OAKS   Leave a comment

 

DEFINITION:1 any of a genus (Quercus) of large hardwood trees and bushes of the beech family, bearing acorns 2 the wood of an oak 3 any of various plants with oak like leaves 4 a wreath of oak leaves 5 woodwork, furniture, etc. made of oak.

The majestic monarchs of the forest may take 100 years to reach maturity and then may live for another 900 years. Their wood provides one of the strongest and most durable of timbers.

Oaks range in size from shrubs to giants 150 feet (45 meters) high. The trees develop thick trunks and large, wide-spreading branches. The leaf is usually deeply lobed, but in some species it is almost smooth at the edge. Oaks are easily recognized by their fruit the acorn, a round nut set in a woody cup. American Indians and New England pioneers boiled and ate the acorns of the white oak, and acorns are part of the diet of some forest and tree-dwelling animals.

About 450 species of ornamental and timber oaks constitute the oak genus Quercus (a member of the beech family Fagaceae). They grow widely throughout the Temperate Zone of the Northern Hemisphere and at high altitudes in the tropics. About 75 species are native to the United States.

White oak, name (Quercus alba) applied to the group of oaks with grey-brown heartwood, usually without a reddish tinge, and with pores filled with a fibrous growth that makes this wood resistant to decay; includes the species white, swamp white, chestnut, swamp chestnut, chinquapin, bur, live, and post oaks.

One of the best-known species in the United States is the white oak (Q. alba). This stately tree grows from 70 to 150 feet (21 to 45 meters) high. The leaves are large and deeply lobed, light green above and whitish beneath. In autumn the foliage turns deep violet and clings to the tree throughout the winter, falling only just before new leaves appear. This is characteristic of many oaks. The trunk of the white oak, which often is 4 feet (1.3 meters) in diameter, has furrowed whitish bark; this gives the tree its name.

The bur, or mossy-cup, oak (Q. macrocarpa) is the most common oak of the prairie states. Its average height is about 75 feet (23 meters), but some bur oaks tower to 150 feet (45 meters). Its deep-green leaves are very large, sometimes up to 1 foot (0.3 meter) in length, deeply lobed at the lower part and rounded at the apex.

The acorns are large and set in rough fringed cups. The bur oak grows from Pennsylvania to Montana and is largest in the Ohio Valley.

Red oak, name Quercus rubra or Quercus borealis applied to the group of oaks with brown wood that has a red tint; includes the species northern red, southern red, swamp red, scarlet, black, blackjack, laurel, pin, shumard, water, and willow oaks.

The red oak (Q. rubra, or Q. borealis) is colourful in all seasons. The round solid crown of the tree is covered with large, sharply lobed leaves. These are pink and furry in the spring, green in the summer, and deep purple-red in the autumn. The bark is dark brown, thick, and furrowed. The red oak bears large acorns set in shallow saucer like cups.

The pin oak or Spanish oak (Q. palustris) is a quick-growing medium sized tree raised generally as a street tree. Its deeply cut leaves are brilliant in autumn. The trunk and larger limbs are studded with tough branchlets, which probably account for the tree’s name. It grows in the Eastern United States, usually on moist lowlands.

Chestnut, Live, and English Oaks

The chestnut oak (Q. muehlenbergii or Q. acuminata), also called the yellow oak, has the major characteristics of the oak family but has chestnut like leaves. These are serrated, or saw-toothed, instead of deeply lobed. The tree is tall and stately, with stout trunk and limbs. It grows in the central states.

The live oak (Q. virginiana) is a beautiful southern tree that sometimes reaches 60 feet (18 meters) in height. Its branches are spreading and graceful, covered with small evergreen foliage and often festooned with mosses. It rarely grows far from the Gulf of Mexico.

The well-known English oak (Q. robur) is the largest and most celebrated of all the world’s oak trees. The “wooden walls” of Britain, the ships of the Royal Navy, were built from the timber of this kingly tree. Some fine specimens still standing in England date from the Anglo-Saxon period. The majestic English oak is a veritable giant, with sturdy limbs and enormous girth. The peculiar zigzag growth of the limbs in older trees gives them a twisted look and adds to their picturesque appearance.

Uses

Tannin (or tannic acid), organic chemical compound used in tanning leather, dyeing fabric, making ink, and in various medical applications.

The value of oak timber varies with the species. The English oak is tough, hard, close grained, and comparatively easy to work. It is exceedingly durable and defies drought and moisture. The bur oak ranks next to the English oak in importance. It is used for shipbuilding, furniture, and other manufactures. The bark is especially rich in tannin and is used in the preparation of leather. The timber of the white oak is adapted to the same purposes as that of the English oak and the bur oak, though it is slightly inferior in quality.

The live oak produces strong yellow wood that is difficult to work. It is highly valued for shipbuilding, however, because it is very durable under water. The timber of the red oak is porous and so has little commercial value, but it is useful for making barrels, and the bark is used for tanning leather. The chestnut oak also yields good timber.

Galls

Gall (or gall nut), abnormal growth on leaves, stems, buds, flowers, or roots of plants caused by various parasites, especially insects and mites, and more rarely by nematodes, bacteria, fungi, slime moulds, and algae; found on almost all forms of plant life, but especially common on oak trees, willows, roses, and goldenrod.

The galls or gall nuts so frequently found on oaks are usually produced by gall flies They lay their eggs in the tissues of the trees. The tissues swell at the point of puncture and form firm nut like structures within which the young of the insects develop to maturity. Each kind of gall fly produces a different kind of gall. Some galls are rich in tannin.

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Posted 2012/02/11 by Stelios in Education

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