Impact of tree species on carbon in forest soils

Different tree species differ in productivity, litter quality and quantity, canopy structure and nitrogen deposition. Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and birch (Betula pendula and B. pubescens) are the three dominant tree species in Sweden. This thesis compares soil C fluxes and the accumulation of soil organic carbon under adjacent Norway spruce, Scots pine and silver birch stands growing on similar soils and examines the different processes involved. This was achieved mainly through field measurements of carbon pools and fluxes in southern Sweden, combined with respiration and decomposition studies in the laboratory. Soil carbon fluxes and the accumulation of soil organic carbon were found to differ between the three species, with the strongest differences in humus layers between spruce and birch, with pine intermediate. Most carbon was stored in soils in spruce stands. Birch stands had the fastest root turnover and the highest carbon mineralisation rate. Species differences can be explained by differences in tree growth rate and decomposition. The three tree species differed in terms of litter quality, carbon mineralisation, DOC fluxes and fine root turnover.