Carbon stocks in four forest stands in Sweden 25 years after harvesting of slash and stumps

Abstract

The long-term effect of slash and stump harvesting on carbon (C) stocks in soil, tree biomass, and total ecosystem were studied in four field experiments that commenced in 1980–1982 along a climatic gradient from north to south Sweden. The treatments consisted of complete tree harvesting, i.e., harvesting of slash, stumps, and stems (SSS); harvesting of stumps and stems, but leaving logging residues on site (SS); and, conventional stem-only harvesting (S). The northern site with Pinus sylvestris represented a relatively harsh, boreal climate (N-pine). Two additional sites were established in south-central Sweden with Picea abies (M-spruce) and Pinus sylvestris (M-pine) in a south-boreal climate. The fourth site with Picea abies (S-spruce) was established in south-west Sweden in the temperate zone.Ecosystem C stock in tree and soil was lower after SSS than after SS and S, however, there was no significant difference between S and SS.The treatment effect on C stock in tree biomass was site-specific rather than general. Stump-harvest (SS, SSS) increased C stock in N-pine, whereas a decrease was only observed for SSS in M-spruce. A logical explanation for the decreased C stock was the increased nutrient removal caused by harvest intensity. However, this could be counteracted by an increase in release of nutrients from the organic layer and a decrease in competition from the field vegetation promoted by soil disturbance due to stump harvesting.Soil C stock was lower after SSS than after S, due to lower C content in the organic layer after SSS (12Mgha−1) than S (18Mgha−1): no difference was detected in the mineral soil (0–20cm). Soil C stocks after SS did not differ from S and SSS, but were lower in the organic soil layer after SS than after S.These results implied that stump harvest caused a lower C stock in the soil organic layer, 25years after the harvest. However, this study did not show whether this difference would remain over time as remaining stumps and logging residues continue to decompose and the regenerated stand develops. The effects on the C stock in trees appear site- or time specific. More studies are needed to investigate the factors that control this stock, and the final carbon balance should be evaluated over at least one rotation period.