Terrestrial Laser Scanning for the Estimation of Above Ground Biomass of Mangrove Roots by Modelling Them as Inverted Trees

The complex root systems of mangroves such as Rhizophora spp. can hold up to 40% of the total tree biomass yet have usually been neglected in the assessment of the aboveground biomass (AGB). Traditional measurements of AGB can be laborious, costly, time consuming, and require the destruction of the tree. Terrestrial laser scanning (TLS) has increasingly been applied to recreate the architecture of trees to reduce the need for destructive sampling. Modelling Rhizophora mangle L. prop and aerial roots as inverted trees allowed recreation of the volumes using a largely automated methodology. Trees were scanned using a Leica (Switzerland) BLK360 TLS, scans registered and combined, individual tree point clouds extracted and cleaned, the root and trunk point clouds automatically disaggregated, the branches and leaf point cloud separated using auto segmentation techniques, and finally then the volume of the woody fraction of the tree generated in TreeQSM. Two trees were scanned and destructively harvested to assess the modelled wood volume and weight. Wood volume was overestimated by 6.18 and 8.31%, while AGB was overestimated by 2.07 and 2.93%. The robustness of these results demonstrate that this methodology can be applied to improve the estimation of mangrove aboveground biomass. It can facilitate the development of site and species specific allometric equations, that would contribute towards the improved accuracy of carbon estimates at the landscape scale.