Soil carbon and nitrogen contents were determined at four coniferous forest sites in Sweden (Scots pine and Norway spruce in southern and northern Sweden, respectively) over a period of 15-16 years after clear-felling. Three levels of logging-residue harvesting had been applied: (i) conventional stem harvest (residues left on site); (ii) harvesting all above-ground tree parts except needles; (iii) above-ground whole-tree harvesting (no residues remaining), The forest floor and the top mineral soil layers (0-20 cm) were examined, excluding coarse woody detritus (i,e. dead branches and roots). When measured, 15-16 years following clear-felling, the content of C and N in the humus layer had decreased markedly at all sites, whereas increased amounts were frequently observed in the mineral soil, Total C pools decreased by 22% at the northern site with Norway spruce, and by 17% at the southern spruce site. The corresponding figures for N were 22% and 13%, No changes in the total pool were detected at the southern site with Scots pine, whereas at the northern pine site C decreased by 7% and N increased by 7%, Changes in C and N storage were accompanied by decreases in the C/N ratio in the humus layer and increases in the C/N ratio in the top 5 cm of the mineral soil, No general effect of harvest intensity on soil C or N pools was shown in analyses over all sites, but there was a site and treatment interaction for N, indicating site-specific effects on this element, At the northern spruce site, whole-tree harvesting as well as removal of woody residues only (i.e, needles left on site) resulted in a greater reduction of N pools in the humus compared with conventional harvest. In contrast, at the southern spruce site conventional harvesting resulted in a greater reduction in total N pools compared with the other treatments, Whole-tree harvesting increased C/N ratios in the humus and 0-5 cm mineral soil layers compared with the other treatments. This effect was detected in the humus layer only 8 years after harvest at the southern sites, whereas at the northern sites it was observed in the mineral soil 16 years after felling. The implications of these results on N mineralization rates are discussed.
