Mobile laser scanning in support of national and regional forest inventories

In the context of a growing need to diversify forest information, national and regional forest inventories (NFI and RFI) could benefit from mobile Light Detection and Ranging (LiDAR) technologies. Ground-based mobile laser scanning (MLS) and unmanned aerial laser scanning (ULS) can potentially retrieve a large panel of forest attributes quickly, efficiently, and accurately. In this study, conducted in Wallonia (southern Belgium), we aimed to evaluate, in the context of an NFI, the accuracy of MLS at tree, plot, and inventory levels and the potential benefits of fusing ULS with MLS. In total, 60 circular forest plots of 0.1 ha containing 2,497 trees were measured by traditional inventory means and scanned using MLS. Among them, 27 were additionally scanned by ULS, and ULS and MLS scans were fused to produce an enhanced point cloud. We then evaluated the accuracy of MLS considering, at tree level, the diameter at breast height, total height, merchantable wood volume, and crown projected area and volume; at plot level, the total merchantable wood volume, number of trees, and total basal area; and for the whole inventory, the total volume and number of trees. Tree, plot, and inventory metrics were accurately acquired with a strong correlation to field measurements (r2 ranging from 0.83 to 0.98). Out of all estimated metrics, height has a potential accurately estimated by MLS than by field measurements. The fusion of ULS and MLS allowed for a more accurate crown measurement, but height estimation was not significantly better than with MLS scan alone. The accuracy of soft- and hardwood forest plot estimations differed considering total plot wood volume, number of trees, and individual tree height. In this study, we explored the possibility and limitations of MLS in undertaking large-scale inventory in terms of accuracy, time, and reliability.