Response of Mineral Soil Carbon to Clear-Cutting in a Northern Hardwood Forest

Northern New England is characterized by extensive forest cover (84%) and large reservoirs of soil carbon (C). There has been an increasing demand for forests to serve both as a C sink and a renewable energy source. Our understanding and management of the ecosystem C balance relies on accurate modeling of each compartment of the ecosystem. However, the dynamics of soil C storage with respect to forest use are poorly understood. For example, current regional models assume negligible mineral soil C loss after forest harvesting, while some studies on soil C demonstrate that belowground mineral soil C pools can be affected by disturbances at the soil surface. We investigated harvesting-related changes in mineral soil C to a depth of 60 cm in the Bartlett Experimental Forest in New Hampshire, USA. We found significantly lower concentrations of C in some recently harvested stands compared with >100-yr-old stands. Carbon concentrations among harvested stands varied significantly in all but the 0- to 10-cm depth increment. Mineral soil C pools were lower in some stands that had been harvested, with isolated significant differences occurring between the 120-yr-old stand and stands that were cut 5 or 55 yr before sampling. However, there were no trends in mineral soil C pools over time after harvest, and the isolated differences in C pools do not suggest widespread C loss with forest harvesting. When combined, stands that had been harvested within the last 100 yr had significantly lower C pools than the >100-yr-old stands. Further work is needed to elucidate the mechanisms underlying the observed loss of C after forest harvest. However, changes in C inputs and outputs to and from mineral soil in the decades following harvest could potentially lead to appreciable differences in C concentrations and pools across the landscape.