Abstract: Primary challenges with a forest inventory program are surveyors with various levels of experience and the turnover of inexperienced surveyors. Few studies have looked at the consistency of an instrument’s results among inexperienced surveyors. Most studies have assessed whether instruments were significantly different. These tests do not indicate whether instruments were statistically equivalent, i.e., that choosing either one would be acceptable under a certain level of tolerance. This study evaluated the consistency and statistical equivalence among instruments for measuring diameter at breast height (DBH) and for total tree height (HT) among inexperienced surveyors. The study was conducted as a randomized experiment with students from an introductory tree measurement course, using four types of DBH and HT instruments, and with different tree attributes. For DBH, the results show that D-tape was the most consistent across tree attributes and teams of inexperienced surveyors and was only statistically interchangeable with Caliper with a tolerance ≥ 3 cm. For HT, Ultrasound was the most consistent but only statistically interchangeable with Laser with a tolerance ≥ 8 m. A single type of instrument for measuring DBH and for HT is recommended, especially when field crews may be a mixture of experienced and inexperienced surveyors. Our study provides initial recommendations on the choice of instruments when either purchasing new ones or replacing old ones in forest inventories.

Key words: Biltmore stick, Bitterlich Treemeter, Clinometer, Test of equivalence, Tree measurements