Uncertainty in growth and yield projections due to annual variation of diameter growth

Abstract

The growth models used for predictions are usually built to predict growth under average weather conditions. The annual variation in diameter growth may, however, be quite large. Since the annual variation affects the growth of each tree in the same direction, it does not cancel out in larger areas. The aim of this study is to analyze the uncertainty in stand growth and yield projections due to annual variation in tree diameter growth. The annual variation is described with an ARIMA model fitted to a series of growth indices. The diameter growth variation increases the coefficient of variation (CV) of stand volume growth markedly. The CV of stand volume also increases unless the stand is too dense: in a dense forest stand the variation of stand volume is restricted by the predicted self-thinning in the stand. The effect of annual variation on the accuracy of growth predictions is important, especially in short-term predictions. In long-term predictions other components of uncertainty may be more important.