Estimating Stem Volume in Eucalyptus Plantations Using Airborne LiDAR: A Comparison of Area- and Individual Tree-Based Approaches

• Published in: Remote sensing (Basel, Switzerland) Switzerland), 2020-05, Vol.12 (9), p.1513
• Main Authors: Leite, Rodrigo Vieira, Amaral, Cibele Hummel do, Pires, Raul de Paula, Silva, Carlos Alberto, Soares, Carlos Pedro Boechat, Macedo, Renata Paulo, Silva, Antonilmar Araújo Lopes da, Broadbent, Eben North, Mohan, Midhun, Leite, Hélio Garcia
• Format: Article
• Language: English
• Subjects: Accuracy; Algorithms; Artificial neural networks; Canopies; Carbon sequestration; Estimates; Estimation; Eucalyptus; Lasers; LiDAR; machine learning; Morphology; Mountain regions; Neural networks; Plantations; remote sensing; Sensors; Software; Stems; Studies; Support vector machines; Timber; tree detection; Trees
• ISSN: 2072-4292; 2072-4292
• DOI: 10.3390/rs12091513

Forest plantations are globally important for the economy and are significant for carbon sequestration. Properly managing plantations requires accurate information about stand timber stocks. In this study, we used the area (ABA) and individual tree (ITD) based approaches for estimating stem volume in fast-growing Eucalyptus spp forest plantations. Herein, we propose a new method to improve individual tree detection (ITD) in dense canopy homogeneous forests and assess the effects of stand age, slope and scan angle on ITD accuracy. Field and Light Detection and Ranging (LiDAR) data were collected in Eucalyptus urophylla x Eucalyptus grandis even-aged forest stands located in the mountainous region of the Rio Doce Valley, southeastern Brazil. We tested five methods to estimate volume from LiDAR-derived metrics using ABA: Artificial Neural Network (ANN), Random Forest (RF), Support Vector Machine (SVM), and linear and Gompertz models. LiDAR-derived canopy metrics were selected using the Recursive Feature Elimination algorithm and Spearman’s correlation, for nonparametric and parametric methods, respectively. For the ITD, we tested three ITD methods: two local maxima filters and the watershed method. All methods were tested adding our proposed procedure of Tree Buffer Exclusion (TBE), resulting in 35 possibilities for treetop detection. Stem volume for this approach was estimated using the Schumacher and Hall model. Estimated volumes in both ABA and ITD approaches were compared to the field observed values using the F-test. Overall, the ABA with ANN was found to be better for stand volume estimation ( r y y ^ = 0.95 and RMSE = 14.4%). Although the ITD results showed similar precision ( r y y ^ = 0.94 and RMSE = 16.4%) to the ABA, the results underestimated stem volume in younger stands and in gently sloping terrain (