by Matt Drury and Natrieifia Miller
Forest Health: Impacts of the Emerald Ash Borer on Trail Maintenance
A.T. stewardship is often thought of as the physical Trail: the treadway itself – sidehill, steps, and waterbars; campsites and shelters; or caring for the corridor boundary. However, trail maintainers who extend their consideration to the natural resources may find that, too, offers great benefits for planning and the long term care of the Trail. In this post we’ll look into a very important piece of the natural resource network which has been garnering a significant amount of attention from the USFS, ATC, and many other organizations, the Emerald Ash Borer (EAB, Agrilus planipennis) and it’s decimation of the Ash tree (Fraxinus spp.).
In the early 1990s EAB, an invasive exotic insect that kills all Ash trees in North America, was accidentally introduced from Asia to North America, although it was not discovered until 2002. Prior to this invasion ash trees were widely distributed across temperate forests in the eastern United States. A study in southeastern Michigan observed EAB-induced ash mortality of greater than 99 percent (Herms et. al. 2010). (Knight et al. 2008) revealed that individual ash trees can decline from healthy to dead in as little as 2 years in forests with high EAB densities. Within the past 10 years, EAB has devastated eastern deciduous forests, killing billions of ash trees, subsequently changing the species composition, structure, and associated functions of these ecosystems (Flower et al. 2013a). There are EAB infestations in all A.T. states excluding Vermont and Maine, check this map to see how close you are to an infestation: http://www.emeraldashborer.info/documents/MultiState_EABpos.pdf
(Photo of EAB adult in tunnel by Eric R. Day)
(Photo of adult EAB by Leah Bauer)
Impact on Forest Biodiversity: Being aware of this type of destructive force is important because it can drastically affect the various ecosystems through which the Appalachian Trail passes. For example, when siting a new camping area one could note the abundance of Ash trees in the area. Though alive at the initial point of observation, with knowledge of the detrimental impacts of EAB, one could infer that many of those trees would likely become potential hazards and maintenance problems in as little as 2 years. The death of these Ash trees could also promote the growth of non-native plant species which may lead to increased maintenance resources being allocated to stop their spread. Research also suggests that increased light in the forest floor, resulting from canopy gaps created by dying ash trees, may facilitate the establishment and spread of invasive plants. Exotic species such as oriental bittersweet, honeysuckle, multiflora rose, and autumn olive flourish in disturbed sites with higher light such as those created when EAB kills ash trees.
Impact to Ecosystems and Wildlife: Disturbance from widespread ash mortality can negatively affect native animals as well. As EAB continues to kill ash trees, many species including butterflies, beetles, moths, flies, and true bugs are becoming at risk of extinction as they rely on North American ash trees for food and shelter. With decline in ash trees, the species that feed on them as well as a couple other host plants may shift, feeding more on the other host plants, thereby leading to potential problems for these plants which are not adapted to withstanding such high use and consumption.
Local extinction of arthropods dependent upon ash could cause multiple extinctions of affiliated species with which they may be inextricably linked. Native butterfly populations may also be affected, as some plants on which caterpillars feed become more toxic when grown in sun rather than in shade. Therefore, canopy gaps created by dying ash trees may increase the toxicity of native plants, thus negatively affecting insects that feed on them.
White-tailed deer browse white ash; beaver, porcupine, and rabbits may eat the bark of young trees. The seeds are eaten by wood duck, northern bobwhite, turkey, grouse, finches, grosbeaks, cardinals, fox squirrel, mice, and many other birds and small mammals. The tendency of white ash to form trunk cavities makes it valuable for cavity nesters such as redheaded, red-bellied, and pileated woodpeckers. Loss of white ash as a structural forest component, food source, and habitat will have a devastating effect on these forests.
Scientists studying the effects of EAB on ash regeneration and forest succession have collected soil samples from southeast Michigan EAB-impacted forests for several years and have found no viable ash seeds and no new germinating ash seedlings. Their findings suggest that these areas lack an ash seed bank in the soil and that ash trees may not return after an EAB invasion affecting the composition of future forests. It is important to make note of signs of EAB infestation so that action can be taken to stop their spread before all of the surrounding ash trees can become infected.
In many areas, it is too late to protect trees, however there are many places that EAB has yet to reach. Much like protecting hemlock trees from the hemlock wooly adelgid, ash trees can be protected from EAB using systemic pesticides. Protection can last 1-3 years depending on the treatment product being used. While it is not feasible to treat the billions of remaining ash trees in the Eastern US, it is important to protect some trees in their environment. This will help protect the localized genetics of these trees and keep some seed bearing trees in the forest. Also, there are currently 3 species of parasitoid wasps identified as possibilities for biocontrol of EAB, this work is being completed by USDA Animal Plant Health Inspection Service (APHIS). To learn more visit this link.
It is thought that the parasitoid wasps will not be able to keep up with the initial killing wave of EAB moving through an unimpacted ash forest, but they may be instrumental in managing remnant populations of EAB.
Appalachian Trail Conservancy (ATC) is currently working with volunteers, Mountain True, and the United States Forest Service to survey for white ash trees along the A.T. corridor in North Carolina. ATC is also currently seeking funding to treat 500 white ash trees along the A.T. corridor with emamectin benzoate (providing 3 years of protection). If you have any questions or would like to get involved, contact ATC’s Southern Region Resource Management Coordinator Matt Drury at firstname.lastname@example.org.
More info regarding emerald ash borer and ash trees can be found at: http://www.emeraldashborer.info/