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The evolutionary dynamics of tree species are influenced by their specific climatic environments, and their ability to persist is determined by adaptive strategies such as broad climate tolerance, phenotypic plasticity or genetic differentiation. Biogeographical predictions indicate that populations located at the edges of their ranges are more likely to experience heightened vulnerability to climatic fluctuations due to approaching tolerance limits. However, if local phenotypic acclimation or genetic adaptation has taken place, trees near the edge of their range could demonstrate comparable sensitivity to freeze and drought as the rest of the sampled population. Nevertheless, there remains uncertainty regarding the extent of developmental and evolutionary adjustments in climate sensitivity across the entire ranges of many tree species.Here, we document the biogeography of tree growth sensitivity to freeze and soil water and vapour pressure deficits during 1950–2018 using an extensive multi‐species tree‐ring dataset of 35,784 trees at 4535 sites covering boreal, temperate conifer and temperate deciduous forests of Canada. We quantify the relationships between tree radial growth increment and seasonal climate variables and explore factors driving the observed patterns of annual growth and climate sensitivity such as species, regional climate and local site conditions, and tree age and size.Freeze and drought had widespread impacts on tree growth that were contingent on the presence of focal species in interaction with tree size. An indirect growth thermal limitation towards cold/wet edges, occurring through the site moisture conditions, was observed in seven widespread species (e.g. Picea glauca, Picea mariana and Larix laricina). Moreover, six species had negative drought impacts more strongly expressed towards their warm/dry edges (e.g. Abies balsamea, Betula papyrifera and Pseudotsuga menziesii). However, widespread Picea, Pinus and Populus species showed no indication of increased sensitivity to soil water conditions at these edges.Synthesis. Our findings support the idea of evolutionary or acclimatization adjustments in the development of populations in response to long‐term climate conditions experienced in their respective locations. This underscores the importance of incorporating phenotypic and genomic data into future analyses of climate change impacts, which would enhance our ability to predict potential ecological shifts. [ABSTRACT FROM AUTHOR]

Under climate change circumstances, increasing studies have reported the temporal instability of tree growth responses to climate, which poses a major challenge to linearly extrapolating past climate and future growth dynamics using tree‐ring data. Space‐for‐time substitution (SFTS) is a potential solution to this problem that is widely used in the dendrochronology field to project past or future temporal growth response trajectories from contemporary spatial patterns. However, the projected accuracy of the SFTS in the climate effects on tree growth remains uncertain. Here, we empirically test the SFTS method by comparing the effect of spatial and temporal climate variations on climate responses of white spruce (Picea glauca), which has a transcontinental range in North America. We first applied a response surface regression model to capture the variations in growth responses along the spatial climate gradients. The results showed that the relationships between growth and June temperature varied along spatial climate gradients in a predictable way. And their relationships varied mainly along with local temperate condition. Then, the projected correlation coefficients between growth and climate using SFTS were compared against the observed. We found that the growth response changes caused by spatial versus temporal climate variations showed opposite trends. Moreover, the projected correlation coefficients using the SFTS were significantly lower than the observed. This finding suggests that applying the SFTS to project the growth response of white spruce might lead to an overestimation of the degree of tree maladaptation in future climate scenarios. And the overestimation is likely to get weaker from Alaska and Yukon Territory in the west to Quebec in the east. Although this is only a case study of the SFTS method for projecting tree growth response, our findings suggest that direct application of the SFTS method may not be applicable to all regions and all tree species. [ABSTRACT FROM AUTHOR]

As northern latitudes experience rapid winter warming, there is an urgent need to assess the effect of varying winter conditions on tree growth and forest carbon sequestration potential. We examined tree growth responses to variability in cold-season (November–- April) frequency of freeze days (FFD) over 1951 to 2018 using tree-ring data from 35,217 trees and 57 species at 4,375 sites distributed across Canada. We found that annual radial growth responses to FFD varied by species, with some commonalities across genera and clades. The growth of gymnosperms with late spring leaf-out strategies was negatively related to FFD; years with high FFD were most detrimental to the annual growth of Pinus banksiana, Pinus contorta, Larix lyalli, Abies amabilis, and Abies lasiocarpa. In contrast, the growth of angiosperms with early leaf-out strategies, namely, Populus tremuloides and Betula papyrifera, was better in the coldest years, and gymnosperms with intermediate leaf-out timing, such as widespread Picea mariana and Picea glauca, had no consistent relationship to FFD. Tree growth responses to FFD were further modulated by tree size, tree age, regional climate (i.e., mean cold-season temperature), and local site conditions. Overall, our results suggest that moderately warming winters may temporarily improve the growth of widespread pines and some high-elevation conifers in western Canada, whereas warming winters may be detrimental to the growth of widespread boreal angiosperms. Our findings also highlight the value of using species-specific climate-growth relationships to refine predictions of forest carbon dynamics. [ABSTRACT FROM AUTHOR]

Increasing air temperatures and changing precipitation patterns due to climate change can affect tree growth in boreal forests. Periodic insect outbreaks affect the growth trajectory of trees, making it difficult to quantify the climate signal in growth dynamics at scales longer than a year. We studied climate‐driven growth trends and the influence of spruce budworm (Choristoneura fumiferana Clem.) outbreaks on these trends by analyzing the basal area increment (BAI) of 2058 trees of Abies balsamea (L.) Mill., Picea glauca (Moench) Voss, Thuja occidentalis L., Populus tremuloides Michx., and Betula papyrifera Marsh, which co‐occurs in the boreal mixedwood forests of western Quebec. We used a generalized additive mixed model (GAMM) to analyze species‐specific trends in BAI dynamics from 1967 to 1991. The model relied on tree size, cambial age, degree of spruce budworm defoliation, and seasonal climatic variables. Overall, we observed a decreasing growth rate of the spruce budworm host species, A. balsamea and P. glauca between 1967 and 1991, and an increasing growth rate for the non‐host, P. tremuloides, B. papyrifera, and T. occidentalis. Our results suggest that insect outbreaks may offset growth increases resulting from a warmer climate. The observation warrants the inclusion of the spruce budworm defoliation into models predicting future forest productivity. [ABSTRACT FROM AUTHOR]

As boreal forests face significant threats from climate change, understanding evolutionary trajectories of coniferous species has become fundamental to adapting management and conservation to a drying climate. We examined the genomic architecture underlying adaptive variation related to drought tolerance in 43 populations of a widespread boreal conifer, white spruce (Piceaglauca [Moench] Voss), by combining genotype–environment associations, genotype–phenotype associations, and transcriptomics. Adaptive genetic variation was identified by correlating allele frequencies for 6,153 single nucleotide polymorphisms from 2,606 candidate genes with temperature, precipitation and aridity gradients, and testing for significant associations between genotypes and 11 dendrometric and drought‐related traits (i.e., anatomical, growth response and climate‐sensitivity traits) using a polygenic model. We identified a set of 285 genes significantly associated with a climatic factor or a phenotypic trait, including 110 that were differentially expressed in response to drought under greenhouse‐controlled conditions. The interlinked phenotype–genotype–environment network revealed eight high‐confidence genes involved in white spruce adaptation to drought, of which four were drought‐responsive in the expression analysis. Our findings represent a significant step toward the characterization of the genomic basis of drought tolerance and adaptation to climate in conifers, which is essential to enable the establishment of resilient forests in view of new climate conditions. see also the Perspective by Lars Opgenoorth and Christian Rellstab [ABSTRACT FROM AUTHOR]

Understanding the magnitude and cause of variation in tree growth and forest productivity is central to sustainable forest management. Measurements of annual growth rings allow assessments of individual-tree, tree population, and forest ecosystem vulnerabilities to drought stress or other changing forest disturbance regimes (insects, diseases, fire), which can be used to identify areas at greatest risk of forest losses. Given a heightened demand for tree-ring data, we consolidated and synthesized tree-ring studies and datasets gathered over the past 30 years in Canada by scientists with the Canadian Forest Service and research partners. We incorporated these datasets into a data repository that currently contains tree-ring measurements from 40 206 tree samples from 4594 sites and 62 tree species from all Canadian provinces and territories. Through our synthesis, we demonstrate the value of such large ensembles of tree-ring data for identifying patterns in tree growth over large spatial scales by mapping pan-Canadian drought sensitivity. Overall, we found high coherence in the samples analyzed; low coherence was generally limited to data-poor regions and species. Drought sensitivity was widespread across species and regions: 34% of sampled trees displayed a significant positive relationship between annual growth increment and summer soil moisture index. Dependence upon water availability in species Picea mariana (Mill.) BSP, Pinus banksiana Lamb., Pinus contorta Douglas ex Loudon, and Pseudotsuga menziesii (Mirb.) Franco was more strongly expressed in the warmest regions of the species' range; for species Picea glauca (Moench) Voss and Populus tremuloides Michx., drought sensitivity was stronger in the driest regions. This unprecedented consolidation and synthesis of tree-ring data will enable new research initiatives (e.g., meta-analyses) aimed at improved understanding of the drivers, patterns, and implications of changes in tree growth, as well as facilitating new research collaborations in earth and environmental sciences. Among other things, there is a need for expanding the spatial distribution of sites across Canada's northern regions, increasing the number of samples collected from older stands and angiosperm species, and integrating datasets from studies that evaluate the effects of silvicultural experiments, including provenance and progeny trials, on tree growth. [ABSTRACT FROM AUTHOR]

Increase in frost damage to trees due to earlier spring dehardening could outweigh the expected increase in forest productivity caused by climate warming. We quantified the impact of growing‐season frosts on the performance of three spruce species (white, black, and Norway spruce) and various seed sources with different frost tolerance in two plantations, established on both sides of the eastern Canadian boreal‐temperate forest ecotone. The objectives of this study were to determine (a) if spruce species and seed sources planted in sites far from their natural provenance would be less adapted to local site conditions, leading to increased frost damage and reduced height growth; (b) at which height above the ground growing‐season frosts ceased to damage apical meristems; and (c) if height growth was best predicted by extreme climatic events (growing‐season frosts) or by mean annual or summer temperature. At each site and for all spruce species and seed sources, we cross‐sectioned spruce trees at different heights above the ground. Tree rings were cross‐dated and screened for frost rings, which were then given a severity score based on cellular damage. Frost severity reduced height growth of all spruce species and provenances at both sites. Height growth of the non‐native Norway spruce was the most reduced by frost severity and was the smallest species at both sites. Frost caused the highest growth reduction in white spruce at the boreal mixedwood site and had the least effect on black spruce at both sites. For all spruce species, height growth was affected up to 2 m above the ground. Model selection based on corrected Akaike's information criteria (AICc) identified that minimum temperature in May was by far the best climate variable predicting tree growth (AICc weight = 1), highlighting the importance of considering extreme climatic events, which are likely to increase in the future. [ABSTRACT FROM AUTHOR]

The ecological function of boreal forests is challenged by drastically changing climate conditions. Although an increasing number of studies are investigating how climate change is influencing growth and distribution of boreal tree species, there is a lack of studies examining the potential of these species to genetically adapt or phenotypically adjust. Here, we sampled clonally and non-clonally growing white spruce trees (Picea glauca [Moench] Voss) to investigate spatial and genetic effects on tree ring width and on six xylem anatomical traits representing growth, water transport, mechanical support, and wood density. We compared different methods for estimating broad sense heritability (H2) of each trait and we evaluated the effects of spatial grouping and genetic grouping on the xylem anatomical traits with linear models. We found that the three different methods used to estimate H2 were quite robust, showing overall consistent patterns, while our analyses were unsuccessful at fully separating genetic from spatial effects. By evaluating the effect size, we found a significant effect of genetic grouping in latewood density and earlywood hydraulic diameter. However, evaluating model performances showed that spatial grouping was a better predictor than genetic grouping for variance in earlywood density, earlywood hydraulic diameter and growth. For cell wall thickness neither spatial nor genetic grouping was significant. Our findings imply that (1) the variance in the investigated xylem anatomical traits and growth is mainly influenced by spatial clustering (most probably caused by microhabitat conditions), which (2) makes it rather difficult to estimate the heritability of these traits in naturally grown trees in situ. Yet, (3) latewood density and earlywood hydraulic diameter qualified for further analysis on the genetic background of xylem traits and (4) cell wall thickness seems a useful trait to investigate large-scale climatic effects, decoupled from microclimatic, edaphic and genetic influences. [ABSTRACT FROM AUTHOR]

Analyses of maximum early tree ring growth within a regional curve standardization (RCS) framework were used to construct ring width chronologies in mm year−1 to estimate historical growth rates in southwest Yukon (Canada), without the necessity of correcting for age related changes. The analysis relied on the use of the 11th–50th year growth rings to standardize chronology comparisons. This age range represents the period of peak radial growth for Picea albertiana and P. glauca (white spruces), which are common trees on upland boreal sites in the study area. Of 1,460 available Picea ring series, 1,029 fit the criteria for inclusion in the study and they represented five commonly occurring RCS curve types. When converted to chronologies, all curve types had year-to-year fluctuations in average ring widths (RW11–50), but nine of the 12 RCS types (four types in three study areas) also had long-term growth rate increases of 15–132% between ad 1850 and 2000, based on regression modeling (R/r = 0.54–0.76, p < 0.001). Associated with these increases were changes through time in RCS curve type and the timing of peak growth. Among studied areas, RW11–50 values on average increased 47% from 1.59 to 2.35 mm year−1 between 1850 and 2000. The greatest increase (71% vs 35–38%) occurred in the coldest study area. RW11–50 values were significantly (p < 0.001) and strongly correlated (r > 0.94, n > 100) with conventional tree ring width index values derived from multiple RCS curves. This indicates that the two chronology construction approaches have very similar temporal patterns despite the maximum early growth analysis technique representing ring widths in mm. [ABSTRACT FROM AUTHOR]

Abstract: A growing body of evidence suggests that climate change will have complex effects on the boreal forests of western Canada. Studies that examine historical species responses over large geographic and climatic distances may provide insights into the temporal and spatial complexities underlying forest vulnerabilities to climate change. We analyzed annual tree-ring data collected from 56 white spruce (Picea glauca (Moench) Voss) populations across the species’ distribution in Yukon, Canada. Regional growth patterns were identified and correlation and response functions were computed to determine primary climatic influences on growth within each region. The temporal stability of climate–growth relationships was also tested in regions with sufficient climate records. Key results showed that white spruce radial growth shows strong geographic patterns across Yukon, likely reflecting large-scale climatic influences on growth. Drought appears to be a primary limitation to white spruce growth across much of southern Yukon, whereas snowfall and summer temperatures may be more important limitations in other regions. Spruce populations growing at high-elevations in central Yukon may be changing their climatic sensitivity over time and are converging with low-elevation populations in terms of climate–growth relationships. The considerable spatial and temporal complexity of climate–growth responses suggest that climate change will have varying implications for white spruce growth across Yukon. [Copyright &y& Elsevier]

The tree annual ring is defined and geometrically described by two new physical quantities designated as golden ring cube (GRC) and golden ring volume (GRV). The quantities were used to derive a two-level system dynamical coarse-graining framework for annual rings by applying non-equilibrium equality of free energy differences of dynamical repetitive transitions from earlywood to latewood and vice versa. The scaling properties of growth rings interaction parameter β, GRC and GRV were then numerically quantified and tested for Douglas-fir and white spruce. Although parameter β was different for Douglas-fir and white spruce, its invariant property was tested and found to be the same for both species. The parameter β was thereafter used to derive a novel heterogeneity test criterion that was described and tested. β is an important parameter that provides integrated information for the dependence of the GRV and GRC on species, growth factors, and environmental interaction signals. [ABSTRACT FROM AUTHOR]

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Research Highlights: This research presents a novel approach for comparing structural carbon allocation to tree growth and to climate in a dendrochronological analysis. Increasing temperatures reduced the carbon proportion of wood in some cases. Background and Objectives: Our goal was to estimate the structural carbon content of wood within hybrid white spruce (Picea glauca (Moench) × engelmannii (Parry) grown in British Columbia, Canada, and compare the percent carbon content to wood properties and climate conditions of the region. Specific objectives included: (i) the determination of average incremental percent carbon, ring widths (RW), earlywood (EW) and latewood (LW) widths, cell wall thickness, and density over time; (ii) the determination of differences between percent carbon in individual forest stands and between regions; and (iii) the evaluation of the relationships between percent carbon and climate variation over time. Methods: Trees were sampled from twelve sites in northern British Columbia. Wood cores were analyzed with standard dendrochronology techniques and SilviScan analysis. Percent structural carbon was determined using acetone extraction and elemental analysis for 5 year increments. Individual chronologies of wood properties and percent carbon, and chronologies grouped by region were compared by difference of means. Temperature and precipitation values from the regions were compared to the carbon chronologies using correlation, regression, and visual interpretation. Results: Significant differences were found between the percent structural carbon of wood in individual natural and planted stands; none in regional aggregates. Some significant relationships were found between percent carbon, RW, EW, LW, and the cell wall thickness and density values. Percent carbon accumulation in planted stands and natural stands was found in some cases to correlate with increasing temperatures. Natural stand percent carbon values truncated to the last 30 years of growth was shown as more sensitive to climate variation compared to the entire time series. Conclusions: Differences between the stands in terms of structural carbon proportion vary by site-specific climate characteristics in areas of central interior British Columbia. Wood properties can be good indicators of variation in sequestered carbon in some stands. Carbon accumulation was reduced with increasing temperatures; however, warmer late-season conditions appear to enhance growth and carbon accumulation. [ABSTRACT FROM AUTHOR]

Trees growing near the Arctic treeline have long been used to reconstruct past climates. However, recent studies have shown deterioration of historically strong positive correlations between air temperature and tree growth (known as "divergence"). Divergence has important implications for confidence in paleoclimate reconstructions and ecosystem–atmosphere carbon exchange. Studies in the Brooks Range of northern Alaska showed that white spruce in the west increased growth in response to late 20th century warming, whereas those in the east failed to show a growth increase. In an earlier study across four watersheds in the Brooks Range, we tested and rejected the hypothesis that divergence in the easternmost watershed reflects moisture limitation of growth. Here, using 16 sites distributed across the same four watersheds, we tested an alternative hypothesis, that greater nutrient limitation in the east may have impeded positive growth responses to warming. Climate comparison across the four Brooks Range study watersheds revealed that, although the easternmost watershed generally had a drier growing‐season climate, the most consistent difference was that winter air temperature and both winter and summer soil temperatures were much colder in the central and eastern watersheds. Soil nutrient availability, foliar nutrient concentrations, and tree growth were all generally lower in the central and eastern than in the western watersheds. Foliar phosphorus concentration was the best predictor of spatial variation in branch extension growth—a finding that is somewhat inconsistent with the theory that forest productivity on young, glacially derived soils should be strongly nitrogen limited. Experimental fertilization yielded the greatest growth increase in the eastern, an intermediate response in the central, and the smallest growth increase in the western watershed, generally mirroring trends in soil temperature, soil nutrient availability, foliar nutrient concentrations, and growth of control trees. Our results confirm that growth in the easternmost watershed is more nutrient limited and suggest that phosphorus limitation may be at least as important as nitrogen limitation of growth. We hypothesize that cold soil effects on tree access to nutrients might explain divergence in the eastern Brooks Range and elsewhere near the Arctic treeline, particularly in areas with cold winters and widespread permafrost. [ABSTRACT FROM AUTHOR]

We examined phenotypic relationships among radial growth-related, physical (i.e., related to wood density), and anatomical (i.e., related to tracheid dimensions) wood properties in white spruce (Picea glauca (Moench) Voss), in order to determine the strength and significance of their correlations. Additionally, principal component analysis (PCA) was used to establish if all of the properties must be measured and to determine the key properties that can be used as proxies for the other variables. Radial growth-related and physical properties were measured with an X-ray densitometer, while anatomical properties were measured with a Fiber Quality Analyzer. Fifteen wood properties (tracheid length (TL) and diameter (TD), earlywood tracheid length (ETL) and diameter (ETD), latewood tracheid length (LTL) and diameter (LTD), ring width (RW), ring area (RA), earlywood width (EWW), latewood width (LWW), latewood proportion (LWP), ring density (RD), intra-ring density variation, earlywood density (EWD), and latewood density (LWD)) were assessed. Relationships were evaluated at intra-ring and inter-ring levels in the juvenile wood (JW) and mature wood (MW) zones. Except for a few cases when mature tracheid diameter (TD) was involved, all intra-ring anatomical properties were highly and significantly correlated. Radial growth properties were correlated, with stronger relationships in MW compared to JW. Physical properties were often positively and significantly correlated in both JW and MW. A higher earlywood density coupled with a lower latewood density favored wood uniformity, i.e., the homogeneity of ring density within a growth ring. Managing plantations to suppress trees growth during JW formation, and enhancing radial growth when MW formation starts will favor overall wood quality. In order, RW-EWW-RA, TL-ETL-LTL, and RD-EWD-LWP are the three clusters that appeared in the three wood zones, the whole pith-to-bark radial section, the juvenile wood zone, and the mature wood zone. [ABSTRACT FROM AUTHOR]