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 our results, the attributes that had the highest variance between appraisers were the Trunk Area and the Condition Rating.

In the presentation, we show the observed variances for each measured input variable and between arborists based on level of experience. We explain some of the possible sources of error, and we offer suggestions for improving the practical application of the trunk formula method.