Application of Acoustic Tomography in Urban Tree Risk Assessment: A Case Study from Jarocin (Poland)

Urban trees constitute a key component of sustainable urban green infrastructure, providing ecosystem services related to climate regulation, biodiversity conservation, and human well-being. At the same time, mature and veteran trees in public spaces are frequently perceived as a safety risk due to visible structural defects, often resulting in precautionary removal decisions based solely on visual assessment. This study evaluates the applicability of acoustic tomography as a non-invasive diagnostic tool supporting sustainable urban tree management using the city of Jarocin (western Poland) as a case study. Following preliminary Visual Tree Assessment (VTA), 20 mature urban trees were identified, of which six representative specimens were subjected to detailed analysis using the PiCUS Sonic Tomograph 3. The internal condition of tree trunks, sound wave propagation velocity, residual wall thickness (t/R ratio), and structural stability were analysed in relation to species characteristics and site conditions. The results demonstrated considerable variation in the internal condition of the analysed trees and revealed that visible external defects did not necessarily correspond to a critical reduction in mechanical stability. Five out of six examined trees met or approached the accepted safety threshold (t/R ≥ 0.30), supporting their retention rather than removal. In several cases, acoustic tomography identified substantially larger zones of structurally sound wood than suggested by visual inspection alone. The findings confirm that integrating acoustic tomography into urban tree risk assessment can improve decision-making accuracy, reduce unnecessary tree removal, and support biodiversity-oriented and climate-adaptive urban green space management. The proposed approach may serve as a transferable framework for sustainable management of mature urban trees in medium-sized cities.