Sunday, October 22, 2017

Paul Hetzler: If An Ash Tree Falls

Call it an infection or an epidemic, but even the most docile and pleasant woods will soon be transformed into Fangorn Forest. As far as anyone knows, local trees will probably not become animate like the ones in the fictional woodland of J.R.R. Tolkein’s trilogy. However, they may be just as dangerous, only for a different reason.

In The Lord of the Rings, trees were inherently good, and if provoked sufficiently could take up arms and kill lots of bad guys. Presumably our trees are also of good will, or at least do not have anything against humans in particular. But changes are coming within the next decade that will render them dangerous through no fault or intent of their own.

Farmers, camp owners, woodlot owners, and anyone who cuts their own firewood will be affected by this turn of events. By now we have all heard that the emerald ash borer (EAB) has been confirmed in the Town of Hammond in St. Lawrence County, as well as in Franklin County, not far from Massena. And also by now we may be tired of hearing about this invasive wood-boring beetle and how it will wipe out all species of ash trees. Chestnuts and elms died out and the world didn’t end, so why all the fuss about EAB?

Most of the time, when a healthy tree is killed by a pest, disease or flood, it just waits 5 or 10 or 15 years for you to cut it for firewood. If you don’t show up, it shrugs, mumbles something about your lack of work ethic, and topples over. Think of all the dead trees in beaver ponds that stand for a decade or more as herons nest in their bleached crowns. And after the chestnut blight wiped out that species, there were reports of the dead snags remaining upright for 30 or more years.

But the emerald ash borer has a peculiar effect on the ash trees it kills. Ash that succumb to EAB become dangerous in as little as one year, and after only two years, they start leaping onto cars, trucks and busloads of schoolkids. OK, that is taking it a little too far, but many people have been injured, and many homes and vehicles damaged in the wake of EAB infestations. In Ohio, a school bus was hit by a large dead (EAB-killed) ash tree, injuring 5 students and the driver, and pretty well totaling the bus.

No one seems to have an adequate explanation for this rapid and profound loss of wood strength, but I’ll pass along what we do know. According to the Davey Resource Group, the consulting and research branch of Davey Tree, the shear strength of ash wood undergoes a five-fold decrease after the tree is infested by EAB. Trees become dangerous so quickly that Davey Tree will not allow its climbers into any infested ash that shows a 20% decline or more.

In the words of Mike Chenail, an International Society of Arboriculture Certified Arborist from Pennsylvania, “Two realities make an ash tree killed by EAB especially dangerous. EAB cuts off the flow of water and nutrients through the tree. Additionally, the fatal pest creates thousands of exit wounds. Both conspire to dry out the tree and make it brittle.”

Dr. John Ball of South Dakota State University quantifies the moisture loss, saying “Moisture goes from 80% on a recently infested tree to less than 40% standing dead…There is also some drying of localized sapwood.” Sapwood is the outermost layer of wood, often just a few inches thick, so having it suddenly dry out may not seem like much. Jerry Bond, a Consulting Urban Forester with the Davey Resource Group, and a former Cornell Extension Educator, explained it to me this way: “Ninety percent of the structural strength of a tree resides in the outermost ten percent of the trunk.” In other words, when sapwood is weakened, there’s not much strength left in the tree. There may be yet another facet to the picture. Anecdotes from arborists and other tree workers point to the surprisingly advanced decay in some ash wood that had only been infested one season. How widespread or significant this may be is not yet known.

But none of that is really the point. The point is that those who work in the woods, or spend any amount of time there, need to be aware that when EAB kills ash trees, they act differently. Think of it like a zombie infection. Wait, no, don’t. Just look out for trees behaving strangely, and remember it is nothing personal.

Woodlot owners, farmers, and others who want to learn best management practices for their property may want to attend an upcoming EAB informational session with foresters from the NYS Department of Environmental Conservation, and NYS Ag and Markets representatives. The meeting will take place from 5:45 to 8 PM on Wednesday November 1 at the Cornell Cooperative Extension Learning Farm in Canton.The session is free and open to the public, but pre-registration is requested. To register, or for more information, call Paul Hetzler at (315) 379-9192 ext. 232, or email

Photo of an emerald ash borer courtesy David Cappaert, Michigan State University.

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Paul Hetzler has been an ISA Certified Arborist since 1996. His work has appeared in the medical journal The Lancet, as well as Highlights for Children Magazine.You can read more of his work at or by picking up a copy of his book Shady Characters: Plant Vampires, Caterpillar Soup, Leprechaun Trees and Other Hilarities of the Natural World

14 Responses

  1. Paul says:

    Anybody know what the DEC plan is when we find EAB on Forest Preserve land?

    • Boreas says:

      Dunno. But I reported to them a few months ago that one of my Mountain Ash trees is infested with Asian Longhorn Beetles and the silence has been deafening. I live in the Forest Preserve.

      • Paul says:

        What do you mean? If it’s your tree it is on private land? Nobody lives on/in the Forest Preserve. That is state land in the park.

        But I too have heard no plans. Only about traps and waiting to see when it get there.

        Boreas, are you sure it is Asian long horn and not the other one that looks similar that is common around here? Did you tray and call them? They are usually pretty good if you try that.

        • Boreas says:

          I guess I meant within the Park. But there are state lands within 1/2 mile.

          I sent them pictures of the pencil-sized exit holes which seems to be pathognomic for that particular species. I did converse a bit by email, but that is as far as it went. They said ALB also target maples, but I have better things to do that check out all the maples in my area. If they are interested in stopping infestations, they will need to do the work.

          The NE longhorn beetle has a smaller exit hole, and tend to target softwoods. I do have those around in my pines. The exit holes are much smaller.

          • Paul says:

            Did you see the beetles? Mountain ash are a favorite for yellow bellied sap suckers they make lots of holes in Mt. Ash like the size you are describing. Sure these were beetle holes? I have one Mt. Ash in my front yard that is littered with these holes. It’s weird it doesn’t seem to bother the tree. The birds must be after some kind of insect in there? See this link. I did a search for “mt ash and yellow bellied sapsucker”. This is what my tree looks like:


            • Paul says:

              I take that back the sap sucker isn’t looking for insects – sap!

            • Boreas says:

              Plenty of Sapsucker holes – no confusing them. The ALB holes are near the base of the tree and are a perfect pencil-sized hole. BTW, Sapsuckers CAN kill a tree if they are too aggressive. They killed an old mountain ash on my property by girdling it. My new ones I have to wrap with bark tape if I have a particularly Sapsucker around. It is quite effective.

  2. Paul–not sure what the DEC is doing on forest preserve land…probably is location-specific. I would guess that at most, they would remove ash trees that could pose a threat to hiking trails.
    Boreas–It may have been a different borer. Worldwide there has been only one case of ALB infesting any tree in the genus Sorbus, including European mountain-ash, the popular but short-lived ornamental tree commonly planted in landscapes in the US. Mountain-ash are attractive, but are fraught with many pests and diseases. The flat-headed apple-tree borer is of particular concern, as it makes a pretty good-size tunnel in the wood.

    • Boreas says:

      Paul H.,

      Thanks – I’ll check it out. I can’t rule anything out as I am no expert, but the people I did correspond at iMapInvasives didn’t rule it out based on the pix and description. I guess I was expecting some response from the state after spending my time researching, taking pix, reporting, etc.. Probably too busy.

    • Paul says:

      Paul, thanks. The state has had lots of time. They should have a comprehensive plant to deal with a threat to (something like) 20% of the trees in the Adirondacks.

  3. ALB would start near the top and leave a hole 3/8 inches dia. or slightly larger. The flatheaed borer makes a pencil-sized hole and would only be found near the base. Too bad about the lack of NYSDEC response…disappointing.

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