DEVELOPMENT OF A TREE MODEL APPLIED TO TH E GROWTH OF IRREGULAR HARDWOOD STANDS IN SOUTHERN BELGIUM

A model predicting circumference growth of individual trees has been d eveloped for mixed irregular stands dominated by Fagus silvatica L. in southeastern Belgium. This model integrates simultaneously tree, stan d, and growing site characteristics without considering distances betw een individual trees. It has a determination coefficient of 40.1% and a residual standard deviation of 0.45 cm/year. Forest mensuration vari ables considered in the model are circumference, tree social position represented by the total basal area of trees greater than the subject tree, stand basal area, and some index of stand structure correspondin g to the ratio of the variance over the mean circumference. The site c omponent is essentially expressed by the length of the growing period. The low accuracy obtained for individual tree growth is relative beca use the results are used mainly after individual trees have been distr ibuted into size classes. We have been able to show that the introduct ion of crown description in the model can increase its accuracy. But t his modification requires a submodel describing crown changes over tim e.