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Emerald Ash Borer: What to do to save our ash trees

Adult Emerald Ash Borer. Photo Credit: Vermont Department of Forest, Parks, and Recreation.

Map of the EAB infested areas in Vermont. Photo Credit: Vermont Department of Forest, Parks, and Recreation.

Green Ash. Photo Credit: Charlie Hohn.

Black Ash. Photo Credit: Charlotte Bill

White Ash. Photo Credit: Stew Stryker.

by Nancy Patch, CHC Vice Chair

It has been over a year since the first confirmed sighting of Emerald Ash Borer in Vermont. The Emerald Ash Borer (EAB) is, as its name suggests, a metallic green beetle whose larvae feed on the inner bark of ash trees, disrupting the tree's ability to transport water and nutrients. EAB was first discovered in Vermont in 2018 and since then it has been found in several locations.  Though EAB has not yet been found in Franklin County, it is likely already here; EAB has been found both to the east, in Orleans County, and to the west, in Grand Isle County.  

The insect impacts all three ash trees that are native to Vermont; white ash, green ash, and black ash. The ash component of forests across the state is around 5% but has a much larger concentration in the wetlands of Grand Isle County and the Champlain Valley, where Green Ash and Black Ash can be found in large number. White ash, a more upland species, can be found in nutrient-rich sites.  

All three ash species play important ecological roles as nutrient cyclers, accessing and metabolizing nutrients more efficiently than other species. White Ash serve this purpose in richer, limestone soils where they are found as companions with Sugar Maple. In limestone soils, nutrients taken up by White Ash are made available in a new form to other species through the decomposition of the White Ash leaves. In a young Sugar Maple forest this nutrient availability is important for optimum growth rates. Like their White Ash cousin, Green and Black Ash act as nutrient cyclers, though they fill this niche in wetland habitats rather than limestone soils. In fact, the Green Ash and Black Ash growing in wetlands can often be the most dominant tree.  

Alarmingly, EAB will cause mortality in much of the ash throughout the state over time. Some resistance to EAB has been found in green ash but no resistance has been found in black ash.  The long term effects of tree loss in our wetlands can cause a change of state from a forested wetland to an herbaceous or shrub wetland and a loss of forest function. However, there is a glimmer of hope.  White ash has been found to show some resistance by pushing out or walling off the insect as it attacks. In fact, pockets of white ash with a 90% survival rate have been found in the Midwest in the aftermath of the EAB wave.  

WHAT DO WE DO?

We can accept that many or most of our ash trees may die.  Landowners need to decide what their goals are. Harvesting to capture the value of high-quality ash is one option.  Identifying ash removal based on safety near infrastructure (roads, trails, buildings) is another option and critical for community road maintenance.  In Franklin County, the towns of Richford, Enosburgh, Bakersfield, and Fairfax all have ash management plans for town roads. Grand Isle County is developing a county master plan. An individual landowner may choose to not harvest any of their ash trees and let nature decide. Then, there are the variations.

It is important to recognize that if we cut all our ash, we are removing the future potential for ash on the landscape.  One recommendation is to maintain ash in all age classes, even retaining large trees. Some of the resistant ash found in the Midwest were large diameter, very healthy ash.  Leaving large ash can ensure a seed source for a longer period of time as big trees have more seed. Ash can also be targeted for insecticide treatment. The chemical injection treatment for EAB works but needs to be applied every 2-3 years.  Ash have male and female flowers on separate trees so for the best result, insecticide treatment should include at least one male tree to pollinate the female trees and develop the future seed source.  

Management in wetland forests is a little trickier.  First, they are hard to harvest and the trees have lower value. These forests, however, are also at higher risk and may need more care.  Landowners can try to enhance the diversity of the wetland by going in early and releasing any other species found such as silver maple, swamp white oak, burr oak and others.  The larger crowns will have more seed and help to occupy the site as the ash trees die. Harvesting small pockets of ash and then planting with other species is another option to try to prevent the loss of transpiration and the change of state from a forested wetland to a non-forest. We should start collecting and saving seed for future planting.  This may be the only current action to take for black ash.

The bottom line is that if we want to maintain ash as a species on our landscape, we need to find ways to manage for future seed availability and to maintain a soil moisture condition that facilitates tree growth.  Instead of cutting everything in anticipation of EAB, we need to focus on keeping the ash where it means the most.