Sonic and Electrical Resistivity Tomography of Pinus densiflora Stems Infected with Pine Wood Nematode

The structural integrity of tree stems can be evaluated using tomography, a minimally invasive method. We used sonic tomography (SoT) and electrical resistivity tomography (ERT) to compare internal states and electrical properties between healthy and pine wood nematode-infected Pinus densiflora stems. A total of 25 trees, consisting of five healthy and 20 infected trees, were assessed. Both SoT and ERT were performed at 50, 100 and 200 cm above ground level. Heartwood and sapwood electrical resistivity (ER) values were extracted from the tomograms to quantitatively evaluate the ERT results. The SoT results showed that all trees had sound sapwood and heartwood. Significant differences in mean ER were found between the healthy trees (1037.54 Ωm) and infected trees (764.94 Ωm). While the ER of sapwood remained constant in healthy trees, it increased with measurement height in infected trees, and differences in ER between heartwood and sapwood were significantly lower in infected trees than in healthy trees. These ER differences were likely to be attributed to decreases in resin production and changes in microbial communities within the stems of infected trees. These results suggest that SoT and ERT could be used as minimally invasive diagnostic tools for pine wilt disease.