CORK OAK: CHARACTERISTICS, HABITAT, CULTIVATION, CARE - BIOLOGY - 2025

The cork oak (Quercus suber) is a medium-sized arboreal species with evergreen foliage that belongs to the Fagaceae family. Natural of the Mediterranean basin, it usually forms dense and leafy forests, especially in hot and humid environments.

Robust in appearance and slow growing, it is 10-15 m high, sometimes reaching 25 m, it has an abundant and irregular crown. Its main characteristic is a thick, cracked, waxy bark that is collected periodically due to its ability to restore once harvested.

Cork oak (Quercus suber). Source: LPLT

It grows on loose, slightly acidic soils devoid of lime, in areas with a cool and somewhat humid climate with a certain coastal influence. Unlike other species of the Quercus genus, this species does not tolerate soils of limestone origin and is susceptible to frost.

The cork oak is a very prolific tree from which cork, wood and its acorns are used. Cork is used in the manufacture of stoppers for the wine industry, soles for footwear, ropes and sheets for thermal or acoustic insulation.

On the other hand, the hard and tenacious wood is used in the manufacture of barrels and shipbuilding, as well as firewood for combustion. In addition, acorns are the ideal food to fatten Iberian pigs, and in some urban areas it is sown as an ornamental species.

General characteristics

Appearance

- Subgenus: Quercus

- Section: Cerris

- Species: Quercus suber L.

Shapes

- Quercus suber f. brevicupulata (Batt. & Trab.) FM Vázquez 1998

- Quercus suber f. clavata (Cout.) FM Vázquez 1998

- Q. suber f. dolichocarpa (A. Camus) FM Vázquez 1998

- Q. suber f. longicalyx (A. Camus) FM Vázquez 1998

- Quercus suber f. macrocarpa (Willk. & Lange) FM Vázquez 1998

- Quercus suber f. microcarpa (Batt. & Trab.) FM Vázquez 1998

- Q. suber f. racemosa (Borzí) FM Vázquez 1998

- Q. suber f. suboccultata (Cout.) FM Vázquez 1998

Cork oak leaves (Quercus suber). Source: Krzysztof Ziarnek, Kenraiz

Etymology

- Quercus: the name of the genus comes from Latin to designate oak and holm oak in a similar way.

- Suber: specific adjective derived from Latin meaning "cork."

Synonymy

- Quercus mitis Banks ex Lowe, Trans. Cambridge Philos. Soc. 4 (1): 15 (1831).

- Quercus corticosa Raf., Alsogr. Amer.: 24 (1838).

- Q. occidentalis Gay, Ann. Sci. Nat., Bot., IV, 6: 243 (1856).

- Q. suberosa Salisb. in AP de Candolle, Prodr. 16 (2): 392 (1864).

- Quercus rises St.-Lag., Ann. Soc. Bot. Lyon 7: 133 (1880).

- Quercus cintrana Welw. ex Nyman, Consp. Fl. Eur.: 662 (1881).

- Q. sardoa Gand, Fl. Eur. 21:58 (1890), opus utique oppr.

- Q. occidentalis f. Globa-Mikhailenki heterocarpa, Byull. Glavn. Bot. Sada 80: 29 (1971).

Habitat and distribution

Quercus suber is a species native to the Mediterranean basin, southwestern Europe and northwestern Africa. It is even found in the wild in Morocco, Algeria, Tunisia, Spain, Portugal, France, Italy and the islands of Sardinia, Corsica and Sicily.

In the Iberian Peninsula it predominates in the southwestern quadrant, being cultivated as an ornamental in parks and gardens, especially in the Andalusia region. Some references place the origin of Quercus suber in the Iberian Peninsula, a region where it currently has great phenotypic diversity.

Cork oak forest. Source: Georges Jansoone

In Portugal and Spain it is widely marketed for its high quality cork used in the wine industry. Likewise, it is found in the wild throughout the Eastern Pyrenees, in the Italian peninsula and the region of the former Yugoslavia.

This species grows on soils of siliceous origin with good drainage, in regions with cold and humid winters, but not very dry warm summers. On hills or slopes with low inclination, between 300-600 meters above sea level and even up to 1,000 meters above sea level.

The optimal range of temperature oscillates between 13-18 ºC of annual average, being the winter cold a limitation of growth at continental level. Usually, its vegetative activity is paralyzed at temperatures below 3 ºC and it does not tolerate values ​​lower than 0 ºC.

It requires full sun exposure as an adult, but during its juvenile phase it requires some level of semi-shading. Regarding humidity levels, it adapts to rainfall values ​​above 450 mm per year, its optimum being between 600-1,000 mm per year.

On the other hand, it has particular edaphic requirements, since it only develops on acid substrates with good drainage and excellent aeration. It is a calcifugal species, that is, it does not develop on soils rich in calcium or magnesium carbonates, unless they are completely decarbonized.

It is one of the most representative species of Mediterranean forests. Indeed, it requires a greater amount of humidity, is susceptible to low temperatures and does not support limestone soils compared to holm oaks more adapted to continental conditions.

Culture

These plants reproduce sexually by seeds, being collected directly from the tree and stored for a short time in humid and cold environments. For its use, the dome covering the seed must be eliminated through a screening, winnowing and flotation process.

Cork oak seeds do not require pregerminative treatment, but it is advisable to soak them for 48 hours before sowing. The seeds collected in autumn can be stratified in sand or humid peat for 30-60 days at 0-2 ºC to favor their rooting.

Cork oak seedlings (Quercus suber). Source: Auckland Museum

Sowing is done in autumn with freshly collected seeds or in spring with previously stratified seeds. When the seeds have been stratified, there is a small root 2-5 cm in length, which it is recommended to prune prior to sowing.

Under nursery conditions, sowing is done in polyethylene bags with fertile and humid substrate. Maintaining the conditions of temperature and humidity, germination begins 4-6 weeks after sowing. The seedlings will be ready to transplant at 25-40 cm tall.

Care

It adapts to various types of soils, whether they are loose, deep, well drained and slightly acidic, never of calcareous origin. In addition, it requires full sun exposure to develop properly.

During its youthful phase it needs regular watering during the summer and spring, with less intensity during the autumn and winter. Adult plants, already established and well rooted, are more resistant to drought and require occasional watering.

It grows effectively in Mediterranean conditions with a mild climate and less intense frosts, where the sea breeze softens the temperature and the environment is more humid. On the contrary, the ripening of the fruits would be delayed if the plant is grown in cold and temperate climates.

In the growth phase it is recommended to carry out maintenance pruning during the spring, in order to structure a rounded crown. Likewise, frequent sanitation pruning is necessary during autumn and winter to remove damaged, dry or diseased branches.

Commercial harvest of Quercus suber cork. Source: Adrian Michael

Plagues and diseases

The cork oak is a rustic, undemanding and low-maintenance species that is not exempt from the attack of certain pests or diseases. Among these, the beetle Coraebus undatus stands out, which feeds on cork and phytopathogenic fungi such as Phytophthora sp. and Botryosphaeria sp.

The beetle Coraebus undatus is a monophagous species that feeds exclusively on the cork of the cork oak, causing serious damage. In turn, the larvae of some Lepidopterans of the Noctuidae family feed on the foliage causing great losses. If the attacks are severe, chemical control is required.

The phytopathogenic soil fungus Phytophthora cinnamomi is the causal agent of root rot that occurs during crop establishment. The symptoms are manifested as chlorosis, leaf spots, defoliation and the progressive death of branches and apical shoots. The best control is the elimination of infected plants.

Chanco is caused by the pathogen Botryosphaeria dothidea that manifests as cortical lesions at the branch and bark level. Once the disease is detected, the tree must be isolated. Control measures are usually of the preventive type since curative techniques are inefficient.

Applications

Quercus suber is one of the species of the genus Quercus of greatest economic importance in the region of influence of the Mediterranean basin. From the bark of this tree a high-quality cork is obtained every 8-10 years, used at an industrial level as buoys, floats, plugs or shoe soles.

In addition, its firm and hard wood is made of handles for tools and musical instruments, as well as for cooperage. On the other hand, the fruits of high nutritional content are used as a food supplement for pigs.

Cork separation process. Source: Cazalla Montijano, Juan Carlos

Cork

The main use of the cork obtained from the bark of the cork oak is in the production of stoppers for wine bottles. It is also used for the manufacture of insulating material, shoe inserts, floats, washers, gaskets, handles for fishing rods and sheets or planks.

Cork has been used as an insulator to protect homes from the severe cold during the winter or cool during the summer. It is obtained by separating it from the trunk, leaving only a thin layer that constitutes the secondary phloem that is regenerated into new cork.

The first cork is separated when the plant is 22-25 years old, from there every 9-12 years a new harvest can be made. Due to its regenerative capacity, the cork of the cork oak can be harvested 12-15 times during its useful life.

Cork is considered a renewable resource, since its harvest does not damage the tree and is renewed each time it is cut. Its harvest does not damage the tissues of the stem, obtaining from the third a better quality cork.

The cork industry is generally considered to be environmentally friendly. In fact, cork production is a sustainable process and cork waste is easily recyclable.

Agroforestry

Large plantations of cork oaks, either alone or in association with other species, prevent the desertification of intervened areas. In addition, they are home to various wild and endangered species such as the imperial eagle and the Iberian lynx.

On the other hand, the cork oak forests provide an economic value associated with livestock, grazing, hunting, cultivation and mushroom gathering. Indeed, these forests present a social importance related to traditional forestry and agricultural practices.

Quercus suber cork. Source: pixabay.com

Nutritional

Acorns have a high content of carbohydrates, fats and proteins that favors their use as forage or food supplement for livestock. Indeed, the cork oak acorns, together with other species, form the food base of the Iberian pig, resulting in a ham with an excellent aroma.

Ornamental

The Quercus suber species has a wide and dense crown, being of adequate size for planting as an ornamental in parks, squares and large gardens.

Medicinal

The bark of the cork oak has certain chemical elements such as tannins that provide it with astringent properties. In addition, it has anti-inflammatory and analgesic properties useful for the treatment of gingivitis or inflammation of the gums.

References

1. Cork oak. Quercus suber (2018) Region of Murcia Digital. Recovered at: regmurcia.com
2. Díaz-Fernández, P., Jiménez Sancho, MP, Catalán Bachiller, G., Martín Albertos, S. & Gil Sánchez, LA (1995). Regions of origin of Quercus suber L. Ministry of Agriculture, Fisheries and Food. ETSI de Montes, Madrid. ICONA - VPM Agreement for Genetic Improvement of Frondosas. ISBN: 84-8014-118-2.
3. Esteban Díaz, M., Pulido Díaz, FJ & Pausas, JG (2009) Alcornocales de Quercus suber. General Directorate of Natural Environment and Forest Policy (Ministry of the Environment, Rural and Marine Affairs).ISBN: 978-84-491-0911-9.
4. Huesca, M. (2018) Alcornoque-Quercus Suber. For my Garden. Recovered in: paramijardin.com
5. Montero, G., & López, E. (2008). Quercus suber L. Forestry In: Compendium of Applied Forestry in Spain, Fundación Conde del Valle de Salazar. Madrid, Spain. pp, 779-829.
6. Quercus suber. (2019). Wikipedia, The Free Encyclopedia. Recovered at: es.wikipedia.org
7. Quercus suber (2018) List of Species. Canary Tree App. Recovered at: arbolapp.es
8. Saugar, FM (2012). The cork oak (»Quercus suber») in Alto Tiétar. Trasierra: bulletin of the Tiétar Valley Studies Society, (10), 119-130.