Deniz Koca

The overall aim of this thesis was to provide a representative estimate of the potential impacts of climate change and increased atmospheric CO2 concentrations on Swedish forest ecosystems and the key ecosystem services they provide. In order to achieve this task, fi rst LPJ-GUESS, a process-based regional ecosystem modelling framework, was applied to explore how possible shifts in climatic zones according to a range of regional climate scenarios may lead to changes in the tree species distribution and composition, net primary productivity (NPP) and carbon sequestration capacity of potential natural ecosystems on species level and at the regional scale. Following that, LPJGUESS was employed to simulate and investigate further the interactions between different environmental drivers (temperature, CO2 and precipitation), and their individual and overall effects on community structure and ecosystem functioning of the natural ecosystems for a deeper understanding. Given that nearly all Swedish forest ecosystems are subject to human management and it is more of such management activities that have determined the species composition in these ecosystems rather than other natural factors, a forest management module was later implemented into LPJ-GUESS. The performance of the model was evaluated by comparing the simulated forest composition and growth with the observed forest inventory data from Swedish forest regions. Finally, modified version of LPJ-GUESS was applied to evaluate the possible consequences of alternative regional climate change scenarios and elevated atmospheric CO2 concentration on net primary productivity and stem wood volume increment of Swedish managed forests under existing silvicultural management practices.

Potential natural vegetation (PNV) simulations showed that all climate scenarios were associated with an extension of the boreal forest treeline with respect to altitude and latitude. The model also predicted substantial increases in net primary productivity, especially in central Sweden. Expansion of forest cover and increased local biomass enhanced the net carbon sink over central and northern Sweden. In southern Sweden, reduced growing season soil moisture levels counterbalanced the positive effects of a longer growing season and increased carbon supply on NPP, with the result that many areas were converted from a sink to a source of carbon by the late 21st century.

Model estimates of annual stem wood volume increment in managed forests were generally comparable with observations in all regions of Sweden. Again under all regional climate change scenarios the model predicted substantial increases in NPP and wood volume increment of managed forests, especially in central and northern Sweden due to combined effects of warmer and wetter climate and higher levels of atmospheric CO2 concentrations.