Abstract
In order to use the electrical resistance method to accurately and timely detect and evaluate the internal decay defects of living trees, the effects of the seasonal temperature and moisture content on the electrical resistance of standing trees were investigated. At the Northeast Forestry University Experimental Forest Farm, Harbin, Heilongjiang Province of China, Populus simonii Populus simonii Carr. and Larix gmelinii (Rupr.) Rupr. were selected as the objects and the electrical resistance of standing trees was tested through different seasons from December 2016 to December 2017. Meanwhile, the effects of changes in the seasonal temperatures (−20 to −10 °C, −10 to −5 °C, −5 to 0 °C, 0 to 5 °C, 5 to 10 °C, 10 to 15 °C, 15 to 25 °C) as well as changes in the moisture content (MC) (Populus simonii, MC ≥ 103%; Larix gmelinii, MC ≥ 77.5%) on the electrical resistance in the cross-sections of living trees were studied. The influence of temperature at different moisture contents, the moisture content at different temperatures, and their combined effects on electrical resistance were analyzed, following which a regression model was also established. The obtained results indicated that ambient temperature had a significant effect on the average value of electrical resistance in the cross-section of living trees when temperatures were below the freezing point. There was a sudden discontinuity near the freezing point, and logR (logarithm value of electrical resistance) in the cross-sections of sound trees and decayed trees changed in a similar trend with variations in the temperature. While the effect of moisture content on logR in the cross-sections of threes was insignificant at different temperatures because of the moisture content above FSP (fiber saturation point). It indicated that the temperature and moisture content had interactive effects on logR in the cross-sections. The binary linear regression model between moisture content, temperature, and logR was highly fitted with a correlation coefficient (R2) higher than 0.8. The outcome of this investigation indicates that when non-destructive testing is performed on living trees using electrical resistance at different seasonal temperatures, the measured results need to consider both the temperature and moisture content. For practical work, it is not recommended to consider testing living trees near the freezing point temperature using the electrical resistive tomography. Below the freezing point, the electrical resistance changes with temperature greatly relative to the normal temperature. Therefore, when performing the detection of electrical resistance, it is necessary to calibrate the effects of temperature
Highlights
An effective use of existing timber resources and improving the quality of wood products are considered to be the important issues faced by the forestry management and timber industries
Forests 2018, 9, 550 phenomenon, the relationship of LogR–temperature diagram (logR–T) was divided into three temperatures: below the freezing point, the logarithm of the mean electrical resistance (logR) decreased with increasing temperature; near the freezing point, the logR changed rapidly with increasing temperature; above the freezing point, the logR changed slowly with
The results showed that the electrical resistance in the cross-sections of tress was significantly affected by the temperature and moisture content, and it was of great significance to the accuracy of electrical resistance of wild living trees
Summary
An effective use of existing timber resources and improving the quality of wood products are considered to be the important issues faced by the forestry management and timber industries. Many researchers have conducted studies based on non-destructive testing to examine the effects of species, density, decay, and electrolyte content in the accurate determination of electrical resistance non-destructive testing technique [13,16] Some of these studies [17,18] conducted a comparative analysis of the electrical resistance method with other commonly used non-destructive testing techniques for wood, such as ultrasonic and resistograph, and found that electrical resistance method has its own advantages in terms of sensitivity and image accuracy. This method of detection using electrical resistance is a convenient tool as it is easy to carry out and is useful for field work
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