Abstract
Exact knowledge over tree growth is valuable information for decision makers when considering the purposes of sustainable forest management and planning or optimizing the use of timber, for example. Terrestrial laser scanning (TLS) can be used for measuring tree and forest attributes in very high detail. The study aims at characterizing changes in individual tree attributes (e.g., stem volume growth and taper) during a nine year-long study period in boreal forest conditions. TLS-based three-dimensional (3D) point cloud data were used for identifying and quantifying these changes. The results showed that observing changes in stem volume was possible from TLS point cloud data collected at two different time points. The average volume growth of sample trees was 0.226 m3 during the study period, and the mean relative change in stem volume was 65.0%. In addition, the results of a pairwise Student’s t-test gave strong support (p-value 0.0001) that the used method was able to detect tree growth within the nine-year period between 2008–2017. The findings of this study allow the further development of enhanced methods for TLS-based single tree and forest growth modeling and estimation, which can thus improve the accuracy of forest inventories and offer better tools for future decision-making processes.
Highlights
Tree growth is a result of an increase in the length, diameter, and thickness of tree stem, roots, and branches, leading to changes in the size and form of the tree [1]
The results showed that it was possible to identify stem volume growth with Terrestrial laser scanning (TLS) data acquired at two points of time, in 2008 and 2017
Changes were discerned in attributes characterizing stem form, and gave evidence that TLS point clouds can be used in follow-up measurements for determining stem volume growth
Summary
Tree growth is a result of an increase in the length, diameter, and thickness of tree stem, roots, and branches, leading to changes in the size and form of the tree [1]. Tree growth can be determined through changes in the most typical tree attributes such as diameter at breast height (DBH) and height (h). A diameter can be measured from any height along the stem. Measures of tree DBH and h are used separately or together in addition with tree species in estimating other important single-tree attributes such as the cross-sectional area, stem volume, or biomass of a tree [16,17,18]. Changes in height-specific diameters and h are the most important factors when determining the increment in stem volume or biomass, especially with coniferous trees in question. Periodic measurements of DBH and h are used when estimating the growth of the stem volume, basal area, or cross-sectional area [1]
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