| Summary: | This study investigated soil characteristics and response to logging in a forested watershed of coastal British Columbia (Roberts Creek Study forest). We focused on soil organic carbon (SOC), labile and exchangeable elements, and short-range order (SRO) inorganic phases. These soil attributes were investigated in each pedogenic horizons (FH, Ae, Bf1, Bf2, BC, Cg) of 27 soil profiles. The profiles formed a disturbance chronosequence including undisturbed (control) forested sites, recently logged (cleared) sites harvested 1 to 5 years prior to sampling, and older logged (regenerating) sites harvested 8 to 15 years prior to sampling.
Soils were coarse-textured humo-ferric Podzols developed on a glacial till underlain by granodioritic bedrock. We found that the average soil profile stored approximately 15.9 kg C / m2 over a depth of 1 m. Over 60% of the profile’s SOC was found at depth greater than 20cm. Predictors of SOC concentration included pyrophosphate and oxalate-extractable Al and Fe and the clay content.
The forest floor of logged plots stored more C than undisturbed plots, most likely due to the addition of logging slash decay products. In the mineral subsoil, SOC was higher in cleared plots and similar to control levels in regenerating plots. This suggests that logging resulted in SOC gains to the mineral soil, but that these inputs were not stabilized. The subsoil played a key role in the overall response of SOC storage after logging and must therefore be taken into consideration in C dynamics studies.
Short-range order inorganic phases such as imogolite-type material and ferrihydrite were a major component of the soil reactive fraction and were estimated to represent approximately 45% of clay-sized subsoil component. The major constituent of SRO phases was likely low-crystallinity proto-imogolite.
Exchangeable ions and nutrients concentration were relatively constant in logged and control plots, with the exception of nitrate. Overall, the impacts of logging were not severe. We hypothesize that the good retention of SOC stores in logged plots and the presence of SRO material in lower mineral horizons contributes to the retention of nutrients in the profile and reduces the ecological effects of forest disturbance.
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