Trees killed by emerald ash borer (EAB) can be dangerous to climb and rig. In this article, we’ll look at felling, climbing and rigging critical-risk trees killed by EAB.
A quick EAB refresher
Emerald ash borer was first discovered in the United States in southeastern Michigan in 2002, but experts think it probably was introduced sometime in the 1990s. This pesky little “pest” most likely caught a free ride over from Asia on infected ash wood used in shipping pallets.
Since then, it has migrated east and west, causing death and destruction to North American native ash trees. According to at least one pest-control professional I’ve talked with, EAB also has indirectly caused the death of tree workers who were unfamiliar with the process in which ash trees die after being infested by the pest, and were tasked with having to rig or fell the dead trees.
Here in New Hampshire, where I live and work, EAB was first discovered in 2013 in Merrimack County, which is in the central part of the state. This extremely destructive, invasive insect has since invaded nine out of the 10 counties here, and shows no signs of stopping until it infests and likely kills every last ash tree.
Restoring a woods line
Recently, Girard Tree Service LLC, which I co-own and operate with my wife, Heide, had the opportunity to restore an old woods line along a stone wall on an historic farm site. (Photos 1 and 2) The property has an abundance of beautiful sugar maples (Acer saccharum), as well as many ash trees (Fraxinus), of which there are 18 types, or species, in this country. Every last one of the ash trees along this stone wall was dead. On top of that, wouldn’t you know it, the location is in Merrimack County, less than five miles from “ground zero” of the first EAB detection site in New Hampshire. So I knew most – if not all – had been dead for years.
To restore the wood line to its former glory was going to be a multiday task, as most of the trees also were heavily entangled with and being “choked out” by bittersweet vines, another invasive species from Asia. Anyone who has ever had the “pleasure” of working and climbing in trees with this horrible tangle of Mother Nature’s finest knows how time consuming and frustrating the work can be.
We started the work knowing most of the ash trees could be felled into the open field adjacent to the stone wall. But a few were going to have to be climbed and rigged with pull ropes, and one was going to have to be rigged/pieced out. Ours is a small, family-run business, and I have a policy that I will not put my climbers in any seriously dead trees. I won’t take a chance on something happening to them. Therefore, I always climb the really sketchy trees myself, and all these dead ash were more than sketchy – they were in critical-risk condition.
Assessing the category of risk
Tree work is an inherently dangerous job, as everyone knows. For that reason, climbers must perform a tree and site inspection before beginning any climbing operation. According to various sources I’ve come across, there are four categories to be aware of when doing an evaluation: 1. low-risk; 2. moderate-risk; 3. high-risk; and 4. critical-risk trees. There is so much that goes into evaluating whether a tree is safe to climb that it is beyond the scope of this article. Please refer to TCIA’s “Best Practices for Rigging in Arboriculture” manual for additional information that will help you make a sound judgment.
Suffice it to say, all the ash trees we were dealing with fell into the category of critical-risk trees, but not all for the usual best-management-practices (BMP) reasons. What a lot of tree workers fail to realize about trees killed by EAB is that the way they die greatly affects the condition they are left in. EAB will usually kill a tree in two to five years, generally on the earlier end of that span. The larvae tunnel up and down under the bark, feeding on the xylem and phloem, interrupting the nutrient flow to the tree, depriving it of the necessary food source and leading to a fast decline and death.
Once this happens, the transpiration cycle stops within the tree. The structural integrity breaks down quickly and can leave the tree in a very brittle, but hard, condition. So even though you do your pre-climb inspection, sounding the stem with a mallet, and it sounds and feels strong, the actual condition may be just the opposite. You can use a drill to check the soundness of the stem, but this also can be misleading, as the tree will appear solid, without any internal cavities or rot.
A false sense of security
This solid appearance lulls the climber into a false sense of security. When they begin rigging operations as they normally would, thinking the tree is solid, it can fail on them, possibly causing injury or a fatality.
Typically, critical-risk ash trees will break off within the first 10 feet or so of the ground. This is especially true during negative-rigging operations, when the stem/trunk begins oscillating as a piece comes over. Yes, the BMPs for rigging can help with your initial evaluation, but this is where knowing the species of the tree and the history of EAB, and having someone with a lot of experience, can save your life.
All the ash trees I had to climb and rig with a pull rope on this job were taken down safely without any mishaps. By the last day of the work, we had one more ash to take down, and this was the largest and most critical one. I decided to rig it down. Although I could have just cut and chucked down pieces without any rigging, I decided to use this tree as a training opportunity for my crew.
Encountering a utility guy line
This particular tree was being used as a “guy pole” for all the utilities across the street. (Photo 3) The utility guy line was non-energized and was located about 20 to 25 feet up the stem. I decided to leave the guy line in place and use it to my advantage before having the utility companies come in and remove it. Knowing how I was planning to rig and load the ash tree, I knew leaving it in place would give me added stability during the removal process.
Some might think this was an unsafe thing to do, but I used to do utility relocation work as a New Hampshire DOT engineering technician. Most utility poles in the U.S. are 40 feet in height and sunk approximately 6 feet into the ground. This is more than enough hold for a back guy on a tree stem that I was not planning on loading heavily. Now don’t get me wrong, I am not advocating that tree workers should use their local utility poles for anchoring lowering devices and other hardware! But my margin of error here was minimal.
Full tree-risk assessment
We had the honor of having Tchukki Andersen, BCMA, CTSP and TCIA staff arborist, on site for a visit, and she and I did a full tree-risk assessment before I started climbing. This particular ash was about 60 feet tall with a diameter at breast height (DBH) of around 20 inches, and had been dead for six to eight years. It had severely compromised basal roots – with more than 60% significantly decayed. Most of the bark had sluffed off years earlier. (Photo 4)
It is recommended not to climb trees in this condition, and to use an aerial lift or other access method to gain entry instead. However, with proper training and knowledge, there are – in my opinion – acceptable ways to climb and work in critical-risk trees.
The first thing I did was bring out my bags of 10,000-pound load-binder straps. Using these ratchet straps on the stem and placing them every 5 to 6 feet greatly reinforces the trunk. Doing so in this case also gave me some reassurance, especially knowing how this tree was being stressed and the forces it was going to need to endure during rigging operations.
Basic stresses within a tree
There are four basic stresses within a tree: compression, tension, shear and torsion. (Diagram 1) This ash was being stressed across all four planes, having cracks both longitudinally (vertically) and latitudinally (horizontally). I made sure to put the straps along both lines of compromise to try and mitigate the strength loss as much as possible.
For anyone interested in learning more about tree mechanics and failures, I highly recommend the German author Claus Mattheck’s book, “The Body Language of Trees.” It is not an inexpensive book but is worth every penny spent on it (especially for engineering nerds like me).
My plan and equipment
As I began climbing the tree, it felt just as I thought it would: hard and brittle. As I climbed, I was able to cut off some of the lower front and rear branches below the guy wire and along the stone wall and field. I climbed to where I was planning to take out the top of the tree and set up the next stage of mitigation and rigging equipment.
My plan was to rig out the top, almost directly opposite the utility guy line, but first I wanted to set an additional side guy line and run it down to a sturdy ground tree in the woods. I used our Maasdam rope come-along with Samson Tree-Master ½-inch (12-mm), three-strand, hard-lay line. This little rope puller has a 1,500-pound pulling capacity, though in this scenario I only put a few hundred pounds of tension on the line. (Photos 5 and 6)
Next, I installed a Rock Exotica 2.6 Swivel Omni-Block (working load limit [WLL] = 20 kN), directly opposite (180 degrees) from the three-strand, side guy line. From this block, I installed a Samson Stable-Braid ½-inch (12-mm) rigging line (minimum breaking strength [MBS] = 8,800-pounds), which was going to be my lowering line. (Photo 7) This line also would act as a stabilizing line, working in conjunction with the other two guy lines that were in the tree. This setup (including the utility guy wire) would form a stable triangle, allowing the vector forces to act in the most favorable and safe direction when rigging out the pieces.
Also, the lowering line was not run straight down to the base of the ash tree and the lowering device, as I did not want to set up a large bending-moment arm. Nor did I want to load the tree in tension. Instead, I ran the lowering line down at an angle of approximately 45 degrees to an adjacent rescue pulley and sling on a nearby maple tree. Then, the line ran over to another small redirect fairlead pulley, which guided the lowering line into our Hobbs H2 Lowering & Lifting Device (LD) mounted on another sturdy maple tree. (Photos 8 and 9). There are many new and great LDs out there now in the tree care industry, which is a wonderful thing, but we must always remember that it was the late, great arborist Ed Hobbs who gave us the first one.
Advantages of the rigging system
Installing the rigging line and hardware in this manner achieved multiple things for me.
1.It gave my ground worker, who was running the LD, a safer place to stand away from the drop zone. With the condition of this critical-risk tree, it was imperative that everyone stayed far away from the rigging operations.
2. It added rope to the rigging system. Any time you can add more rope to your system, you increase the energy absorption and manage the forces better. This is due to having more elongation (stretch) with the additional rope.
3.It reduced forces on the rigging system. By changing the angle into the block (opening up the angle more) and having the LD located on another tree, I was able to lessen the reaction force on the rigging point (Diagram 2) and load the stem into compression rather than tension. (Refer back to Diagram 1)
There are more reasons why you may want to move your LD to another tree. For additional information, see “Seven Great Reasons to Relocate Your Lowering Device,” by Anthony Tresselt, in the July 2022 issue of Tree Care Industry Magazine.
Setup is complete and rigging begins
After everything was set up, we began rigging out the tree. I made sure to pre-tension each piece before cutting it. This limits the fall distance and reduces that initial “hit” as the piece is caught by the rigging line. This in turn reduces the “shock load” on the stem and climber. Shock loading is the sudden impact from a load coming rapidly onto a slack rope, also called dynamic loading. The following is a good rule of thumb and comes from my friend and mentor Don Blair: For every foot of fall, the piece gains a unit of weight plus one. For example, a 500-pound chunk falling 4 feet will hit the rigging with about 2,500 pounds of force.
My foreman, Brandon Eldridge, did an excellent job of letting the pieces run smoothly. We were able to rig everything above the attachment of the utility guy wire down safely. For that last piece, I actually decided to just put a tag line on it and pull it over without having to press my luck. (Photo 10) We left the stem with the guy line attached. I was not about to cut their support, but we did notify the utility that they were going to have to come in and set a new guy pole of their own. Then they were going to fell the remaining stem.
Everything came down just as planned. I was able to demonstrate (even though my crew already knew) that climbers can sometimes work in critical-risk trees if the necessary precautions and mitigation steps are adhered to. But again, it is always up to each individual to decide if the job can be completed safely. Many thanks to my great crew – Brandon Eldridge, Sam Wagner and Cody Leblanc – for helping accomplish this technical removal.
Chris Girard is an ISA Certified Arborist, a Society of Professional Rope Access Technicians (SPRAT) Level 1 Technician. He is the owner of Girard Tree Service, a 15-year TCIA member company based in Gilmanton, New Hampshire.