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Compatible stem taper and volume models were developed for Brutian pine (Pinus brutia Ten.), Cedar of Lebanon (Cedrus libani A. Rich.), and Cilicica fir (Abies cilicica Carr.) in Bucak forest region of Southern Turkey. The proposed models generally performed better for the whole tree for all tree species. Diameter and volume predictions at 10 points along the stem were made to verify the accuracy and precision of these models for the three species. More specifically, differences among different tree species in one region and regional differences of the taper equation were examined using the nonlinear extra sum of squares method. The results of the non-liner extra sum of squares method indicated that species-specific taper equations for estimating diameters along the stem and predicting merchantable or total volume for each region are required.

The Max and Burkhart segmented taper model was fitted using nonlinear mixed-effects modeling techniques to account for within- and between-individual stem profile variation for Lebanon cedar ( Cedrus libani A. Rich.), brutian pine ( Pinus brutia Ten.), and cilicica fir ( Abies cilicica Carr.) in Turkey. About 75% of the trees were randomly selected for model development, with the remainder used for model validation. Diameter measurements from various heights were evaluated for tree-specific calibrations by predicting random-effects parameters using an approximate Bayesian estimator. The procedure was tested with a validation dataset. Predictive accuracy of the model was improved by including random-effects parameters for a new tree based on upper stem diameter measurements. Prediction in stem diameter was less biased and more precise across the all sections of bole when compared to predictions based only on fixed-effects parameters. In the future, the proposed mixed models can be applied to region wide three species stands by fitting the model to a larger data set that more closely represents regional variation. [ABSTRACT FROM AUTHOR]