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''Fraxinus pennsylvanica'' (green ash or red ash)〔 is a species of ash native to eastern and central North America, from Nova Scotia west to southeastern Alberta and eastern Colorado, south to northern Florida, and southwest to eastern Texas. It has spread and become naturalized in much of the western United States and also in central Europe from Spain to Russia.〔Germplasm Resources Information Network: (''Fraxinus pennsylvanica'' )〕〔(Kew World Checklist of Selected Plant Families, ''Fraxinus pennsylvanica'' )〕〔(Biota of North America Program, ''Fraxinus pennsylvanica'' )〕 It is a medium-sized deciduous tree reaching 12–25 m (rarely to 45 m) tall with a trunk up to 60 cm in diameter. The bark is smooth and gray on young trees, becoming thick and fissured with age. The winter buds are reddish-brown, with a velvety texture. The leaves are 15–30 cm long, pinnately compound with seven to nine (occasionally five or eleven) leaflets, these 5–15 cm (rarely 18 cm) long and 1.2–9 cm broad, with serrated margins and short but distinct, downy petiolules a few millimeters long. They are green both above and below. The autumn color is golden-yellow and depending on the climate, Green Ash's leaves may begin changing color the first week of September. The flowers are produced in spring at the same time as the new leaves, in compact panicles; they are inconspicuous with no petals, and are wind-pollinated. The fruit is a samara 2.5-7.5 cm long comprising a single seed 1.5–3 cm long with an elongated apical wing 2–4 cm long and 3–7 mm broad.〔Common Trees of the North Carolina Piedmont: (''Fraxinus pennsylvanica'' )〕〔Northern Ontario Plant Database: (''Fraxinus pennsylvanica'' )〕〔Virtual Herbarium of the Chicago Region: (''Fraxinus pennsylvanica'' )〕〔Oklahoma Biological Survey: (''Fraxinus pennsylvanica'' )〕 It is sometimes divided into two varieties, ''Fraxinus pennsylvanica'' var. ''pennsylvanica'' (red ash) and ''Fraxinus pennsylvanica'' var. ''lanceolata'' (Borkh.) Sarg. (syn. var. ''subintegerrima'' (Vahl) Fern.; green ash) on the basis of the hairless leaves with narrower leaflets of the latter, but the two intergrade completely, and the distinction is no longer upheld by most botanists.〔 ==Ecology== It is the most widely distributed of all the American ashes, although its range centers on the Midwestern US and Great Plains. A pioneer species, it naturally grows along streambanks and disturbed areas. The large seed crops provide food to many kinds of wildlife.〔USDA Forest Service Silvics Manual: (''Fraxinus pennsylvanica'' )〕 Green ash is threatened by the emerald ash borer, a beetle introduced accidentally from Asia to which it has no natural resistance.〔Emerald ash borer: (EAB website )〕 A common garden experiment showed that green ash is killed readily when exposed to emerald ash borer, while the Asian species ''F. mandschurica'' shows resistance against emerald ash borer. The United States Forest Service has discovered small numbers of green ash in the wild that have remained healthy after emerald ash borer swept through the population. The possibility of these trees possessing genetic resistance to the beetle is currently being investigated with the hope that green ash could be restored using the surviving trees. The spread of emerald ash borer was facilitated by the extensive use of green ash as an ornamental tree in the central US following the loss of American elms in the 1950s-60s due to Dutch elm disease. That epidemic was the result of a similar overuse of elms in urban environments, leading to a monoculture that lacked any disease or pest resistance. Scientifically for red ash this is because modern cultivars utilized regionally were parented from sometimes only four individual trees selected for unique traits and male seedless flowering. Proclaiming a harsh lesson learned, cities like Chicago did not replace dead elms with a 1:1 ash:elm ratio. Norway, silver, red and sugar maples, honey locust, linden/basswood and hackberry, among others, were also utilized during this recovery period and in new urban and suburban areas. Ironically most of these other ''lesser urban species'' alternatives utilized barely survived 50 years, and are today also being removed in great numbers. Both American elm and green ash were extremely popular due to rapid growth and tolerance of urban pollution and road salt, so many housing developments in Michigan were lined from end to end with ashes, a result of which the beetles had an enormous food supply to boost their population well above Infestation thresholds. The tree was also extensively propagated and sold by local nurseries. After the lesson of these twin disasters, urban planners in the region began a more sustainable planting program with a mixture of lindens, oaks, maples, and other trees to prevent a monoculture from existing again, the ideal planting ratio considered to be no more than 7% of an urban forest consisting of trees from the same genus. The emerald ash borer proved to be a far worse and potentially more serious threat than epidemics of the past such as chestnut blight and Dutch elm disease because those diseases spread at a slower rate, only affected one species, and did not kill the trees before they could attain reproductive maturity. Many areas have banned the sale of ash seedlings in nurseries, although seeds may be sold as they are not a vector for the insect. 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「Fraxinus pennsylvanica」の詳細全文を読む スポンサード リンク
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