Testing accuracy of log volume calculation procedures against water displacement techniques (xylometer)

Abstract

The accuracy of three traditional formulas to calculate log volumes (Smalian, Huber, and Newton) and three recent methods (cubic splines, centroid sampling, and overlapping bolts) were compared and tested against volumes determined by the water-displacement technique (xylometer). Fifty-two felled trees were measured in a Pinus elliottii Engelm. plantation. The accuracy of these six procedures was analyzed considering total and merchantable outside bark volumes with 1-, 2-, 4-, and 6-m log lengths. The results showed that Huber's formula was superior for all volumes and log lengths considered. Centroid and Newton had a similar performance to Huber but with some higher errors. As expected, Smalian was the procedure with the worst performance. When log lengths of 1 and 2 m were employed, all procedures used to calculate total volume presented errors lower than 4.77%. However, the errors increased when the merchantable volume involves a large top diameter (veneer volumes, for example) or for calculating volumes from trees with large diameters. The results of this and other research have shown that Huber's formula has been accurate for several species, ages, geographic regions, etc. Thus, Huber's formula could be used in the majority of circumstances with log lengths greater than 2 m, reducing drastically the costs and sampling effort.