Effect of ice formation on cross-section electrical resistance and stress wave velocity in living trees at low temperatureAuthorship

Abstract

Accurate tree decay detection and quality evaluation at low temperature is a scientific problem. The electric resistance tomography (ERT) and stress wave tomography (SWT) are two widely recognized methods for decay detection, but the influence of ice formation on the detection has not been studied. The objective of this study is to investigate the effect of ice formation on cross-section electrical resistance (ER) and stress wave velocity (SWV) in living trees at low temperature. Larix gmelinii and Populus simonii living tree specimens were conducted on moisture content (MC) measurement using time domain reflectometry (TDR), trunk ER and SWV test using ERT and SWT methods, respectively. Ice content (IC) was calculated based on the MC data. The effects of IC on ER and SWV were then explored. We find IC of both tree species shows a general trend that is first rising and then decreasing, it is opposite with ambient temperature. With the decrease of ambient temperature, daily average IC increases, but the variation range narrows gradually and both ER and SWV increase. The ER and SWV increase rapidly near 0℃, which is mainly caused by ice formation (phase change and freezing of free water) in living trees. Furthermore, the ER and SWV are both positively correlated with IC (R2 > 0.87, p < 0.01). The results suggest that IC should be considered as an important factor for improving the test accuracy in the process of tree decay detection and quality evaluation using ERT and SWT methods under low temperature.