Estimating coarse root biomass with ground penetrating radar in a tree-based intercropping system
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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.
KeywordsTemperate agroforestry Belowground biomass Root detection Geo-imaging Tree root system Volatile carbon Carbon storage
We would thank the faculty, staff, and students at the University of Guelph Agroforestry Research Station. Amy Wotherspoon from the University of Guelph graciously provided root excavation data and Stephanie Gagliardi provided important assistance during field work and laboratory analysis. We also thank Tom Meulendyk for assistance. We thank two anonymous journal reviewers for their insightful and constructive comments on earlier versions of the manuscript. Funding was provided by the Faculty of Forestry at the University of Toronto, Agriculture and Agri-Food Canada’s Agricultural Greenhouse Gases Program, and the Natural Sciences and Engineering Research Council of Canada.
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