Assessing main and interactive effects of early silvicultural treatments and local competition on drought response in planted white spruce

Climate-induced droughts pose growing risks to the resilience of planted forests. Early silvicultural treatments, including scarification and early fertilization, may enhance tree establishment and mitigate the impacts of drought on planted tree growth. However, the legacy effects of these treatments and their interaction with competition from ingrowth and other planted individuals on drought resilience remain poorly understood. We thus investigated how scarification and early fertilization influenced the drought responses of ~19-year-old planted Picea glauca in a long-term silvicultural experiment in eastern Canada. Using tree-ring analysis, we quantified drought resistance, relative resilience, and recovery period following a drought in 2005. We also assessed tree-level competition using a modified Hegyi index. We observed significant main effects of the treatments: fertilization reduced relative resilience and scarification decreased drought resistance. Competition alone did not influence growth response to drought. Interactions with competition were observed but limited; fertilization increased resistance and shortened recovery periods under increasing competition, while scarification effects were independent from competition levels. Results suggest that early silvicultural treatments can have lasting effects on tree growth response to drought. Our findings contribute to a better understanding of how to design adaptive silviculture strategies for maintaining plantation resilience in the face of climate change.