A site‐index model for pure and mixed stands ofBetula pendulaandBetula pubescensin Sweden

A site‐index model was constructed based on stem analysis data for 266 top‐height trees of Betula pendula Roth and Betula pubescens Ehrh. growing on 155 temporary sample plots and 12 remeasured, permanent sample plots in pure and mixed stands scattered throughout Sweden. Different growth functions and techniques for modelling the top‐height growth over breast‐height age were assessed. A difference model based on the Hossfeld IV growth equation performed best, and its practical application was therefore recommended. For birch stands over 40 yrs of age, top‐height growth predicted by the new model was significantly slower than that predicted by a site‐index model used previously.