Acoustic tomography to assess hidden decay in Şişli’s century-old trees

ISTANBUL

Local experts view a color scan of an old trunk in Şişli, as sound waves map deep inner decay with strict care. (AA Photo)

An estimated 200 large and old trees in Istanbul’s Şişli district will undergo acoustic tomography to detect internal decay that may not be visible from the outside and assess their risk of falling, with authorities aiming to preserve them in place wherever possible.

The survey will cover trees in parks and gardens as well as those lining busy streets and located in areas with heavy pedestrian and vehicle traffic. Century-old trees at the Darülaceze complex, where residents spend much of their time, will also be examined.

In the first stage, experts will record each tree’s height, trunk structure, crown diameter, lean and branching pattern. Its approximate age will be established through previous records and, where necessary, by examining annual growth rings obtained with an increment borer. Some plane trees in the district are estimated to be more than 100 years old, with some reaching 130-150 years.

Acoustic tomography will then be used to examine the trees internally without cutting into or otherwise significantly damaging them. Sensors placed around the trunk transmit sound waves, whose travel speeds vary depending on whether they pass through healthy tissue, decayed areas or cavities. The measurements are used to create a three-dimensional picture of the trunk and identify where decay begins and how far it extends.

If decay is detected, measurements will be repeated at different heights to determine its full extent. However, the presence of decay alone will not automatically lead to a tree being removed. Experts will combine the tomography results with the tree’s physical characteristics and local wind data, including the strongest recorded winds, to calculate its potential risk of falling.

According to Istanbul University-Cerrahpaşa faculty member Serhun Sağlam, the project was prompted in part by the recent collapse of a large plane tree in the Teşvikiye neighborhood. Although the tree had appeared healthy, significant decay extending from its roots into the trunk was found after it fell.

“An old tree with decay does not necessarily mean we will cut it immediately,” Sağlam said, adding that pruning to reduce crown weight, cleaning visible cavities and installing mechanical supports could be used to lower the risk.

Removal would be considered only when a tree has reached an irreversible condition and can no longer be safely maintained. In such cases, it would be replaced with a new tree.