Variable-exponent taper equations for jack pine, black spruce, and balsam fir in eastern Canada

A variable-exponent taper equation was developed for jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana (Mill.) B.S.P.) and balsam fir (Abies balsamea (L.) (Mill.)) trees grown in eastern Canada. The equation was derived from the dimensionally compatible taper equation. Stem analysis data from several of Forintek’s research projects on these tree species grown across eastern Canada were used to fit the taper equation, and the equation was then evaluated with independent data collected by Forintek and other organizations in eastern Canada. The taper equation presented in this paper was superior to the segmented polynomial, variable-exponent, and variableform taper equations developed for different tree species in estimating diameters along the bole. Moreover, stand density or thinning effect on the taper of these tree species was examined, and the taper equation was modified in order to incorporate this effect.