Estimating Stand and Fire-Related Surface and Canopy Fuel Variables in Pine Stands Using Low-Density Airborne and Single-Scan Terrestrial Laser Scanning Data

Abstract

In this study, we used data from a thinning trial conducted on 34 different sites and 102 sample plots established in pure and even-aged Pinus radiata and Pinus pinaster stands, to test the potential use of low-density airborne laser scanning (ALS) metrics and terrestrial laser scanning (TLS) metrics to provide accurate estimates of variables related to surface and canopy fires. An exhaustive field inventory was carried out in each plot to estimate the main stand variables and the main variables related to fire hazard: surface fuel loads by layers, fuel strata gap, surface fuel height, stand mean height, canopy base height, canopy fuel load and canopy bulk density. In addition, the point clouds from low-density ALS and single-scan TLS of each sample plot were used to calculate metrics related to the vertical and horizontal distribution of forest fuels. The comparative performance of the following three non-parametric machine learning techniques used to estimate the main stand- and fire-related variables from those metrics was evaluated: (i) multivariate adaptive regression splines (MARS), (ii) support vector machine (SVM), and (iii) random forest (RF). The selection of the best modeling approach was based on a comparison of the root mean square error (RMSE), obtained by optimizing the parameters of each technique and performing cross-validation. Overall, the best results were obtained with the MARS techniques for data from both sensors. The TLS data provided the best results for variables associated with the internal characteristics of canopy structure and understory fuel but were less reliable for estimating variables associated with the upper canopy, due to occlusion by mid-canopy foliage. The combination of ALS and TLS metrics improved the accuracy of estimates for all variables analyzed, except the height and the biomass of the understory shrubs. The variability demonstrated by the combined use of both types of metrics ranged from 43.11% for the biomass of duff litter layers to 94.25% for dominant height. The results suggest that the combination of machine learning techniques and metrics derived from low-density ALS data, drawn from a single-scan TLS or a combination of both metrics, may represent a promising alternative to traditional field inventories for obtaining valuable information about surface and canopy fuel variables at large scales.

Estimating Forest Variables for Major Commercial Timber Plantations in Northern Spain Using Sentinel-2 and Ancillary Data

“…Multivariate Adaptive Regression Splines (MARS), a well-known nonparametric technique first proposed by [62], provides very good results for estimating forest variables from remote sensing data (e.g., [26,63,64]). MARS enables modelling a target variable based on multiple predictor variables using splines.…”

Operational fuel model map for Atlantic landscapes using ALS and Sentinel-2 images

“…Various efforts have been made to identify and characterize the most common fuel models in Galicia; the most prominent is the fuels photoguide published by Lourizán CIF (photo-guide from now on) (Arellano et al 2017). Other researchers have characterized some fuel variables through remote sensing; some examples are Alonso-Rego et al (2021), Alonso-Rego et al (2020), Fidalgo-González et al (2019 and Arellano-Pérez et al (2018). However, these methodologies do not result in a map with the distribution of fuel models; these maps are needed to be used with simulation software to obtain reliable results about the behavior of wildfires in a certain area.…”

Delineating and Reconstructing 3D Forest Fuel Components and Volumes with Terrestrial Laser Scanning

“…From these measurements, 3D branch and crown reconstruction, spatial distribution and the connectivity of fuels, and any unexplored fuel-related metrics can be quantified from very high spatial resolution 3D point clouds [34]. For example, García et al [35] used TLS to extract fuel attributes including canopy cover, canopy base height (CBH), and fuel strata gaps, while Alonso-Rego et al [36] further extracted canopy fuel load (CFL) and canopy bulk density (CBD) for use in fire behavior models.…”