Mineral soil carbon and nitrogen still low three decades following clearcut harvesting in a typical Acadian Forest stand

•Decrease in mineral SOM was observed 3 decades following clearcut harvesting.•Losses of soil C and N may not be evident without inclusion of deep soil.•Mineral soil pool is more susceptible to harvesting impacts than previously thought.

Intensive forest management practices can alter forest soil organic matter (SOM) storage (kg C ha− 1) due to changes in the environmental variables that control SOM cycling and stability. Here we investigate whether SOM losses are observed three decades following clearcut harvesting in a temperate forest ecosystem that includes the deep mineral soil (to a depth of 50 cm). We compared SOM stored as carbon (C) and nitrogen (N) in paired (35-year-old; 110-year-old reference) Acadian Forest sites that differed only in their time since harvest. We found lower mineral soil carbon (C) and nitrogen (N) storage (27% and 26% respectively), and lower C and N concentrations at the 35-year-old site compared with the 110-year-old reference site. Isotopic compositions of C and N through the soil profile did not provide insight into the dominant mechanisms driving SOM losses at the 35-year-old site in this study. This is the second study to document decreases in mineral soil C and N storage in a red spruce forest within the Acadian Forest Region three decades following clearcut harvesting.