Generalized height-diameter models for Populus tremula L. stands

Using permanent sample plot data, selected tree height and diameter functions were evaluated for their predictive abilities for Populus tremula stands in Turkey. Two sets of models were evaluated. The first set included five models for estimating height as a function of individual tree diameter; the second set also included six models for estimating height as a function of individual tree diameter and some stand-level-attributes. The inclusion of the stand-level-attributes (basal area, dominant height, dominant diameter, number of trees) and BAL index (which simultaneously indicates the relative position of a tree and stand density) into the base height-diameter models increased the accuracy of prediction for P. tremula. As a result, the second set models gave high performance than the first models. On average, by including stand level attributes, root mean square values were reduced by 21 cm. In the second set, the best results were obtained by the Schnute's function. In this function, dominant diameter and dominant height independent variables in addition to tree diameter were found significant at 0.01 significant level (R-2 = 0.949, S-y,S-x = 1.226, P < 0.01). Root mean square was reduced 35 cm Schnute's function alone. Thus, a generalized height-diameter model based on Schnute's function was developed for P. tremula L. stands in Turkey. Based on the residual plots and fit statistics, the model can be recommended for estimating tree heights for P. tremula L. in Turkey. The model coefficients are documented for future use.