# 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  
Figure 13a shows graphs of the temperature and tree impedance data measured from 3 August to 9 August, when the tree was in full leaf. The left y-axis represents the impedance value and the right y-axis represents the ambient temperature value. The lower line is the impedance data and has values ranging from approximately 0.8 k\(\Omega\) to a maximum of 0.95 k\(\Omega\), and the ambient temperature fluctuates in the range of approximately 17 to  
Figure 12: Long-term monitoring of zelkova tree during seasonal changes: (**a**) impedance data measured using the 4-point probe method, (**b–d**) appearance of zelkova tree according to seasonal changes. 36 degrees. In general, as the temperature increases, the impedance tends to decrease, and as the temperature decreases, the impedance tends to increase. Additionally, on days with large temperature changes, the impedance change is large, and on days with small temperature changes, the impedance change is small. This effect of temperature on the impedance change can be interpreted in two ways. First, the impedance may have been observed to change as the tree's physiological phenomenon is activated by temperature, and second, it may be unrelated to the tree's physiological phenomenon and the impedance value may have been directly affected by temperature changes. In a previous study, [PERSON] observed a synchronized pattern between the temperature and electrical conductivity of paprika [21]. This is consistent with the observation that the impedance of zelkova trees growing outdoors is inversely proportional to temperature, as shown in Figure 13a. [PERSON] also measured the relative humidity as well as the  
Figure 13: Graph of ambient temperature and impedance data: (**a**) when the leaves are lush, (**b**) without leaves, and (**c**) trajectory plot on a specific day. impedance according to the temperature. When the impedance is low, the relative humidity is also low. However, the relative humidity has a flat shape of 60% in the evening and dawn, but drops to 20% in the morning and day, which is not synchronized with the change in the impedance. Figure 13b shows the ambient temperature and impedance measurements when there are no leaves. The absence of any leaves means that the tree is not carrying out physiological activities, and the fluctuating impedance at this time cannot be said to be related to physiological activities. It seems desirable to interpret the tree impedance fluctuations when there are no tree leaves as being directly caused by changes in ambient temperature. Therefore, even when the leaves are in full bloom, the daily impedance fluctuations will include a mixture of the influence of the tree's physiological activation and the influence of changes in the ambient temperature. Figure 13c is a graph plotting the ambient temperature on the x-axis and the impedance on the y-axis for a specific day. The closed loops formed at the bottom, middle, and top plot the intraday impedance change according to the intraday temperature change for one day in summer, fall, and winter, respectively. The characteristic of the summer trajectory (5 August) is that the impedance position is the lowest and shows a straight line with almost no hysteresis. The centrally located fall trajectory (5 October) has a mid-level impedance level and shows some hysteresis in the shape of the trajectory. The winter trajectory has a relatively large impedance, so it is located at the top, and the hysteresis is relatively large, so the trajectory shape is oval. Even in winter trajectories where all the leaves have fallen, the impedance shows fluctuations depending on the daily temperature ranges, so an analysis excluding the effects of the daily temperature ranges is necessary. There have been previous research results that have observed changes in wood resistance depending on temperature or humidity. [PERSON] measured the electrical resistance of excised olive tree tissue in response to temperature changes [22].