Improving tree health assessment accuracy at low temperatures: considering the effect of trunk ice content on electrical resistance and stress wave tomography

Accurate decay detection and health assessment of trees at low temperatures is an important issue for forest management and ecology in cold areas. Low temperature ice formation on tree health assessment is unknown. Because electric resistance tomography and stress wave tomography are two widely used methods for the detection of tree decay, this study investigated the effect of ice content on trunk electrical resistance and stress wave velocity to improve tree health assessment accuracy. Moisture content, trunk electrical resistance and stress wave velocity using time domain reflectometry were carried out on Larix gmelinii and Populus simonii. Ice content is based on moisture content data. The ice content of both species showed a trend of increasing and then decreasing. This was opposite with ambient temperatures. With the decrease of temperatures, daily average ice content increased, but the range narrowed gradually and both electrical resistance and stress wave velocity increased. Both increased rapidly near 0 °C, mainly caused by ice formation (phase change and freezing of free water) in live trees. In addition, both are positively correlated with ice content. The results suggest that ice content should be considered for improving the accuracy of tree decay detection and health evaluation using electric resistance tomography and stress wave velocity methods under low temperatures.