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.

Abstract Introduction Mining activities can lead to the formation of degraded, barren, or metal-contaminated ecosystems. Resource-poor ecosystems such as rocky outcrops are more sensitive to mining degradation, and their natural regeneration can be challenging due to soil erosion, lack of resources or seeds, and soil acidification. Objectives Our aim was to test the effectiveness of using locally collected bryophyte (Ceratodon purpureus [Hedw.] Brid.) mats as a restoration treatment to protect and promote the establishment of tree seedlings in mining-polluted rocky outcrops in Rouyn-Noranda (Canada). Methods The bryophyte restoration treatment inspired by natural succession processes was compared to a control, where only local soil was used as substrate, and to a liming treatment that increases soil pH. The three treatments were applied to sixty 1???1?m?units located on five outcrops at various distances (1.9?26.9?km) from the pollution source. Four tested tree species were each seeded at a density of 100?seeds/m2 on all units. Results The bryophyte treatment had a positive effect on the establishment success of Jack pine seedlings (Pinus banksiana Lamb.) with an establishment rate of 12% compared to 5 and 4% for liming and control treatments, respectively. Wind exposure had a significant negative effect on seedling establishment, potentially masking any negative effects of soil heavy metal concentration, which were not statistically significant. Conclusions Our strategy using bryophytes and mimicking natural succession has the potential to effectively regenerate trees in degraded rocky outcrops.