Predicting the future diameter of stems in Norway spruce stands subjected to different thinning regimes

Abstract

The future diameter of stems in even-aged Norway spruce (Picea abies (L.) Karst.) stands subjected to different thinning regimes was modelled, using data from a thinning experiment established in 25 localities in southern Sweden. Separate models were developed for stands thinned from below, stands thinned from above, and unthinned stands. A bivariate approach was used to construct the models, based on DBH data from the initial stand and from the same trees at future points in time. The approach entails that the dependency between initial and future DBHs can be directly used to predict the future DBH. Also, the modelling used stand and site characteristics together with information about the stand density management regime. The initial stands were assumed to be unthinned, and the dominant height was assumed to be 12–18 m. A logistic function was used to predict which individual trees would remain at future points in time. The mean and standard deviation of the differences between observed and predicted future diameters were used to validate the models. When the prediction period was approximately 33 years, the mean was typically underestimated by 4 mm, and the standard deviation was approximately 40 mm.