Predicting the growth of stands of trees of mixed species and size: A matrix model for Norway

The objective of this study was to predict the growth of forest stands of mixed tree species and size with natural recruitment. The stand state was defined by the number of spruce, pine, birch and other broadleaved trees by hectare in 15 diameter classes from 50 to 750 mm. The change in stand state over 5 years was predicted with state-dependent matrices based on equations for recruitment, growth and mortality. The data came from 7241 plots of the National Forest Inventory of Norway, measured from 1994 to 2005. A short-term validation was carried out by comparing predicted and actual growth over 10 years on 416 plots not used in model estimation. The model was also used to predict the long-term growth of stands with different initial species composition and diameter distribution. Irrespective of the initial condition the same steady state resulted, with characteristics similar to those observed in stands that had been undisturbed for 75 years.