Merchantable volume system for Populus x euramericana (Dode) Guinier cv. ‘I-214’ plantations in central and northern Spanish plateau
AbstractA model is required to accurately estimate the merchantable volume of the poplar clone more widely used in Spain (Populus x euramericana cv. ‘I-214’). The present study was therefore carried out to obtain equations for predicting merchantable volume of this poplar clone. Data from 1,289 sampled trees collected in experimental plots, installed by INIA in central Spain, were available for analysis. The volume system fitted allows determining volume to a minimum diameter or height which establishes a merchantability threshold. Also two taper functions were derived to predict the diameter outside bark along the stem and the height at which that diameter occurs. A third-order continuous autoregressive error structure was used to account for autocorrelation. Weighted non linear regression was used to take into account the problem of heteroscedasticity observed in the volume equations. Comparison of the models was carried out using overall goodness-of-fit statistics (R2 and RMSE) and box plots of residuals against position or diameter classes.
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