Application of terrestrial LiDAR and modelling of tree branching structure for plant-scaling models in tropical forest trees

Terrestrial Laser Scanner has the potential to capture the complex 3D structure, and in combination with 3D tree reconstruction models would allow us to model the shape of the trunk and main branches of trees. This is a step further into a more precise determination of whole-tree architecture and branching patterns; which would lead us into a better understanding of scaling exponents and metabolic rate at branch and whole-tree level in tropical forest trees without the need of destructive sampling. For this study, we extracted three trees from a TLS pointcloud data acquired during November 2013 in the Peruvian amazon rainforest. Quantitative structure model was used to calculate branch length, diameters and architecture from the individual trees. These parameters were used in the WBE plant-scaling model. This model calculated the following exponents: length ratio scaling, radii ratio scaling and estimated metabolic rate scaling and compared to the theoretical values. The theoretical exponent expected from WBE for branch length scaling is 0.3 and for branch radii scaling is 0.5. Across our samples, the calculated branch-level length scaling exponent varied from 0.04 to 0.11 and the calculated branch-level radii scaling exponent ranged from 0.30 to 0.32 (Table 1). The calculated (estimated) metabolic rate scaling exponent was 0.72, 0.71 and 0.76 for Tachigali polyphylla, Jacaranda copaia and Sclerolobium bracteosum (expected to be 0.75 from the WBE model). Estimations of tree scaling metabolism derived from architecture via TLS scans showed consistent and comparable values to the model predictions for all scaling exponents. Since the scanned trees were different species, these results provide evidence to support the WBE assumption of similarities in branching structure and common set of branching rules across trees. To conclude, tree scaling metabolism derived from TLS evidenced that (1) length ratio exponent, radii ratio exponent and architecture estimated metabolic rate converge between the tropical trees analysed, and (2) length ratio exponent, radii ratio exponent and estimated metabolic rate from the analysed samples are comparable with the predicted values.

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