An Analysis of the Field Precision of the CTLA Trunk Formula Method
James Komen and Donald R. Hodel
Abstract: The CTLA Trunk Formula Method is an industry-standard tool for appraising large trees. The goal of this study was to measure its precision in the field and to look for possible ways to improve the formula or its implementation. Fourteen certified arborists independently appraised the same ten trees, and the results of their appraisals were analyzed. This study focused on the attributes of Trunk Area, Species, Location, and Condition. In the results, the attributes with the highest variance among appraisers were Trunk Area and the Condition Rating. In the past, much of the variation among appraisers has been attributed to personal bias due to lack of experience, and it has been suggested that variance would decrease with experience. These results give evidence to the contrary—the group of appraisers with the highest variance was the group that performed appraisals most frequently. The most valuable information from this study was the identification of four key elements of error involved in the appraisal process: personal value error, personal observation error, measurement error, and systematic error.
Keywords: Cross-Sectional Area; Guide for Plant Appraisal; Measurement Error; Personal Observation Error; Personal Value Error; Rating; Systematic Error; Tree Appraisal; Trunk Formula Method.