Assisted migration is plausible for a boreal tree species under climate change: A quantitative and population genetics study of trembling aspen (Populus tremuloides Michx.) in western Canada

Abstract

A novel method was tested for improving tree breeding strategies that integrate quantitative and population genetics based on range‐wide reciprocal transplant experiments. Five reciprocal common garden tests of Populus tremuloides were investigated including 6450 trees across western Canada focusing on adaptation traits and growth. Both genetic parameters and home‐site transplant models were evaluated. We found a genetic trade‐off between growth and early spring leaf flush and late fall senescence. Coefficients of phenotypic variation ( CVp ) of cell lysis (CL), a measure of freezing injury, shrank from 0.28 to 0.10 during acclimation in the fall, and the CVp slope versus the freezing temperature was significantly different from zero ( R 2 = 0.33, p = .02). There was more between‐population genetic variation in fall phenology than in spring leaf phenology. We suggest that P. tremuloides demonstrated a discrepancy between the ecological optimum and the physiological optimum minimum winter temperature. The sub‐optimal growing condition of P. tremuloides is potentially caused by the warmer ecological optimum than the physiological optimum. Assisted migration and breeding of fast growers to reforest cooler plantation sites can improve productivity. Transferring the study populations to less than 4°C of extreme minimum temperature appears safe for reforestation aligning with the historical recolonization direction of the species. This is equivalent to a 5–10° latitudinal northward movement. Fall frost hardiness is an effective criterion for family selection in the range tested in this study.

Climate lags and genetics determine phenology in quaking aspen (Populus tremuloides)

“…Genetic trade-offs exist between phenology and growth (Ding & Brouard, 2022). The heritability of phenology was 20-30% in one common garden study (Ding et al, 2020), 30-50% in a different common garden study (Kanaga et al, 2008) and a field study (Drobyshev et al, 2019), or 50-90% in clonal trials (Gylander et al, 2012;Ding & Brouard, 2022).…”

“…Our estimates adjust for these parameters statistically rather than experimentally. Values correct for the influence of the physical environment, but are not narrow-sense heritabilities sensu (Ding & Brouard, 2022). They reflect the proportion of the variance explained by genetic variance given the measured environmental variation, which likely does not reflect the overall contribution of genetics to phenology.…”

“…From a genetic perspective, phenology in aspen often differs among clones within populations (Egeberg, 1963; Barnes, 1969; Jelínková et al ., 2014). Genetic trade‐offs exist between phenology and growth (Ding & Brouard, 2022). The heritability of phenology was 20–30% in one common garden study (Ding et al ., 2020), 30–50% in a different common garden study (Kanaga et al ., 2008) and a field study (Drobyshev et al ., 2019), or 50–90% in clonal trials (Gylander et al ., 2012; Ding & Brouard, 2022).…”

“…The environmental cues that influence phenological responses remain under investigation in aspen (Meier et al ., 2015) and its close relative, Populus tremula (Luquez et al ., 2008; Strømme et al ., 2017; Michelson et al ., 2018). In provenance trials, greenup date is responsive to frost risk (Li et al ., 2010; Ding & Brouard, 2022), while greendown date is responsive to day length and nighttime warmth (Schreiber et al ., 2013). Growth is reduced by heat (Hogg et al ., 2008), drought (Anderegg et al ., 2013), spring frosts (Sutton & Tardif, 2005; Birch et al ., 2022), and herbivory (Marchetti et al ., 2011; Seager et al ., 2013).…”

Unravelling the biogeographic determinants of tree growth sensitivity to freeze and drought in Canada's forests

“…In the boreal hardwood tree Populus tremuloides , populations diverged in cold adaptation and fall leaf phenology marking a genetic adaptation to frost (Ding & Brouard, 2022; Girardin et al., 2022). Since the colder ecological optimum for this species will not match current and future warmer climatic conditions (Ding & Brouard, 2022), the greater sensitivity of growth to cold in the warm edge compared to the cold edge may indicate a maladaptation and a potential decline of local populations in the southernmost part of the range in this species.…”