Distance-dependent models for predicting the development of mixed coniferous forests in Finland

Distance-dependent growth models and crown models, based on extensive mater ial, were built for Scots pine and Norway spruce growing in a mixed forest. The crown ratio was also used as a predictor in a diameter growth model to better describe the thinning reaction. The effect of crown ratio on the gr owth dynamics was studied in simulation examples. Monte Carlo simulation wa s used to correct the bias caused by nonlinear transformations of predictor s and response. After thinnings the crown ratio as a predictor was found to be a clear growth-retarding factor. The growth retarding effect was strong er among pines with thinnings from below, whereas the estimated yield of sp ruces over rotation was slightly greater when the crown ratio was included than without it. With each type of thinning the effect of crown ratio on pi ne growth was almost the same, but the growth of spruces was clearly delaye d when the stand was thinned from above. Simulation examples also showed th at it is profitable to raise the proportion of spruces during rotation, sin ce spruces maintain the growth more vigorous at older ages. The total yield during 90 years rotation was about 20 % higher if the stand was transforme d into a pure spruce stand instead of pine.