Soil carbon and nitrogen cycling processes and composition of terpenes five years after clear-cutting a Norway spruce stand: Effects of logging residues

- Logging residue and wood ash stimulated N cycling processes at clear-cut site.
- Changes were visible especially in net nitrification.
- C mineralization, microbial biomass C and N were less affected by the treatments.
- Logging residue slightly increased tannin and terpene concentrations in soil.

The aim of this study was to determine the effects of logging residues on C and N cycling in relation to abundant plant secondary compounds, terpenes and tannins in a Norway spruce clear-cut site. The study site was located in Southern Finland. After clear-cutting piles having 0, 10, 40 kg m−2 of fresh Norway spruce logging residues were built and as additional treatment commercial wood ash was provided to study the possibilities for recycle of wood ash. Samples were taken from the organic layer and uppermost mineral soil layer five years after the treatments. Logging residues increased net N mineralization, especially net nitrification. Addition of wood ash also increased net nitrification. C mineralization, microbial biomass C and N were less affected by the treatments. Observed changes were more visible in organic layer than in mineral soil. Logging residues did not affect much tannin and terpene concentrations in the organic layer; however, we observed increase in terpene concentration in treatment with the highest amount of logging residues. In conclusions, on this study site logging residues did not affect much soil C cycling. However, logging residues and wood ash seemed to stimulate N cycling processes.