Decomposition of Beech and Spruce Litter in Neighbouring Beech and Spruce Forests

Climate change is expected to cause a transformation from spruce to beech dominated forests in a large part of southeast Norway. A shift in dominating tree species may have a large effect on the factors controlling the rate of litter decomposition, and consequently the rate of greenhouse gas induced climate change. To better understand how this transformation will influence the carbon balance in these forest ecosystems, we need to understand the factors controlling decomposition. A litter bag experiment was conducted in neighbouring beech and spruce forests in southeast Norway. Litter bags with beech and spruce litter was placed in manipulated litter layer plots in the two forest types. This was done to investigate the relative importance of litter type, forest type, the litter layer, and their interactions as determinants of litter decomposition rate. The litter layer manipulations were: transplanted beech litter, transplanted spruce litter, and removal of litter. Un-manipulated plots served as control. After incubation, litter mass loss and nitrogen release as a function of mass were calculated.\n The interaction between litter type and forest type had a significant effect on mass loss. In the spruce forest, spruce litter lost significantly more mass than beech litter, but there were no significant differences between the two litter types when placed in the beech forest. Litter layer transplantations also had significant effects. More mass was lost when litter was placed in the transplanted beech compared to the transplanted spruce and removal plots. Individually, neither the litter type nor the forest type had significant effects on mass loss. This indicates that litter type in the litter layer is more determining for the decomposition rate than forest\n type. Higher mass loss in plots with beech compared to spruce in the litter layer indicates that a transformation from spruce to beech forests will likely lead to a faster decomposition rate. This may especially be true in the transitional phase when the forests are mixed. The implication of a transformation from sprue to beech dominated forests may thus be a faster release of CO2 to the atmosphere, contributing to increased global warming.