Some defects you can’t read from the ground. A 10-foot fissure in the canopy of a mature Dawn Redwood needs the climber to ascend and look up close.
Some defects can’t be read from the ground. A 10-foot vertical fissure 30 feet up the trunk of a mature Dawn Redwood is one of those defects. The arborist’s answer is to climb. Aerial Tree Risk Assessment — ATRA — is the protocol for ascending a tree to get a closer look at a problem area when the ground-level visual reading isn’t enough to make the structural call.
View from the Field · Paul Biester · Tree Awareness
“A couple weeks back we looked at this tree from the ground and decided to do a proper tree risk assessment was to work from aloft. So I’m going to head on up — got a rope installed, ready to rock and roll and get an up-close look. Here I am about 20 feet off — the cavity is a good deal above my head, but even here there’s a fissure and evidence that the tree’s been dealing with this a good while. The fissure opens right about here — I’m just over the second story of the house and the first sign of a crack is right here, and then you have this adjacent rib that’s formed that has split out and formed callus wood, so that’s closed — probably not connected very deeply — and then she opens up into this. Unfortunately, like that limb right there, there’s not much behind it, and the crack meanders up. It’s probably a 10-foot crack, and you’ve got some adjacent odd stuff forming here.”Paul Biester · NJ LTE #408 · TRAQ
The Tree Risk Assessment Qualification (TRAQ) framework recognizes three levels of assessment. Level 1 is a limited visual check from a distance — the kind of fast scan a contractor might do driving past a property. Level 2 is a full ground-level visual inspection by a qualified arborist, the standard most assessments use. Level 3 is detailed assessment using specialized tools or techniques — resistograph drilling, sonic tomography, or, in this case, aerial inspection.
ATRA is the right call when the defect’s position on the tree makes it inaccessible to a meaningful ground-level read. A crack at 30 feet on a hardwood trunk, a suspected cavity at the union of major scaffold limbs, or an indicator fungus growing high in the canopy — in each case, the data the arborist needs to make the structural call requires hands-on examination at the defect’s location.
Step 1: Ground-level Level 2 first. Before any climb, the standard Level 2 assessment establishes that there’s a defect significant enough to justify the additional risk and cost of an aerial inspection. The Plant Healthcare technician on this property had identified the canopy crack from the ground, and the recommendation was to escalate to ATRA.
Step 2: Set the rope. The climber installs a working line into a sound limb above the inspection area. Anchor selection on a tree with known defects is its own discipline — you don’t want your anchor on the same compromised structure you’re trying to assess.
Step 3: Approach the defect carefully. The ascent is staged to allow visual reads at multiple heights as the climber approaches the defect zone. Reading the tree as it’s climbed is part of the assessment — bark texture, wound history, callus formation patterns are all data points that the ground-level read couldn’t access.
Step 4: Read the defect. At the defect’s position, the climber gets to do something a ground inspector can’t: see daylight through the wood. Pull bark fragments. Read the depth and length of the crack. Look at how the tree has tried to close it — the “adjacent rib” Paul references is callus wood the tree formed in response to the wound, evidence of a decay column the tree has been working to wall off for years.
Step 5: Make the structural call. Based on what the climber sees up close, the recommendation crystallizes. On this Dawn Redwood, the verdict was removal — cambium loss along a 10-foot crack, decay column already established, target zone over the homeowner’s house and the neighbor’s house meaning consequences-of-failure were unacceptable.
This Dawn Redwood was a tree the property owner wanted to save. Most homeowners do. The ATRA didn’t produce the answer they were hoping for, but it produced the right answer — supported by data from a position no ground-level inspection could have generated. A removal recommendation that comes from an ATRA carries a different weight than one that comes from a curb-side opinion. The homeowner can act on it confidently.
The flip side is the case where ATRA reveals the defect is less serious than it looked from the ground — a crack that’s been fully compartmentalized for years, callus wood successfully holding the structural integrity of the tree. On those trees the ATRA justifies keeping a tree that less rigorous assessment might have ended in unnecessary removal.
One of the more useful arboricultural arguments Paul makes in this clip is why not to do something. A common impulse on a tree like this is to deleverage by reducing the top, and to lag-bolt through the cracked area to physically hold the wood together. Sounds like preservation. Actually accelerates the decline.
“A lot of people would say, and I thought of it too from the ground, that we can deleverage by taking a little piece of this top and bringing it down and then perhaps lagging through here. The problem is you’ve got a decay column already setting up in here, and when you break through the tree this way with lag bolts, you’re actually breaking down wall four of the tree’s compartmentalization — and what that means is you’re going to add some potential new decay columns.”Paul Biester · NJ LTE #408
This is the kind of judgment call that matters. The lag-bolt “fix” satisfies the homeowner’s desire to do something. It also breaks Wall 4 — the chemical and structural barrier the tree has built around the decay column — and seeds new decay pathways into healthy wood. The intervention that looks like preservation is actually a removal accelerator. The honest call is removal now, not lag-bolting and watching the tree decline faster over the next several years.
For aerial tree risk assessment on a tree with suspected canopy defects, request a Level 3 evaluation →
