Current carbon balance of the forested area in Sweden and its sensitivity to global change as simulated by Biome-BGC

Detailed information from the Swedish National Forest Inventory was used to simulate the carbon balance for Sweden by the process-based model Biome-BGC. A few shortcomings of the model were identified and solutions to those are proposed and also used in the simulations. The model was calibrated against CO2 flux data from 3 forests in central Sweden and then applied to the whole country divided into 30 districts and 4 age classes. Gross primary production (GPP) ranged over districts and age classes from 0.20 to 1.71 kg C m(-2) y(-1) and net ecosystem production (NEP) ranged from -0.01 to 0.44. The 10- to 30-year age class was the strongest carbon sink because of its relatively low respiration rates. When the simulation results were scaled up to the whole country, GPP and NEP were 175 and 29 Mton C y(-1), respectively, for the 22.7 Mha of forests in Sweden. A climate change scenario was simulated by assuming a 4 degrees C increase in temperature and a doubling of the CO2 concentration; GPP and NEP then increased to 253 and 48 Mton C y(-1), respectively. A sensitivity analysis showed that at present CO2 concentrations NEP would peak at an increase of 5 degrees C for the mean annual temperature. At higher CO2 levels NEP showed a logarithmic increase.