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Diagnostic methods

Brudi & Partners use only tree-friendly diagnostic procedures for their advanced tree inspections, to cause as little injury to the tree as possible. Invasive examination procedures for inspections regarding public safety have not been used for years. Deciding which procedure to follow in each individual case depends on the particular issue at hand.

Pulling tests

Pulling tests – or static load tests –have been used for around 25 years to determine whether a tree poses a risk to public safety. The test involves applying relatively low load to the tree by means of a cable that is secured in the tree crown. As the load increases, the trunk and the root system respond by deforming slightly. These reactions are not visible to the human eye but can be measured by highly sensitive instruments. The three values that are continually recorded are:

  • the force applied to the tree
  • the extension or compression of the trunk’s marginal fibers
  • the tilt of the root base.

These values can be electronically stored and monitored on a computer. This ensures that the tree is not “overloaded” and that its load-bearing structure, bark and roots remain undamaged. Each pulling test is stopped once a relatively small reaction has occurred.

The test values are then evaluated in the ArboStat software that was specially developed for the task. The wind load exerted on the tree, the material properties of the green wood, and the geometry of the loaded trunk are all taken into account. (See our pdf-downloads on this topic.)


The instruments used for pulling tests are:

  • elastometers (stem strength), accurate to 1/1000 mm
  • inclinometers (anchoring strength of the root system), accurate to 1/ 500 °
  • dynamometers (tensile force and cable angle), accurate to 30 daN (kp)
  • laser altimeters

Sonic tomography

Sonic tomography conducted on a tree trunk cross-section can give clues as to the extent of hollowness at certain levels.

The speed with which sound waves travel through wood depends on the wood’s anatomy, density and modulus of elasticity. Decayed wood is less dense and therefore affects the distribution of sound waves. Even the beginnings of decay can alter the wood’s properties, affecting the distribution of sonic velocities. A sonic tomogram enables the trunk’s inner condition at various levels to be displayed and analyzed according to color images ranging from brown (stable wood) to blue (cavity).

Brudi & Partners always combine the evaluation of ultrasound tomograms with an individual estimation of wind load. Reliable evaluations of risk can only be made when wind load is considered as part of the risk potential.

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The instrument used for this is:

EIT- Electric Impedance Tomography

Electric impedance tomography can be used to supplement the sonic examination with further important information about the internal condition of a tree trunk. An electric current is fed into the trunk through its outer growth ring, and spreads quickly or slowly depending on the wood’s moisture content and density. A very high moisture content puts up little resistance and points to the beginnings of or the existence already of decay. Color codes are also used in this method to show the internal condition of the tree, ranging from blue (high moisture and high conductivity) to red (high electric impedance due to low moisture, decaying wood, or cavities).

Brudi & Partners always combine sonic tomograms and electric impedance tomography with an individual estimation of wind load. Reliable evaluations of risk can only be made when wind load is included in the safety statement.

The device used for this method is:

  • Picus TreeTronic, electrical resistivity tomograph for tree trunks of  30-200 cm in diameter

Tree ring analysis

In our moderate climate, trees produce new wood every year. In spring, the new wood has large pores and is light in colour, whereas in summer it has smaller pores and appears darker. Both growths together form an annual ring.

This enables examinations of past occurrences with reference to time.


Applications:

  •  limitation of action in disputes among neighbors
  • age determination of trees
  • evidence of the frequency of transplantation
  • determination of the time of damage.