Volume system for Picea chihuahuana, Abies durangensis and Pseudotsuga menziesii in northwestern Mexico

Abstract

Picea chihuahuana, an endemic species of northern Mexico, is classified as endangered on the Red List of the International Union for Conservation of Nature (IUCN) and NOM-059-SEMARNAT-2010. Pseudotsuga menziesii is listed under special protection in the same regulation, whereas Abies durangensis faces significant anthropogenic pressure. This study aimed to develop a compatible equation system to estimate stem volume, branch volume, total tree volume with bark, and merchantable volume for these species in northwestern Mexico. A total of 100 trees per species were measured using non-destructive techniques to segment stems and branches. Nine volume equations were fitted for stem volume, as well as several linear and nonlinear models for branch volume. To ensure additivity, the parameters of the equations were simultaneously estimated using the ITSUR procedure, addressing heteroscedasticity and autocorrelation using weighted regression and a second-order continuous autoregressive model. The equations explained over 97 % of the variability in diameter along the stem, 96 % of the merchantable volume at different stem heights, 95 % of the total volume, and 58 % of the branch volume. The developed equations provide a novel tool for analyzing the total tree volume distribution, supporting the management, conservation, and sustainable use of these species.