Development of ecoregion-based merchantable volume systems for Pinus brutia Ten. and Pinus nigra Arnold. in southern Turkey

Estimating individual tree volume is one of the essential building blocks in forest growth and yield models. Ecologically based taper equations provide accurate vol- ume predictions and allow classification by mer- chantable sizes, assisting in sustainable forest management. In the present study, ecoregion-based compatible volume systems for brutian pine and black pine in the three ecoregions of southern Turkey were developed. Several well-known taper functions were evaluated. A second- order continuous-time autoregressive error structure was used to correct the inherent autocorrelation in the hierar- chical data, allowing the model to be applied to irregularly spaced and unbalanced data. The compatible segmented model of Fang et al. （For Sci 46：1-12, 2000） best described the experimental data. It is therefore recommended for estimating diameter at a specific height, height to a specific diameter, merchantable volume, and total volume for the three ecoregions and two species analyzed. The nonlinearextra sum of squares method indicated differences in ecoregion and tree-specific taper functions. A different taper function should therefore be used for each pine spe- cies and ecoregion in southern Turkey. Using ecoregion- specific taper equations allows making more robust esti- mations and, therefore, will enhance the accuracy of diameter at different heights and volume predictions.

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

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.