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  • Writer's pictureWRC Trees

Assessing decay using Sonic Tomography

WRC Trees were pleased to be able to put our new IML Picus 3 Sonic Tomograph to use recently as part of an advanced tree risk assessment. This specialist diagnostic tool uses sound waves to quantify decay and cavities in trees, and can be used to produce two or three-dimensional images of the internal structure of a tree (an example image is shown below). There are several advantages associated with this approach to decay detection, in particular, it is less invasive than some other methods, and less likely to spread any decay present. This specialist tool can be particularly useful in monitoring the progression of tree defects over several years.


Our Survey Manager Steve Woollard used the Picus Sonic Tomograph to assess the integrity of a mature beech Fagus sylvatica. The tree was in a high-use area and fruiting bodies of the decay fungus Ganoderma spp. were present at the base of the main stem – this prompted concerns over the integrity of the stem wood. To carry out an assessment, a number of sensors are spaced out evenly around the stem of the tree. Sound waves are then generated around the stem manually by tapping with a hammer, and the sensors record the time taken for these sound waves to travel through the wood. Sound travels faster through solid wood and slower through decayed wood, and it is this variation that is used to produce the visual image that can then be interpreted by a fully trained professional arboriculturalist. The information provided by sonic tomography can be used in combination with a range of other factors related to tree stability to make sound management recommendations.


Many thanks to Sorbus International Limited for supply of the kit and training.






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