Soil carbon storage and stability controlled by site properties more than forest management in a humid boreal forest

Abstract Soils of managed boreal forests are a significant carbon (C) reservoir, and maintaining or increasing their ability to store C could play an important role for climate change mitigation. We investigated the effects of forest logging through clearcut and partial cut compared to forest conservation on total soil C stocks, particulate organic matter, and mineral‐associated organic matter (MAOM) physical fractions down to 55 cm in the mineral soil in a humid boreal balsam fir forest of Eastern Canada. We analyzed the variables that best explained the observed variations in soil C stocks, including topographic variables, deadwood, and soil physicochemical properties. Our results showed that harvesting treatments had no significant effect on soil C stocks for the entire soil profile. The variables that contributed most to explaining variations in soil C stocks for the FH horizons were exchangeable manganese, C stocks in buried wood, aboveground woody debris and mosses, slope inclination, and pH; pH, metal oxide, and rock content for mineral horizon C stocks; and pH, metal oxide content, and exchangeable iron for the MAOM fraction of mineral horizons. This study highlighted the complex and indirect role of deadwood and the significant influence of local site and soil properties (mainly metal oxide content) on soil C stocks in managed boreal forests.