On a warm, balmy August morning, an arborist and I walked the length of the Louisville Loop from North Beckley Paddling Access to the Oxbow on Floyds Fork. As we walked, we paused frequently, gazing upward. I marked nearly two dozen trees with a dot of white paint while the arborist took quick notes. Each tree we marked had blonde, flaking bark and a skeleton-like, bare canopy. These trees were being marked for removal, and almost all of them were ash trees.
The decline and death of these towering, proud ash trees (Fraxinus spp.) is attributable to a small, green, winged beetle known as the emerald ash borer. A logical and often asked question is: How could a tiny beetle, smaller than the diameter of a penny, kill millions of mature, hardwood ash trees? The answer, in a broad and conceptual sense, can be distilled down to a biological term that most of us learned in elementary school- adaptation.
The emerald ash borer (Agrilus planipennis) is endemic to East Asia (it was inadvertently brought to the United States in the 1990s in wooden pallets), where there are species of ash trees that are not found in North America. These Asian species of trees evolved alongside the borer beetle over millennia, and the trees slowly developed adaptations that armed them with a biological resistance to the beetle. The Asian ash trees most likely have compounds within the wood that makes digestion difficult for the beetle larvae, which deters the insect from eating more. The North American species of ash trees do not have this specific biological adaptation, and are therefore much more susceptible to decline and death from emerald ash borer.
The susceptible trees in North America are first preyed upon by adult emerald ash borers. The beetles feed upon the leaves of the tree with little to no effect on the tree. The real damage begins after the beetles have mated and the females have deposited eggs into the bark of the ash tree. Within two weeks, the eggs have hatched and the larvae chew through the bark of the tree. Over the next six weeks, the larvae feed upon the pulpy, soft wood of the cambium, creating a serpentine shaped gallery, cutting off the nutrient pathways of the tree. The tree is effectively girdled, preventing the tree from moving sugars and water to the leaves and roots. This leads to the decline of the canopy and eventual death of the tree. Once the insects develop into adult beetles, they bore (hence the ash borer name) through the bark, creating a ‘D’ shaped exit hole.
Losing thousands of hardwood trees throughout the Parklands (and millions throughout Kentucky and the eastern United States) presents a conundrum and another question that needs to be answered: What can be done?
The Parklands has a multipronged plan to deal with the issue of ash tree loss. The first action in this plan is to ensure safety for park visitors. Frequent visitors have noticed, and will continue to see, arborist crews throughout the parks felling dead trees that could potentially fall on the parkways, the Louisville Loop, or other high traffic areas.
Once safety is ensured, the focus will pivot to habitat restoration and ash tree preservation. Areas of dense ash loss will be reforested or maintained to promote regeneration of diverse hardwood species such as oaks, hickories and maples. In low traffic areas with a lower potential for dangerous falling trees, regeneration of ash will be promoted in an effort to repopulate the canopy with the missing ash trees. As these ash trees mature, they will either be preyed upon by the borer, or individual, successful trees will have a natural resistance to the borer. There is a chance that for several generations, the resistant trees will reproduce and hybridize, eventually developing adaptations to deter the exotic beetle. The trees that develop these adaptions will then create a new generation of resilient ash trees. This outcome, though, may be unlikely. The best hope for ash trees may be preservation.
In addition to reforestation and ash tree regeneration, the park has preserved some mature ash trees. Several specimen ash trees throughout the parks (that have not developed resistance to the borer) have been treated with a pesticide that prevents the larvae of the borer from eating the soft wood of the tree. These trees can be seen at the Miles Oak Savanna, and the Grand Allee, and they are marked with a small metal tag, signifying that they have been treated.
The next time you visit the Parklands, remember to be present and aware. Arborist crews are operating throughout the parks. Be mindful of parkway, Louisville Loop and trail closures and heed signage. Also, have the presence to gaze upward and observe. What do you see? Are there bare canopies? What are the rippling effects of ash tree loss in a Kentucky woodland?
If you find yourself asking these questions and want to assist the Parklands with habitat restoration and ash tree preservation, consider volunteering for upcoming tree planting and reforestation projects in October and November.
Evan began his career with the Parklands in 2013 as a park attendant and part-time helper on Natural Areas projects. In 2014 he joined the Natural Areas team as a technician and in the spring of 2015 was promoted to Natural Areas Team Leader. While working he spends his time promoting healthy habitats for the plants and animals that live in the park. Patrick was born in Morehead, Kentucky near the Daniel Boone National Forest, where his appreciation for nature, conservation and stewardship was cultivated. Patrick is a graduate of the University of Louisville, where he earned a degree in anthropology. His interests include cooking, mushroom foraging, craft beer and the outdoors.
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