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Climate warming is modifying the movement of air masses over Northern latitudes, producing warming and cooling events across the boreal regions. These new conditions changes may mismatch plant phenology from weather conditions, and affect the growing period of trees. Understanding the processes of local adaptation in bud phenology can help to predict the response of plants to these rapid and unexpected environmental changes.Our study monitored bud burst and bud set weekly during four growing seasons in black spruce [Picea mariana (Mill.) B.S.P.] saplings planted in a common garden and originating from five provenances representing the whole latitudinal distribution of the closed boreal forest in Quebec, Canada. We compared the variance in bud phenology among populations and years, and analysed the relationships with temperatures at the origin sites.Bud burst and bud set occurred in mid‐May and mid‐July, respectively, with a large variability among provenances and between the study years. A delayed bud phenology was observed in the provenances from warmer sites, with bud burst and bud set being 1.1 and 1.4 days later for every additional degree in mean annual temperature at the origin site respectively. Populations with earlier bud bursts also showed earlier bud sets, thus the growing season was similar among provenances. The heritability of bud set was higher than that of bud burst, with estimates of 0.26 and 0.21 respectively. On average, variance in bud phenology among provenances reached 5.3%, which was higher than that within provenances (2.6%). The factor year explained 37.7%–69.7% of the variance in bud phenology.Synthesis. The findings demonstrate the evolutionary response to climate variations in the boreal biome. Endogenous and environmental components have different effects on the phases of bud burst and bud set. This complex interaction among drivers of bud phenology may prevent reliable predictions of changes in the growing season under changing climate. An earlier growth reactivation due to higher spring temperatures could result in higher frost risks to the developing buds. Despite a longer period for photosynthesis expected for the evergreen black spruce under warmer conditions, the period spent for bud development could remain unchanged. [ABSTRACT FROM AUTHOR]

• Performance of shoot extension is the result of internal and external factors. • Growth rate and duration reflect the temperature of their provenance. • Differences in shoot length are related to both rate and duration of growth. Under the same environmental conditions, southern and northern populations of temperate and boreal ecosystems exhibit different growth performance. However, which growth trait drives this difference is still unresolved. This study aimed to disentangle the effect of duration and rate of growth on shoot extension of five black spruce [ Picea mariana (Mill.)] populations originating from a latitudinal gradient in Quebec, Canada, and growing in a common garden at the southern border of the boreal forest to simulate warming conditions. Bud phenology was monitored weekly during the growing seasons 2017–2019, and shoot length was recorded in autumn, representing annual growth of the primary meristem. Populations originating from the colder sites showed a lower annual shoot increment compared to those originating from the warmer sites. Despite similar durations of bud phenology, the period of shoot extension occurred between the beginning of June and the beginning of July and was longer in the provenances originating from the colder sites. The period of shoot extension, on average, was shortened by 0.9 days for each degree Celsius of increase in annual mean temperature of the site of origin. Moreover, the populations originating from warmer sites showed higher growth rates, which increased by 0.1 cm day−1 for each degree Celsius of increase in the annual mean temperature of the site of origin. Our results confirmed ecotypic variation in growth performance among black spruce populations and demonstrated that differences in shoot length are related to both rate and duration of growth. In the context of a warming climate, northern populations may be unable to reach the current growth performance of southern ones because of their adaptations to harsh local conditions and low intrinsic growth rates. [ABSTRACT FROM AUTHOR]

Satellite remote sensing is a widely accessible tool to investigate the spatiotemporal variations in the bud phenology of evergreen species, which show limited seasonal changes in canopy greenness. However, there is a need for precise and compatible data to compare remote sensing time series with field observations. In this study, fortnightly MODIS-NDVI was fitted using double-logistic functions and calibrated using ordinal logit models with the sequential phases of bud phenology collected during 2015, 2017 and 2018 in a black spruce stand. Bud break and bud set were spatialized for the period 2009–2018 across 5000 stands in Quebec, Canada. The first phase of bud break and the last phase of bud set were observed in the field in mid-May and at the beginning of September, when NDVI was 80.5% and 92.2% of its maximum amplitude, respectively. The NDVI rate of change was estimated at 0.07 in spring and 0.04 in autumn. When spatialized on the black spruce stands, bud break was detected earlier in the southwestern regions (April–May), and later in the northeastern regions (mid to end of June). No clear trend was observed for bud set, with different patterns being detected among the years. Overall, the process bud break and bud set lasted 51 and 87 days, respectively. Our results demonstrate the potential of satellite remote sensing for providing reliable timings of bud phenological events using calibrated NDVI time series on wide regions that are remote or with limited access. [ABSTRACT FROM AUTHOR]