Academics in Istanbul are using acoustic tomography to detect hidden decay inside century-old trees as authorities assess the falling risks of around 200 large and old trees and determine ways to preserve them whenever possible.
The study is being conducted by researchers from Istanbul University-Cerrahpaşa’s Faculty of Forestry, which covers trees in parks and gardens, along streets with heavy pedestrian and vehicle traffic, and sites where people spend much of their day.
Researchers will first record each tree’s physical characteristics, including its height, trunk structure, crown diameter, leaning angle and branching pattern. The trees’ ages will also be estimated based on previous experience and, in some cases, by examining annual rings obtained with an increment borer.
Researchers will then use acoustic tomography, a non-destructive method, to examine the condition of the trunks.
Sensors placed at intervals on the trunk send sound waves through the tree. Because sound travels differently through healthy tissue and areas containing decay or cavities, researchers can identify hidden damage by measuring the speed of the waves.
If decay is detected, measurements are repeated at different heights to determine where it begins and how far it extends. The data is then evaluated in three dimensions.
However, the discovery of decay does not automatically mean a tree will be cut down. Researchers will combine the tomography results with the tree’s height, crown diameter, leaning angle, branching structure and exposure to wind to calculate its risk of falling.
Historical data on the strongest winds recorded in the area will also be included in the assessment. Trees classified as high or extreme risk will be evaluated for measures such as pruning to reduce crown weight, cleaning visible cavities and installing mechanical supports where appropriate.
Cutting will be considered only as a last resort if a tree has reached an irreversible condition and cannot be safely preserved. In such cases, it will be removed and replaced with a new tree.
The project seeks to identify hidden internal decay before it poses a risk, according to Serhun Sağlam at Istanbul University-Cerrahpaşa’s Faculty of Forestry.
“Finding decay in a tree does not mean we will immediately cut it down. If we determine that the tree can safely live for another 10 or 20 years, we definitely try to keep it in place,” Sağlam said.
He noted that trees can be strengthened through pruning and mechanical supports when necessary, but those posing a serious risk to human life may ultimately need to be removed.
The importance of the project became particularly clear after a large plane tree fell in Istanbul’s Teşvikiye district last month. Although the tree appeared healthy from the outside, significant decay extending from its roots into its trunk was discovered after it fell.
Sağlam said the district has a significant population of old trees despite being relatively small. Many plane trees are more than 100 years old, while some have reached 130 to 150 years. Some are also officially registered as monumental trees by the relevant authorities.
The study also includes the century-old trees at Darülaceze, an institution with a history spanning more than 130 years.
Sağlam stressed that protecting urban trees is important because they provide clean air, help reduce flooding, cool cities during summer and lower energy consumption during winter.
He also called for greater public awareness to prevent damage to trees, including harm to their roots, trunks and branches.
