Stem taper equations for diameter and volume predictions of Abies cilicica Carr. in the Taurus Mountains, Turkey

Abstract

Taper equations are an important tool in estimating stem volumes at a multi-product level for sustainable forest management. Nine taper equations are tested from three categories to estimate diameter at specified point on the stem, height at specified diameter, volumes of any desired portion of the stem, and whole tree volume of Taurus fir in Taurus Mountains of Turkey. To account for autocorrelation and multicollinearity present among multiple stem data observations collected from the same tree, proper statistical approaches were used in model fitting. Comparisons are made to determine which equation provides the best overall fit to all data based on four goodness-of-fit statistics, Coefficient of determination (R2); Root mean square error (RMSE), Akaike’s Information Criterion (AIC), and Bayesian information criterion (BIC). Results indicated that all taper equations tested could be used to accurately estimate section diameter at given height and stem volume. Clark et al.’s taper equation provided better results than the others for Taurus fir when an additional stem diameter observation at 5.30 m was available. Segmented and variable-form taper models consistently provided better results than the simple taper models except for Max and Burkhart’s model. Fang et al.’s and Kozak’s taper models showed equally good performance to describe stem taper and to predict tree stem volume. Therefore, these taper equations are able to be used to estimate diameter and volume for Taurus fir trees, if an upper stem diameter measurement was not available.