Abstract
Aim of study: In this study we applied 3D point clouds generated by images obtained from an Unmanned Aerial Vehicle (UAV) to evaluate the uniformity of young forest stands.Area of study: Two commercial forest stands were selected, with two plots each. The forest species studied were Eucalyptus spp. and Pinus taeda L. and the trees had an age of 1.5 years.Material and methods: The individual trees were detected based on watershed segmentation and local maxima, using the spectral values stored in the point cloud. After the tree detection, the heights were calculated using two approaches, in the first one using the Digital Surface Model (DSM) and a Digital Terrain Model, and in the second using only the DSM. We used the UAV-derived heights to estimate an uniformity index.Main results: The trees were detected with a maximum 6% of error. However, the height was underestimated in all cases, in an average of 1 and 0.7 m for Pinus and Eucalyptus stands. We proposed to use the models built herein to estimate tree height, but the regression models did not explain the variably within the data satisfactorily. Therefore, the uniformity index calculated using the direct UAV-height values presented results close to the field inventory, reaching better results when using the second height approach (error ranging 2.8-7.8%).Research highlights: The uniformity index using the UAV-derived height from the proposed methods was close to the values obtained in field. We noted the potential for using UAV imagery in forest monitoring.
Highlights
The major source of wood in Brazil is commercial tree plantations, responsible for 91% of the wood production in the country in the last year (IBGE, 2015; IBÁ, 2016)
The Pinus and Eucalyptus stands have distinct characteristics regarding the density of points generated, which is much higher in the Eucalyptus stand
We found maximum values of 3.10-4.42 m in the Pinus stand, and 4.66-6.24 m in the Eucalyptus stand
Summary
The major source of wood in Brazil is commercial tree plantations, responsible for 91% of the wood production in the country in the last year (IBGE, 2015; IBÁ, 2016). These plantations are mostly composed by species of the genus Eucalyptus and Pinus, which represents, respectively, 72% and 21% of the total planted area (IBÁ, 2016), and from the total wood production, around 41% is used by the pulp and paper companies (IBGE, 2015). According to IBÁ (2016), Brazil has the best productivity rate per year for Eucalyptus and Pinus genus compared to other countries, showing an average growth rate of more than 35 m3 ha-1 year-1 for Ângela M.
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