Estimating coarse root biomass with ground penetrating radar in a tree-based intercropping system

Abstract

Conventional measurements of tree root biomass in tree-based intercropping (TBI) systems can be inadequate in capturing the heterogeneity of rooting patterns or can be highly destructive and non-repeatable. In this study, we estimated coarse root biomass using ground penetrating radar (GPR) of 25-year-old trees inclusive of five species (Populus deltoides × nigra clone DN-177, Juglans nigra L., Quercus rubra L., Picea abies L. Karst, and Thuja occidentalis L.) at a TBI site in Southern Ontario, Canada. Subsurface images generated by GPR were collected in grids (4.5 × 4.5 m) centred on tree stems. The predictive relationship developed between GPR signal response and root biomass was corrected for species effects prior to tree-scale estimates of belowground biomass. Accuracy of the tree-scale estimates was assessed by comparing coarse root biomass measured from complete excavations of the corresponding tree. The mean coarse root biomass estimated from GPR analysis was 54.1 ± 8.7 kg tree−1 (mean ± S.E.; n = 12), within 1 % of the mean coarse root biomass measured from excavation. Overall there was a root mean square error of 14.4 kg between measured and estimated biomass with no detectable bias despite variable conditions within the in-field and multi-species study. Root system C storage by species, calculated with species-specific root carbon concentrations, is estimated at 5.4 ± 0.7–34.8 ± 6.9 kg C tree−1 at this site. GPR is an effective tool for non-destructively predicting coarse root biomass in multi-species environments such as temperate TBI systems.