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Climate change is having complex impacts on the boreal forest, modulating both tree growth limiting factors and fire regime. However, these aspects are usually projected independently when estimating climate change effect on the boreal forest. Using a combination of three different methods, our goal is to assess the combined impact of changes in growth and fire regime due to climate change on the timber supply at the transitions from closed to open boreal coniferous forests in Quebec, Canada. To identify the areas that are likely to be the most sensitive to climate change, we projected climate-induced impacts on growth and fire activity at three different time periods: 2011-2040 RCP 8.5 for low growth change and minimum fire activity, 2071-2100 RCP 4.5 for moderate growth change and medium fire activity, and 2071-2100 RCP 8.5 for high growth change and maximum fire activity. Our study shows the importance of incorporating fire in strategic forest management planning especially in a context of climate change. Under the most extreme scenarios, the negative impact of fire activity on productive area and total volume mostly offsets the positive effects of climate change via improved tree growth. Key words: boreal forests, climate change, productivity, growth, fire regime Le changement climatique a des impacts complexes sur la foret boreale, modulant a la fois les facteurs limitant la croissance des arbres et le regime des feux. Cependant, ces derniers sont generalement projetes independamment lors de l'etude de l'effet du changement climatique sur la foret boreale. En utilisant une combinaison de 3 methodes differentes, notre objectif est d'evaluer l'impact combine des changements de croissance et de regime des feux dus au changement climatique sur l'approvisionnement en bois a la transition entre les forets boreales de coniferes fermees et ouvertes au Quebec, Canada. Afin d'identifier les zones susceptibles d'etre les plus sensibles au changement climatique, nous avons projete les impacts induits par le climat sur la croissance et l'activite des feux a trois periodes differentes : 2011-2040 RCP 8.5 pour un faible changement de croissance et une activite de feux minimale, 2071-2100 RCP 4.5 pour un changement de croissance modere et une activite de feux moyenne, et 2071-2100 RCP 8.5 pour un fort changement de croissance et une activite de feux maximale. Notre etude montre l'importance d'integrer le feu dans la planification strategique de l'amenagement forestier, en particulier dans un contexte de changement climatique. Dans les scenarios les plus extremes, l'impact negatif de l'activite des feux sur la superficie productive et le volume total annule en grande partie les effets positifs du changement climatique via l'amelioration de la croissance des arbres. Mots-cles: forets boreales, changement climatique, productivite, croissance, regime des feux, Introduction The boreal forest is a key ecosystem on many levels (ecological, economic, cultural, etc.), particularly in Canada where the timber industry is one of the most important industries in [...]

Non-technical summary We summarize what we assess as the past year's most important findings within climate change research: limits to adaptation, vulnerability hotspots, new threats coming from the climate-health nexus, climate (im)mobility and security, sustainable practices for land use and finance, losses and damages, inclusive societal climate decisions and ways to overcome structural barriers to accelerate mitigation and limit global warming to below 2°C. Technical summary We synthesize 10 topics within climate research where there have been significant advances or emerging scientific consensus since January 2021. The selection of these insights was based on input from an international open call with broad disciplinary scope. Findings concern: (1) new aspects of soft and hard limits to adaptation; (2) the emergence of regional vulnerability hotspots from climate impacts and human vulnerability; (3) new threats on the climate-health horizon - some involving plants and animals; (4) climate (im)mobility and the need for anticipatory action; (5) security and climate; (6) sustainable land management as a prerequisite to land-based solutions; (7) sustainable finance practices in the private sector and the need for political guidance; (8) the urgent planetary imperative for addressing losses and damages; (9) inclusive societal choices for climate-resilient development and (10) how to overcome barriers to accelerate mitigation and limit global warming to below 2°C. Social media summary Science has evidence on barriers to mitigation and how to overcome them to avoid limits to adaptation across multiple fields.

Assisted gene flow according to expected climate gradients is considered as a forest management strategy to mitigate impacts of environmental change on forest growth. However, the effects of seed translocation on wood properties and lumber quality remain unknown. This study evaluated the effect of provenance origin on lumber production and quality at rotation age in two white spruce provenance trials established in contrasting environments in eastern Canada. Based on 108 sample trees, which resulted in 943 pieces of lumber, average volume production per tree at the southernmost site was twice that of the production at the northern site. Provenance had a significant influence on growth and lumber strength in the first sawlog but had no effect on lumber stiffness and wood density. Although visual grade yields of No. 2 and better were high in both trials (over 86%), the machine stress rated (MSR) grade potential and percentage of lumber that met the bending stiffness design values of the visual grades were generally low (12%-26%). Hence, plantation-grown lumber should preferably be machine stress rated to ensure its fitness for structural applications in buildings. Management strategies aiming to efficiently sequester carbon should primarily maximize volume productivity in northern sites, as moving seed sources north still reduces provenance productivity, while breeding programs should aim to prevent decrease in lumber stiffness due to augmented productivity and shortened rotation cycles. Key words: assisted migration, lumber visual grade, provenance trial, MOE (stiffness), MOR (strength), wood density, tree breeding Le flux genetique assiste, selon les gradients climatiques prevus, est considere comme une strategie de gestion des forets visant a attenuer les impacts des changements environnementaux sur la croissance des forets. Toutefois, les effets de la translocation des graines sur les proprietes du bois et la qualite des sciages demeurent inconnus. La presente etude a evalue l'effet de l'origine de la provenance sur la production et la qualite du bois d'reuvre a un age de rotation dans deux essais de provenance d'epinettes blanches etablis dans des environnements contrastes dans l'Est du Canada. Fonde sur 108 arbres echantillons qui ont produit 943 pieces de bois d'reuvre, la production moyenne en volume par arbre sur le site le plus au sud etait le double de la production du site au nord. La provenance a eu une influence significative sur la croissance et la resistance du bois d'reuvre dans la premiere bille de sciage, mais n'a pas eu d'effet sur la rigidite des sciages et la densite du bois. Meme si les rendements en grades visuels No. 2 et meilleur etaient eleves dans les deux essais (plus de 86 %), le potentiel de classer les sciages dans les categories de bois MSR (bois evalues par contrainte mecanique) et le pourcentage de bois d'reuvre qui respectait les valeurs de conception de la rigidite en flexion des grades visuels etaient generalement faibles (12 % a 26 %). Par consequent, le bois d'reuvre qui a pousse en plantation devrait de preference etre classe par contrainte mecanique afin d'assurer sa conformite a des applications structurales dans des batiments. Les strategies de gestion visant a sequestrer efficacement le carbone devraient avant tout maximiser la productivite en volume dans les sites du nord, puisque le deplacement des sources de graines au nord reduit toujours la productivite de la provenance, alors que les programmes de selection devraient viser a prevenir la diminution de la rigidite du bois d'reuvre en raison de l'augmentation de la productivite et de la diminution des cycles de rotation. [Traduit par la Redaction] Mots-cles : migration assistee, qualite visuelle du bois d'reuvre, essai de provenance, MOE (rigidite), MOR (resistance), densite du bois, amelioration des arbres, Introduction Canada's forest economy has largely developed around the utilization of abundant, high-quality, but largely unmanaged softwood resource (Barbour and Kellogg 1990). However, the increasing pressure on fibre resources from [...]

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. Key words: tree rings, multispecies database, annual growth responses, drought, Canada. II est essentiel de comprendre l'ampleur et la cause de la variation de la croissance des arbres et de la productivity des forets pour une gestion durable de celles-ci. Les mesures des cernes de croissance annuels permettent d'evaluer la vulnerabilite des arbres individuels, des populations d'arbres et des ecosystemes forestiers au stress de la secheresse ou a d'autres regimes changeants de perturbation des forets (insectes, maladies, incendies), ce qui peut etre utilise pour identifier les zones les plus exposees au risque de pertes forestieres. Compte tenu de la demande accrue de donnees sur les cernes de croissance des arbres, les auteurs ont consolide et synthetise les etudes et les ensembles de donnees sur les cernes de croissance d'arbres, recueillis au cours des 30 dernieres annees au Canada par les scientifiques du Service canadien des forets et des partenaires de recherche. lis ont integre ces ensembles de donnees dans un depot de donnees qui comprend actuellement les mesures des cernes de 40 206 echantillons d'arbres provenant de 4594 sites et de 62 especes d'arbres de toutes les provinces et territoires du Canada. Grace a cette synthese, les auteurs demontrent la valeur de ces grands ensembles de donnees sur les cernes de croissance des arbres pour identifier les patrons de croissance des arbres a de grandes echelles spatiales en cartographiant la sensibilite a la secheresse a l'echelle pancanadienne. Dans l'ensemble, ils ont constate une grande coherence dans les echantillons analyses; la faible coherence etait generalement limitee aux regions et aux especes pour lesquelles les donnees etaient insuffisantes. La sensibilite a la secheresse etait tres repandue parmi les especes et les regions : 34 % des arbres echantillonnes presentaient une relation positive significative entre l'augmentation annuelle de la croissance et l'indice d'humidite du sol en ete. La dependance a l'egard de la disponibilite de l'eau chez les especes Picea mariana (Mill.) BSP, Pinus banksiana Lamb., Pinus contorta Douglas ex Loudon et Pseudotsuga menziesii (Mirb.) Franco etait plus fortement exprimee dans les regions les plus chaudes de l'aire de repartition des especes; pour les especes Piceaglauca (Moench) Voss et Populus tremuloides Michx., la sensibilite a la secheresse etait plus forte dans les regions les plus seches. Cette consolidation et cette synthese sans precedent des donnees sur les anneaux des arbres permettront de nouvelles initiatives de recherche (par exemple, des meta-analyses) visant a ameliorer la comprehension des facteurs, des patrons et des implications des changements dans la croissance des arbres, ainsi qu'a faciliter de nouvelles collaborations de recherche en sciences de la terre et en environnement. II est notamment necessaire d'elargir la repartition spatiale des sites dans les regions nordiques du Canada, d'augmenter le nombre d'echantillons preleves dans les vieux peuplements et les especes d'angiospermes, et d'integrer les ensembles de donnees provenant d'etudes qui evaluent les effets des experiences sylvicoles, y compris des essais de provenance et de descendance, sur la croissance des arbres. [Traduit par la Redaction] Mots-cles: anneaux des arbres, base de donnees multiespeces, reponses de croissance annuelle, secheresse, Canada., 1. Introduction Tree rings--succeeding bands of light wood produced in the spring (earlywood) and dark wood formed at the end of the summer (latewood)--reflect the life history and environment of [...]

Climate change (CC) necessitates reforestation/afforestation programs to mitigate its impacts and maximize carbon sequestration. But comprehending how tree growth, a proxy for fitness and resilience, responds to CC is critical to maximize these programs' effectiveness. Variability in tree response to CC across populations can notably be influenced by the standing genetic variation encompassing both neutral and adaptive genetic diversity. Here, a framework is proposed to assess tree growth potential at the population scale while accounting for standing genetic variation. We applied this framework to black spruce (BS, Picea mariana [Mill] B.S.P.), with the objectives to (1) determine the key climate variables having impacted BS growth response from 1974 to 2019, (2) examine the relative roles of local adaptation and the phylogeographic structure in this response, and (3) project BS growth under two Shared Socioeconomic Pathways while taking standing genetic variation into account. We modeled growth using a machine learning algorithm trained with dendroecological and genetic data obtained from over 2600 trees (62 populations divided in three genetic clusters) in four 48‐year‐old common gardens, and simulated growth until year 2100 at the common garden locations. Our study revealed that high summer and autumn temperatures negatively impacted BS growth. As a consequence of warming, this species is projected to experience a decline in growth by the end of the century, suggesting maladaptation to anticipated CC and a potential threat to its carbon sequestration capacity. This being said, we observed a clear difference in response to CC within and among genetic clusters, with the western cluster being more impacted than the central and eastern clusters. Our results show that intraspecific genetic variation, notably associated with the phylogeographic structure, must be considered when estimating the response of widespread species to CC. [ABSTRACT FROM AUTHOR]

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]