INDIVIDUAL TREE BASAL AREA GROWTH-MODELS FOR YOUNG STANDS OF NORWAY SPRUCE IN SWEDEN

Models for predicting the basal area growth of individual trees of Nor way spruce (Picea abies (L.) Karst.) in young stands in Sweden were de veloped. The models were based on data obtained from 146 operationally planted stands with Norway spruce, mainly established during the 1950 s. The main feature of the study was to compare different approaches t o include site effects in the models (site index or primary site facto rs) Models were developed both with and without site index, competitio n index and tree age included in the functions, There were no apparent differences in fit statistics between models using site index accordi ng to site properties, and models using an independent variable based on average yearly temperature during the growing season. Models based on a distance-dependent competition index and tree age explained about 79% of the variance in basal area increment, while models without dis tance-dependent competition index and tree age explained 74%. Inclusio n of tree age in the models accounted for about 3% of the explained va riation and the competition index for about 2% of the explained variat ion in basal area growth. (C) 1997 Elsevier Science B.V.