Adaptation of white spruce populations to extreme climate events: implications for assisted migration practices in Western Canada

  • Author / Creator
    Sebastian Azcona, Jaime
  • The movement of seed sources from south to north has been proposed as a tool to mitigate the effect of climate change on forest productivity and mortality. Southern provenances, coming from warmer regions are expected to better utilize the extended growing seasons expected under climate warming. But even if temperatures are warming overall, early fall frost events or late spring frost events may still occur at similar or even increased frequencies relative to the growth phenology of plants. If trees are not correctly adapted to the length of the growing season, and they release dormancy to early or stop growing too late, they will suffer frost damage. To find the best adapted provenances I studied here different physiological adaptations to climate that should help delineate safe transfer distances of white spruce (Picea glauca [Moench] Voss), using a range-wide provenance trial in Central Alberta. I measured physiological and anatomical traits related to drought resistance and cold hardiness, and implemented a novel tree ring approach to detect xylem anomalies induced by past climate events. My results showed tradeoffs between fall cold hardiness and tree growth primarily along a latitudinal cline. Southern provenances showed higher growth but a later onset of cold hardiness. Latitude of source origin was the most influential environmental variable for both tree height and cold hardiness, suggesting a strong effect of day length regimes in the control of the length of the growing season. Provenances from southern latitudes of origin and from eastern maritime climate conditions showed high productivity, but were also more susceptible to the occurrence of abnormally thin cell wall thickness and unlignified tracheids in the latewood during cold years, indicating a mismatch of growth phenology with the available growing season. Provenances from maritime and warm source environments also had higher mortality rates despite showing good growth. In contrast, provenances from the northern part of the distribution were more vulnerable to late spring frosts when grown in at a warmer test site than their origin climate. The physiological traits related to drought resistance and anatomy measured in this study did not show any significant difference throughout the range of the species, although we found some tradeoffs between hydraulic safety and efficiency. Based on population differentiation observed in this study, hardiness zones could also be used to limit the distance of seed transfers within the species range. The results of this study support moderate northward movement of populations to address climate trends that have already occurred over the last decades. The best performing provenances in this trial came from the southern central part of the distribution (South East Manitoba), about 500 km south and 1,500 km east of the test site and a region with warmer summers and similar winter temperatures and precipitation. These climatic conditions are consistent with expected climate change, and therefore assisted migration prescriptions northward and upward in elevation to moderately cooler temperature (–1 to –2°C difference) seem well supported by this study.

  • Subjects / Keywords
  • Graduation date
    Spring 2019
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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