The effects of various site preparation treatments on the control of Alnus incana and forest regeneration in boreal forests of Western Quebec, Canada

Our study, conducted in the mixed boreal forest of western Quebec, Canada, assessed the effectiveness of various site preparation treatments to promote black spruce ( Picea mariana (Mill.) BSP) regeneration on wet sites invaded by speckled alder ( Alnus incana subsp. rugosa (du roi) R.T. Clausen) following harvest. In 2019, four treatments were established: scalping, mulching, soil inversion, and an untreated control. Black spruce seedlings were planted in 2020. Measurements taken in 2021, at the end of the second growing season, revealed that the treatments doubled the growth and size of seedlings compared to the control group. While differences were small, seedlings in mulched plots showed significantly greater height growth and annual shoot elongation compared to those in inverted plots. The treatments also reduced competing species cover, while promoting the presence of grasses. Environmental conditions and soil properties did not vary significantly between treatments and the control group, except for pH and potassium in some cases. These results suggest that all three site preparation treatments tested are effective in establishing black spruce regeneration on wet sites invaded by speckled alder. Long-term monitoring is needed to assess the economic impact of treatments and better understand the role of alder in nitrogen availability on treated sites.