Integrating Empirical Data and Simulation Models to Assess Strength Loss in Urban Trees with Internal Decay

The structural stability of urban trees can be significantly affected by internal decay and open cavities, highlighting the need for reliable assessment methods. Traditional evaluations often rely on simplified analytical formulas to estimate strength loss caused by trunk defects. In parallel, computational biomechanical models have emerged as powerful tools for simulating tree behaviour under loading and for quantifying failure risk. This study evaluates the agreement between classical empirical strength-loss equations and structural simulations generated by a biomechanical model for 80 urban trees representing 21 species affected by trunk defects. Strength-loss estimates, derived from literature-based equations, were calculated using non-destructive diagnostic data, including tomographic imaging and resistance drilling. These results were then compared with model-based estimates of failure probability under wind loading. The findings indicate that equations incorporating cavity eccentricity, as well as formulations accounting for geometric asymmetry and the residual strength of decayed wood, produced estimates more consistent with the biomechanical simulations obtained for this sample. Overall, the results highlight the importance of considering cavity position and material degradation when estimating strength loss. The integration of tomographic diagnostics, resistance drilling, structural modelling, and refined analytical formulations can improve the mechanical interpretation and transparency of urban tree stability assessments.