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Overview

Brief Summary

The evergreen Cork Oak (Quercus suber) is native to the western and central Mediterranean region, but is cultivated elsewhere, e.g., in California and the southeastern United States. The bark covering the trunk and branches (i.e., the cork), which can be 30 cm thick in older trees, is harvested commercially in southwestern Europe. Portugal is the world’s biggest cork producer (and cork is Portugal's most important forest product). At various times, developing commercial cork production in the Mediterranean climate of central California (U.S.A.) has been explored. 

Cork Oak is well-adapted to the challenges of the Mediterranean climate, such as high summer temperatures, limited water availability, and fire. Adaptations range from root and water transport system architecture and function to phenology, leaf morphology and physiology, fire-related protective structures (e.g. thick cork), and resprouting ability.

Cork Oak woodlands occupy around 1.7 million ha in the western Mediterranean Basin. Portugal (with 713,000 ha of Cork Oak-dominated forest) and Spain (with 550,000 ha) account for much of this area, but Cork Oak is also present elsewhere in southern Europe (France and Italy), as well as in northern Africa (Algeria, Morocco, and Tunisia).

Throughout the lifespan of a Cork Oak (which may exceed two hundred years), the tree maintains the ability to regenerate the cork layers after each harvest through many cork production cycles, provided the vascular cambium has not been damaged. Although cork has been sustainably harvested and used by humans for thousands of years, the cork industry grew substantially with the broad use of glass bottles in the 17th century, creating a growing demand for cork stoppers. The widespread use of stoppers for glass bottles capitalized on cork’s resistance to deterioration and its high coefficient of friction. (Although cork stoppers are by far the most economically important use of cork, cork has a range of uses, some less broadly familiar than others, e.g., pruned cork oak tree branches or bark provide a highly desirable media for growing orchids and other epiphytes.) In recent years, as the wine industry has been promoting alternatives to cork stoppers, environmentalists have become increasingly concerned that reduced demand for cork may threaten the sustainable cork industry, which has been relatively effective in protecting the unique cork oak ecosystems of southwestern Europe and North Africa. WWF has initiated a campaign to promote the use of cork and to protect the Cork Oak landscapes.

(Brooks 1997; Sibley 2009;  Oliveira and Costa 2012 and references therein)

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© Leo Shapiro

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Ecology

Associations

Foodplant / endophyte
Biscogniauxia mediterranea endophyte within living Quercus suber

Foodplant / pathogen
Phytophthora cinnamomi infects and damages root of Quercus suber

In Great Britain and/or Ireland:
Foodplant / mycorrhiza / ectomycorrhiza
fruitbody of Russula pseudoimpolita is ectomycorrhizal with live root of Quercus suber
Remarks: Other: uncertain

Foodplant / saprobe
Engyodontium anamorph of Sporothrix rectidentata is saprobic on cork of Quercus suber

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Evolution and Systematics

Functional Adaptations

Functional adaptation

Cork bars water, dissolved ions and gases: cork oak
 

Cork of cork oak provides a barrier to water, dissolved ions and gases due to tissues containing long-chain aliphate molecules.

     
  "The unique properties of cork combine low permeability, low temperature conductivity, and high chemical resistance with high elasticity and low weight. These properties and cork's chemical composition, which is dominated by long-chain aliphates with terminal functional groups, have drawn attention to the use of suberin biosynthetic products in industrial applications." (Franke and Schreiber 2007:257)
  Learn more about this functional adaptation.
  • Franke, R.; Schreiber, L. 2007. Suberin - a biopolyester forming apoplastic plant interfaces. Current Opinion in Plant Biology. 10(3): 252-259.
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Wikipedia

Quercus suber

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. It is native to southwest Europe and northwest Africa.

It grows to up to 20 m (66 ft), although it is typically more stunted in its native environment. The leaves are 4 to 7 cm (1.6 to 2.8 in) long, weakly lobed or coarsely toothed, dark green above, paler beneath, with the leaf margins often downcurved. The acorns are 2 to 3 cm (0.79 to 1.18 in) long, in a deep cup fringed with elongated scales.

Ecology[edit]

Natural stands of cork oak can support diverse ecosystems. For example, in parts of northwestern North Africa, some cork oak forests are habitat to the endangered Barbary Macaque, Macaca sylvanus, a species whose habitat is fragmented and whose range was prehistorically much wider.[1] In Western Europe, namely in Portugal and Spain, the cork oak forests are home to endangered species such as the Iberian Lynx, the most critically threatened feline in the world.[2] The tree has a thick, insulating bark that may have been the cork oak's evolutionary answer to forest fires. After a fire, while many of the other tree species merely regenerate from seeds (as, for example, the maritime pine) or resprout from the base of the tree (as, for example, the Holm oak) the cork oak branches, protected by cork, quickly resprout and recompose the tree canopy. The quick regeneration of the tree seems to be an advantage compared to other species that, after a fire, return to an initial stage of development.[3]

Harvested cork trees south of Ubrique in Andalusia, Southern Spain, May 2008
Quercus suber / Portugal

Cultivation[edit]

The tree forms a thick, rugged bark containing high levels of suberin. Over time the cork cambium layer of bark can develop considerable thickness and can be harvested every 9 to 12 years to produce cork. The harvesting of cork does not harm the tree, in fact, no trees are cut down during the harvesting process. Only the bark is extracted, and a new layer of cork regrows, making it a renewable resource. The tree is cultivated in Spain, Portugal, Algeria, Morocco, France, Italy and Tunisia. Cork oaks are considered to be soil builders and their fruits have been shown to have useful insecticidal properties. Cork oak forests cover approximately 25,000 square kilometres in those countries (equivalent to 2,500,000 hectares (6,200,000 acres)). Portugal accounts for around 50% of the world cork harvest. Cork oaks cannot legally be cut down in Portugal, except for forest management felling of old, unproductive trees, and, even in those cases, farmers need special permission from the Ministry of Agriculture.

A cross section of the trunk of a cork oak
Weathered trunk of a cork oak trunk. The cork aged light gray, the trunk aged dark

Cork oaks live about 150 to 250 years.[4] Virgin cork (or 'male' cork) is the first cork cut from generally 25-year-old trees. Another 9 to 12 years is required for the second harvest, and a tree can be harvested about twelve times in its lifetime. Cork harvesting is done entirely without machinery, being dependent solely on human labor. Usually five people are required to harvest the tree's bark, using a small axe. The process requires training due to the skill required to harvest bark without harming the tree. 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 regular, both in the wild in southwest Europe and in cultivation; the hybrid is known as Lucombe oak Quercus × hispanica. Some cork is also produced in eastern Asia from the related Chinese cork oak (Quercus variabilis)

Pathogens[edit]

References[edit]

Notes[edit]

  1. ^ C. Michael Hogan, 2008
  2. ^ Santos Pereira, João; Bugalho, Miguel Nuno; Caldeira, Maria da Conceição, 2008
  3. ^ Santos Pereira, João; Bugalho, Miguel Nuno; Caldeira, Maria da Conceição, 2008
  4. ^ Abigail Hole, Michael Grosberg and Daniel Robinson, 2007

Sources[edit]

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