Relative Accuracy of a New Base-Age Invariant Site Index Model

A new base-age invariant site index model was developed based on the constrained version of the Chapman-Richards function. It was compared with that of Goelz and Burk's (1992) in terms of relative accuracy and average bias across a range of potential base ages. The data format for fitting the above models was also simplified. Comparing the models on a set of white spruce (Picea glauca [Moench] Voss) stem analysis data indicated that the choice of predictor age influences the models' accuracy and bias. Except for very young ages, the new model performed as well as that Goelz and Burk's (1992) model in relative accuracy. For. Sci. 40(2):341-348.