Emerald Ash Borer

A few days after returning from Anguilla we spotted a large tree newly cut down, lying by the side of the road in our neighborhood. Always on the lookout for good firewood for the woodstove, I collected a few twigs and identified them using Muenscher’s Keys to Woody Plants (Cornell University Press). The tree was white ash, Fraxinus americana (Oleaceae).

This was good news and bad news. Good news, because white ash’s relatively high BTU value means it makes good firewood. Bad news, because of the emerald ash borer.

Emerald ash borer (Agrilus planipennis) is a bright green, half-inch long beetle native to Asia. It was discovered infesting ash trees in Michigan and Ontario in 2002, but is thought to have been there for at least ten years prior. The adults are known to travel more than ten miles; the larvae travel through wood harvested as lumber and firewood. Since 2002, EAB has spread throughout most of the US (and parts of Canada) east of the Rocky Mountains.

There are about sixteen species of ash (Fraxinus) native to the US, and all of them are vulnerable to EAB attack. Adult beetles lay eggs in the tree bark; the larvae then burrow in and start feeding on the inner bark and outer sapwood, emerging as adults after one or two years and leaving characteristic D-shaped exit holes. Although adults eat the leaves, it’s the physical damage to a tree’s vascular system caused by feeding larvae that leads to tree death.

Ash trees are major components of certain hardwood forests, as co-dominants with maples and beeches; in some of these plant communities they are considered keystone species.* There are an estimated eight billion ash trees growing wild in North America. More than one hundred million of them have died since 2002. (1)

Nature abhors a vacuum. When a large die-off occurs in an ecosystem, every other organism in that system is disrupted. Imagine if, say, one tenth of the trees in a hardwood forest die in a short time. Now there are large holes in the tree canopy, and more sunlight reaches the understory and the forest floor. As a result, shade-loving plants will decline and eventually die, to be replaced by plants that like more sun. Some tree species will germinate and grow better as a result, and some will do worse. The soil ecology will change: there will be less competition for water from tree roots, and the fungal communities that form mycorrhizal associations may be affected. And as plant communities change, so do the insects and birds and larger animals that depend on them.

Ash trees don’t just grow in the wild. They’re also cultivated for the straight, hard, dense wood, which is used in just about anything that any other hardwood is used for: tool handles, flooring, cabinetry, doors. It’s the best wood for baseball bats, even. And ash are popular species for street trees: about ten percent of Baltimore’s are ashes. (2)

The economic impact (forestry products, plant nurseries, municipalities) has already been measured in the hundreds of millions of dollars. (1) One source has declared it “the most destructive and economically costly forest insect to ever invade North America.” (3)

So what can be done? The answer is unclear. There are some pesticides that are effective if applied correctly, at the right time, which is good news for homeowners and municipalities. But we can’t selectively treat eight billion wild trees. Research is on-going, of course.

If you’re a property owner, first determine if you have any ash trees. Or Chionanthus species (fringetree) – EAB attacks them as well. Then educate yourself so you can watch for signs and symptoms of infestation. One sign is an increase in woodpecker activity. Then check with your local extension service for current accepted practices and go from there. (See below for links.)

As for firewood, check with your county or state government. There are quarantine areas, but moving wood within an area is usually okay. Before collecting the wood in my neighborhood, I checked with an extension agent, a DNR employee, and a forestry expert; all said it was okay to take the wood so long as I didn’t transport it over county lines.

Why was the tree in my neighborhood taken down? I had a good close look at the collected wood, and didn’t see any larvae-filled galleries or D-shaped holes. Was it cut down as a preventive measure? I don’t know, but I sure hope things don’t get to the point where we have to remove healthy trees to contain this threat.

*keystone species definition from britannica.com:

 …in ecology, a species that has a disproportionately large effect on the communities in which it occurs. Such species help to maintain local biodiversity within a community either by controlling populations of other species that would otherwise dominate the community or by providing critical resources for a wide range of the species.


references and further information
(1) Emerald Ash Borer Information Network
(2) Maryland Dept. of Agriculture
(3) via a New York Times article
EAB Information Network Insecticide Options for Protecting Ash Trees from Emerald Ash Borer
Coalition for Urban Ash Tree Conservation – Emerald Ash Borer Management Statement
Purdue University Managing Emerald Ash Borer Decision Guide
University of Maryland Extension Emerald Ash Borer
Maryland DNR Emerald Ash Borer
Ontario Ministry of Natural Resources A Visual Guide to Detecting Emerald Ash Borer Damage
Washington Post article from January 2016
and there’s even a website called dontmovefirewood.org

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