DOI: 10.5061/dryad.866t1g1pr
title: Common-garden experiment reveals clinal trends of bud phenology in black spruce populations from a latitudinal gradient in the boreal forest

description: 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 analyzed the relationships with the 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. Results demonstrate the plastic response of
 bud burst to changing temperatures and suggest the effects of endogenous
 factors on bud set. The earlier growth reactivation due to global warming
 occurring under higher frost risks in spring are expected to produce
 damage to the developing buds. Meanwhile, the ability of bud phenology to
 match the inter-annual variability in weather could help to cope with the
 changing environmental conditions expected in the future.
description: Seed collection and common
 garden Seeds were
 collected in June 2012, from 8-11 mother trees randomly selected in each
 site (Table 1). According to the availability and accessibility of the
 canopy,  a minimum of 10 cones were collected per trees from each stand.
 Seeds from each tree were kept separated to characterize the variability
 among half-sib families within populations. After seed extraction, the
 seedlings were grown under controlled conditions until reaching a suitable
 size to be planted in the field. In July 2014, a total of 422 seedlings
 were planted in a 0.5 ha forest gap in SIM, the southernmost site (Table
 1).  Seedlings were planted according to a random design at a distance of
 2 m × 2 m. Two rows of non-experimental black spruce seedlings were
 planted on each side of the plantation to avoid edge effects. 
 Phenology Bud phenology was recorded weekly
 between May and October in 2015, 2017-2019. The apical buds were used to
 discriminate the different phenological phases of bud burst and bud set
 (Dhont et al., 2010). Six bud burst phases were defined (1) open bud, with
 a pale spot at the tip; (2) elongated bud, with lengthening brown scales;
 (3) swollen bud, with smooth and pale-coloured scales; (4) translucent
 bud, with needles visible through the scales; (5) split bud, with needles
 still clustered; and (6) exposed shoot, with needles spreading outwards.
 Five phases of bud set were defined: (1) white bud; (2) beige bud, with
 beige scales; (3) brownish bud, with a substantial increase in bud size;
 (4) brown bud, with needles spreading outwards; and (5) spread needles,
 with the needles completely spread outwards.