Preussner functions for volume estimation of Pinus taeda L. in Southern Brazil

Background: Taper modelling and volume estimation are key procedures in the management and planning of planted forests. The objective of this work was to evaluate the taper and volume behaviour of Pinus taeda L. species, along the stem in different ages, using the Preussner taper functions, compared to Schopfer's Th-polynomial, Kozak's and Max-Burkhart's models. This work focused on plantations of Pinus taeda L., due to its wide use as a source of raw material in the forest industry of southern Brazil. Methods: The data were collected in the last 22 years from the Midwest region of Santa Catarina, of trees ranging in age from 3.5 to 18 years. This dataset consisted of a collection of volume sections, with relative diameter measurements along the stem, used in conventional forest inventory. The total volume of the trees, obtained by integrating the Preugner taper functions, was equated by dividing the stem into four parts, in which parabolas were fitted, and compared with the total and merchantable volume estimated by Schopfer's 5th-degree polynomial, Kozak's and Max-Burkhart's functions. Results: Bias, RMSE and r were generally better with the application of Kozak's model, and AIC and BIC for the Preussner's model. Conclusions: Kozak functions were better to provide the merchantable volume. In terms of total volume both functions, Kozak and Preussner, provided reliable estimates. The advantage of the procedure proposed by Preussner is the flexibility of the fitted taper functions, the simplicity of volume calculations by integration, and the feasibility for interpreting their coefficients.