Detection of Cryptomeria japonica roots with ground penetrating radar

Coarse tree roots, which are responsible for most root carbon storage, are usually measured by destructive methods such as excavation and coring. Ground penetrating radar (GPR) is a non-destructive tool that could be used to detect coarse roots in forest soils. In this study, we examined whether the roots of Cryptomeria japonica, a major plantation species in Japan, can be detected with GPR. We also looked for factors that impact the analysis and detection of roots. Roots and wooden dowels of C. japonica were buried 30cm deep in sandy granite soil. From GPR measurements with a 900 MHz antenna, the distribution and diameter of samples in several transects were recorded. The buried roots were detected clearly and could be distinguished at diameters of 1.1-5.2cm. There were significant positive relationships between root diameter and parameters extracted from the resultant GPR waveform. The difference in water content between roots and soil is a crucial factor impacting the ability to detect roots with GPR. We conclude that GPR can be used as a non-destructive tool, but further investigation is needed to determine optimal conditions (e.g. water content) and analytical methods for using GPR to examine roots in forest sites.