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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]

Global change in the climate is affecting tree/forest growth. There have been many studies that analyzed climate effects on tree growth. Results presented in these studies showed that the climate had both positive and negative effects on tree growth. The nature (positive/negative) and magnitude of the effects and the climate variables affecting growth depended on tree species. Climate-sensitive diameter growth models are not available for white pine (Pinus strobus L.) and white spruce (Picea glauca (Moench) Voss) plantations. These models are needed to project forest growth and yield and develop forest management plans. Therefore, diameter growth models were developed for white pine and white spruce plantations by incorporating climate variables. Four hundred white pine and white spruce trees (200 per species) were sampled from 80 (40 per species) even-aged monospecific plantations (five trees per plantation) across Ontario, Canada. Diameter–age pairs were obtained from these trees using stem analysis. A nonlinear mixed-effects modeling approach was used to develop diameter growth models. To make the models climate sensitive, model parameters were expressed in term of climate variables. Inclusion of climate variables significantly improved model fit statistics and predictive accuracy. For evaluation, diameters (inside bark) at breast height were estimated for three geographic locations (east, west, and south) across Ontario for an 80-year growth period (2021–2100) under three climate change (emissions) scenarios (representative concentration pathway or RCP 2.6, 4.5, and 8.5 watts m−2). For both species, the overall climate effects were negative. For white spruce, the maximum pronounced difference in projected diameters after the 80-year growth period was in the west. At this location, compared to the no climate change scenario, projected spruce diameters under RCPs 2.6 and 8.5 were thinner by 4.64 (15.99%) and 3.72 (12.80%) cm, respectively. For white pine, the maximum difference was in the south. Compared to the no climate change scenario, projected pine diameters at age 80 under RCPs 2.6 and 8.5 at this location were narrower by 4.54 (13.99%) and 7.60 (23.43%) cm, respectively. For both species, climate effects on diameter growth were less evident at other locations. If the values of climate variables are unavailable, models fitted without climate variables can be used to estimate these diameters for both species. [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]

Climate change may have spatially variable impacts on growth of trees in topographically diverse environments, making generalizing across broad spatial and temporal extents inappropriate. Therefore, topography must be considered when analyzing growth response to climate. We address these topo-climatic relationships in the Canadian Rocky Mountains, focusing on lodgepole pine (Pinus contorta Douglas ex Louden) and interior spruce (Picea glauca (Moench) Voss × Picea engelmannii hybrid Parry) growth response to climate, Palmer drought severity index (PDSI), aspect, and slope angle. Climate variables correlate with older lodgepole pine growth on south- and west-facing slopes, including previous August temperature, winter and spring precipitation, and previous late-summer and current spring PDSI, but younger lodgepole pine were generally less sensitive to climate. Climate variables correlate with interior spruce growth on all slope aspects, with winter temperature and PDSI important for young and old individuals. Numerous monthly growth–climate correlations are not temporally stable, with shifts over the past century, and response differs by slope aspect and angle. Both species are likely to be negatively affected by moisture stress in the future in some, but not all, topographic environments. Results suggest species-specific and site-specific spatiotemporally diverse climate–growth responses, indicating that climate change is likely to have spatially variable impacts on radial growth response in mountainous environments. [ABSTRACT FROM AUTHOR]

Under a changing climate, tree improvement programs should revise breeding zones to improve climate change adaptation and program efficiency once information about adaptive capacity of breeding populations and genotype × environment (G × E) interaction becomes available. In this study, we evaluated the adaptation and growth, as well as G × E interactions, shown by white spruce (Picea glauca (Moench) Voss) open-pollinated (OP) families across two adjacent breeding zones (i.e., the BZ3300 and BZ4300, respectively) in northwestern Ontario using progeny test data, including 80 OP families (40 from each) that were cross-tested between the breeding zones. Results showed that the OP families from the southerly BZ4300 breeding zone averaged higher survival and significantly greater mean tree height growth than the local OP families in the more northern BZ3300 breeding zone at tree age of 14 years, with no notable difference in frost damage. Estimates of type-B genetic correlation from pairwise tests or combined-test analyses were almost all greater than 0.7, suggesting weak G × E interactions. Greater variation among families and higher heritability estimates in tree height were observed for families from the BZ3300 breeding zone or when families from the two breeding zones were combined. The weak G × E interactions, in addition to better survival and growth of the southerly families in the more northern breeding zone, suggested benefits from deploying seed from current seed orchard in the BZ4300 breeding zone to the BZ3300 breeding zone and merging the two breeding zones when starting the second generation breeding to increase tree improvement efficiency and likely higher genetic gain under future climate. [ABSTRACT FROM AUTHOR]

Growth of trees at their altitudinal and latitudinal range limits is expected to increase as climate warms, but trees often exhibit unexplained spatial and temporal variation in climate-growth responses, particularly in alpine regions. Until this variability is explained, predictions of future tree growth are unlikely to be accurate. We sampled Picea glauca (white spruce) growing at forest and tree line on north and south aspects in two mountain ranges of southwest Yukon to determine how and why ring-width patterns vary between topographic settings, and over time. We used multivariate statistical analysis to characterize variation in ring-width patterns between topographic factors and time periods, and calculated correlations between ring-width indices and climate variables to explain this variation. Ring-width patterns varied more between mountain ranges than elevations or aspects, particularly in recent decades when ring-widths increased in one mountain range but not the other. Growth responses to summer temperature were notably weaker during warmer time periods, but growth was not positively correlated to summer precipitation, suggesting trees may not be suffering from temperature-induced drought stress. Rather, ring-width indices began responding positively to spring snow depth after 1976. We conclude that tree growth is unlikely to increase in synchrony with rising air temperatures across subarctic tree lines in southwest Yukon. Instead, they may decline in areas that are prone to thin snowpacks or rapid spring runoff due to the negative influence warming springs will have on snow depth and, consequently, early growing season soil moisture. [ABSTRACT FROM AUTHOR]

Climate change is expected to increase winter temperatures in boreal climates. White spruce ( Picea glauca (Moench) Voss) is vulnerable to spring frost damage due to its habit of early budbreak, which may be exacerbated or lessened with increasingly warm winters at its southern range edge. We tested the effects of episodic warming during the quiescent stage on budbreak time and growth of seven seed sources grown in a common garden setting in Minnesota, USA. Treatment plots were warmed with infrared lamps for 4 days each in February, March, or February and March to simulate a midwinter thaw. Control plots for each treatment and an overall control were included for comparison. Trees warmed in February experienced a slight delay in spring budbreak, but differences in budbreak time were generally not significant. Terminal growth was significantly and negatively correlated with time of budbreak but not with time to growth cessation. Our results suggest that white spruce is relatively resilient to the effects of intermittent warming but that warming early in the season may delay budbreak time, which is expected to reduce terminal growth. [ABSTRACT FROM AUTHOR]

Aim A critical concern for boreal ecosystems centres on broad-scale responses to warming, i.e. declining growth and mortality, or enhanced growth and greater productivity. However, few studies have synthesized tree growth along biogeographic gradients to address this issue. This study develops a broader understanding of how growth of a dominant conifer has responded to recent warming near the western forest margin of Alaska. Location Alaska, United States. Methods Thirty Picea glauca sites in south-west Alaska (1216 trees ≥ 4 cm dbh) were evaluated for growth differences from the southern boreal forest to the western forest-tundra margin across low-elevation forests and woodlands, and altitudinal tree line. Regional climate records were used to evaluate (1) whether tree growth near western tree line showed greater sensitivity to temperature and/or precipitation than southern boreal sites, (2) if the climate-growth response varied through time, across ecoregions and ecosystems, with spruce beetle disturbance, and by tree age, and (3) if there was a temperature threshold that limited growth. Results Positive growth trends since the 1980s in many open stands were consistent with the predicted expansion of western and altitudinal tree line. However, growth levelled off with temperatures ≥ 13°C at all but altitudinal tree line. An increasingly positive effect of precipitation on growth occurred after 1985, particularly at boreal tree line and closed forest sites. Closed-canopy forests showed lower rates of growth, greater spruce beetle activity and less potential for resiliency to warming than other ecosystem types. Main Conclusions Warming has led to markedly different growth responses according to ecosystem type and ecoregion near the forest-tundra margin. Altitudinal tree line sites showed consistently positive growth with warmer temperatures in recent decades, whereas low-elevation forests had reduced growth and greater beetle mortality. Strong positive correlations between growth and summer-fall precipitation since the mid-1980s suggest that precipitation will become an increasingly important factor with further warming. [ABSTRACT FROM AUTHOR]

Abstract: We present a reconstruction of June–July minimum temperatures since AD1245 for the Mackenzie Delta region based on a 29-site network of white spruce (Picea glauca) ring-width series. Most but not all trees experienced a divergent temperature–growth response, similar to the divergence that has affected other white spruce trees across Yukon and Alaska. However, divergence in the study region began as early as AD1900 and we have documented our methods to avoid including divergent signals in the reconstruction. Calibration/verification testing based on local temperature data, and multi-century coherence with nearby and large-scale temperature proxy records, confirm that our reconstruction is robust. The reconstruction shows cool conditions in the late 13th, early 18th and early 19th centuries, corresponding with solar minima and increased volcanism. These cool periods are interrupted by warm periods consistent with early to mid-20th century warmth. The late 20th century is the warmest interval, and the last decade is estimated to be 1.4°C warmer than any decade before the mid-20th century. The reconstructed climate history corroborates other proxy-based inferences and supports the notion that high-latitude regions such as the Mackenzie Delta have experienced rapid warming in recent decades that is exceptional in the last eight centuries. [Copyright &y& Elsevier]

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]

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]

• Climate change may cause reduced forest productivity and higher tree mortality. • We infer white spruce growth limitations from 9795 tree cores from 227 sample sites. • Water deficits make trees vulnerable to climate change in its west-central range. • Future climate projections imply water deficits in the southwest and central boreal. • The north-east may be a climate change refugium due to lack of water deficits. Climate change may cause reduced forest productivity and higher tree mortality due to water deficits that result from increased evapotranspiration. Such limitations may occur in some areas of the North American boreal forest where precipitation is low and warming trends are high. This paper analyzes climatic factors that limit the growth of a commercially important and widespread boreal tree species, white spruce (Picea glauca (Moench) Voss), based on a range-wide dendroclimatological analysis of 9795 trees from 227 sample sites across the North American boreal forest. A bootstrapped response function analysis was conducted for monthly temperature and precipitation variables, and a multivariate regression tree analysis was used to group white spruce populations with similar response coefficients where climatic factors explained 46% of the total variance in response coefficients. The results of this study show that white spruce populations in the west-central boreal forest of North America are the most precipitation-limited group and therefore likely to be most susceptible to climate change. Populations both to the north and south of this group appear less vulnerable, and eastern populations generally do not experience growth-limiting moisture deficits. Regional climate change projections suggest that moisture limitations will become more pronounced in the future, especially for southwest and west-central boreal tree populations. [ABSTRACT FROM AUTHOR]