Carbon loss in mineral soil horizons: The effects of 120 years of forest harvesting in northern New England

Soils are the largest global terrestrial carbon reservoir. In New England forests, mineral soil horizons store the largest fraction of the soil carbon pool. It is well established that the harvesting of forests results in a loss of carbon in aboveground biomass and organic soil horizons, but the response of mineral soil carbon to harvesting is poorly understood. We examined a chronosequence in central NH, USA, of forest plots harvested 3, 25, 55, 75, and 120 years ago, as well as a Control Site, to determine the magnitude and timing of carbon loss following forest biomass harvest. Our results showed a 47% (61 Mg/ha) depletion in total solum carbon and a 35% (31 Mg/ha) depletion in mineral soil carbon ∼80 years following forest harvesting. The soil carbon pool recovered to pre-harvest levels (131 Mg/ha) 120 years after harvesting. Carbon depletion was most significant in the free and intra-aggregate soil organic matter fractions. Isotopic enrichment of delta 13C (∼ 0.25--1.00 per mil) at the harvested sites is consistent with microbially mediated processes, which could explain the depletion of mineral soil carbon following harvest. When accounting for carbon fluxes in forests, our study reveals the need to consider the influence of harvesting on mineral soil carbon.