Net carbon balance of Finnish forests under climate change - Forest management induced differences between local and global model estimates

Abstract

Several studies predict increases of forest growth and carbon stocks under climate change. Increases can be largely attributed to increasing temperature and CO2 concentration of atmosphere, and the assumption that water does not limit to growth. However, in intensively managed regions such as Finland, forests carbon stocks are perpetuated foremost by forest management, which means that little additional C from atmosphere may be stored in the biomass stock forests if management remains intensive. In this study, we simulated forest growth and carbon balances using a stand model PREBAS and a land surface model JSBACH under bias-corrected forcings of three AR5 climate scenarios run by 5 climate models. PREBAS was initialized with high resolution maps of forest inventory data covering Finland, which realistically represent the structure and biomass distribution in Finnish forests. Forest management followed (a variant of) forest management guidelines yielding realistic level of removals at the national level. JSBACH used PFT-based areal classification as a starting point of the simulations and it did not simulate harvests. Simulations of both models showed positive responses of GPP and NPP of forests to longer and warmer growing seasons little influenced by drought. Biomass carbon stocks and NEE, on the other hand, were sensitive to the management assumption. The study highlights the importance of simulating forest management also in land-surface models, because it directly affects how much C will be removed from atmosphere and how much of it will be stored in the managed ecosystems in future.