Assessing the effects of thinning on stem growth allocation of individual Scots pine trees

Abstract

Forest management alters the growing conditions and thus further development of trees. However, quantitative assessment of forest management on tree growth has been demanding as methodologies for capturing changes comprehensively in space and time have been lacking. Terrestrial laser scanning (TLS) has shown to be capable of providing three-dimensional (3D) tree stem reconstructions required for revealing differences between stem forms and growth allocation. In this study, we used TLS-based 3D reconstructions of tree stems to investigate how forest management (i.e., varying thinning treatments and the following growth effects) has affected stem size and form of Scots pine (Pinus sylvestris L.) trees. The results showed that intensive thinning resulted in more stem volume and therefore total biomass allocation and carbon uptake compared to the moderate thinning. Scots pines growing in plots from which suppressed trees were removed (i.e., thinning from below) had larger bottom part of stems (i.e., volume accumulated more below 50% of tree height) compared to Scots pines growing in plots from which part of the dominant trees had been removed (i.e., thinning from above). Furthermore, intensive thinning, especially from below, produced less variation in relative stem attributes characterizing stem size and form. Thus, it can be concluded that thinning intensity, type, and the following growth effects have an impact on post-thinning stem growth as well as stem form of individual Scots pine trees. Our study presented detailed measurements on postthinning growth of Scots pines that have been laborious or impracticable before the emergence of TLS technology. Moreover, TLS-based stem reconstructions provided variety of attributes characterizing stem growth allocation that have not traditionally been feasible to obtain. The study demonstrated that TLS technology can be used to generate new knowledge for supporting forest management and silviculture as well as improving ecological understanding of boreal forests.

Performance of terrestrial laser scanning to characterize managed Scots pine (Pinus sylvestris L.) stands is dependent on forest structural variation

“…thinning from below, thinning from above, systematic thinning from above) with two levels of thinning intensity (i.e. moderate, intensive) resulting in six different thinning treatments (see (Saarinen et al, 2020)).…”

“…A multi-scan approach was used in the TLS campaign to ensure point cloud quality and completeness with sufficient digitization of the trees within the sample plots. The scan setup consisted of two centre scans placed a few meters apart from each other near the plot centre, and six auxiliary scans placed closer to the plot borders making eight scanning locations in total (Saarinen et al, 2020) (see Fig. 1).…”

Detailed point cloud data on stem size and shape of Scots pine trees

“…Detailed and quantitative information on stem size and shape has not been available for studies investigating variation in tree architecture as well as the effects of forest management and resultant growing conditions. Thus, 3D point cloud data were acquired for investigating the effects of different thinning treatments on stem size and shape of Scots pine (Pinus Sylvestris L.) trees without the need for destructive sampling (Saarinen et al 2020a). The data set (Saarinen et al 2020b) includes point cloud data from Scots pine trees from sample plots with different thinning treatments from southern Finland.…”

Multisensorial Close-Range Sensing Generates Benefits for Characterization of Managed Scots Pine (<em>Pinus sylvestris </em>L.) Stands

“…The multisensorial point cloud data consisted of TLS point clouds and photogrammetric UAV point clouds. TLS data acquisition was carried out with Trimble TX5 3D laser scanner (Trimble Navigation Limited, USA) for all three study sites between September and October 2018 (see [44]). Eight scans were placed to each sample plot and scan resolution of point distance approximately 6.3 mm at 10-m distance was used.…”

“…Site fertility for all of the sample plots is mesic heath. The tree-level field inventory data consisted of 2102 Scots pine trees that were measured using callipers and clinometers [27,44] with expected precision of 0.3 cm for diameter-atbreast height (dbh) and 0.5 m for tree height [27]. The plot-level forest structural attributes were computed based on tree species and measured dbh and height.…”