Decay Detection Equipment
Why would you need detailed investigation?
Trees require structural integrity to support their own weight combined with external forces such as wind and rain to remain stable. There are many damaging agents that can dimmish the structural integrity which can make trees unstable. When there is a possibility that the tree might be unstable because of underground damage or decay in the roots we can use Dyna Root and Dyna Tree to evaluate stability.
When there are clear and obvious above ground features such as an open cavity or a possibility that the tree might be unstable because of internal decay or damage we need to try and qualify the impact of the affected area on whole tree stability in a low invasive way.
What is PiCUS® 3 Tomography & IML-RESI-F500?
The PiCUS® 3 Sonic Tomograph by Argus-electronic gmbh was designed to examine living trees in a low invasive way. It detects differences in the ability of the wood to transmit sound. The velocity of sound in the wood depends on the modulus of elasticity (MOE) and the wood density. Healthy wood is expected to transmit sound at a higher velocity than decayed wood or anomalous growth, new growth following wounding or adaptive growth can also increase the velocity. The tomogram can indicate if the tree is managing the decay with good compartmentalization or if there is decay or damage, direct us to areas in the stem cross section that need further testing with our IML-RESI-F500 ‘twist drill’ device, a purpose designed measuring instrument for trees and wood, to try and determine the density (and inferred strength) of any residual stem around the decayed area.
What does it entail?
For the tomography, nails (measuring points, MP’s) are arranged around the circumference of the trunk at a vertical level so that they penetrate the bark layer and reach the sapwood. Their positions are recorded accurately with digital callipers to create a geometrical cross section of the trunk (we need to know how far apart the MP’s are to determine velocity). Sensors are connected to each nail which is lightly tapped in turn at each measuring point to propagate a sound wave which is recorded by the other sensors. The number of measuring points used depends on the size and shape of the stem.
The PICUS creates a dense network of the recordings connecting each measuring point. The software evaluates the data to identify areas of reduced velocities that may indicate damage, decay or disease.
The equipment software also produces a coloured tomogram which illustrates the relationship between the fastest sound speed and the slowest sound speeds with gradations in-between as an indication of stem condition.
The IML-RESI-F500 ‘twist drill’ works by feeding a very fine drill made of high-quality steel into the wood at a predetermined rate. Variations in wood quality cause resistance to the drill tip which necessitates increases and decreases in the amount of torque applied to the drill shaft to maintain the predetermined rate. The device simultaneously uses mechanical and electronic sensors to measure the changes in torque applied and produces a paper and electronic graphical record of the measuring results. The drill is slightly more invasive than the Picus and should only be used in very specific circumstances.
PiCUS® 3 Tomography & IML-RESI-F500 are often used together but can be used independently, neither purport to deliver absolutes so our experience and expertise to interpret results is still an essential part of any assessment with careful consideration of the tree in its setting.
When would you use it?
It can be used where a tree has clear and obvious defects or suspected defects at any height from ground level up. The minimum diameter for PiCUS is approximately 380mm..
Interpretation of the tomograms and resi drill readings can be used as evidence-based justification for tree retention or recommended action.
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