Phenology of black spruce populations: implications and perspectives in a context of climate change

Forest managers use artificial regeneration to modify tree species composition and productivity. The selection of plant material could assume a leading role in forest planning, mainly when aiming to increase the adaptation of stands in a context of climate change. This project aimed to test the effect of provenance on height growth and timing of both bud burst and bud set in five black spruce [Picea mariana (Mill.) B.S.P.] provenances growing in a common garden and originating from a latitudinal range in the boreal forest of Québec, Canada. Bud phenology and shoot extension were monitored weekly during the growing seasons 2015-2021. We demonstrated that both bud burst and bud set occurred earlier in individuals from colder sites. Moreover, variance in bud phenology among provenances was higher than that within provenances and the heritability of bud set was higher than that of bud burst. Despite the lag in timing, provenances from colder sites highlighted a longer duration of the shoot extension than provenances originated from warmer sites. However, northern provenances exhibited lower growth rates, resulting in a smaller increment in height growth than in Southern provenances. We also provide evidence that the timings of bud phenology affect sensitivity to frost. Phenological timings and height growth are key adaptive traits strongly associated with local environmental conditions. Endogenous and environmental components have different effects on height growth and phenological timing. This clinal variation in growth and phenological traits confirms the ecotypic differentiation of black spruce populations and reflects a long-lasting adaptation to the local temperatures at the origin sites. Our findings represent an useful knowledge on the potential growth dynamics of stands artificially regenerated or submitted to assisted migration for the dominant species of the boreal forest.