A field test of the accuracy of the Barr and Stroud Type FP-12 optical dendrometer

Abstract

Trees in a 55-year-old stand of Douglas-fir were measured with a Barr and Stroud Type FP-12 dendrometer while standing, then measured with tape and caliper after they were felled. The chi-square test of accuracy for diameters, whether determined according to size, elevation, or distance, fell within a range from ±0.222 to ±0.298 inch, and percentage accuracies varied from ±2.12 to ±3.25. The chi-square test of accuracy for stem lengths decreased from ±0.272 foot (±0.991 percent) at an average elevation of 23.30 feet for an 11.40-foot segment to ±0.782 foot (3.96 percent) for a 14.22-foot average segment at an average elevation of 62.91 feet.This study indicates that upper-stem diameters and segment lengths determined by the Barr and Stroud optical dendrometer are highly accurate under field conditions. Thus, the optical dendrometer provides the forester with a means of eliminating tree-volume tables. Results suggest that, for the first time, volume growth of the upper stem can be accurately determined on standing trees by making repeated measurements over an extended time.