Assessing Precision in Conventional Field Measurements of Individual Tree Attributes

Abstract

Abstract:Forest resource information has a hierarchical structure: individual tree attributes are summed at the plot level and then in turn, plot-level estimates are used to derive stand or large-area estimates of forest resources. Due to this hierarchy, it is imperative that individual tree attributes are measured with accuracy and precision. With the widespread use of different measurement tools, it is also important to understand the expected degree of precision associated with these measurements. The most prevalent tree attributes measured in the field are tree species, stem diameter-at-breast-height (dbh), and tree height. For dbh and height, the most commonly used measuring devices are calipers and clinometers, respectively. The aim of our study was to characterize the precision of individual tree dbh and height measurements in boreal forest conditions when using calipers and clinometers. The data consisted of 319 sample trees at a study area in Evo, southern Finland. The sample trees were measured independently by four trained mensurationists. The standard deviation in tree dbh and height measurements was 0.3 cm (1.5%) and 0.5 m (2.9%), respectively. Precision was also assessed by tree species and tree size classes; however, there were no statistically significant differences between the mensurationists for dbh or height measurements. Our study offers insights into the expected precision of tree dbh and height as measured with the most commonly used devices. These results are important when using sample plot data in forest inventory applications, especially now, at a time when new tree attribute measurement techniques based on remote sensing are being developed and compared to the conventional caliper and clinometer measurements.

A Case Study of UAS Borne Laser Scanning for Measurement of Tree Stem Diameter

“…A robust cylinder fit was applied to the points on the tree stems in six circular plots in an alluvial forest. [23] stated for the manual DBH measurements an accuracy of about 1.5%, which is almost the same level achieved here for the calculated DBH from the UAS LiDAR for trees with DBH > 30 cm. For small stems with DBH < 30 cm the DBH estimation becomes more challenging due to random and systematic errors, i.e., ranging accuracy and co-registration of the strips.…”

Use of Multi-Temporal UAV-Derived Imagery for Estimating Individual Tree Growth in Pinus pinea Stands

“…However, some field measurements, such as h and ca, have unavoidable associated error and large variation [2,[4][5][6] and thus may not be suitable for validation of the SfM-derived tree growth measurements, especially in dense stands or for trees which do not have well-defined top [70]. In our study, h SfM was less variable than field-based measurements in both 2015 and 2017.…”

Nondestructive Estimation of the Above-Ground Biomass of Multiple Tree Species in Boreal Forests of China Using Terrestrial Laser Scanning

“…The DBH and tree height values obtained from point cloud data were also compared with those obtained from field measurements. Analysis of variance (ANOVA) was used to test whether the differences in DBH and tree height estimates were statistically significant at the 95% level of significance, and to analyze DBH and tree height, respectively [41]. The linear regression models between estimates and reference values are also used to show the differences between estimates and reference values.…”