Instrumental tree diagnostics

A visual inspection shows symptoms; instruments show the cause. With sonic tomography, resistography and pulling tests we measure the condition of trunk and roots and derive a risk assessment that stands up to scrutiny.

How we read the scan

One cross-section is not enough

A cavity in the trunk changes shape and size with height. That is why we measure several layers and only from their relationship assess the trunk's real load capacity. Drag the slider.

2428874 m/s

Measured range 30–250 cm

80 cm

measurement height

305080110150200250

20 % of section under decay

Scan summaryThe example is based on a real scan of a pedunculate oak measured in seven layers (30, 50, 80, 110, 150, 200 and 250 cm). The share of decay changes with height: largest at the base, smallest around 150 cm, rising again above the fork. Had the tree been measured at a single favourable height, the danger at the base would have gone undetected. That is why we base the assessment on the weakest section, not the average.

What the m/s figures mean

The tomograph measures how fast a sound wave travels through the wood between sensors. In this measurement, sound oak wood carries sound at around 2000–2400 m/s. Through decayed wood, a cavity or a crack the wave travels more slowly: below 1200 m/s. The colours simply render the measured velocities: dark green is sound wood, red is the transition zone, blue and pale are cavity.

A cavity is not a verdict in itself

A tree is a tube, and load-bearing capacity comes from the outer shell of sound wood. What matters is the ratio of that shell's thickness to the trunk radius, not the percentage of cavity. That is why we measure several layers and calculate the weakest section, and always relate the finding to wind loading and to what stands within the tree's reach.

Request instrumental diagnostics Schematic rendering. Actual scan: pedunculate oak, Bozhurishte, Bulgaria, 2025.

Instrumental diagnostics

When a visual inspection is not enough

Tomography shows the cross-section, but not how strong the remaining wood is nor how well the roots hold the tree. That is what the other two methods are for. We work with latest-generation diagnostic instruments from the renowned manufacturers Rinntech and Fakopp.

Resistography

A needle with a 3 mm tip drills into the trunk and records wood resistance by depth. The channel is very narrow, and the needle's high rotation speed heats it enough to char the sawdust and the edges of the bore, which reduces the ability of fungi to decay the wood at the drilling point.

0 cmdrilling depth23 cm

sound wood
incipient decay
advanced decay

Based on a real resistograph profile (Rinntech Decom).

What it gives. The exact boundary between sound and decayed wood at the drilling point, and the thickness of the remaining load-bearing shell.
Why alongside tomography. Tomography measures sound velocity and can over- or under-state decay; the resistograph confirms the finding at the critical point.
Limitation. It yields data along a single line only, so drillings are kept to the necessary minimum.

Pulling test

The tree is loaded by cable with a force equivalent to storm wind, but far below the damage threshold. We measure how much the stem yields and how much the root plate tilts.

1 Inclinometer at the root collar measures root-plate tilt
2 Elastometer on the stem measures strain in the outer fibres
3 Pull-force sensor records the applied force
4 Anchor on a neighbouring tree or in the ground, at a safe distance
5 The winch in the cable gradually loads the tree with a force equal to storm wind; the anchor tree provides the counter-force
6 A computer logs force, tilt and strain in real time

What it gives. Safety against stem fracture and windthrow, expressed as a safety factor at a given wind speed.
Why it matters. A sound stem does not mean a safe tree: a large share of failures are root-plate failures, invisible from outside.
Non-invasive. The load stays within the elastic range, with no permanent deformation and no damage to the tree.

Three methods give three different answers. Tomography shows where the decay is, resistography how much sound wood remains, the pulling test how well the tree actually holds. Only together do they give an assessment on which a decision to retain or remove a tree can rest.

Request instrumental diagnostics

Methods

What each method really shows

We openly list methods we don't perform ourselves. If you need something outside our scope, we'll tell you where to get it.

Method	Reveals	Invasiveness	When	Scope
Visual Tree Assessment (VTA)	External symptoms, defects, risk rating	Non-invasive	Routine check, first inspection	In-house
Sonic tomography	Decay and cavities in the trunk cross-section	Non-invasive	Suspected internal decay	In-house
Resistography	Wood density along the drilling depth	Minimally invasive	Confirmation of tomography findings	In-house
Pulling test	Root and stem resistance to windthrow	Non-invasive	Leaning tree, exposed site	In-house
Physiological assessment (chlorophyll fluorescence)	Plant stress before visible symptoms	Non-invasive	After construction, drought or transplanting	In-house
Soil microbiology analysis	Soil microbial condition (Soil Food Web School certified)	Sampling	Poor growth, crown decline	In-house
Laboratory pathogen analysis	Fungus or pathogen species	Sampling	Suspected quarantine pest	Via partner
Dendrochronology	Age and growth history	Core sample	Heritage trees, research	Via partner

Frequently asked questions

Questions about tree diagnostics

What is sonic tomography of a tree?

A non-invasive method in which a ring of sensors is placed around the trunk and the speed of sound waves between them is measured. Sound wood transmits sound faster than decayed or hollow wood, so the measurements produce an image of the cross-section showing the extent and position of decay. We measure at several heights, because a cavity changes along the trunk.

Does resistography damage the tree?

Minimally. A needle with a tip about 3 mm wide drills a very narrow channel. At its high rotation speed it heats up and chars the sawdust and the edges of the bore, which reduces the ability of fungi to decay the wood at the drilling point. We keep the number of drillings to the minimum necessary and drill only where tomography has flagged a critical zone.

When is a pulling test needed?

When the question is root stability rather than just trunk breakage: leaning trees, excavation or construction in the root zone, trees on exposed sites, and valuable trees whose removal is being considered. The test gives a safety factor against uprooting and breakage at a given wind speed.

Contact

Let's talk about your trees

We work with cities, municipalities, public institutions, designers and owners of valuable trees. For a quote, send us the basics: which tree or planting it concerns, where it is and what worries you.

How a quote comes about

Price depends on the number of trees, the methods required and the depth of documentation, so we do not publish it in advance. After an introductory call and basic site details you receive a written quote with a clear price and timeline. For public-sector clients we prepare documentation in tender-ready form.

ARBORING j.d.o.o.

Matije Gupca 6, HR-10450 Jastrebarsko
+385 98 411 431
fran@arboring.hr

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