# Effect of Ambient Temperature on Impedance-Based Physiological Activity Evaluation of Zelkova Tree
## 3 Tree Physiological Activity Monitoring System
### TPAM System Application to Tree  
The developed TPAM system was applied to the long-term monitoring of zelkova trees. Figure 8 shows the configuration of the TPAM system mounted on a tree and a measurement being conducted. Figure 8a shows the tree being measured and the TPAM system mounted on the tree. The diameter of the tree was measured at 21.6 cm at a height of 1.2 m above the ground. The box containing and protecting the measurement board was installed facing southwest. The use of an opaque box prevents direct sunlight from affecting the temperature sensor on the measurement board. To maximize solar harvesting, solar panels can be placed on the tops of trees or in front of tree trunks so they receive ample sunlight. Since the light intensity sensor must be installed in a place that receives light well, it is also installed where the solar panel is located. Figure 8b shows the inside of the TPAM system box mounted on a tree. A Li-ion battery with a capacity of 5000 mAh is also installed in the system box. The antenna and probe connection cables are routed out of the box through a hole in the bottom, which helps keep it waterproof. Figure 8c shows the probe inserted into the tree. A total of eight probes were installed in a four by two array at a north-facing point. The distance between the two probe columns is 15 mm, and the four probes in one column on the left are inserted to a depth of 13 mm, and the four probes in the other column on the right are inserted to a depth of 6 mm. To remove the  
Figure 7: TPAM system evaluation (**a**) with known resistance and (**b**) with known capacitance. impact on the impedance measurements if the probes become wet due to rain, the exposed areas are coated with photosensitive epoxy for electrical insulation. If the diameter of the tip of the probe inserted into the tree is excessively large, cracks may occur in the tree at the insertion point. If a crack occurs at the insertion site, a void is created between the probe and the wood tissue, preventing complete contact between the probe and the wood tissue. Additionally, since the tissue at the crack area is exposed to the outside, the area may dry out or rot, making proper long-term impedance monitoring difficult. Therefore, care must be taken to avoid cracking the wood by inserting the probe, and in this study, a probe with a tip diameter of 1 mm was used. Since the needle probe is tightly clamped by the pressure of the dense tree tissue, the contact between the probe and the tree is solid, and no abnormalities in the insertion state, such as the probe falling out, occur even after several seasons. Figure 8: Application configuration of TPAM system: (**a**) zelkova tree to be measured and installed TPAM system, (**b**) TPAM hardware box and built-in PCB, (**c**) inserted probes, (**d**) hub, (**e**) zelkova core samples and growth rings. The hub shown in Figure 8d is located indoors, 18 m away from the tree where the TPAM hardware is installed. The wireless communication antenna and ZigBee module plugged into the laptop are shown. The GUI of the TPAM software 1.0 is displayed on the laptop screen, and measurement data are received in real time and a graph is plotted. Figure 8e shows a core sample of a tree collected to determine the tree's age. The age of a tree can be determined from the number of growth rings formed on the cross section of the tree. A tree ring sample was taken at a height of 1.2 m above the ground, towards the center of the tree cross section. The tree ring sample is a thin, cylindrical shape with a diameter of 5 mm and a length of 11.7 cm. The repeating rings of a tree are made up of two parts: early wood and late wood. Each year in the spring and early summer, trees grow rapidly, forming broad, bright early wood sections, while in late summer and fall, trees grow more slowly, forming dark, narrow late wood sections. In the enlarged scanning electron microscope (SEM) image, it can be seen that the early wood region is porous and the late wood region is dense.