Data from: Using terrestrial laser scanning data to estimate large tropical trees biomass and calibrate allometric models: a comparison with traditional destructive approach

1. Calibration of local, regional or global allometric equations to estimate biomass at the tree level constitutes a significant burden on projects aiming at reducing Carbon emissions from forest degradation and deforestation. The objective of this contribution is to assess the precision and accuracy of Terrestrial Laser Scanning (TLS) for estimating volumes and above-ground biomass (AGB) of the woody parts of tropical trees, and for the calibration of allometric models. 2. We used a destructive dataset of 61 trees, with diameters and AGB of up to 186.6 cm and 60 Mg respectively, which were scanned, felled and weighed in the semi-deciduous forests of eastern Cameroon. We present an operational approach based on available software allowing the retrieving of TLS volume with low bias and high accuracy for large tropical trees. Edition of the obtained models proved necessary, mainly to account for the complexity of buttressed parts of tree trunks, which were separately modelled through a meshing approach, and to bring a few corrections in the topology and geometry of branches, thanks to the amapstudio-scan software. 3. Over the entire dataset, TLS-derived volumes proved highly reliable for branches larger than 5 cm in diameter. The volumes of the remaining woody parts estimated for stumps, stems and crowns as well as for the whole tree proved very accurate (RMSE below 2.81% and R² above of .98) and unbiased. Once converted into AGB using mean local-specific wood density values, TLS estimates allowed calibrating a biomass allometric model with coefficients statistically undistinguishable from those of a model based on destructive data. The Unedited Quantitative Structure Model (QSM) however leads to systematic overestimations of woody volumes and subsequently to significantly different allometric parameters. 4. We can therefore conclude that a non-destructive TLS approach can now be used as an operational alternative to traditional destructive sampling to build the allometric equations, although attention must be paid to the quality of QSM model adjustments to avoid systematic bias.

1. 针对树木层级生物量估算开展局域、区域乃至全球尺度异速生长方程（allometric equations）的校准工作，对于以降低森林退化与毁林碳排放为目标的相关项目而言，是一项颇具挑战性的繁重任务。本研究旨在评估地面激光扫描（Terrestrial Laser Scanning, TLS）技术在估算热带树木木质部体积与地上生物量（above-ground biomass, AGB），以及校准异速生长模型方面的精度与可靠性。
2. 本研究使用了喀麦隆东部半落叶林中采集的61株破坏性采样数据集，这些树木的直径最高可达186.6 cm，地上生物量最高可达60 Mg，均经过扫描、砍伐与称重处理。我们提出了一套基于现有软件的可操作流程，可针对大型热带树木实现低偏差、高精度的地面激光扫描体积估算。研究表明，对所得模型进行编辑是必要的：一方面需通过网格化方法（meshing approach）单独建模以适配树干板根结构的复杂性，另一方面可借助amapstudio-scan软件对枝条的拓扑与几何结构进行少量修正。
3. 在整个数据集范围内，地面激光扫描得到的体积估算结果针对直径大于5 cm的枝条时，表现出极高的可靠性。针对伐桩、树干、树冠乃至整株树木的其余木质部体积估算结果均十分精准（均方根误差（Root Mean Square Error, RMSE）低于2.81%，决定系数R²高于0.98）且无系统偏差。在采用局域平均木材密度值将体积转换为地上生物量后，基于地面激光扫描的估算结果可用于校准异速生长模型，其模型系数与基于破坏性采样数据得到的模型系数在统计学上无显著差异。然而，未经编辑的定量结构模型（Quantitative Structure Model, QSM）会导致木质部体积出现系统性高估，进而得到显著不同的异速生长参数。
4. 综上，尽管需关注定量结构模型的调整质量以避免系统偏差，但非破坏性地面激光扫描方法现已可作为传统破坏性采样的实用替代方案，用于构建异速生长方程。