|Section:||Fraxinus sect. Melioides|
|Natural range of Fraxinus americana|
|Wikimedia Commons has media related to Fraxinus americana.|
Fraxinus americana, the white ash or American ash, is a species of ash tree native to eastern and central North America. It is found in mesophytic hardwood forests from Nova Scotia west to Minnesota, south to northern Florida, and southwest to eastern Texas. Isolated populations have also been found in western Texas, Wyoming, and Colorado, and the species is reportedly naturalized in Hawaii.
The name white ash derives from the glaucous undersides of the leaves. It is similar in appearance to the green ash, making identification difficult. The lower sides of the leaves of white ash are lighter in color than their upper sides, and the outer surface of the twigs of white ash may be flaky or peeling. Green ash leaves are similar in color on upper and lower sides, and twigs are smoother. Despite some overlap, the two species tend to grow in different locations as well; white ash is a forest tree that commonly occurs alongside sugar maple while green ash is a pioneer species that inhabits riparian zones and disturbed areas. Its compound leaves more often than not have 7 leaflets per leaf whereas other ash trees are usually more diverse.
Cultivation and uses
White ash is one of the most used trees for everyday purposes and, to keep up with high demand, is cultivated almost everywhere it can be. The wood is white and quite dense (within 20% of 670 kg/m3), strong, and straight-grained. It is the timber of choice for production of baseball bats and tool handles. The wood is also favorable for furniture and flooring. Woodworkers use the timber mainly for interior uses due to high perishability in contact with ground soil. It is also used to make lobster traps. Since the 1950s, it has also become a popular choice for solid electric guitar bodies. It makes a very servicable longbow if properly worked. The wood was used in ceiling fan blades from the 1970s through the mid-1980s, though cane was sometimes simulated with plastic then. It is no longer used for ceiling fan blades in most countries.
White ash is not seen in cultivation as often as green ash due to its preference for undisturbed forest sites away from urban pollution and soil compaction, but sometimes has been planted for its consistently reliably autumn colors, which typically are bright orange and red hues as opposed to other species of ash that produce a uniform yellow color.
North American native ash tree species are used by North American frogs as a critical food source, as the leaves that fall from the trees are particularly suitable for tadpoles to feed upon in ponds (both temporary and permanent), large puddles, and other water sources. Species such as red maple, which are taking the place of ash, due to the ash borer, are much less suitable for the frogs as a food source — resulting in poor frog survival rates and small frog sizes. It is the lack of tannins in the American ash variety that makes them good for the frogs as a food source and also not resistant to the ash borer. Varieties of ash from outside North America typically have much higher tannin levels and resist the borer. Maples and various non-native invasive trees, trees that are taking the place of American ash species in the North American ecosystem, typically have much higher leaf tannin levels. Ash species native to North America also provide important habit and food for various other creatures that are native to North America.
Emerald ash borer
In North America the emerald ash borer is an invasive species, highly destructive to ash trees in its introduced range. The damage of this insect rivals that of chestnut blight and Dutch elm disease. To put its damage in perspective, the number of chestnuts killed by the chestnut blight was around 3.5 billion chestnut trees while there are 3.5 billion ash trees in Ohio alone. Dutch elm disease killed only 200 million elm trees while EAB threatens 7.5 billion ash trees in the United States. The insect threatens the entire North American genus Fraxinus, while past invasive tree pests have only threatened a single species within a genus. Since its accidental introduction into the United States and Canada in the 1990s, and its subsequent detection in 2002, it has spread to eleven states and adjacent parts of Canada. It has killed at least 50 million ash trees so far and threatens to kill most of the ash trees throughout North America. The green ash and the black ash trees are affected. White ash is also killed rapidly, but usually only after green and black ash trees are eliminated. Blue ash displays some resistance to the emerald ash borer by forming callous tissue around EAB galleries; however, they are usually killed. White ash has been less affected by emerald ash borer due to its small population (unlike its cousin, F. americana is not commonly seen in cultivation) compared to green ash, which was planted in huge numbers as an ornamental.
An infested tree can be recognized with a yellowing of the leaves, upper crown dieback, epicormic shoots or sprouts, bark lesions, insect galleries and deformed exit holes ; when the beetle has fully devoloped, it will bore out of the tree, in this instance, with a hole in a deformed "D" shape. Once any of the symptoms have started to show, it is likely to be too late.
Ash fungal disease
Hymenoscyphus fraxineus is a fungal disease that attacks ash trees. The disease causes leaf loss, crown dieback, and lesions in the bark. This fungus is, for the most part, fatal, both directly and indirectly, by weakening the tree's immune system so that it is more succeptible to attacks from pests or pathogens. Because of this fact, younger trees are affected far worse, and fully matured ash trees are capable of living long enough to reproduce.
The disease has spread over most of Europe and has been confirmed in Britain, however, it has not yet been found in North America.
The scale of the threat is not yet known, but is thought to be able to cause significant damage to the ash landscape of Europe and the UK.
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