Probability of Spring Frosts, Not Growing Degree-Days, Drives Onset of Spruce Bud Burst in Plantations at the Boreal-Temperate Forest Ecotone

Abstract

adapting the temperature-driven hypotheses of ecophysiological models predicting leafout to include spring frost probability.

Growing‐season frost is a better predictor of tree growth than mean annual temperature in boreal mixedwood forest plantations

“…This study shows that at the regional scale, the different frost tolerance and growth potential of spruce species and seed sources need to be considered to maximize wood production of future plantations established in frost‐prone environments (Park et al., 2014). Black spruce buds flush later than white spruce, which reduces its exposure to spring frost, and increase growth during years of spring frost compared to white spruce (Man et al, 2017; Marquis et al., 2020). However, whereas black spruce grows more than white spruce during years of growing‐season frosts, white spruce's greater growth rate makes it grow taller compared to black spruce during years without or with few growing‐season frosts.…”

“…Consistent with our hypothesis at the intra‐species level, the white spruce seed source closest to the boreal mixedwood forest plantation outperformed extra‐local white spruce seed sources. This suggests that assisted migration may not be a good option in boreal environments, where growing‐season frost intensity is high, probably because seed sources from southern temperate forests exit dormancy too early and are more damaged by frost (Lu & Man, 2011; Marquis et al., 2020). However, at the temperate forest site, both seed sources K24 and J70, growing, respectively, 350 km south and 150 km north, grew equally well and were taller than the K20 seed sources growing 600 km south.…”

“…This study shows that at the regional scale, the different frost tolerance and growth potential of spruce species and seed sources need to be considered to maximize wood production of future plantations established in frostprone environments (Park et al, 2014). Black spruce buds flush later than white spruce, which reduces its exposure to spring frost, and increase growth during years of spring frost compared to white spruce (Man et al, 2017;Marquis et al, 2020).…”

“…To test our hypothesis, we conducted three analyses: (a) we determined if species and seed sources showing severe frost damage to cambial cells would be smaller than species and seed sources showing undamaged cambial cells; (b) we determined the height along the stem at which growing‐season frosts ceased damaging the apical meristem by analyzing cross‐sections sampled at various heights along the stem; and (c) we determined whether climate variables measuring extreme climatic events like frost intensity and frost frequency better explained inter‐ and intra‐species variations in height growth compared to conventional aggregated climate variables (mean annual temperature and summer temperature) that are less physiologically meaningful to the annual dormancy‐growth cycle of trees. For our first analysis, we expected four outcomes: (a) Norway spruce, the most foreign and least‐adapted species to local site conditions, should show the greatest frost damage (in the form of frost rings), causing it to have the lowest height growth even if it has the highest growth rate; (b) white spruce should show a higher frequency of frost rings and lower height growth than black spruce during years of growing‐season frosts, even if it has a higher growth rate, because it exits dormancy earlier than black spruce, which increases its exposition to growing‐season frosts (Marquis, Bergeron, Simard, & Tremblay, 2020); (c) all Norway spruce seed sources should perform poorly as all seed sources are foreign and are not adapted to local conditions; and (d) the closest white spruce seed source to each plantation site should perform the best and show less frost damage. For our second analysis, we expected that above 2 m from the ground, radiative frosts stop damaging the apical meristem and for our third and last analysis, we expected that tree height will be best explained by the minimum temperature in spring (frost intensity) and frost frequency (number of frost days).…”

Impacts of Climatic Variation on the Growth of Black Spruce Across the Forest-Tundra Ecotone: Positive Effects of Warm Growing Seasons and Heat Waves Are Offset by Late Spring Frosts

“…Accordingly, the growth response of trees to a changing climate is considered a key indicator for anticipating how forest structure and function may be altered by climate change (Payette et al, 1989;Callaghan et al, 2002). However, because of their remote location, tree-ring series and corresponding climatic data are scarce in northern regions, so there are fewer studies on growthclimate relationships in the forest-tundra ecotone compared with the southern boreal forest (i.e., Goldblum and Rigg, 2005;Huang et al, 2010;Girard et al, 2011;D'Orangeville et al, 2016D'Orangeville et al, , 2018Ols et al, 2018;Marchand et al, 2019;Marquis et al, 2020). This is particularly true for northeastern North America, where very few studies have investigated the relationships between tree growth and climatic conditions at such high latitudes (but see Dufour-Tremblay et al, 2012;Nicault et al, 2015).…”