Incorporating forest growth response to thinning within biome-BGC

Large-scale ecosystem models are designed to reproduce and quantify ecosystem processes. Based on plant functions or species-specific parameter sets, the energy, carbon, nitrogen and water cycles of different ecosystems are assessed. These models have been proven to be important tools to investigate ecosystem fluxes as they are derived by plant, site and environmental factors. The general model approach assumes uniform and fully stocked forests but since most European forests are managed (e.g., thinned) it is essential to understand the limits and precision of such models when applied to managed forest ecosystems. The purpose of this study is to investigate and incorporate common forest management practices within the large-scale ecosystem model Biome-BGC. Using “Monte-Carlo” simulations we analyze the theoretical response to current model settings assuming steadily decreasing changes in stand density. Results of the MC simulations as well as the comparison with measured data suggest that the resulting predictions will be biased. Using long-term experimental plots of Norway spruce ( Picea abies L. Karst.) and common beech ( Fagus sylvatica L.) forests with a well-documented thinning history, we propose a thinning subroutine, which addresses the changes in allocation patterns after stand density changes. Validation tests of improved model structure across different long-term experimental sites in Central Europe revealed unbiased and consistent simulation results.