Terrestrial photogrammetry: a non‐destructive method for modelling irregularly shaped tropical tree trunks

Abstract

Summary Irregularly shaped trees including trees with buttresses, flutes or stilt roots are frequent in tropical forests. The lack of an international standard to measure the diameter of such trees leads to high uncertainties in biomass estimation, tree growth and carbon budget monitoring. In this study, we developed a new method based on terrestrial close‐range photogrammetry for measuring and modelling irregular stems. This approach is cheap and easy to implement in the field as it only requires a camera and a graduated rod. We validated the approach with destructive cross‐section measurements along the stem of three buttressed trees. To demonstrate the broader utility of this method, we extended the validated approach to 43 additional trees belonging to two species: Celtis mildbraedii (Ulmaceae) and Entandophragma cylindricum (Meliaceae). Based on the three dimensional models, we computed shape indices for each tree, and we analysed the stem morphology of the two species. Finally, we analysed some standardized predictors for the estimation of above‐ground biomass. We found a high concordance between diameters derived from the photogrammetric process and destructive diameter measurements along the stem for the three calibration trees. We found that C. mildbraedii develop much stronger irregularities than E. cylindricum. We also identified a large intraspecific variation in trunk morphology for E. cylindricum. The basal area at 1·3 m height (Darea130) seems to be a more robust predictor for biomass estimates (lowest Akaike information criterion and relative squared error) than diameter measured above buttresses (DAB) or diameter at breast height estimated from available taper model. Finally, Darea130 might be estimated with a good precision [root mean square error (RMSE) < 5%] with linear model based on the field measurements DAB and the perimeter of the convex hull of the buttresses at 1·3 m height (Dconvhull130). In this study, we showed the high potential of the photogrammetry for measuring and modelling irregular stems. Photogrammetry could then be used as a non‐destructive measurement tool to produce correction factors for standardizing the diameter of irregular stems at a reference height which is a key issue in tree growth monitoring and biomass change estimation.

High Precision Individual Tree Diameter and Perimeter Estimation from Close-Range Photogrammetry

“…The diameter is related strongly to other descriptors of tree size such as total height [3] and crown dimensions [4]. Thus, it is a key predictor to estimate the stem and tree volume [5], biomass [6], and other information [7]. In addition to the forestry practice, the high demand for precise and complex three-dimensional (3D) data is evident in multiple research fields; for example, in functional-structural models [8] where it is crucial to obtain accurate temporal 3D data.…”

Extraction of Sample Plot Parameters from 3D Point Cloud Reconstruction Based on Combined RTK and CCD Continuous Photography

“…Zhang et al [20] described two main point cloud data sources in photogrammetry -optical image and laser radar data-and pointed out their advantages and disadvantages. Among many modern forest survey techniques, the terrestrial photogrammetry method is attaining foresters' attention with its high precision and low price [21,22].…”

Tree architecture description using a single-image photogrammetric method

“…The architectural approach is crucial in understanding tree structure and function (Sievänen et al, 2014). However, to make progress in the field, empirical data are needed; low-cost, non-destructive and accurate acquisition of architectural data is still a concern (Bauwens et al, 2017).…”