Climate change risk management in tree improvement programs: selection and movement of genotypes

Abstract

Tree improvement programs usually consist of multiple breeding populations that target different climatic or ecological regions. Parent breeding material normally originates from and is deployed within the same breeding region, assuming optimal local adaptation of populations. Given the climate trends observed over the last several decades in western Canada, this assumption is unlikely to still be valid. This problem needs to be addressed either by delineating new deployment areas for improved planting stock or by selecting genotypes suitable for changed climatic environments. In a case study for white spruce, we analyzed height data from 135,000 trees grown in 44 genetic tests established and evaluated over a period of 35 years by industry and government agencies in Alberta. We show how the risk of planting maladapted trees can be minimized by moving planting stock to new areas, or by eliminating genotypes from breeding programs that are sensitive to anticipated future climate environments. Transfers that outperformed local sources consistently originated from locations with higher temperatures, suggesting north or northwest transfers. However, adaptation to cold appears to be a prevalent driver for genetic population differentiation in spruce, thus limiting how far material may be moved in current reforestation efforts to address future climate change.

Growth gains from selective breeding in a spruce hybrid zone do not compromise local adaptation to climate

“…Adaptation to cold dominates signals of local adaptation in our study of interior spruce. Strong associations among hybrid index, cold injury, and cold‐related climatic variables are congruent with patterns of adaptive variation in autumn cold hardiness for widespread conifer species (Bansal, Harrington, & St. Clair, ; Gray et al., ; Hurme, Repo, Savolainen, & Pääkkönen, ; Liepe et al., ; Rehfeldt, ), and genotype–environment associations for adaptive markers associated with cold tolerance in interior spruce and lodgepole pine (Yeaman et al., ). Adequate autumn cold hardiness development prior to potentially damaging temperatures is essential to seasonal climatic synchrony, survival, and growth.…”

“…Across AB and BC interior spruce populations, height growth in common gardens is greatest in populations from the valleys of southern BC, and decreases as tolerance to extreme cold increases with latitude. Growth also decreases locally as tolerance of deep snow pack and short growing seasons increases with elevation (De La Torre, Jaquish, et al., ; Gray et al., ; Liepe, Hamann, Smets, Fitzpatrick, & Aitken, ; Rehfeldt, ).…”

Adaptations of white spruce to climate: strong intraspecific differences in cold hardiness linked to survival

“…Although this study was not designed to study local optimality or to be used to derive practical assisted migration guidelines, provenances that originated near the vicinity of the study site showed the best combination of long-term performance in growth and survival in the field. Local provenances (central Alberta) originated slightly southeast of the study site which corresponds to a short northwest transfer as was recommended by Gray et al, 2016 to account for climate change that has already occurred over the last several decades. The provenances that showed both poor growth and low survival came from the Alberta Foothills (lower-left quadrant in Figure 2…”

“…Previous work on white spruce provenances in different parts of its distribution suggests that transfers toward the north can increase growth rates (e.g., Gray et al., ; Lesser & Parker, ; Li, Beaulieu, & Bousquet, ; Lu et al., ; Rweyongeza, Yang, Dhir, Barnhardt, & Hansen, ). A recent study proposed relatively short northward transfers for Alberta, with growth and survival of transferred seed sources putatively limited by cold temperatures in the north of the province (Gray et al., ). All these studies analyzed the response of tree growth to different planting environments, but there is little understanding of the physiological causes of different local adaptations.…”

Stability of species and provenance performance when translocated into different community assemblages

“…For long‐lived species such as trees, future climate models are being used to guide translocation decisions with the aim to develop resilient plantings better adapted to future climates (Harrison et al ). Assisted gene flow (the movement of germplasm within the species' natural distribution) and assisted migration (the movement of germplasm within or outside their natural distribution) are thus being increasingly integrated into conservation strategies (Aitken & Whitlock ; Gray et al ). In a restoration context, this involves strategies, such as climate‐adjusted provenancing, which aim at enriching local plantings with seed predicted to be genetically adapted to future climates of the planting site (Prober et al ).…”