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''Betula populifolia'' (Gray Birch) is a deciduous tree native to North America. Range: It ranges from southeastern Ontario east to Nova Scotia, and south to Pennsylvania and New Jersey, with disjunct populations in Indiana, Virginia, and North Carolina. It prefers poor, dry upland soils, but is also found in moist mixed woodlands. Living only about 30 years, it is a common pioneer species on abandoned fields and burned areas. Characteristics: Gray birch grows quickly to 20 to 30 feet tall and 15 inch trunk diameter, with an irregular open crown of slender branches. The tree often has multiple trunks branching off of an old stump. The leaves are 5-7.5 cm long by 4–6 cm wide, alternately arranged, ovate, and tapering to an elongated tip. They are dark green and glabrous above and paler below, with a coarsely serrated margin.〔 The bark is chalky to grayish white with black triangular patches where branch meets trunk. It is most easily confused for the paper birch (''Betula papyrifera'') by means of its bark; it is smooth and thin but does not readily exfoliate like paper birch does. The flowers are wind-pollinated catkins 5–8 cm long, the male catkins pendulous and the female catkins erect. The fruit, maturing in autumn, is composed of many tiny winged seeds packed between the catkin bracts. The wood is medium hard and is used for high grade plywood, furniture, drum shells, spools and firewood. Like other North American birches, gray birch is highly resistant to the Bronze birch borer (''Agrilus anxius'').〔 The leaves of the Gray Birch serve as food for various Lepidoptera, such as the leaf miner moth ''Cameraria betulivora''. Gray Birch has been commonly planted as a landscaping tree in southern Pennsylvania and New Jersey as it tolerates heat and humidity better than Paper Birch and is more resistant to Bronze Birch Borer and leaf miners. Gallery: Image:betula_populifolia_leaves.jpg|''Betula populifolia'' leaves, New Brunswick, Canada ==Reference List== 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「Betula populifolia」の詳細全文を読む スポンサード リンク
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