Abstract
Understanding local adaptation of tree populations to climate allows the development of assisted migration guidelines as a tool for forest managers to address climate change. Here, we study the relationship among climate, a wide range of physiological traits, and field performance of selected white spruce provenances originating from throughout the species range. Tree height, survival, cold hardiness, hydraulic, and wood anatomical traits were measured in a 32‐year‐old common garden trial, located in the center of the species range. Provenance performance included all combinations of high versus low survival and growth, with the most prevalent population differentiation for adaptive traits observed in cold hardiness. Cold hardiness showed a strong association with survival and was associated with cold winter temperatures at the site of seed origin. Tree height was mostly explained by the length of the growing season at the origin of the seed source. Although population differentiation was generally weak in wood anatomical and hydraulic traits, within‐population variation was substantial in some traits, and a boundary analysis revealed that efficient water transport was associated with vulnerable xylem and low wood density, indicating that an optimal combination of high water transport efficiency and high cavitation resistance is not possible. Our results suggest that assisted migration prescriptions may be advantageous under warming climate, but pronounced trade‐offs between survival and cold hardiness require a careful consideration of the distances of these transfers.
Highlights
Geographic patterns of local adaptation of forest trees have been studied since the 18th century, and most studies found that local populations were the best fit to a specific environment (Langlet, 1971)
The specific goals were to (1) quantify genetic population differentiation among provenances from across the entire range of the species for a wide selection of hydraulic, anatomical, and cold hardiness traits, (2) detect possible relationships among resistance to climate, tree growth, and survival, and (3) analyze how these traits are related to the climate of origin of the provenances
Plant material for this study came from two contiguous white spruce (Picea glauca [Moench] Voss) trials in a single site in central Alberta, Canada (55°17′N, 113°10′W)
Summary
Geographic patterns of local adaptation of forest trees have been studied since the 18th century, and most studies found that local populations were the best fit to a specific environment (Langlet, 1971). 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, 2016) 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. The specific goals were to (1) quantify genetic population differentiation among provenances from across the entire range of the species for a wide selection of hydraulic, anatomical, and cold hardiness traits, (2) detect possible relationships among resistance to climate (cold and drought), tree growth, and survival, and (3) analyze how these traits are related to the climate of origin of the provenances The results of this range-wide experiment could point to key traits for climate adaptation that could serve as a reference for more geographically limited studies with higher sample densities to support regional assisted migration prescriptions
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