Effects of compaction by heavy machine traffic on soil fluxes of methane and carbon dioxide in a temperate broadleaved forest

Abstract Soil compaction decreases soil aeration and water infiltration, lowering air-filled porosity, which may impact biological processes involved in soil fluxes of carbon dioxide ( F CO2 ) and methane ( F CH4 ), and decrease the greenhouse gas emissions mitigation potential offered by the forestry sector. We recorded F CO2 and F CH4 continuously for two years using automated chambers connected to a laser-based gas analyser in an experimental forest site on an acidic ruptic Luvisol that was established to assess the long-term impact of a loaded forwarder. Heavy machine traffic had considerably increased soil surface roughness. Air-filled porosity ( AFP ) in the first 0.1 m was lower in the trafficked plot – especially in hollows – than in the control almost all year long. The temperature sensitivity of F CO2 was higher for the control plot than for both mounds and hollows in the trafficked plot. Cumulative F CO2 was much higher in the control than in hollows and mounds of the trafficked plot. In contrast, annual F CH4 did not significantly differ between the control plot and either the mounds or the hollows in the trafficked plot, but was significantly higher in mounds than in hollows. F CH4 was negative all year round indicating a net uptake of CH 4 , except during winter when a net emission of CH 4 was occasionally observed in the hollows on the trafficked plot. While seasonal variations of F CH4 were well related to variations in AFP , the potential rate of methane uptake at optimal air-filled porosity was higher in the trafficked plot than in the control.