COMPATIBILIDADE ENTRE O VOLUME TOTAL DO MODELO DE SPURR E FUNÇÃO DE AFILAMENTO PARA Pinus elliottii ENGELM

Abstract

This study evaluated the compatibility between total volumes estimated by taper functions and by a traditional volumetric model for Pinus elliottii Engelm trees, both tapped for resin and untapped. The hypothesis investigated was that resin tapping alters stem form, compromising the equivalence between volumetric estimation methods. The data were collected from plantations in the southern region of Rio Grande do Sul, Brazil, with 28 years of age. Taper equations from Schöepfer (1966) and the modified Kozak (1969) model were fitted, as well as the Spurr volumetric model. Compatibility was achieved by incorporating a constant (𝑐), extracted from the taper function, into the Spurr model. The equations showed satisfactory fits (adjusted R² > 0.92; Syx% < 16%), and the constant 𝑐 successfully harmonized total volume estimates. The absolute mean difference between the volumes from the harmonized models was less than 0.02 m³, with a mean percentage error below 4%. Residual analysis indicated greater divergence between groups in larger diameter classes, suggesting an influence of resin tapping on stem form. The methodology was also validated with out-of-sample data, demonstrating robustness. It is concluded that the use of the constant 𝑐 is effective in harmonizing volumetric and taper functions, providing more consistent estimates, especially in inventories under different management regimes.