Abstract

Traditional studies aimed at developing allometric models to estimate dry above-ground biomass (AGB) and other tree-level variables, such as tree stem commercial volume (TSCV) or tree stem volume (TSV), usually involves cutting down the trees. Although this method has low uncertainty, it is quite costly and inefficient since it requires a very time-consuming field work. In order to assist in data collection and processing, remote sensing is allowing the application of non-destructive sampling methods such as that based on terrestrial laser scanning (TLS). In this work, TLS-derived point clouds were used to digitally reconstruct the tree stem of a set of teak trees (Tectona grandis Linn. F.) from 58 circular reference plots of 18 m radius belonging to three different plantations located in the Coastal Region of Ecuador. After manually selecting the appropriate trees from the entire sample, semi-automatic data processing was performed to provide measurements of TSCV and TSV, together with estimates of AGB values at tree level. These observed values were used to develop allometric models, based on diameter at breast height (DBH), total tree height (h), or the metric DBH2 × h, by applying a robust regression method to remove likely outliers. Results showed that the developed allometric models performed reasonably well, especially those based on the metric DBH2 × h, providing low bias estimates and relative RMSE values of 21.60% and 16.41% for TSCV and TSV, respectively. Allometric models only based on tree height were derived from replacing DBH by h in the expression DBH2 x h, according to adjusted expressions depending on DBH classes (ranges of DBH). This finding can facilitate the obtaining of variables such as AGB (carbon stock) and commercial volume of wood over teak plantations in the Coastal Region of Ecuador from only knowing the tree height, constituting a promising method to address large-scale teak plantations monitoring from the canopy height models derived from digital aerial stereophotogrammetry.

Highlights

  • The main objective of this study aims at developing locally calibrated allometric equations based on terrestrial laser scanning (TLS) data obtained in leaf-off conditions teak plantations located in the Coastal Region of Ecuador

  • It is necessary to highlight the added value of the methodology and allometric models provided by this study for the sustainable management of teak plantations located in the Coastal Region of Ecuador

  • The results obtained in this study have proved that TLS-derived point clouds constitute an efficient tool to capture teak tree geometry at stem level under leaf-off conditions in the Coastal Region of Ecuador, further work is needed to deal with an accurate extraction of tree branches in order to count on the full tree skeleton

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Summary

Introduction

The importance of teak plantations around the world can be appraised from the report “State of the World’s Forest Genetic Resources” [2]. It lists tree species that are considered national. Forests 2019, 10, 1050 priorities by the reporting countries for the conservation and management of forest genetic resources, teak taking the top rank in this list in more than 20 countries due to its economic value. In 2010 the global area of planted teak forests reported from 38 countries was conservatively estimated at 4.35 million ha, which 83% grew in Asia, 11% in Africa, 6% in tropical America, and less than 1% in Oceania [3]. More recent estimations of the area of planted teak forests based on FAO (Food and Agriculture Organization of the United Nations) and ITTO

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