Effect of the interaction between user experience and hypsometer type on the uncertainty of ground-based tree height measurement

Abstract The ground-based measurement of tree height is a basic routine to collect data for estimating volume, biomass and carbon content in forest ecosystems. It can be assumed that user experience and the applied hypsometer introduce a level of uncertainty to these measurements which is yet not fully understood. The main goal of the present study was to evaluate the impact of two levels of user experience (novice and experienced) and two commonly used types of hypsometers (analog Suunto and ultrasonic Vertex) on the accuracy and precision of ground-based tree height measurement. The experiment included a total of 609 height measurements of 18 individual of silver fir trees, performed by 198 operators who had been classified as novice and three operators who had been classified as experienced. The relative and absolute percentage error of each measurement was calculated by introducing a straightforward and efficient method for determining the reference tree height based on projecting the tree apex on the ground. A mixed-model approach was employed to control for additional factors, including the tree height, tree lean magnitude and direction and terrain slope. It was found that none of the hypsometers exhibited substantial bias. However, the precision of the measurements was found to be influenced by the interaction between the user experience and the type of hypsometer. Novice users tended to be slightly biased (−1.7%) and 2.5–3.5 times less precise than experienced users when using either the Vertex or Sunnto hypsometer.