Quercus suber

General appearance and bark The cork oak grows as an evergreen tree, reaching an average height of or in rare cases up to 25 m and a trunk diameter (DBH) of . It forms a dense and asymmetrical crown that starts at a height of and spreads widely in free-standing trees. The crown can be divided into several separate, rounded partial crowns. 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 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. Leaves '', 1887 The leathery leaves are alternate and are long and wide. The shape varies between round, oval and lanceolate-oval. The leaf blade has five to seven sharp teeth on both edges and a pointed vegetation cone (apex). The midrib stands out clearly on the underside of the leaf, the first-order lateral nerves usually lead to the teeth of the leaf margin. The upper side of the leaf is light green, the underside of the leaf whitish and densely hairy. There is no hair on young trees. The leaf stalks are long and are also hairy. At the base of the petiole are two narrow, lanceolate, long and bright red stipules that fall off in the first year. The new leaves appear in April and May, when older leaves are also shed. They usually stay on the tree for two to three years, less often only one year, the latter especially in severe environmental conditions and on the northern border of the distribution area. Extremely cold winters can also lead to complete defoliation. Inflorescence and flower The cork oak is single sexed (monoecious), with both female and male flowers on one specimen. The female flowers form upright inflorescences in the leaf axils of young branches. These are formed from a hairy axis long with two to five separate flowers. The female flowers contain a small, hairy, four- to six-lobed flower envelope and three to four styles. The male catkins also arise on the leaf axils of young branches. They are bright red at the beginning and stand upright, older catkins are yellow and pendulous, long and have a whitish hairy axis. The single flowers are sessile and have a densely hairy flower cover that is colored red when opened. The four to six stamens are whitish with yellow, egg-shaped anthers. They are longer than the bracts. Infructescence, fruit and seed The fruit clusters are long and carry two to eight acorns. About half of the fruits are enclosed in the fruit cup (cupule); the fruit cups are in diameter. The upper scales of the cupula are gray and hairy, in the subspecies Quercus suber occidentalis the scales are close together or are fused. The size of the acorns varies between lengths of and diameters of . The fruit casing (pericarp) is bare, smooth and shiny brownish red. The hilum (the starting point of the seed) is convex and has a diameter of . Quercus fg04.jpg|Leaves Quercus suber Blatt.jpg|Leaf, front and back Quercus suber (Cork Oak) Sapling.png|Sapling Quercus suber g4.jpg|Acorn with fruit cup Quercus suber MHNT.BOT.2021.17.19.jpg|Seeds Quercus suber - San Luis Obispo Botanical Garden - DSC05998.JPG|Unharvested trunk Denuded cork oak (2874384025).jpg|Denuded trunk Alcornoques Helechosa 2.jpg|Contrast between old and new cambium ==Taxonomy==

Quercus suber is a species of the section Cerris to which, for example, the following species also belong: • Valonia oak (Quercus macrolepis) • Turkey oak (Quercus cerris) • Quercus × crenata • Macedonian oak (Quercus trojana) 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: • Quercus suber subsp. suber: Nominal taxon • Quercus suber subsp. occidentalis (Gay) Bonnier & Layens: It differs from the nominate form in the shape of the cupula scales, the longer development time of the fruits and the semi-evergreen foliage. The distribution area of the subspecies is the Portuguese Atlantic coast. ==Distribution and habitat==

The cork oak occupies the area around the western Mediterranean basin. In Portugal, natural and cultivated stands cover an area of 750,000 hectares. The subspecies Quercus suber occidentalis also thrives in mild areas of England. The species needs a lot of 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 calcareous soils, but they are often found on crystalline slates, on gneiss, granite and sands. The acidity of the soil 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. ==Ecology==

, a resident of the cork oak forests of the southern Iberian Peninsula The cork oak forest is one of the major plant communities of the Mediterranean woodlands and forests ecoregion. In natural populations, the cork oak grows together with the holm oaks (Quercus ilex, Quercus rotundifolia), the Portuguese oak (Quercus faginea), the Pyrenean oak (Quercus pyrenaica), Mirbeck's oak (Quercus canariensis), the maritime pine (Pinus pinaster), the stone pine (Pinus pinea), the strawberry tree (Arbutus unedo) and the olive tree (Olea europaea), in cooler locations also with the sweet chestnut (Castanea sativa). In addition to these tree species, the shrub-forming species include the Kermes oak (Quercus coccifera), the Lusitanian oak (Quercus lusitanica) the holly buckthorn (Rhamnus alaternus), species of the genus Phillyrea, the myrtle (Myrtus communis), the green heather (Erica scoparia), the common smilax (Smilax aspera) and the Montpellier cistus (Cistus monspeliensis) are often found together with the cork oak. Symbiosis The cork oak enters into a mycorrhizal symbiosis with several types of fungus. The fine root system of the oak is in close contact with the mycelium of the fungus. The oak receives water and nutrient salts from the fungus in exchange for products of photosynthesis. Such a symbiosis exists among others with the following species: Leaf spot can be caused by the fungus Apiognomonia errabunda. Other fungi can cause leaf scorching, powdery mildew, rust, and cankers. The most virulent cork oak pathogen may be Diplodia corticola, a sac fungus 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. 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. ==Uses==

Guardadores de Porcos.jpg|Cork oaks are an important component of the montado/dehesa Quercus suber corc.JPG|Bark storage IAPH Saca del corcho.jpg|Cork harvesting 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. These mostly extensively managed habitats are called montados in Portugal and dehesas in Spain. They are considered to be extremely valuable from the point of view of biodiversity and cultural heritage. 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 phellogen 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. while others suggest a single tree can produce on average of cork per harvest, 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. 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. The European cork industry produces 300,000 tonnes of cork a year, with a value of €1.5 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). ==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. 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. 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. Cork oaks of California While native to the Mediterranean, cork oaks have been planted across several U.S. states with warm, mild climates, particularly in California. One of the oldest recorded cork oaks in the state, was planted in 1858, by Mexican miners, in the town of Campo Seco in the Central Valley. Another historic cork oak is in Napa and stands 89 feet tall with a 20 ft circumference. There are several streets or lanes in California with the name 'Cork Oak'. A street in Palo Alto, named 'Cork Oak Way' was established in 1960, in an area densely populated with cork oaks. , eleven of these trees still lined this street. Cork industry during World War II By 1940, the United States imported nearly half the world’s cork production, for making everything from bottle caps to parts for military equipment. When Nazi Germany blockaded all Atlantic trade and cut off cork imports from Europe, the shortage was deemed a threat to U.S. national security. To address this threat, individuals such as Charles McManus Sr, CEO of Crown Cork and Seal and Woodbridge Metcalf, a Forestry Professor, participated in a national project to map and cultivate the domestic growth of cork oaks. As a result, a military transport plane delivered a load of cork oak acorns from Morocco to the US. Throughout this project, over five hundred cork oaks were planted in the University of California at Davis. ==References==