Aboveground carbon stock of scarified black spruce stands—A 20-year study in boreal ecosystems

Scarification followed by planting is a widely used silvicultural practice in eastern North American boreal forests to promote black spruce (Picea mariana) regeneration after clear-cutting, especially in ericaceous-dominated stands where tree growth is limited. Given the role of these forests as carbon sinks, we evaluated the medium-term impact of scarification on aboveground carbon stocks. We conducted vegetation inventories and carbon stock calculations in ~ 20-year-old experimental plantations in Québec, Canada. Scarified plots were compared to naturally well-regenerated clearcuts and to non-scarified plantations in two contrasting regions: the colder, wetter Côte-Nord, with dense ericaceous cover, and the warmer, drier Abitibi, with lower ericaceous abundance. Scarification increased tree carbon stocks in sites where advance regeneration was limited. However, it also caused a long-lasting reduction in understory biomass, particularly bryophytes, with limited recovery after two decades. This shift in carbon allocation—from understory to trees—resulted in similar or higher total aboveground carbon stocks in scarified plots, especially in the wetter region where ericaceous competition was strongest. These findings emphasize the importance of considering both climate and initial site conditions in silvicultural planning. They also highlight the role of understory vegetation in carbon cycling and the trade-offs between forest productivity and biodiversity conservation.