Assessment of Wood Decay in Platanus occidentalis and Zelkova serrata Street Trees Using Sonic and Electrical Resistivity Tomography

A minimally invasive analysis of the internal defects in an American sycamore (Platanus occidentalis) and a Japanese elm (Zelkova serrata) with fungal fruiting bodies was conducted, and the results were compared with wood cross-sections. The trees were evaluated at multiple heights above ground level (AGL) using sonic tomography (SoT) and electrical resistivity tomography (ERT). The fruiting bodies were identified as Perenniporia fraxinea on the American sycamore and Ganoderma applanatum and Auricularia cornea on the Japanese elm using DNA sequence data. In the American sycamore, SoT detected abnormal wood at 20 cm AGL, while wood at 73 cm AGL remained sound. ERT revealed low-resistivity areas corresponding to the SoT-detected abnormalities at 20 cm AGL. In the Japanese elm, SoT detected abnormal areas at 28 cm AGL, corresponding to the location of G. applanatum fruiting bodies on the bark. Wood at 88 cm AGL, corresponding to the location of A. cornea fruiting bodies, appeared sound. However, ERT revealed low resistivity at all measurement heights, which corresponded to discolored regions on the wood cross-sections. SoT detected no wood abnormalities in the locations where ERT detected low resistivity. These findings suggest that combining the two techniques improves the accuracy of wood defect detection.