# Effect of Ambient Temperature on Impedance-Based Physiological Activity Evaluation of Zelkova Tree
## 4 Monitoring Results and Discussion
### Relationship between Ambient Temperature Change and Impedance Change
When the temperature was lowered from about 25 degrees to 10 degrees, there was a slight slope of resistance increase, and when the temperature was lowered from 10 degrees to \(-20\) degrees, the resistance clearly increased linearly. As reported in the previous paper using wood specimens, hysteresis in the resistance trace was also reported when the temperature was lowered and then raised again. In Figure 13c, the data on 5 August 2023, measured from a tree growing outdoors, belong to the high-temperature region, and the impedance change in response to temperature changes is weak, as was the trend in the high-temperature region in the previous study. In the data from 20 November 2023 in Figure 13c, the change in the impedance in response to the temperature change shows hysteresis, as in the previous study. Figure 14 shows a plot of the tree impedance values at daily ambient temperatures of 15 degrees, 20 degrees, and 25 degrees from 1 September to 30 November. In Figure 13b, impedance fluctuations were observed under the influence of ambient temperature even in the absence of tree leaves. Therefore, in order to exclude the influence of intraday temperature fluctuations and investigate impedance changes due to seasonal changes, the data for specific temperatures were graphed. The impedance data at 25 degrees, 20 degrees, and 15 degrees are marked with squares, triangles, and circles, respectively. Whether based on 15 degrees, 20 degrees, or 25 degrees, the impedance value tends to gradually increase linearly as the season changes. The slope of the increase in the impedance as the day goes by appears to be generally similar, specifically showing a slope of 8.4 \(\Omega\)/day at 25 degrees, 9.7 \(\Omega\)/day at 20 degrees, and 11.9 \(\Omega\)/day at 15 degrees. Therefore, over 50 days, the impedance values extracted from 25 degrees, 20 degrees, and 15 degrees showed increases of approximately 420 \(\Omega\), 485 \(\Omega\), and 595 \(\Omega\), respectively. It can be seen that the lower the extraction temperature, the greater the impedance change. By comparing the impedance values over time at the same temperature, the effect of temperature could be ruled out. When the effect of temperature is excluded, it can be seen that the impedance of the tree has a linear relationship with the electrical impedance value as the season changes. It is a known fact that trees' physiological activity, which is active in the summer, decreases as winter approaches. It was revealed through the measurement data that the impedance values of  
the trees extracted at the same temperature have a linear correlation with the season. The R\({}^{2}\) value (coefficient of determination), which indicates that the closer it is to 1, the closer it is to the linear fit line, was calculated to be 0.89, 0.77, and 0.86 at 25 degrees, 20 degrees, and 15 degrees, respectively. Therefore, it is inferred that the impedance value of a tree extracted at the same temperature can be an indicator of the tree's physiological activity. Among previous studies, there has been an example of using the resistance value of wood at a certain temperature. [PERSON], when using the resistance value of wood measured using a Shigometer, also measured the temperature and converted the measured resistance to a corrected resistance value at 15 degrees using pre-prepared temperature correction data [23]. This is consistent with the need for temperature compensation in previous studies, as Figure 13 shows a change in the impedance of the tree due to temperature changes even after all the leaves have fallen. In previous studies, resistance values measured at different temperatures were corrected and used, but in Figure 14, there was an impedance value measured directly at the corresponding temperature, so there was no need for correction. Figure 15 is a plot showing the maximum light intensity during the day as the season changes. As the seasons change, the impedance value gradually increases, but no particular trend can be seen in the light intensity.