Fraxinus pennsylvanica
Fraxinus pennsylvanica, the 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 Oklahoma and eastern Texas. It has spread and become naturalized in much of the western United States and also in Europe from Spain to Russia.
Other names more rarely used include downy ash, swamp ash and water ash.
Description
Fraxinus pennsylvanica is a medium-sized deciduous tree reaching tall with a trunk up to 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 long, pinnately compound with seven to nine leaflets, these long and 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 long comprising a single seed long with an elongated apical wing long and broad.It is sometimes divided into two varieties, Fraxinus pennsylvanica var. pennsylvanica and Fraxinus pennsylvanica var. lanceolata Sarg. 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 U.S. and Great Plains. The natural habitat of green ash is almost exclusively stream sides and bottomlands. The large seed crops provide food to many kinds of wildlife.Green ash is threatened by the emerald ash borer, a beetle introduced accidentally from Asia. Asian ashes have a high tannin content in their leaves which makes them unpalatable to the beetle, while most American species do not. 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.
are more deeply recessed within their corresponding leaf scars, giving the latter a more C-shaped appearance.
The spread of emerald ash borer was facilitated by the extensive use of green ash as an ornamental tree in the central U.S. 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 green 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. Instead, Norway, silver, red and sugar maples, honey locust, linden/basswood, redbud, crabapples, and hackberry, among others, were also utilized during this recovery period and in new urban and suburban areas. Fortunately, with these additional species, many cities were able to reduce the percent of ash and other species to much lower levels than during the Dutch elm disease era where from 56% to 100% of the trees were elm.
Injections and spraying of ashes with pesticides has been used in city parks to protect valued trees from emerald ash borer.
Record cold temperatures during the winter of 2018–19 are estimated to have killed as much as 80% of ash borer larva in the Upper Midwest.
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. According to the American Nursery Industry, "Back in the late 1980s, Dr. Frank Santamour Jr., then a research geneticist with the U.S. National Arboretum, proposed the 10-20-30 formula for diversity in the urban forest, limiting the plantings in a community to no more than 10 percent within a single species, 20 percent within a genus and 30 percent within a family." Many communities are using a more strict 5-10-20 rule today, because of the threat posed by emerald ash borer.
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.
Green ash is also vulnerable to many other diseases including ash yellows and dieback that can cause gradual loss of vigor and exhibit similar symptoms to emerald ash borer infestation such as crown dieback, bark cracking, and epicormal sprouts. These conditions are most common on stressed trees in areas of poor soil, urban pollution, and lack of moisture. A wave of ash dieback struck the northeastern United States in the 1950s–60s that killed an estimated 70% of ashes in the region.
Uses
Urban ornamental trees
Green ash is one of the most widely planted ornamental trees throughout the United States and much of Canada but mostly Alberta, including in western areas where it is not native. It is also widely planted in Argentina. It is very popular due to its good form and resistance to disease. About 40% of boulevard trees in Edmonton, Alberta are green ash.For the last two centuries American elm and ash, which both belong to the ancient Elm-Ash-Cottonwood Bottomland ecosystem, achieved distinction as North America's two most popularly planted urban species, used primarily for their superior survival traits and slowly maturing 180–300 year majestic natural beauty. Today used as living national monuments, the National Park Service is protecting Thomas Jefferson's 200-year-old planted example, and George Washington's 250-year-old white ash which has a 600-year possible lifespan. Green ash had been widely used as a primary ornamental and long lived monument tree until the elm fad of the 1880s, and regained top position once again after Dutch elm disease arrived.
Other continents learned of American ash species' urban survivability and unique beauty through the worldwide popularity of Midwestern Prairie style ecology and architectural movement. Modernizing cities in Russia and China then began using imported green ash a century ago to line streets and landscape new public parks.Advantages of green ash include its tolerance of harsh urban environmental conditions, ease of propagation, and its value for wildlife as a native keystone species.