The phrase "this tree looks fine" has cost Tallahassee homeowners millions of dollars.
It's the answer a neighbor gives. It's the answer a lawn-service crew gives. It's the answer a homeowner gives themselves when they don't want to call anyone.
The problem is that tree failure has almost nothing to do with whether a tree looks fine. Trees that fail in storms are usually green and full-canopied right up until the moment they aren't. The decay is internal. The roots are buried. The codominant stem with included bark looked like every other branch union — until the day it didn't.
The ISA Certified Arborist Study Guide is explicit about this: "high-risk trees can appear healthy and have a dense, green canopy." Tree health and tree stability are different things.
Here's the formal framework arborists actually use.
Risk Is the Combination of Two Things
The ISA defines tree risk as likelihood × consequences. That's the whole framework, and almost every other piece of risk assessment derives from it.
Likelihood has two sub-components: the chance the tree (or part of it) fails within a stated time frame, and the chance that failure impacts a target that matters. A dead branch over an empty corner of the lot is high likelihood of failure, low likelihood of impact — not very risky. The same dead branch over a kid's play area is the same likelihood of failure but very high likelihood of impact — high risk.
Consequences is what happens if it does impact. Negligible (a fence panel), minor (a parked car), significant (the roof), severe (a person). A small dead branch hitting a sidewalk is low consequence. A 12-inch limb hitting a person is severe.
Risk is the combination. Two trees with identical visible defects can have very different risk ratings based on what's underneath them.
The Three Levels of Assessment
ISA recognizes three levels. We pick the level that fits the assignment.
Level 1 — Limited Visual Assessment. A drive-by or walk-by screening of many trees at once, looking for obvious red flags: dead trees, huge cavities, severe leans, hangers. Useful when you're triaging a population — a 50-tree property line, a municipal block, a utility right-of-way.
Level 2 — Basic Assessment. A detailed visual inspection from all sides of one tree. Root flare, buttress roots, trunk, branch unions, canopy, the surrounding site. Simple tools — mallet, probe, binoculars — but no advanced diagnostics. This is what 90% of homeowners need: an arborist who walks every side of the tree, looks at it the way they were trained to look, and tells you what they see.
Level 3 — Advanced Assessment. Specialized techniques for specific concerns. Resistance-recording drilling (a thin spade bit measures wood density along a drill path — solid versus decayed). Sonic tomography (sound waves sent through the trunk and mapped to a cross-section). Root collar excavation with an air-spade. Aerial inspection from a climber or lift. Used when a Level 2 reveals something that needs internal investigation.
The right level depends on the question. We don't run advanced diagnostics on every tree — they're expensive and time-consuming, and most trees don't need them. We escalate when the visible findings warrant it.
What Arborists Are Actually Looking For
The ISA framework identifies seven major defect categories. We walk through every one of these on every assessment.
1. Dead, dying, or hanging parts. Dead branches in the canopy, branches partially detached and lodged in the crown ("hangers"), entirely dead trees. Some species hold dead branches for years — local knowledge matters here.
2. Cracks. Longitudinal cracks (along the trunk) versus transverse cracks (across the short axis). Transverse cracks usually mean failure is imminent. Shear-plane cracks from old branch overloads can look severe but be stable.
3. Weakly attached branches and codominant stems with included bark. Two trunks of nearly equal diameter forking from a common point, with bark embedded inside the union instead of wood. This is the classic mode of failure on Tallahassee water oaks — they grow a beautiful symmetric Y for forty years, and then one side splits off in a tropical storm.
4. Unusual architecture. Severe lean (especially a recent one — that often means root failure has started), unbalanced canopy, lack of trunk taper, long unattached lateral branches that have no support beneath them.
5. Loss of root support. Soil heaving on one side, depressions on the lean side, severed buttress roots, recent construction within the drip line. Buried buttress roots — soil piled against the trunk over time — are easy to miss and a real problem.
6. Decay and missing wood. Cavities, fruiting bodies (conks, mushrooms) on the trunk or root flare, soft or crumbly wood under bark, carpenter ant nests (ants only nest in decayed wood — they're a definite indicator, not just a suspicious sign).
7. Mechanical damage and cankers. Old pruning wounds that never closed (especially from topping), lightning scars, weed-trimmer damage at the base, bark canker infections.
A tree with one moderate defect is often low risk. The same tree with three combined defects in the same trunk often isn't. We rate each, and we combine them.
Decay Type Matters
The ISA Study Guide identifies three fungal decay types, and they don't behave the same way.
- White rot (Armillaria, Ganoderma) — decays the lignin that gives wood its compressive strength. Reduces stiffness; leaves some flexibility. Trees often respond with compensating growth.
- Brown rot (Laetiporus, Phaeolus) — decays the cellulose. Wood becomes dry and brittle, fails by snapping. Faster strength loss than white rot.
- Soft rot (Kretzschmaria deusta) — characteristics of both. A serious finding.
In Tallahassee, the diagnosis we make most often with the most consequences is Ganoderma at the root flare of a live oak. It's a root rot. There's no effective treatment in advanced stages. It leads to uprooting failure under storm loads. A live oak with a dark, varnished-looking shelf fungus at its base is a tree with a clock running.
Response Growth: Why Defects Don't Always Mean Removal
Trees adapt. When a defect develops, the tree often produces response growth — denser, sometimes chemically different wood that compensates for the weakness.
A 30% basal cavity in a tree with extensive bulging, ridging, and flexure wood at the base is a very different risk profile than the same cavity in a tree that hasn't responded. The first tree might be stable for another fifty years. The second tree probably isn't.
This is the kind of judgment a quick visual scan can't make. It's the reason a real assessment is worth getting before reflexively removing a tree that has a single visible defect.
Mitigation Hierarchy
If the assessment finds elevated risk, the ISA mitigation hierarchy works from least invasive to most. We work down the list, not up.
- Target management. Move what's under the tree. Fence the area. Reroute foot traffic. Relocate the swing set. Cheapest, lowest impact on the tree.
- Pruning. Selective removal of dead, hanging, or weakly attached parts. Reduction pruning to lower wind load. Never topping.
- Structural support. Cables, braces, lightning protection on trees worth keeping.
- Removal. When no other mitigation works. Last resort.
A removal recommendation should come with the reasoning. If a quote says "remove the tree" without explaining why the other three options don't work, ask why.
When You Should Get an Assessment
The triggers that warrant a Level 2 basic assessment by an ISA Certified Arborist:
- A tree near your home or other target shows any of the seven defect categories above
- A storm just passed and trees that "made it" need to be evaluated for hidden damage
- You're buying or selling property with mature trees and need a documented evaluation
- An insurance company or municipal permit office requires a written report
- A neighbor's tree is leaning toward your house and you need a defensible third-party assessment
- A tree's lean has visibly increased in the last year
Our tree hazard inspection service is built around this framework — every Miller's assessment is a Level 2 by default, with Level 3 escalation when conditions warrant. The report you receive uses the ISA risk-rating categories so an insurer, lender, municipality, or attorney can read it as a defensible professional document.
Tree failure is rarely random. It almost always follows defects that were there to find. The question is whether someone trained to find them was actually looking.
