Ground‐penetrating radar amplitudes to roots: A numerical modelling framework for mapping coarse root system architecture

Abstract

Abstract Observations of three‐dimensional (3D) coarse root system architecture remain limited because most measurement approaches require excavation. Here, we combined dense single‐ and multi‐channel 500 MHz ground‐penetrating radar (GPR) surveys with a flow‐guided connectivity framework to non‐destructively characterise the coarse root architecture of two trees. Migrated and depth‐normalised GPR amplitudes were treated as spatially variable hydraulic conductivities in a steady‐state numerical model. The resulting connectivity fields transformed spatially discontinuous, collapsed diffraction hyperbolae into continuous 3D representations of root architecture extending 10–15 m from the trunk. We applied this approach to a swamp oak ( Quercus palustris ) and a river red gum ( Eucalyptus camaldulensis ). The two trees were surveyed under different environmental conditions and acquisition parameters. The reconstructed architectures revealed shallow, laterally extensive coarse root systems and captured substantial variation in root structure between the two trees. The oak roots exhibited an asymmetrical architecture with preferential development towards the upslope, wind‐exposed side of the tree, whereas the river red gum displayed a more radially distributed root architecture with deeper roots near the trunk. Approximately 80% of reconstructed roots for both trees occurred within 6.2 m of the trunk and above 60 cm depth. Together, these results demonstrate that dense GPR surveys, coupled with connectivity‐based modelling, provide a non‐destructive and repeatable approach for characterising coarse root architecture.