Impacts of harvesting and mechanical site preparation on soil chemical properties of mixed-wood boreal forest sites in Alberta

We examined the impacts of harvesting and mechanical site preparation (MSP) on soil chemical properties of mixed-wood boreal forest sites in west central Alberta. Treatments included: 1) disc trencher, hinge, and trench microsites; 2) ripper plow, hinge, and trench microsites; 3) blading, thin (organic layer depth a cm), and thick (organic layer depth >2 cm) microsites; 4) harvested with no site preparation; and 5) unharvested. Twenty months after harvesting, the forest floor of harvested areas with no MSP (vs. unharvested) had higher carbon:nitrogen ratios, lower pH, and lower concentrations of total and mineralizable nitrogen, available phosphorus, and exchangeable bases. Fifteen months after MSP, treated areas had either reduced or unchanged concentrations of total nitrogen and carbon, available phosphorus, and mineralizable nitrogen in the surface mineral soil, compared with harvested sites with no site preparation. The MSP-treated areas also had increased or unchanged pH, base saturation, and exchangeable base concentrations. Microsites adjacent to the displaced forest floor (hinge for disc and ripper treatments) or with a thicker organic layer (thick for blading) generally had higher concentrations of total nitrogen and carbon, and mineralizable nitrogen in the surface mineral soil as compared to trench and thin microsites.