Determining ages of conifer trees with resistance microdrilling

This study verified the potential for determining the age of conifer trees using resistance microdrilling. A laboratory investigation, comparison of resistance microdrilling and counting branch whorls, and dating of old trees in a historic heritage site were conducted in this study. Two methods were proposed to determine the drilling path for resistance microdrilling. The results showed that resistance microdrilling is suitable for non-destructive testing (NDT) of living conifer trees. Moreover, the drilling path deviation must not exceed 15° to obtain reliable results. The absolute detection error of resistance microdrilling was within ± 3 years for young trees (age < 40 years old), within ± 5 years for old trees, and the relative error for all trees was less than 10%. The two methods for determining the drilling path proposed in this study are recommended for aligning the needle with the pith. For trees with a DBH exceeding the range of a resistance microdrill, the pith and age may be determined by using a “two-way drilling” in a forward and then reverse direction.