Specialist Tree Decay Detection
When a visual tree assessment is not enough — fungal brackets at the base, a cavity of unknown extent, a history of branch failures, response growth suggesting something is changing inside — you need objective evidence of what is happening in the wood before deciding anything.
Urban Tree Management carries out decay detection investigations using Arbotom sonic tomography and the Rinntech Resistograph R650, with structural and wind load analysis where it's needed. We are completely independent from any tree surgery contractor, so there's no interest in the outcome.
Every investigation is carried out personally by Carl Riva, who operates the equipment, interprets the findings on site and writes the report. We don't subcontract this work — other consultancies subcontract theirs to us.
What Tree Decay Is — and Why You Can't See It
Decay is wood being broken down by fungi. It usually starts at a wound, a pruning cut, a broken branch or damaged roots, and works through the stem from the inside, often for years before anything shows on the outside.
Different fungi break wood down in different ways. Some attack the lignin and leave the wood soft and fibrous; others attack the cellulose and leave it brittle and cracked. That matters, because the type of decay changes how the tree is likely to fail.
A hollow tree is not automatically an unsafe one. Trees are structurally efficient hollow cylinders, and many stand for decades with large cavities. What matters is how much sound wood remains, how it's distributed around the stem, and the load on it — and that can only be measured, not estimated from outside. See defects and decay in trees.
When Is Decay Detection Required?
- Fungal brackets or fruiting bodies on the stem or at the base
- A history of branch failures from the same tree
- Visible cavities where the internal extent can't be judged
- Response growth — ribs or swelling — suggesting the tree is compensating for internal change
- Decline or dieback where the cause is unclear
- A tree over a high-use area where a visual opinion isn't enough to defend a decision
- TPO applications where the authority needs objective evidence of condition
- Insurance claims or legal proceedings needing reproducible evidence
- Monitoring a known decay condition over time
The Instruments
Urban Tree Management uses two instruments on every decay detection investigation — used together they provide a complete and defensible picture that neither instrument can give alone.
Sonic Tomography — Non-Invasive
A chain of sensors is placed around the stem and sound impulses are sent between them. Sound travels faster through sound wood than through decayed or hollow wood, so the travel times build up a cross-sectional picture of the inside of the stem — a tomogram.
Our impulse sensor system takes over 100 measurements per cross-section, considerably more than systems limited to a fixed number of sensors. That gives finer resolution, particularly on large stems.
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How the Arbotom works
Rinntech Resistograph R650 — Confirmatory Drilling
A needle about 3mm across is drilled into the stem at a controlled rate, recording the resistance as it goes. Sound wood resists; decayed wood doesn't. It confirms what the tomogram has shown at a precise point, and measures the thickness of the remaining sound wall. Drilling points are GPS-tagged.
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Resistograph testing
Structural, wind load and root analysis
Where the question is how much strength remains, ArboStApp calculates residual load-bearing capacity from the measured wall. ArWiLo models wind loading and the effect of any proposed crown reduction, so reduction is specified at the minimum genuinely needed. ArboRadix maps the root plate where stability, not the stem, is the concern. → Root plate analysis
Where the defect is in the upper crown,
aerial inspection gets the instruments to it.
Why Both Instruments Together
The Arbotom locates. The Resistograph confirms. Neither instrument alone gives the complete picture:
- The Arbotom covers the entire cross-section non-invasively but cannot definitively distinguish decay from other causes of reduced sound velocity such as ring rot, cracks, or frozen wood
- The Resistograph physically confirms the wood condition at a specific point but cannot on its own map the extent of the decay across the full cross-section
- Together they produce objective, independently reproducible evidence of the tree's internal condition — the standard required for planning, insurance, legal, and duty of care purposes
Every investigation report explicitly states whether the Resistograph findings correlate with the tomogram findings — and whether that correlation supports or modifies the initial tomographic assessment.
From Decay to Risk — QTRA on Every Tree
Knowing how much decay a tree has is only half the answer. The other half is what that means for the people and property around it.
Every tree we investigate is also assessed using Quantified Tree Risk Assessment. QTRA combines three things — the likelihood of the tree or part of it failing, the size of what would fall, and how often people or property are in the way — into a single risk figure that can be compared against established thresholds of what is broadly acceptable and what is not.
The diagnostic results are what make that assessment reliable. A visual estimate of how likely a tree is to fail is a judgement; a measured wall thickness and a structural analysis turn it into evidence. So the same decayed tree can come out very differently: acceptable in the middle of a field, unacceptable over a school playground — and the report says which, and why.
The outcome is a recommendation you can defend: retain, monitor, reduce, or remove, with the risk set out in plain terms. See tree risk management.
What Happens on Site
- Visual assessment of the tree and the defect, deciding where the measurements need to be taken
- Sensor placement — small pins tapped through the bark at measured positions around the stem
- Geometry — the exact shape of the stem cross-section is recorded
- Tomography — each sensor is struck in turn and the travel times recorded
- Confirmatory drilling where the tomogram shows an area of concern
- Interpretation on site, so you're told the likely position before you leave
The tree's biological health isn't affected. The pins leave tiny holes; the drilling leaves a needle-width hole the tree seals off.
What the Report Gives You
- Tomograms for each cross-section, with sensor positions recorded
- Resistograph profiles at each drilling point, GPS-tagged
- A statement of whether the drilling results correlate with the tomogram
- Residual wall thickness and its distribution around the stem
- Where relevant, structural strength and wind load analysis
- A clear recommendation — retain and monitor, targeted pruning, or removal — with the reasoning
- Photographs of the tree, the defect and the equipment in position
- A QTRA risk assessment for each tree, setting the decay findings against what's beneath it
Suitable for planning authority submission, insurance, legal proceedings and duty of care records. We advise on the right level of investigation before any work begins.
Training Behind the Instruments
Instruments produce data; the value is in reading it correctly. Carl Riva trained directly under Frank Rinn, the developer of the RINNTECH technology, at an advanced diagnostics seminar in 2024, and returns to the RINNTECH Tree-Care-Research Conference in Frankfurt in October 2026.
Who Commissions thid
Homeowners with valued garden trees, housing associations and local authorities with trees over busy public spaces, estates with veteran and heritage trees, schools, care homes and healthcare sites, and other arboricultural consultancies and tree surgery contractors who subcontract decay detection to us.
Related Case Studies
FAQ
When do I need a decay detection investigation rather than a standard tree inspection?
When a visual inspection has found signs of concern — brackets, cavities, response growth, past failures — but can't tell how far the decay goes or whether it matters. A visual inspection tells you what's visible; decay detection tells you what's inside.
Does it harm the tree?
The tomography is non-invasive apart from small pins through the bark. The Resistograph drills a hole about 3mm across, which the tree compartmentalises without lasting effect — far less harm than removal on assumption.
Is a hollow tree dangerous?
Not necessarily. Many hollow trees are structurally sound. What matters is the thickness and distribution of the remaining wall, which is what the investigation measures.
Why do you add a QTRA assessment?
Because decay on its own doesn't tell you whether a tree is a problem. QTRA sets the measured condition against who and what is beneath the tree, so the recommendation reflects actual risk rather than the presence of decay.
How much does a decay investigation cost?
It depends on the number of trees and cross-sections and whether structural or wind load analysis is needed. Fixed fee, quoted in advance — send the address and a photo of the tree and the defect.
How quickly can you attend?
We aim to visit within five to seven working days of a quote being accepted. Where a tree is an urgent safety concern, call us and we'll prioritise it.
Can you carry out investigations for other consultancies?
Yes — we're regularly subcontracted by other arboricultural consultancies and tree surgery contractors. Contact us about subcontract rates.
Tree Decay Detection — Greater Manchester & the North West
Before a valued tree is felled on suspicion, find out what's actually inside it — and what that means for the people beneath it. Objective, reproducible evidence from a consultant with no interest in the outcome.
Get in contact with our highly experienced and personable team of arboricultural consultants today, to discuss your requirements and to obtain your zero obligation quotation.
