Applying quantitative structure models to plot-based terrestrial laser data to assess dendrometric parameters in dense mixed forests

Abstract

Aim of study: To assess terrestrial laser scanning (TLS) accuracy in estimating biometrical forest parameters at plot-based level in order to replace manual survey for forest inventory purposes.Area of study: Monte Morello, Tuscany region, ItalyMaterial and methods: In 14 plots (10 m radius) in dense Mediterranean mixed conifer forests, diameter at breast height (DBH) and height were measured in Summer 2016. Tree volume was computed using the second Italian National Forest Inventory (INFC II) equations. TLS data were acquired in the same plots and quantitative structure models (QSMs) were applied to TLS data to compute dendrometric parameters. Tree parameters measured in field survey, i.e. DBH, height, and computed volume, were compared to those resulting from TLS data processing. The effect of distance from the plot boundary in the accuracy of DBH, height and volume estimation from TLS data was tested.Main results: TLS-derived DBH showed a good correlation with the traditional forest inventory data (R2=0.98, RRMSE=7.81%), while tree height was less correlated with the traditional forest inventory data (R2=0.60, RRMSE=16.99%). Poor agreement was observed when comparing the volume from TLS data with volume estimated from the INFC II prediction equations.Research highlights: The study demonstrated that the application of QSM to plot-based terrestrial laser data generates errors in plots with high density of coniferous trees. A buffer zone of 5 m would help reduce the error of 35% and 42% respectively in height estimation for all trees and in volume estimation for broadleaved trees.

Individual Tree Volume Estimation with Terrestrial Laser Scanning: Evaluating Reconstructive and Allometric Approaches

“…Also, QSM is generally more accurate in estimating coarse wood volume in leaf-off broadleaves than conifers, due to less occlusion by foliage. Similar differences in accuracy across forest types and species were observed by Torresan et al (2018) and Demol et al (2021bDemol et al ( , 2022a. In our case, the reference data quality might play an additional role in the differences in QSM accuracy, as broadleaf trees were more susceptible to damage during harvesting and weighing operations than conifers.…”

Nondestructive Estimation of the Above-Ground Biomass of Multiple Tree Species in Boreal Forests of China Using Terrestrial Laser Scanning

“…In addition, the height of the understory shrub vegetation in the plots was less than 1.5 m, so the shrub point cloud data in the plot was removed. Third, in order to make the volume of the reconstructed trunks more similar to the volume of the real trees, the noise and outliers were removed from the data, since these could result in the fitting of wrong cylinder models and overestimating the trunk volume [28,33]. A sphere with a radius of 0.3 cm was used to filter noise points in cloud data of plots while removing outliers.…”

Timber Volume Estimation by Using Terrestrial Laser Scanning: Method in Hyperdiverse Secondary Forests

“…TH is one of the tree components that most signifi cantly contribute to the stem volume, and it was therefore expected that stem volume would show a trend similar to that of TH (Torresan et al, 2018). In addition, considering the stem tapering pattern, larger diameters are closer to the target height, which culminates in smaller incidence angles (Buck, 2017;Almeida, 2017).…”