Zelkova serrata (Thunb.) Makino trees, which account for a large proportion of cultural assets and protected trees and have considerable historical and cultural symbolic meaning in South Korea. To verify the reliability of the nondestructive sonic tomography (SoT) method on Z. serrata trees, this study compared the results of SoT with those obtained with the destructive resistance micro-drilling method. With SoT measurement, defects were found in approximately 75% of the target Z. serrata trees and two of these trees were evaluated as having a high risk because their defective portions accounted for approximately 70% or more of the entire cross section. The independent samples t-test indicated that the two methods did not show a significant difference between measurements. Regression analysis indicated that the measurement values of the two methods showed a positive relationship with a high explanatory power of 76%, thus, verifying the reliability of SoT.

Internal decay and cavities in wood are known to reduce the structural functionality of trees. Such damage may lead to detrimental effects not only on the wood, but also on humans. This is especially the case with old, large trees that are more vulnerable to heavy snow and strong wind. Thus, preventative management (e.g., detecting internal wood defects) is essential. The present study investigated the reliability of noninvasive measurements using sonic tomography (SoT) to detect internal defects in Abies holophylla Maxim. trees and compared the results with measurements using the invasive method of resistance microdrilling (RM). The tomograms were visually compared with tree cross-section images. The results of SoT and RM showed no significant differences, while the explanatory power, as determined by a regression analysis, were considerably high at 67% with a positive correlation between the two methods. In comparison to the cross-section images, the tomograms were found to reflect the size and position of internal decay, although the detected size tended to be larger than the actual decay area. Our findings indicate SoT as a promising noninvasive technique for detecting internal defects in A. holophylla trees.

Incidence rates of tree damage are increasing because of the increased intensity and frequency of abnormal climate events such as strong winds and heavy rains. Structural defects inside trees are difficult to detect by visual inspection; therefore, it is difficult to respond to them in advance based on prediction. Noninvasive sonic tomography (SoT) is a method that estimates internal defects while minimizing physical damage to trees; however, its accuracy differs depending on the species. Therefore, in this study, we aimed to compare the performance of noninvasive SoT and invasive resistance micro-drilling (RM) in detecting tree damage in oriental white oak (Quercus aliena Blume) distributed in East Asia and performed wood section analysis to verify the accuracy of noninvasive SoT. Linear regression analysis showed that defects in tomograms tended to increase with an increase in the number of defects in the RM profile, but the value of R² was 0.405, which is lower than that of other tree species. The results from the wood section analysis and SoT were compared; the SoT tomograms appropriately reflected the location and size of the defects with a tendency to overestimate the defects when cracks were present, while the electric resistance tomography was effective for detecting incipient decay.

Large old trees, which provide ecosystem services and serve as a historical and cultural heritage, are exposed to various environmental threats, such as habitat fragmentation and climate change, necessitating diagnosis of tangible and intangible stresses and their effects on tree growth for effective management. This study investigated the photosynthetic characteristics of 25 large old Zelkova serrata (Thunb.) Makino trees in Chungcheong Province, Korea, and identified the physical environmental factors affecting their physiological responses. Maximum assimilation rate (A_max) was the highest in July (summer), transpiration rate (E) and stomatal conductance (g_s) increased from May (spring) to September (fall), and water use efficiency (WUE) was the highest in May (spring) and decreased until September (fall). A_max decreased as tree height increased. Ambient CO₂ and vapor pressure deficit (VPD) were negatively correlated with photosynthetic parameters throughout the growth season and in July (summer) and September (fall), respectively. Physical environmental factors exhibited complex effect on physiological activities, which increased with wide growth space and decreased with deep soil covering and high impervious ground surface ratio. Physiological responses differed with surface types within the growth space, with bare land showing higher mean A_max, E, and g_s than areas with mulching material or concrete. This study quantitatively determined the physiological activities of large old Z. serrata and proposes appropriate management measures for ensuring their healthy growth in abiotic stress environment.

Preventive maintenance through monitoring and early detection is important for trees that are structurally weak due to internal decay. Once internal decay has occurred, recovery of lost strength is irreversible. The decaying tree becomes vulnerable to external impacts, which may lead to breakage or windthrow. The Yoshino cherry (Cerasus×yedoensis (Matsum.) “Somei-yoshino”) accounts for a high proportion of landscape trees in Asia. Testing the reliability of noninvasive sonic tomography (SoT) to estimate internal defects could facilitate structural stability evaluation and proactive preventive management. We performed noninvasive SoT and invasive resistance microdrilling to detect and quantify internal defects in old and large Yoshino cherry trees. Generally, SoT reflected the areas and location of severe structural defects, showing a correlation with the resistance microdrilling results (R² = 0.542, p < .001). However, when cracks were present in disks, the SoT overestimated defects and errors mainly observed in the transition zone (green). Based on these findings, when evaluating the SoT, careful decisions are needed to distinguish between actual defects and broad sonic shadows. Furthermore, additional evidence from drilling resistance is required to differentiate between incipient decay and cracks. The results of this study provide valuable insights for enhancing the interpretation of sonic tomograms. Study Implications: We suggest defect boundaries in sonic tomograms should be redefined to improve the accuracy of interpretation for any new species being studied. Careful drilling resistance measurements should be taken, especially in transition zones (green areas in tomogram) and incipient decay zone (light brown areas). Noninvasive sonic tomograms only reflect acoustic properties of the tested cross-section of a tree and cannot be considered an actual representation of the internal conditions until the readings are calibrated to destructive sampling results.