Detection frequency of Pinus thunbergii roots by ground-penetrating radar is related to root biomass

Tree roots in forest soils can be detected using nondestructive ground-penetrating radar (GPR). However, few studies have investigated root detection frequency; i.e., how many and which roots are identified in a radar profile out of the total quantity of roots present in a forest stand. The objective of this study was to quantify root detection frequency and uncertainty, including relationships between root detection and radar parameters using 1.5 GHz GPR in a Pinus thunbergii forest on sandy soils. We compared the vertical distribution of 829 excavated roots with distributions identified visually in radar profiles using GPR on 17 transects. The detection frequency for number of roots less than 1.0 cm in diameter was only 6.6 %, but 54 % of roots that were larger than 1.0 cm were detected. Roots larger than 2.0 cm were identified with less frequency by GPR at deeper depths (20-30 cm) than were shallower roots. Our study indicates that GPR methods estimate root biomass to be 68 % of the excavated root biomass and that the detection frequency for number of roots in radar profiles using GPR is related to root biomass, although there is uncertainty in the attenuation of radar waves with depth, soil water condition and root orientation.