How Sonic Tomography Helps Arborists Detect Unhealthy Trees to Keep Communities Safe

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Drought and pests, as well as tissue and root damage, put many trees at risk for internal rot and decay, which can pose a risk to property and public safety in the event a tree fails. Sonic tomography allows municipalities and developers to efficiently detect and accurately map tree decay in a non-invasive manner, especially for trees that do not show external signs of decay.

What is sonic tomography?

Sonic tomographs detect decay and cavities in standing trees by measuring the velocity of sound waves in wood. Differences in the velocity can help determine areas of healthy wood and areas of damaged wood that have less elasticity and density than healthy wood. Measuring points on the tree are determined based on external observations and/or tapping with a mallet (to hear potential internal cavities). If there are no external indicators of decay, then the most likely area of internal rot is selected. This technology provides a non-invasive approach to mapping internal decay.

How is sonic tomography performed?

Depending on tree size, 6–12+ nails are lightly inserted at equal intervals around the tree’s circumference. Sensors are then placed over each of the nail heads. In turn, each nail is tapped, and the sensors detect the time it takes for the sound waves to travel from the source to all the other sensors. While data collection time varies depending on tree size, a computer temporarily affixed to the tree processes data in real-time, and arborists can immediately interpret results to glean a picture of tree health and make recommendations, as necessary.

How does this technology help arborists?

Sonic tomography allows foresters to detect rot, decay, damaged wood, cavities, and cracks prior to tree failure, allowing clients to avoid the financial and public safety risk caused by tree failure. Dudek Urban Forester Chris Kallstrand said, “Sonic tomography is useful for evaluating the risk associated with trees but can also be used during the tree relocation process. If a tree is being considered for relocation, this method enables clients to ensure that the tree is structurally sound, so that money is not wasted on relocating trees that may fail due to unseen internal damage.”

Tree trunk that has been cut close to the ground. There is a large circular cavity in the center of the trunk that has been ringed with white spray paint.
Sonic tomography revealed extensive internal decay within this tree, so arborists prioritized it for removal.

How can Dudek help?

As one of the first and most experienced firms in California utilizing sonic tomography, Dudek has helped clients evaluate the risks associated with prominent trees in their management areas. Trees don’t always exhibit external signs of internal degradation and, as such, this technology is necessary to identify an unseen risk. At first glance, many trees may seem suitable for preservation in the landscape. However, upon closer inspection, those same trees may indicate signs of structural decline, presenting a risk to the community. With sonic tomography, we can closely inspect the unseen and determine whether a tree is a risk to a community or project site.

The City of Irvine needed to evaluate the risk of its blue gum eucalyptus trees, so Dudek employed sonic tomography to complete a tree risk analysis on the City’s 1,970 blue gum eucalyptus trees across 24 windrows. Dudek arborists recorded detailed external attributes for each tree and then performed sonic tomography, evaluating each tree at two vertical positions on the trunk. Following the assessment, we prepared arborist reports for each of the 24 windrows. Reports included findings, recommendations, and photographic logs of all trees. Our experts identified hundreds of at-risk trees with extensive internal decay that were likely to fail. As a result of our assessment, the City was able to prioritize unhealthy trees for removal and identify healthy trees suited for long-term preservation and maintenance.

For more information on how sonic tomography could mitigate risk in your community and save your project time and money, contact us.