High spatial resolution imagery provided by unmanned aerial vehicles (UAVs) can yield accurate and efficient estimation of tree dimensions and canopy structural variables at the local scale. We flew a low-cost, lightweight UAV over an experimental Pinus pinea L. plantation (290 trees distributed over 16 ha with different fertirrigation treatments) to determine the tree positions and to estimate individual tree height (h), diameter (d), biomass (wa), as well as changes in these variables between 2015 and 2017. We used Structure from Motion (SfM) and 3D point cloud filtering techniques to generate the canopy height model and object-based image analysis to delineate individual tree crowns (ITC). ITC results were validated using accurate field measurements over a subsample of 50 trees. Comparison between SfM-derived and field-measured h yielded an R² value of 0.96. Regressions using SfM-derived variables as explanatory variables described 79% and 86–87% of the variability in d and wa, respectively. The height and biomass growth estimates across the entire study area for the period 2015–2017 were 0.45 m ± 0.12 m and 198.7 ± 93.9 kg, respectively. Significant differences (t-test) in height and biomass were observed at the end of the study period. The findings indicate that the proposed method could be used to derive individual-tree variables and to detect spatio-temporal changes, highlighting the potential role of UAV-derived imagery as a forest management tool.

Understory management practices and stand density characteristics allow one to distinguish a cork oak traditional silvopastoral system (known as a montado) from a cork oak forest system. Although understanding the manner in which different management practices affect cork growth is imperative, there are still only a few outputs from experimental research that contribute to this knowledge. The effect of potential drivers on annual cork growth was analyzed using a linear mixed model approach. Two dimensions of drivers were considered: intraspecific competition, assessed by tree level distance-dependent indices; and interspecific competition, assessed by variables characterizing understory management. The present dataset was collected from an experimental trial established on a cork oak stand in Podzolic soil on the Tagus river basin, covering two different cork growth cycles over the period from 2003 to 2015. The adjusted models considered two understory management alternatives: spontaneous shrubs maintenance and forage application. In both models, annual precipitation displayed a positive effect on annual cork growth, as expected. However, no significant effect of intraspecific competition was found. Additionally, there was a positive effect on annual cork growth associated with the spontaneous shrubs growth and a negative effect associated with lupine presence; both effects linked to different cork ring ages’ thresholds. The study main contributions are the following: (i) the introduction of the interaction between cork growth cycle stage and understory management practices, only possible with cork sample collections from different cork rotation cycles; (ii) the finding that there was no significant effect of intraspecific competition on cork growth.

Aim of study: Cork oak is one of the main forest tree species in Portugal that typically occurs in montado, where operational practices oriented to the tree, crop or animal management may influence several of the ecosystem components. This study aimed at contributing to fulfil the a lack of knowledge on the effect of these practices on the cork and wood growth, by comparing the wood diameter growth and the annual cork increment under two different understory management options.Material and methods: An experimental trial implemented on an uneven-aged cork oak pure stand during a cork rotation period of 9 years, was established with the specific goal of comparing understory management options: a yellow lupine pasture versus spontaneous vegetation. Cork samples were taken at the beginning and end of the period and were used to measure cork thickness and annual cork rings. The differences between treatments were assessed performing a non-parametric test and a more robust approach using linear mixed model. Precipitation and treatment levels were jointly considered on the analysis.Main results: A slight effect was found on the cork thickness regarding the treatment with lupine application. However, no distinct effect was found, regarding wood and the annual cork increment pattern. Additionally, annual cork ring width showed a positive correlation with precipitation and a negative correlation with ring age.Research highlights: The results of this study indicate no distinct pattern regarding the annual cork and wood increment when comparing the understory effect of yellow lupine pasture versus spontaneous vegetation.