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  1. Oak - Wikipedia

    en.wikipedia.org/wiki/Oak
    • Classification
    • Evolution
    • Hybridization
    • Uses
    • Biodiversity and Ecology
    • Diseases and Pests
    • Conservation
    • Toxicity
    • Cultural Significance
    • Bibliography

    The most recent classification of Quercus divides the genus into two subgenera and eight sections. These divisions support the evolutionary diversification of oaks among two distinct clades: the "Old World" clade, including oaks that diversified mainly in Eurasia; and the "New World" clade, for oaks that diversified mainly in the Americas.

    Records of Quercus have been reported from Late Cretaceous deposits in North America and East Asia, however these are not considered definitive. In a survey of the fossil record of Quercus it was concluded that "pre-Paleogene, and perhaps pre-Eocene occurrences of Quercus macroremains are generally represented by poorly preserved fossils that lack critical features needed for certain identification and need to be treated with caution." The oldest unequivocal records of Quercusdate to the Eocene, around 45 million years ago.

    Interspecific hybridization is quite common among oaks, but usually between species within the same section only, and most common in the white oak group. White oaks are unable to discriminate against pollination by other species in the same section. Because they are wind pollinated and they have weak internal barriers to hybridization, hybridization produces functional seeds and fertile hybrid offspring.Ecological stresses, especially near habitat margins, can also cause a breakdown of mate recognition as well as a reduction of male function (pollen quantity and quality) in one parent species. Frequent hybridization among oaks has consequences for oak populations around the world; most notably, hybridization has produced large populations of hybrids with copious amounts of introgression, and the evolution of new species. Frequent hybridization and high levels of introgression have caused different species in the same populations to share up to 50% of their genetic information. Havin...

    Oak wood has a density of about 0.75 g/cm3 (0.43 oz/cu in) creating great strength and hardness. The wood is very resistant to insect and fungal attack because of its high tannin content. It also has very appealing grain markings, particularly when quartersawn. Oak planking was common on high status Viking longships in the 9th and 10th centuries. The wood was hewn from green logs, by axe and wedge, to produce radial planks, similar to quarter-sawn timber. Wide, quarter-sawn boards of oak have been prized since the Middle Ages for use in interior panelling of prestigious buildings such as the debating chamber of the House of Commons in London and in the construction of fine furniture. Oak wood, from Quercus robur and Quercus petraea, was used in Europe for the construction of ships, especially naval men of war, until the 19th century, and was the principal timber used in the construction of European timber-framed buildings. Today oak wood is still commonly used for furnituremaking an...

    Oaks are keystone species in a wide range of habitats from Mediterranean semi-desert to subtropical rainforest. For example, oak trees are important components of hardwood forests, and certain species are particularly known to grow in associations with members of the Ericaceae in oak–heath forests. A number of kinds of truffles, including the two well known varieties, the black Périgord truffle and the white Piedmont truffle, have symbiotic relationships with oak trees. Similarly many other mushrooms such as Ramaria flavosaponaria also associate with oaks. The European pied flycatcheris an example of an animal species that often depends upon oak trees. Many species of oaks are under threat of extinction in the wild, largely due to land use changes, livestock grazing and unsustainable harvesting. For example, over the past 200 years, large areas of oak forest in the highlands of Mexico, Central America and the northern Andes have been cleared for coffee plantations and cattle ranchin...

    Sudden oak death (Phytophthora ramorum) is a water mould that can kill oaks within just a few weeks. Oak wilt, caused by the fungus Ceratocystis fagacearum is also a lethal disease of some oaks, particularly the red oaks (the white oaks can be infected but generally live longer). Other dangers include wood-boring beetles, as well as root rot in older trees which may not be apparent on the outside, often being discovered only when the trees come down in a strong gale. Oak apples are galls on oaks made by the gall wasp. The female kermes scale causes galls to grow on kermes oak. Oaks are used as food plants by the larvae of Lepidoptera (butterfly and moth) species such as the gypsy moth, Lymantria dispar, which can defoliate oak and other broadleaved tree species in North America. A considerable number of galls are found on oak leaves, buds, flowers, roots, etc. Examples are oak artichoke gall, oak marble gall, oak apple gall, knopper gall, and spangle gall. A number of species of fun...

    According to a comprehensive report by The Morton Arboretumand the International Union for Conservation of Nature (IUCN) an estimated 31% of the world's estimated 430 oak species are threatened with extinction, while the study found an estimated 41% of oak species to be of conservation concern. The countries with the highest numbers of threatened oak species according to the report are China with 36 species, Mexico with 32 species, Vietnam with 20 species and the USA with 16 species. While the cause of decline is still partly unknown for some species, the main causes the scientists determined were climate change and invasive pests in the US, and deforestation and urbanizationin Asia. In the Himalayan region of India, oak forests are being invaded by pine forests due to the increase in temperature. The associated species of pine forest may cross frontiers and become new elements of the oak forests. In eastern North America, rare species of oak trees include scarlet oak (Quercus cocci...

    The leaves and acorns of the oak tree are poisonous in large amounts to livestock including cattle, horses, sheep, and goats due to the toxin tannic acid, causing kidney damage and gastroenteritis. Symptoms of poisoning include lack of appetite, depression, constipation, diarrhea (which may contain blood), blood in urine, and colic. The exception is the domestic pig, which may be fed entirely on acorns in the right conditions, and has traditionally been pastured in oak woodlands (such as the Spanish dehesa and the English system of pannage). Acorns are also edible by humans, after leachingof the tannins.

    National symbol

    The oak is a common symbol of strength and endurance and has been chosen as the national tree of many countries. In England, oaks have been a national symbol since at least the sixteenth century, often used by Shakespeare to convey heritage and power. In England today they remain a symbol of the nation's history, traditions, and the beauty of its countryside. Already an ancient Germanic symbol (in the form of the Donar Oak, for instance), certainly since the early nineteenth century, it stand...

    Religious

    The prehistoric Indo-Europeantribes worshiped the oak and connected it with a thunder or lightning god, and this tradition descended to many classical cultures. In Greek mythology, the oak is the tree sacred to Zeus, king of the gods. In Zeus's oracle in Dodona, Epirus, the sacred oak was the centerpiece of the precinct, and the priests would divine the pronouncements of the god by interpreting the rustling of the oak's leaves. In Celtic polytheism, the name of the oak tree was part of the Pr...

    Historical

    Several oak trees, such as the Royal Oak in Britain and the Charter Oakin the United States, are of great historical or cultural importance. "The Proscribed Royalist, 1651", a famous painting by John Everett Millais, depicted a Royalist fleeing from Cromwell's forces and hidden in an oak. Millais painted the picture in Hayes, Kent, from a local oak tree that became known as the Millais Oak. Approximately 50 km west of Toronto, Canada is the town of Oakville, Ontario, famous for its history as...

    Byfield, Liz (1990) An Oak Tree, Collins book bus, London : Collins Educational, ISBN 0-00-313526-8
    Philips, Roger. Trees of North America and Europe, Random House, Inc., New York ISBN 0-394-50259-0, 1979.
    Logan, William B. (2005) Oak: The Frame of Civilization, New York; London : W.W. Norton, ISBN 0-393-04773-3
    Paterson, R.T. (1993) Use of Trees by Livestock, 5: Quercus, Chatham : Natural Resources Institute, ISBN 0-85954-365-X
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