# Effect of Ambient Temperature on Impedance-Based Physiological Activity Evaluation of Zelkova Tree
## 1 Introduction  
Tree physiological activity has traditionally been measured relying on visual observation. The visual observation method sets indicators such as the tree size and crown density, and the observer records qualitative scores for the indicators [1, 2]. Figure 1 shows photos of zelkova trees in summer and fall. In the summer, the leaves of the trees are lush and green, and in the fall, the leaves turn brown. In the summer, the physiological activity of the tree will be active, and as the leaves fall in the fall, the physiological activity of the tree will gradually decrease. Because these methods require an observer to intervene and perform visual observations, it is difficult to automate them based on quantitative measurements. Therefore, has become necessary to develop a measuring device to quantitatively evaluate the physiological activity of trees. In 1977, Dr. [PERSON] developed the Shigometer, a device that measures the resistance of trees to quantify their physiological activity [3]. If a tree's physiological activity is high, the movement of water and electrolyte nutrients between the roots and leaves will become more active. Water and nutrients are transported between the roots and leaves through the xylem and phloem, respectively, in the outer layer of the tree. The xylem and phloem are located on the outside when viewed from the cross-section of the tree trunk, and are formed in a tubular shape in the direction of the tree pillar. Therefore, the physiological activity of a tree can be estimated by measuring the xylem and/orphloem resistance in the direction of the tree trunk. In other words, if the physiological activity of the tree is high, the amount of electrolytes transported will be abundant, so the measured resistance of the tree will be low. If the physiological activity of the tree is low, the amount of electrolytes transported will be low, so the measured resistance of the tree will be high. Figure 1(a) shows the main body of the Shigometer, and Figure 1(b) shows the measurement probe inserted into the tree. Shigometers are used to assess the tree's physiological activity by inserting a probe into the tree trunk at an appropriate depth and then reading the numbers displayed on the main device. It can be seen that the probe is firmly mechanically supported after being embedded in the wood tissue. However, because the Shigometer uses a one-time measurement method, it is difficult to expect the same contact impedance when newly inserted for each measurement. The number displayed on the body is the same as the impedance value calculated using the DC current flowing through the probe and the voltage derived from the DC current. Therefore, the higher the level displayed in the body, the lower the physiological activity, and the lower the level, the higher the physiological activity. The Shigometer has also recently been used to measure the physiological activity of trees [4]. The Shigometer uses only two probes and measures the resistance through the flowing DC current. When only two probes are used, errors due to contact resistance components cannot be avoided, and when measuring with only the DC current flowing, the influence of the capacitance components cannot be included. Additionally, when the DC current is used when measuring impedance, a polarization impedance is formed at the interface between the electrode and the ionic solution, affecting the contact impedance [5]. Since measurements are made once by poking the probe into the wood, the contact resistance changes with each measurement, which also deteriorates the measurement reproducibility. [PERSON] measured the impedance of small branches before and after dehydration [6]. The tree branch was cut into 3 cm lengths, stainless steel electrodes were placed in surface contact with the cut cross-sections at both ends, and the impedance was measured with an LCR meter. Because the two-contact measurement method was used in the impedance measurement, errors due to the contact impedance of the electrode were not considered.