AN INDIVIDUAL TREE DIAMETER INCREMENT MODEL FOR WHITE SPRUCE IN ALBERTA

Based on a data set from 164 permanent sample plots, an age-independen t individual tree diameter increment model is presented for white spru ce (Picea glauca (Moench) Voss) grown in the boreal mixed-species stan ds in Alberta. The model is age independent in that it does not explic itly require tree or stand age as input variables. Periodic diameter i ncrement is modelled as a function of tree diameter at breast height, total tree height, relative competitiveness of the tree in the stand, species composition, stand density, and site productivity. Because dat a from permanent sample plots are considered time series and cross sec tional, diagnostic techniques were applied to identify the model's err or structure. Appropriate fit based on the identified error structure was accomplished using weighted nonlinear least squares with a first-o rder autoregressive process. Results show that (1) all model parameter s are significant at alpha = 0.05 level, and (2) the plot of studentiz ed residuals against predicted diameter increment shows no consistent underestimate or overestimate for diameter increment. The model was al so tested on an independent data set representing the population on wh ich it is to be used. Results show that the average prediction biases are not significant at alpha = 0.05 level, indicating that the model a ppropriately describes the data and performs well when predictions are made.