|
''Quercus alba'', the white oak, is one of the pre-eminent hardwoods of eastern and central North America. It is a long-lived oak of the beech family, native to eastern and central North America and found from Minnesota, Ontario, Quebec, and Nova Scotia south as far as northern Florida and eastern Texas.〔(Biota of North America Program 2014 county distribution map )〕 Specimens have been documented to be over 450 years old.〔http://www.ldeo.columbia.edu/~adk/oldlisteast/#spp〕 Although called a white oak, it is very unusual to find an individual specimen with white bark; the usual color is a light gray. In the forest it can reach a magnificent height and in the open it develops into a massive broad-topped tree with large branches striking out at wide angles. ==Description== Normally not a very tall tree, typically reaching 80–100 feet at maturity, it nonetheless becomes quite massive and its lower branches are apt to extend far out laterally, parallel to the ground. Trees growing in a forest will become much taller than ones in an open area which develop to be short and massive. The tallest known white oak is 144 feet (43 m) tall. It is not unusual for a white oak tree to be as wide as it is tall, but specimens growing at high altitudes may only become small shrubs. White oak may live 200–300 years, with some even older specimens known. The famous Wye Oak in Wye Mills, Maryland was estimated to be over 450 years old when it finally toppled over in a thunderstorm in 2002. Sexual maturity begins at around 20 years, but the tree does not produce large crops of acorns until its 50th year and the amount varies from year to year. Acorns deteriorate quickly after ripening, the germination rate being only 10% for six-month-old seeds and as they are prime food for animals and insects, in years of a small crop, all of them may be lost.〔 〕 The bark is a light ash-gray and peels somewhat from the top, bottom and/or sides.〔(Flora of North America: ''Quercus alba'' )〕 In spring the young leaves are of a delicate, silvery pink and covered with a soft, blanket-like down. The petioles are short, and the leaves which cluster close to the ends of the shoots are pale green and downy with the result that the entire tree has a misty, frosty look. This condition continues for several days, passing through the opalescent changes of soft pink, silvery white and finally yellow green.〔〔 The leaves grow to be 5-8.5 inches long and 2.75-4.5 inches wide and have a deep glossy green upper surface. They usually turn red or brown in autumn, but depending on climate, site, and individual tree genetics, some trees are nearly always red, or even purple in autumn. Some brown, dead leaves may remain on the tree throughout winter until very early spring. The lobes can be shallow, extending less than halfway to the midrib, or deep and somewhat branching. The acorns are usually sessile, and grow to 0.5-1 inch in length, falling in early October. ''Quercus alba'' is sometimes confused with the swamp white oak, a closely related species, and the bur oak. The white oak hybridizes freely with the bur oak, the post oak, and the chestnut oak.〔 * Bark: Light gray, varying to dark gray and to white; shallow fissured and scaly. Branchlets at first bright green, later reddish-green and finally light gray. A distinguishing feature of this tree is that a little over halfway up the trunk the bark tends to form overlapping scales that are easily noticed and aid in identification.〔 * Wood: Light brown with paler sapwood; strong, tough, heavy, fine-grained and durable. Specific gravity, 0.7470; weight of one cubic foot, 46.35 lbs; weight of one cubic meter 770 kg.〔(Niche Timbers White Oak )〕〔 * Winter buds: Reddish brown, obtuse, one-eighth of an inch long.〔 * Leaves: Alternate, five to nine inches long, three to four inches wide. Obovate or oblong, seven to nine-lobed, usually seven-lobed with rounded lobes and rounded sinuses; lobes destitute of bristles; sinuses sometimes deep, sometimes shallow. On young trees the leaves are often repand. They come out of the bud conduplicate, are bright red above, pale below, and covered with white tomentum; the red fades quickly and they become silvery greenish white and shiny; when full grown they are thin, bright yellow green, shiny or dull above, pale, glaucous or smooth below; the midrib is stout and yellow, primary veins are conspicuous. In late autumn the leaves turn a deep red and drop, or on young trees remain on the branches throughout the winter. Petioles are short, stout, grooved, and flattened. Stipules are linear and caducous.〔 * Flowers: appear in May, when leaves are one-third grown. Staminate flowers are borne in hairy aments two and a half to three inches long; the calyx is bright yellow, hairy, six to eight-lobed, with lobes shorter than the stamens; anthers are yellow. Pistillate flowers are borne on short peduncles; involucral scales are hairy, reddish; calyx lobes are acute; stigmas are bright red.〔 * Acorns: Annual, sessile or stalked; nut ovoid or oblong, round at the apex, light brown, shining, three-quarters to an inch long; cup-shaped, enclose about one-fourth of the nut, tomentose on the outside, tuberculate at base, scales with short obtuse tips becoming smaller and thinner toward the rim.〔 White oak acorns (referring to ''Q. alba'' and all its close relatives) have no epigeal dormancy and germination begins readily without any treatment. In most cases, the oak root sprouts in the fall, with the leaves and stem appearing the next spring. The acorns take only one growing season to develop unlike the red oak group, which require two years for maturation.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「quercus alba」の詳細全文を読む スポンサード リンク
|
