Changes in the Lignic Portion of the Organic Layer Following Harvesting in the Boreal Forest.

Forest harvesting periodically removes lignic materials that would eventually, if not harvested, contribute to the soil organic matter pool. The long term effects of modifying the quality and quantity of lignic material inputs to the soil, specifically on soil organic matter storage and fertility, are poorly known. Recent studies suggest that this material has a modest contribution to stable soil pools. Nevertheless, as this material decays slowly it may contribute to the soil organic matter pool for a certain period and provide water retention capacity as well as to anion and cationic exchange sites as well as habitat. A retrospective approach was used to gain knowledge on the mid-term (10-30 years) effect of the harvest of lignic material on soil C pools in boreal forest sites. Pairs of plots under similar ecological conditions for which historical management and disturbance has created different inputs of lignic material were studied. Paired salvaged and non-salvaged Spruce budworm killed stands as well as paired sites where harvest residues were collected or not were analysed for dead organic matter pools. As expected, the difference in fine woody material between treatment lasted only for a short period of time (<5yr). In general the amount of coarse woody debris were greater in treatments that received more inputs but the mass of the fine forest floor material was not different between treatments. These results suggest that the recent history of woody inputs have little impact on forest floor accumulation.