EFFECTS OF UPPER STEM MEASUREMENTS ON THE PREDICTIVE ABILITY OF A VARIABLE-EXPONENT TAPER EQUATION

Like several other taper equations, the predictive ability of Kozak's (1988. Can. J. For. Res. 18: 1363-1368) variable-exponent taper equati ons can also be improved by an additional upper stem outside bark diam eter measurement. This study indicated that improvements were small an d were mainly restricted to increasing the precision of the estimates. Also, it was demonstrated that if additional diameter measurements ar e justified, they should be taken between 40 and 50% of the height abo ve breast height for greatest improvement. Measurement errors in upper stem diameters and in their heights above breast height affected both the precision and bias of predictions.