When it comes to tree safety, many property owners, estate managers, and professionals still rely on Visual Tree Assessments (VTAs) as their primary inspection method. These involve observing external signs—like bark condition, leaf health, trunk shape, and visible decay. But PiCUS vs Visual Tree Assessment is a debate worth having, especially when hidden decay can go unnoticed.
Although this approach can identify some problems, it often misses one critical factor: what’s happening inside the tree.
Why Tree Decay Detection Requires More Than Visual Checks
This is where PiCUS Sonic Tomography becomes essential. It’s a non-invasive, advanced diagnostic tool that reveals hidden internal decay and structural weakness that visual checks can’t detect.
If you only rely on surface observations, you could easily overlook severe defects just beneath the bark. According to the Arboricultural Association, internal decay can go undetected without specialist testing like PiCUS.
The Limitations of Visual Tree Assessments
VTAs are a helpful first step. They’re quick, accessible, and often good for spotting surface-level issues, like fungal growths, cavities, or deadwood.
However, internal decay can progress without visible symptoms, especially in older trees or species prone to heartwood rot.
For example, a tree might appear healthy, with good leaf coverage and no cracks or wounds. But inside, fungal activity may be hollowing it out. By the time external signs appear, failure could be imminent.
What Is PiCUS Testing?
PiCUS Sonic Tomography works by measuring how sound waves move through the tree. The arborist places sensors around the trunk, then taps them gently with a small hammer.
The system records the speed of the sound pulses and creates a colour-coded scan that shows variations in wood density—highlighting sound wood, decay, or cavities.
Real-World Example: Mature Sycamore at Sizewell B
We recently worked with Freedom Group to assess a mature Sycamore along the main approach road to Sizewell B power station in Suffolk.
The tree had a healthy crown but had been crown-raised previously, creating a top-heavy structure. Two large trunk cavities raised concerns about internal strength—especially given the tree’s location on a steep embankment next to a busy access road.
We carried out a PiCUS tomography scan to evaluate the extent of decay. The results showed that 93% of the wood remained structurally sound, with strong compartmentalisation and no signs of fungal breakdown.
Thanks to this insight, we avoided unnecessary removal. Instead, we recommended a targeted crown reduction and long-term monitoring—maintaining both safety and the tree’s ecological value.
➡️ Read the full case study here: Mature Sycamore PiCUS Testing at Sizewell B
Why Relying Solely on Visual Inspection Isn’t Enough
Important factors when considering a PiCUS vs Visual Tree Assessment
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Hidden decay often has no outward symptoms
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Structural failure can happen suddenly, especially after storms or drought
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Liability risks rise if a tree fails in public or shared spaces
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PiCUS testing provides the evidence needed to manage risks confidently
The Bottom Line: Combine Approaches for Safer Outcomes
Visual Tree Assessments remain important, but they’re not enough, especially for high-risk or high-value trees.
PiCUS Sonic Tomography adds scientific precision, helping you make informed decisions where visual clues fall short. Whether you’re managing a heritage tree, inspecting one in a school or park, or facing ambiguous signs, PiCUS gives you clarity.
Need to assess a tree with visible cavities or uncertain stability?
MB Trees offers expert PiCUS testing across the UK, helping you make informed decisions based on accurate internal diagnostics. Contact us today to book a PiCUS test or discuss your tree safety concerns.