Replacing Norway spruce with European beech: A comparison of biomass and net primary production patterns in young stands

• Predicted climate change will result in altered forest tree species distribution.
• Norway spruce is likely to be replaced European beech in many locations in Europe.
• NPP of slow- and fast-turnover biomass pools of these species was contrasted.
• Differences in biomass allocation and growth phenology were detected.
• Forest C cycle altered by species change will exert a feedback to climate change.

An alteration of species composition in temperate forests – both managed and natural – is one of the expected effects of environmental change. Present forest tree species ranges will be altered by changing environmental conditions. By a combination of continuous and destructive sampling, we compared biomass stocks and annual NPP in naturally regenerated stands of Norway spruce and European beech. We purposely selected a site where future environmental conditions are predicted to favour beech over presently dominant spruce. We found no difference in overall productivity, but biomass allocation differed significantly between the two species. Beech allocated more assimilates to stem and roots than spruce. There was no significant difference between the species in NPP of the fast turnover biomass pool comprising foliage and fine roots. Maximum height growth occurred about a month earlier than in spruce, potentially changing the timing of carbon (C) flow into the soil pools. We show that the replacement of spruce by beech will result in changes in forest biomass allocation and in alterations of belowground C cycle. Such changes will affect forest ecosystem function by modifying the magnitude and timing of certain C fluxes, but also by potentially changing the species composition of forest biota dependent on them.