Evaluierung von Waldwachstumssimulatoren auf Baum- und Bestandesebene

Using the single tree simulator SILVA 2.2 as an example, methods and results of simulation model evaluation are presented. The paper begins with the definition of model evaluation and validation. Model validation as one important part of model evaluation consists mainly of a comparison between simulation results and observed data and between model behaviour and generally valid growth rules or theories. For Norway spruce the bias, precision and accuracy of simulation results are calculated, using long term experimental plots, permanent and temporary inventory plots in spruce stands as independent references. The diameter growth of single trees in a 5 years period is estimated by SILVA 2.2 with a mean accuracy of 30% to 35%, the corresponding accuracy of the volume growth of stands was 19.8% and the 30 years prognosis of standing volume 11.7%. The results of model validation are strongly influenced by weather conditions if the validation period is choosen too short or limited on special sequences of years.