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, a nd trench microsites; 2) ripper plow, hinge, and trench microsites; 3) blading, thin (organic layer depth a cm), and thick (organic layer de pth >2 cm) microsites; 4) harvested with no site preparation; and 5) u nharvested. Twenty months after harvesting, the forest floor of harves ted areas with no MSP (vs. unharvested) had higher carbon:nitrogen rat ios, lower pH, and lower concentrations of total and mineralizable nit rogen, available phosphorus, and exchangeable bases. Fifteen months af ter 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 wi th no site preparation. The MSP-treated areas also had increased or un changed pH, base saturation, and exchangeable base concentrations. Mic rosites adjacent to the displaced forest floor (hinge for disc and rip per treatments) or with a thicker organic layer (thick for blading) ge nerally had higher concentrations of total nitrogen and carbon, and mi neralizable nitrogen in the surface mineral soil as compared to trench and thin microsites.