OOS 28-4 - Is red spruce a good candidate for assisted migration? Lessons from tree-ring analyses of a network of 60-yr-old provenance trials in Atlantic Canada

Background/Question/Methods
Red spruce (Picea rubens) is a keystone species of the Acadian Forest and has high economic value for the forest industry in Atlantic Canada. However, forest simulation models report a low adaptive capacity of red spruce to warmer, drier climates, questioning the resilience of the species to climate change. The plantation of southern, warm-adapted red spruce populations into colder regions of Atlantic Canada – an approach called ‘assisted migration’ – has the potential to help increase the resilience of red spruce stands , but we still lack empirical evidence on the benefits of this approach. This study leverages existing networks of provenance trials to compare the climate sensitivity of various 60-yr-old red spruce populations. In 2020, we collected growth increment cores from 16 populations ranging from North Carolina to Nova Scotia, planted at ten different locations in eastern Canada. We developed a Bayesian model to compare the growth response of different red spruce provenances to historical climate from 1975 to 2018, while controlling explicitly for tree-level competition and size, stand-level development, thinning, blocking design and local soil conditions.

Results/Conclusions
Our model explained a large portion of the variance, with tree-level and stand-level R² ranging between 0.84 and 0.88. While we report a negative effect of reduced available moisture on red spruce growth, we find no difference in moisture sensitivity between provenances. Overall, climate explained only a small portion of stand-level variability, while stand development, thinning events and tree size were the strongest predictors. Our results do not provide strong support for assisted migration of red spruce, as all populations displayed similar phenotypical plasticity in response to 45 years of climate variations.