Predicting height-diameter relationship in uneven-aged stands in Finland

Abstract

Rotation forestry has been the main management practice in Finland for the last 50 years, and the modelling of forest growth and yield is mainly based on even-aged stands. Increasing demands for wider application of continuous cover forestry result in the need for models that are applicable to uneven-aged stands. The existing Finnish height-diameter models showed the need for new models or relatively intensive calibration of the existing Näslund's model. Four alternative height curves were tested, namely Näslund's, Prodan's, Hossfeld's and Richards' functions. However, new modifications were implemented for realistic behaviour with small trees. Prediction models were formulated to include stand basal area, basal area-weighted mean dbh and Lorey's height. Including the temperature sum to either intercept or asymptote affected the level of the curve but not its shape. The evaluation of the models showed a good fit with uneven-aged modelling data (ERIKA), but less accurate performance in the test data sets of recently established uneven-aged stand plots on mineral soils or on peatlands. On peatland stands, the existing Näslund's model for even-aged stands performed better than any of the new height-dbh model for uneven-aged stands. This is probably because the growth of smaller trees has recovered better than that of older trees after drainage.