Post-harvest recovery of soil methane oxidation on skid trails and landings in a managed northern hardwood forest

Abstract

Skid trails and landings are features within managed forest landscapes where soils are moderately to extremely disturbed by forestry vehicles. They have been found to exhibit reduced methane (CH4) oxidation or CH4 emissions six months to a year after a harvest has ended, but little is known about when these changes begin to occur (either during or after harvests) or how they recover over a longer timeframe. We took periodic measurements of soil CH4 flux from skid trails and landings during a harvest, and also quantified CH4 flux rates from sites that had been harvested up to 15 years prior to form a replicated chronosequence of soil recovery. In the thirteen-week period of active harvesting soil CH4 oxidation steadily declined, with small emissions occurring by the end of the measurement period. The chronosequence measurements revealed high rates of CH4 emissions the first year after harvest followed by a decrease in the following years. Emissions were particularly strong from landings and skid trails that had experienced high amounts of traffic and were located on lower slopes. By the end of the 15-year chronosequence landing and skid trail soils had returned to acting as CH4 sinks; however, the rates of oxidation remained lower than undisturbed forest soils. Further, integration of models created to predict CH4 flux over time indicates that CH4 flux from these soils are unlikely to reach a full recovery within a 20-year period - the average length of time of a harvest cycle in this region. On landings the change from emissions back to oxidation was correlated with soil temperatures, which decreased over time. On some skid trails CH4 flux was correlated with soil moisture content, which initially increased from buried wood’s increased water holding capacity and then decreased over time. The results suggest that remediation measures ought to be implemented immediately after harvest to avoid the high emissions that occur in the following few years and should prioritize the removal or prevention of incorporation of wood fragments.