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Quercus suber, commonly called the cork oak, is a medium-sized, evergreen oak tree in the section Quercus sect. Cerris. It is the primary source of cork for wine bottle stoppers and other uses, such as cork flooring and as the cores of . It is native to southwest Europe and northwest Africa. In the Mediterranean basin the tree is an ancient species with fossil remnants dating back to the Tertiary period.Eriksson, E. (2025). 9789292550622, European Forest Genetic Resources Programme (EUFORGEN), Bioversity International. . ISBN 9789292550622 It can survive for as long as two centuries. Typically, once it reaches 25 years old, its thick bark can be harvested for cork every 9 to 12 years without causing harm to the tree.
It endures drought and makes little demand on the soil quality and is regarded as a defence against desertification. Cork oak are home to a multitude of animal and plant species. Since cork for sealing bottles is increasingly being displaced by other materials, these forests are at risk as part of the cultural landscape and as a result animal species such as the Iberian lynx and imperial eagles are threatened with extinction.
The young twigs are densely hairy light gray or whitish. Older branches are strong and knotty. Older trees only form short shoots between in length.
The thick, longitudinally cracked cork layers of the gray-brown trunk bark are characteristic of the cork oak. The Cork cambium of the smooth bark of young trees forms a cork layer very early on, which can be thick. The light and spongy cork fabric shows vertical cracks and is white on the outside and red to red-brown on the inside. After the cork has been harvested, the trunk appears reddish brown, but later it is significantly darker. The wood is ring-pored, has a brown heartwood and a light reddish sapwood. The cork oak develops a taproot that reaches a depth of and from which several meters long, horizontally running side roots extend. The trees can live over 400 years, and harvested specimens can be 150 to 200 years old.
Characteristic for the section are the hairless pericarp and the usually two-year ripening time of the fruits. The cork oak is an exception because the fruits can ripen in both the first and the second year.
In the species Quercus suber two subspecies are distinguished:
Together with the Turkey oak ( Quercus cerris) and the Quercus ilex ( Quercus ilex), the cork oak forms hybrids.
The scientific name Quercus suber is derived from the Latin word quercus, which the Romans used to describe the pedunculate oak ( Quercus robur). The specific epithet suber means in Latin cork oak and also cork. (2025). 9783937872162, Nikol Verlagsgesellschaft. ISBN 9783937872162
The species needs very little light and cannot survive in dense populations. It loves warmth, grows at annual mean temperatures of and can withstand maximum temperatures of up to . In the area of distribution, the temperature rarely falls below freezing point, but temperatures down to without damage and down to without major damage can be tolerated. The cork oak is not hardy in Central Europe. It endures drought and survives dry periods in summer by reducing its metabolism. An annual rainfall of is considered optimal, in cooler locations can be sufficient with enough humidity. Cork oaks have low soil demands and also grow in poor, dry or rocky locations. They rarely thrive on limestone soils, but they are often found on crystalline slates, on gneiss, granite and sands. The Soil pH should be between pH 4.5 and 7.
The cork oak is considered a pyrophyte because it recovers quickly after forest fires as it is protected by the cork.
As a pyrophyte, this tree has a thick, insulating bark that makes it well adapted to . After a fire, many tree species regenerate from seeds (as, for example, the maritime pine) or re-sprout from the base of the tree (as, for example, the holm oak). The bark of the cork oak allows it to survive fires and then simply regrow branches to fill out the canopy. The quick regeneration of this oak makes it successful in the fire-adapted ecosystems of the Mediterranean biome.Santos Pereira, J., Bugalho, M.N., and Caldeira, M.D. (2008). From the Cork Oak to Cork: A Sustainable Ecosystem. APCOR: Portuguese Cork Association.
The most virulent cork oak pathogen may be Diplodia corticola, a Ascomycota which causes sap-bleeding sunken canker wounds in the wood, withering of the leaves, and lesions on the acorns. The fungus Biscogniauxia mediterranea is becoming more common in cork oak forests. Its fruiting bodies appear as charcoal-black cankers. Both of these fungi are transmitted by the oak pinhole borer ( Platypus cylindrus), a species of weevil.
The common water mould Phytophthora cinnamomi grows in the roots of the tree and has been known to devastate cork oak woodlands.
Several species of butterflies damage the cork oak, the most important being the Lymantria dispar ( Lymantria dispar). The species lays its eggs in the bark of the branches and trunks, and the caterpillars that hatch in spring are distributed in the crown and eat them bare. The bacterial species Bacillus thuringiensis is used as a biological plant protection agent against the spongy moth. Another pest is the green oak tortrix ( Tortrix viridana), whose caterpillars eat flowers and young leaves and roll them up with thread to form typical coils. The lackey moth ( Malacosoma neustria) also causes damage to the leaves, sticking its eggs to the bark of thin twigs in multiple rows, and also the brown-tail moth ( Euproctis chrysorrhoea), whose caterpillars skeletonize the leaves and further damage the tree after overwintering in spring. A special cork pest is the jewel beetle Coraebus undatus, which lays its eggs in the cork tissue. Another harmful species of beetle is the great capricorn beetle ( Cerambyx cerdo), whose larvae eat long corridors in the oak wood.
Unfavorable climatic conditions and fungal attack are made responsible for the weakening of trees and for crown damage. Such fungal parasites of weakness are Botryosphaeria stevensii, Biscogniauxia mediterranea, Endothiella gyrosa and representatives of the mold genus Fusarium. Drought and parasite infestation are also considered to be the cause of the weakness syndrome in parts of Spain and Portugal.
The cork consists of dead, air-filled, thin-walled cells and contains cellulose and suberin. Cork is heat and sound insulating, the suberine gives it water-repellent properties. The cork layer is replicated by the cork-producing Cork cambium and can therefore be harvested repeatedly without damaging the tree too much. The first harvest usually takes place after about 25 years with a trunk diameter (DBH) of , though new techniques (such as better irrigation systems) could shorten it to only 8 to 10 years. The first cork layer is called "male cork" or "virgin cork", is still not very elastic and cracked and is only used for insulating mats. The second harvested cork (known as secundeira), has a more regular structure and is softer, but is still only used for insulation and in decorative objects. Only the following cork harvests deliver a higher quality cork, the "female cork", which can be used commercially in full. The best quality cork is obtained from the third and fourth harvest. Cork harvesting takes place every nine to twelve years when a layer thickness of is reached. Under favorable (warm) conditions, the harvest can take place every eight years, in North Africa every seven years. A cork oak can be harvested five to seventeen times in total. In order to minimize the damage to the trunk surface, harvesting can be carried out every three years, whereby only a third of the usable surface is removed. An important maintenance measure is pruning, which begins around the age of ten at a height of about . Some sources say an oak can provide around of cork over its lifespan, and one hectare around per year while others suggest a single tree can produce on average of cork per harvest, a comparatively higher value, as cork oaks can live more than 200 years in good conditions.
The cork is mainly used for the production of bung and wine cork, as well as for heat and sound insulation, cork
paper, badminton shuttlecocks, , handles of fishing rods and hand tools, special devices for the space industry and for other technical applications (including composite materials, shoe soles, floor coverings). Bottle cork production accounts for around 70% of the added value in cork cultivation. Since natural corks are increasingly being replaced by plastic or sheet metal closures, there could be a significant decline in the cork oak population in southwestern Europe, which endangers the biodiversity in these areas.
The bark, which contains around twelve percent extractable tannin, is also used. In addition, the acorns are used as feed in extensive pig fattening (acorn fattening), such as for Iberian ham production; although the Holm Oak (Quercus ilex), is preferred for this due to its sweeter fruits. One cork oak tree can provide of acorns per year.
Cork oaks cannot legally be cut down in Portugal, except for forestry felling of old, unproductive trees, and, even in those cases, farmers need special permission from the Ministry of Agriculture.
Cork harvesting is done entirely without machinery, being dependent solely on human labour. Usually five people are required to harvest the tree's bark, using a small axe. The process mandates specialized training due to the skill required to harvest bark without inflicting too much damage to the tree.
The European cork industry produces 300,000 of cork a year, with a value of Euro1.5 billion and employing 30,000 people. Wine corks represent 15% of cork usage by weight but 66% of revenues.
Cork oaks are sometimes planted as individual trees, providing a minor income to their owners. The tree is also sometimes cultivated for ornament. Hybrids with Turkey oak ( Quercus cerris) are not uncommon, both where their ranges overlap in the wild in southwest Europe and in cultivation; the hybrid Quercus × hispanica is known as Lucombe oak, for William Lucombe, who first identified it.
Some cork is also produced in eastern Asia from the related Chinese cork oak ( Quercus variabilis).
In 2007, a 2 euro commemorative coin with the motif of a cork oak was issued in Portugal in memory of the Portuguese Presidency of the European Union.
Uses
The cork oak is grown for the production of cork in several Mediterranean countries. The centers of cork production are in southern Portugal (accounting for 50% of the total production) and southern Spain, where low trees with large crowns and strong branches are grown in large areas, which provide the highest yield of cork. (2025). 9783933203533, Nikol Verl.-Ges. ISBN 9783933203533 These mostly extensively managed habitats are called dehesa in Portugal and in Spain. They are considered to be extremely valuable from the point of view of biodiversity and cultural heritage.
Culture
The cork oak is featured in the city arms of several cities in Portugal, such as the city of Reguengos de Monsaraz, which shows a freshly harvested cork tree.
Notable trees
In the Portuguese town of Águas de Moura lies the Sobreiro Monumental ( Monumental Cork Oak), also known as 'The Whistler Tree', a tree 236 years old (planted in 1783/1784), over tall and with a trunk that requires at least three people to embrace it. It has been considered a National Monument since 1988, and Guinness World Records lists it as the largest cork tree in the world.
Further reading
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