Performance Analysis of a Process-based Stand Growth Model Using Monte Carlo Techniques

The performance of a carbon-balance model of tree growth is analysed, using a generalized sensitivity test based on Monte Carlo techniques. The tree growth model allocates carbon to different biomass compartments according to the principle of functional balance and the pipe-model theory. A simple stand-level version of the model is presented, based on average tree growth and canopy interactions through shading. Plausible ranges of parameter values are estimated from the literature for Scots pine. The results are compared with yield tables for 4 growing sites, and the most critical parameters and assumptions with respect to model validity are identified. The results indicate that a better understanding of the formation of the woody structure of trees is crucial for the further development of the approach. More reliable data are necessary on the parameters related with sapwood respiration and senescence. Secondly, the results are sensitive to light interception, suggesting that the assumption of horizontal homogeneity should be reconsidered, in particular, in the later stage of canopy development. Other important processes with unreliable and sparse data are those related to root functioning.