Ground-penetrating radar estimates of tree root diameter and distribution under field conditions
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Use of ground-penetrating radar (GPR) can non-destructively estimate diameter and distribution of coarse roots in Cryptomeria japonica in weathered granite soils under field conditions.
Ground-penetrating radar (GPR) has been used as an assessment tool for non-destructive detection of tree root biomass, but few studies have estimated root diameter under forest field conditions. The aim of this study was to clarify whether coarse root diameter of C. japonica in weathered granite soils can be estimated using GPR in a forest. Roots of mature C. japonica were scanned using a 900 MHz GPR antenna before being excavated. The diameter and distribution of excavated roots were compared with those identified by GPR, and the relationships between the diameter and waveform indices in radar profiles were also examined. The detection frequency of the number of roots larger than 5 mm in diameter was 47.7%. Limiting factors affecting root detection using GPR in forest field conditions were small root diameter, increasing root depth, and number of adjacent roots. Only one waveform index, using the sum of time intervals between zero crossings (ΣT, ns) of all reflection waveforms of GPR within the range from the first break time at the root top to the delay point time at the root bottom, had a significant relationship with excavated root diameters. A linear regression model was constructed to estimate root diameter using ΣT, and a significant positive relationship in diameter between GPR-estimated and excavated roots was confirmed. The results in this study indicate that the diameter and distribution of C. japonica coarse roots under forest field conditions could be estimated using GPR and this technique could contribute to future evaluation of slope stability by evaluating tree roots under vulnerable soils, such as weathered granite.
KeywordsNon-destructive root detection Parabolic waveform Root diameter Slope stability Waveform index
We thank I. Endo (University of Hyogo) for improving the manuscript, and N. Hosohata (KANSO Technos), Y. Maekawa, Y. Nakagawa, A. Takamatsu, M. Yoshida, T. Kakizoe, M. Tojyo, A. Hanada (University of Hyogo), N. Amin, J. An, R. Nakahata (Kyoto University), K. Miyatani, K. Ichikawa (Nagoya University), K. Miyata, M. Hayashida (Miyata Jyugyo), T. Nakagawa, T. Hashimoto (Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries) for their invaluable assistance in field and laboratory work. We also thank Y. Shigeto and M. Hata (Kobe City) for permission to use the field site.
This study was funded partly by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (Grant number, 25252027).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflicts of interest.
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