COMPARISON OF NONLINEAR HEIGHT DIAMETER FUNCTIONS FOR MAJOR ALBERTA TREE SPECIES

Twenty nonlinear height-diameter functions were fitted and evaluated for major Alberta species based on a data set consisting of 13 489 felled trees for 16 different species. All functions were fitted using weighted nonlinear least squares regression (w(i) = 1/DBH(i)) because of the problem of unequal error variance. The examination and comparison of the weighted mean squared errors, the asymptotic t-statistics for the parameters, and the plots of studentized residuals against the predicted height show that many concave and sigmoidal functions can be used to describe the height-diameter relationships. The sigmoidal functions such as the Weibull-type function, the modified logistic function, the Chapman-Richards function, and the Schnute function generally gave the most satisfactory results.