White pine decline in managed forests has led to the adoption of ecosystem-based management using natural disturbances, mainly surface fire. However, other natural disturbances, such as spruce budworm (SBW), are present in the native range of white pine but are rarely considered in the management of this species. SBW outbreaks are expected to change in frequency and severity under climate change, increasing the need to understand if and how this disturbance will affect the dynamics of white pine regeneration. In this study, we evaluated the impacts of an SBW outbreak on white pine and balsam fir regeneration and identified environmental variables that affect regeneration dynamics. We evaluated six defoliated and six control study plots in white pine stands close to the northern limit of the Québec’s temperate forest. In each plot, we counted white pine and balsam fir seedlings and measured structural (diameter, height), and abiotic (gap fraction, soil type) variables. White pine seedling density was three times greater in defoliated plots than in controls. By contrast, there was no significant difference in balsam fir seedling density between disturbance types. Seedlings of both species were taller in defoliated plots than in control plots. Overall, the SBW outbreak promoted white pine seedling density and height growth. This research contributes to our understanding of the effects of SBW outbreaks on white pine regeneration dynamics, and it will help forest managers to select harvesting methods that emulate SBW-modulated stand characteristics.

Boreal forest soils store more carbon than the aboveground vegetation and play a critical role in the global carbon cycle and ecosystem function. Despite their importance, the long-term impacts of forest management on soil organic carbon (SOC) remain unclear, especially in boreal forests with contrasting climatic conditions. This study assesses the effects of commercial thinning on SOC stocks (20-year post-treatment) in black spruce stands across two boreal regions in Québec: the warmer, drier Abitibi and the colder, wetter Cote-Nord, accounting also spatial variability from skidding strips. We measured SOC stocks at three soil depths (forest floor, mineral layer: 0–15 and 15–30 cm) in both thinned and unmanaged stands, using bulk density and SOC concentration. Soil pH, cation exchange capacity (CEC), and macronutrients were also conducted to characterize soil fertility. Thinning had no effect on total SOC stocks of the whole profile in either region, but horizon-specific differences were detected. A decrease in forest floor SOC stocks was observed in Côte-Nord, whereas SOC stocks in Abitibi remained similar. These contrasting outcomes reflect regional differences in soil fertility (higher CEC, potassium in Abitibi) and climatic conditions which may have influenced vegetation regrowth and, consequently, SOC stocks’ recovery over time. Although SOC stocks decreased in skidding strips, their small proportion within the stand minimized their effect on total SOC stocks at the plot level. Overall, the study emphasizes the need to consider climatic and soil context, as well as limited spatial extent of skidding strips, in evaluating silvicultural impacts on boreal carbon sequestration.