Effects of Forest Harvest on Soil Carbon and Related Variables in Canadian Spodosols

Abstract

Knowledge about soil organic carbon (SOC) response to forest harvest in conifer stands is limited. The objective of this study was to determine the short- to medium-term effects of bole-only clearcut harvest on SOC and related variables in a Douglas fir [Pseudotsuga menziesii (Mirbel) Franco]-dominated forest of southwestern British Columbia. We collected soil samples from control (mature forest), cleared (harvested 1–5 yr before sampling), and regenerating (harvested 8–15 yr before sampling) stands and measured SOC, pH, texture, moisture, total N, loss-on-ignition, effective cation exchange capacity (CECₑ), and pyrophosphate-extractable Fe and Al. We found that SOC stocks in the forest floor were higher in cleared and regenerating plots than in control. The mineral subsoil played an important role in the overall response of SOC storage after harvest. In mineral horizons, SOC concentration was higher in cleared plots and similar to control levels in regenerating plots. Treatment effects were restricted to SOC associated with the sand size fractions. This suggests that clearcutting resulted in additional soil organic matter (SOM) inputs to the mineral soil, but that these inputs were not stabilized or retained in regenerating plots. Harvest also affected bulk organic matter composition. The C/N and C/SOM ratios were lower in regenerating plots while the CECₑ/C ratio was higher, suggesting an increase in organic matter maturity and oxidation.