In Norse mythology, the giant ash tree Yggdrasil bound together the Nine Worlds, nine distinct realms defined by their inhabitants, among which were gods, goblins, fairies, humans, and the dead. Shaman spirits were said to have climbed Yggdrasil to access the different worlds, and the Norse god Odin hung upside down from the tree for nine days in a tortuous ordeal to gain knowledge and power.
In Celtic culture, the Druids believed that the ash tree was enchanted, that it could, for instance, prophecy a weakened child's well-being, if after the child had been passed three times through a hole made in the tree, the hole later healed. Ash also was an important source of medicine for the Celts and for people elsewhere in Europe.
Today, ash (Fraxinus) continues to be valuable, particularly in Europe and North America, where various species are used in landscaping and in the production of furniture and other wood products. But in North America, the mystical and majestic ash is suffering from infestation with the invasive emerald ash borer (Agrilus planipennis), and in Europe it is battling the fungus Chalara fraxinea, an organism that recently was reported for the first time in wild ash in the United Kingdom. It had been detected there earlier this year, on nursery stock that had been imported from continental Europe, prompting a voluntary ban on ash imports. Legislation to enforce the ban was pursued following the detection of C. fraxinea in England's native woodlands. The pathogen likely spread to affected areas from infected nursery plants that had been imported.
There is concern that chalara ash dieback could give rise to a devastating outbreak, one that could be as severe as Dutch elm disease, which decimated elm populations across the United Kingdom in the 20th century. Chalara ash dieback has already affected an estimated 90 percent of ash trees in Denmark and Sweden and 80 percent in Poland, where the disease was originally discovered in 1992. (C. fraxinea was identified as the causative agent of the disease in the early 2000s.)
The loss of ash in Europe could have significant ecological impacts, particularly in the United Kingdom, where some 80 million ash trees constitute about 15 percent of the country's native broadleaf forests. The ecological fallout from the loss of ash could ultimately alter the appearance of the landscape and lead to declines of other species, including plants, birds, and mammals, such as wood mice (Apodemus sylvaticus) and bank voles (Myodes glareolus). Furthermore, the effort to stop the spread of C. fraxinea could prove costly.
The emerald ash borer invasion in North America might foreshadow what is to come with C. fraxinea in Europe. In the decade since its discovery in southeastern Michigan, U.S., in 2002, the emerald ash borer has killed more than 25 million ash trees and has spread to 12 other U.S. states and to two Canadian provinces. Controlling the insect's spread, which has focused primarily on restricting the movement of wood between states, provinces, and parks in affected areas, has cost tens of millions of dollars.
On both sides of the Atlantic, newly emerged pests and pathogens of ash give new meaning to the phrase “ashes to ashes, dust to dust.” In Europe, the ash's prominence in traditional medicine and in Celtic folklore makes its loss seem all the more conspicuous to me. For, like Yggdrasil, ash brings together different worlds -- the worlds of animals and plants and the worlds of human history and culture. If such unity is to continue to exist, ash must remain a part of this world.
Kara is a freelance science writer and senior editor of biomedical sciences at Encyclopaedia Britannica, Inc. She is the author of Out of Nature: Why Drugs From Plants Matter to the Future of Humanity (University of Arizona Press, 2012).
The views expressed are those of the author and are not necessarily those of Science Friday.
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