An Open-Source Handheld Mobile LiDAR Pipeline for Tree Detection, Stem Reconstruction and Volume Estimation in Pinus pinaster Stands

Forests play a critical role in biodiversity and in the conservation of ecosystems. Reliable and efficient forest inventories are therefore essential for sustainable forest management. Handheld mobile laser scanning (HMLS) is operationally attractive for forest inventory but has rarely been validated against a destructive reference in Mediterranean Pinus pinaster stands. We propose an open-source five-phase HMLS pipeline comprising PDAL pre-processing with CSF ground classification, TLS2trees segmentation, CSF-anchored per-tree setup, slice-wise stem reconstruction with a sequential RANSAC prior, a one-parameter species-specific shape model, and analytical volume integration with a form-factor sanity clamp. The pipeline is calibrated against a destructive reference of 45 Pinus pinaster trees across four plots in central Portugal. Leave-one-plot-out cross-validation produces a volume MAPE of 9.9%, a height MAPE of 4.4% and a DBH MAPE of 3.9%. On the matched sub-sample for which the FJD Trion S1 manufacturer software and a manual CloudCompare workflow also have outputs, the proposed pipeline is competitive with the manual workflow on volume and delivers the lowest median DBH error of the three methods, while remaining fully open-source and reporting per-tree quality and uncertainty diagnostics alongside every estimate.