Arboriculture & Urban Forestry 48(6): November 2022 requirement of the use of a rangefinder is the ability to send an unimpeded laser pulse from the range- finder to the tree’s trunk. Alternative methods have also been made avail- able for assessing height using electronic tools, includ- ing the use of smartphone apps. A study by Vastaranta et al. (2015) found that apps underestimated tree heights, reporting height biases between 5.0% and 8.3% and underestimations between 1.0 and 1.8 m. Within the scholarly literature on more technolog- ically complex height measurement methods, studies have tested the accuracy of aerial and terrestrial laser scanning (Wang et al. 2019); laser scanning and unmanned aerial vehicle (UAV) photogrammetry against handheld laser scanning (Jurjević et al. 2020); smartphone applications in comparison to traditional and spatial methods (Pace et al. 2022); the accuracy of LiDAR against other tree height mensuration methods (Sibona et al. 2017); and the precision of mensurationists in measuring tree height and DBH (Luoma et al. 2017). For the purposes of this study, the stick, clinome- ter, and laser rangefinder methods have been selected based on their wide usage among arboriculture and urban forestry operations. The accuracy and precision of these tree height measurement tools are of impor- tance to those undertaking inventories: for field-based arborists and loggers attempting to determine the fell- ing radius of the tree, and for the education of stu- dents trying to learn the methods of tree mensuration. For the purposes of this study, accuracy is defined as the proximity of the measured height to the true height. Precision is defined as the consistency of mea- sured height values across all 3 methods. While a study by Saliu et al. (2021) examines the accuracy and precision of tree height mensuration methods in measuring mangrove trees, this study seeks to examine the accuracy and precision of tree height mensuration methods in urban forest sites and to evaluate the influence of boreal forest conifer or broadleaf tree types on accuracy and precision of measurements. Two research questions are examined in this paper: (1) “How do accuracy and precision compare between different methods and the established height of the tree?”, and (2) “How does the performance of height measurement tools compare between conifers and broadleaf trees?” MATERIALS AND METHODS Sample Sites and Tree Selection A member of the research team randomly selected and recorded the coordinates of 255 trees at 8 loca- tions within the Rural Municipality of Victoria Beach, Manitoba, Canada, based on a proportionate sam- pling of the number of accessible trees located at each location (i.e., no trees on private property or in enclosed areas). The selection was controlled such that a clear sight of the tree trunk was always estab- lished from at least 1 side of the tree, a clear view of the treetop was present, and no noticeable lean was present. The selected trees were comprised of 136 (53.33%) broadleaf trees and 119 (46.67%) conifer- ous trees. A randomized selection of 127 trees (49.80% of the original sample) was taken from the 255 trees of the proportionate sample. The member of the research team who selected the original 255 trees was not aware of the research question being tested. This methodology and randomized selection procedure were done to reduce selection bias, as it was con- ceived that measurers on the research team might oth- erwise select easy-to-measure trees (i.e., excurrent or fastigiate trees with live crown tops). From the 127 trees selected for testing, 71 trees (55.9%) were located in municipal parks, 36 trees (28.3%) were located at the municipal golf course, 16 trees (12.6%) were located along municipal roads (i.e., “street trees”), and 4 trees (3.1%) were located along a forest trail. There were 85 (66.9%) broadleaf trees and 42 (33.1%) coniferous trees. Height Measurement Methods To examine the research questions, 3 methods were tested for measuring tree height: the stick method, cli- nometer (SUUNTO PM-5 Clinometer; Suunto Oy; Vantaa, Finland), and laser rangefinder (Forestry Pro II Laser Rangefinder/Hypsometer; Nikon Vision Co., Ltd.; Tokyo, Japan). A drone (Mavic Air 2; Shenzhen DJI Science and Technologies Ltd.; Shenzhen, China) was used to determine the absolute tree height using an adapted technique from Saliu et al. (2021). Where Saliu et al. (2021) used a Leica distometer (Leica Geosystems; Heerbrugg, Switzerland) to measure to the base of the drone, this study used a measuring line attached to the base of the drone. The drone was flown to the height of the tree and evaluated using a camera mounted on the drone, consistent with the ©2022 International Society of Arboriculture 321
November 2022
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