Irrigation should be done frequently and abundantly, avoiding saturation of the soil and waterlogging at all times. During their growth they do not require maintenance pruning, only the removal of diseased and damaged branches.

Quercus robur seedling. Source: AnRo0002

- Agroclimatic requirements

Floor

Oak grows effectively on clay, clay-loam and sandy-loam soils. In a wide range of pH, from acid, neutral or alkaline.

Irrigation

Its water needs are subject to environmental conditions, solar radiation, temperature, soil texture and seasonal cycle. During the summer, more frequent irrigation is required, preferably interday, with salt-free rainwater.

Weather

Oak is tolerant of hot weather, occasional droughts, and high winds. It requires full sun exposure and adapts to semi-shade conditions but does not tolerate full shading.

Radiation

It is not demanding in terms of solar radiation. It develops under conditions of full solar radiation or semi-shade, never under severe shading.

- Care

The location is one of the main aspects to take into account when establishing the common oak plantation. Due to its high growth, planting near buildings, roads, drainage channels or underground pipes should be avoided.

In addition, the planting density must be taken care of, since each unit develops a rounded, wide and very extensive crown. During its establishment it requires effective weed control, as well as regular fertilization, preferably with organic fertilizers.

Buds of Quercus robur. Source: AnRo0002

Plagues and diseases

Among the main pests that influence oak forest productivity are gallaritas wasps and lepidopteran larvae. Wasps of the genus Amphibolips and Diplolepis are cynipid insects that produce galls on different parts of the plant.

The presence of galls does not cause substantial damage to the tree, unless it exceeds the economic damage threshold. In this case, it requires special management through cultural management and application of specific insecticides.

On the other hand, some galls produced by certain insects, such as the hymenoptera Cynips gallae tinctoriae, are widely used for their high tannin content. These galls are used to obtain pharmaceutical products, as well as to make blue or black ink.

On the other hand, some Lepidopteran caterpillars feed on the buds or tender shoots of oaks. Marumba quercus is a moth of the Sphingidae family whose caterpillars feed on various species of oak.

Among the most common diseases are anthracnose, chlorosis, chalariosis, black mold and root rot. Sudden oak death is a disease caused by the phytophthora fungus, which affects varieties grown in the US, UK and Germany.

Applications

Nutritional

Oak acorns are usually consumed as nuts in confectionery, as well as cooked and ground to obtain flour. Despite the high content of nutrients, acorns contain low digestible tannins and an unpleasant taste.

The cut and roasted acorns can be dried and ground to be used as a thickener, or mixed with wheat to make bread. The tannins present in acorns destined for human consumption can be easily removed by washing with running water.

To facilitate washing, the acorns are cut and crushed to speed up the removal of astringent elements. In a traditional way, the crushed acorns are wrapped in a cloth, and left in a stream to be washed naturally.

Another method is to bury the whole seeds at the beginning of the winter season. In spring, when starting the germination process, the seeds will have lost their astringent flavor and will be ready for human consumption.

Wood

Its wood is heavy and hard, dark brown in color, highly resistant to humidity and rot. It is widely used in furniture making, carving, cabinetmaking, cooperage and general carpentry.

Due to its resistance to humidity and ability to remain unaltered under water, oak wood is used in the naval industry. In railway construction, the sleepers between the train tracks and the locomotives are made of oak, due to its ability to resist constant vibrations.

In cabinetmaking, oak wood allows the obtaining of furniture and finished pieces of great artistic value.

Quercus robur wood. Source: Sten Porse

Tannery

Tannins used in the leather tanning industry are obtained from the bark and acorns of the Quercus robur species. The tannins processed with iron sulfates allow the production of dyes of purple tones that are highly appreciated for their great resistance to washing.

Ornamental

Oak is a species of great ornamental value widely used in squares, parks and gardens. The color appeal you experience with the arrival of autumn changes profusely from yellow to reddish tones.

Some commercial varieties have been developed for ornamental purposes, such as atropurpurea, fastigiata, filicifolia, longifolia, pendula or variegata, among others.

Insecticide

The remains of leaves that fall under the canopy of oaks are used as biological control to eliminate worms and pests in some horticultural crops. However, fresh leaves are not recommended for mulching as they can inhibit the growth of certain crops.

References

1. Ducousso, A., & Bordacs, S. (2004) Quercus robus / Quercus petraea. Technical guide for genetic conservation and utilization. Euforgen (European Forest Genetic Resources Program).
2. Fernández López, MJ, Barrio Anta, M., Álvarez Álvarez, P., Lopez Varela, B. & Gómez Fernández, JA (2014) Quercus petraea (Matt.) Liebl. Production and management of seeds and forest plants. pp. 264-291.
3. Gómez, D., Martínez, A., Montserrat, P., & Uribe-Echebarría, PM (2003). Oak (Quercus robur L.) and other boreal plants in crisis in the Moncayo Massif (Soria, Zaragoza). Collect. Bot, 26, 141-157.
4. Portillo, A. (2001) Roble. Quercus robur L. (phagaceae). Practical Pharmacy. Medicinal Plants and Vegetable Drugs. Pharmacology and Pharmacognosy Unit. Pharmacy faculty. University of Barcelona.
5. Quercus robur. (2019). Wikipedia, The Free Encyclopedia. Recovered at: es.wikipedia.org
6. Quercus robur (2019) Types of trees. Recovered at: elarbol.org
7. Oak, Carballo, Pedunculated Oak. (2017) Infojardin. Recovered at: infojardin.com
8. Sánchez de Lorenzo-Cáceres, JM (2014) Quercus robur L. Spanish Ornamental Flora. Ornamental Trees. Recovered in: arbolesornamentales.es