The mighty ash tree, the wood of baseball bats, axe handles and even wizarding wands, is quickly disappearing from our streets, yards, parks, and forests, brought down by a bug that measures less than an inch in length.
The perpetrator of the ash trees’ demise is a wood-boring beetle called the emerald ash borer, or EAB. Native to Asia and accidentally introduced to the US in wood packing material in the 1990s, EAB was first positively identified in the Detroit area in 2002.
The emerald ash borer belongs to a family of beetles known for their glossy metallic bodies, long coveted in some cultures for jewelry. While many of them bore into dead wood or stressed trees in Asia, they are not a general threat in their native range. In North America, however, they have run amok, attacking the wood of healthy green, black, and white ash trees.
While the adult only lives a few weeks, feeding on the margins of ash leaves, it is the larvae that cause the most harm, feeding under the tree’s bark on the interior tissue the trees use to transport nutrients and water from roots to limbs and leaves to the rest of the tree. Disrupting this critical part of the anatomy kills the tree.
At home in its native range, the beetle’s populations have been kept in check because Asian ash tree species have a higher tannin content, which is less palatable to the adults. In addition, native predators feast on the adults and parasitic wasps lay eggs in their bodies. But here, with no parasitic wasps that recognize their ability to use them and birds not yet eating them, the beetle has been free to destroy our trees. To make matters worse, we inadvertently spread the insect while moving firewood around on camping trips and planting trees shipped out-of-state in our own yards. As of this fall, 35 states plus five Canadian provinces have reported the beetle’s presence.
EAB’s ecological impact is tremendous, as our forests are comprised of many green and white ash trees. When these trees die, wide gaps in the canopy open up and invasive species are provided with the light they need to thrive and outcompete natives. Some 282 arthropod species—a wide variety of ants, bees, and spiders—feed on ash trees, and at least 43 species of native wood-boring and bark beetles feed solely on ash. All of these are in peril of disappearing with the tree.
From an economic standpoint, EAB is the most costly and destructive forest insect to invade the United States. Ever. It has taken a toll on nurseries, saw mills, and logging companies that rely on ash wood as a commercial product. But it has also been costly for private landowners, municipalities, and state agencies that must deal with treating or removing ash trees from the landscape. Ash trees comprise more than 20% of municipal tree species and were widely planted in parks and as street trees. Specimen trees treated with insecticides need to be retreated every 2-3 years, which still may be cheaper than cutting them down or letting them die in place.
At the Schuylkill Center, we have been taking the ash tree situation seriously. According to Steve Goin, Director of Land and Facilities, “After hearing about the movement of the emerald ash borer over the last several years and bracing for its arrival, it still surprised me when I first discovered its exit hole on a declining ash tree on the property. The speed it tore through our half square mile of forest was devastating.” In an effort to be proactive, the Center has used grant money from the Tree Vitalize Watershed program to foster the establishment of other species over the last four years. To date, over 1,000 trees have been planted across four acres of the property.
We hope we are making wise choices, but the future is unpredictable and the road ahead will be a bumpy one, one without ashes—for a while.