Typologie, dynamique et valeur de conservation des vieilles forêts boréales résineuses de l’Est du Canada en territoire aménagé

La conservation des vieilles forêts, c’est-à-dire les peuplements dynamisés par les perturbations naturelles secondaires, dans les territoires aménagés du biome boréal est désormais un enjeu environnemental majeur. L’efficacité des mesures de gestion prises à leur encontre nécessite néanmoins une bonne connaissance des écosystèmes que l’on regroupe sous le terme « vieille forêt ». L’objectif de cette thèse est donc d’améliorer nos connaissances quant à la diversité, la dynamique et la conservation des vieilles forêts boréales résineuses dans les territoires aménagés de l’Est du Canada. Cette étude se concentre sur un territoire d’étude de 2200km2 situé dans le domaine bioclimatique de la pessière noire à mousse du Québec, Canada. Les caractéristiques structurelles de 74 peuplements, matures à surannés, y ont été échantillonnées. Des analyses dendrochronologiques ont aussi été réalisées pour 21 de ces sites. Enfin, nous avons utilisé les données des inventaires forestiers décennaux réalisés par le gouvernement du Québec depuis les années 60 pour observer l’évolution des vieilles forêts dans le territoire d’étude ainsi que l’acuité avec laquelle elles sont identifiées. Nos résultats montrent que les vieilles forêts boréales sont structurellement très diversifiées. Onze différentes structures ont ainsi pu être identifiées. Cette diversité résulte pour partie de la topographie mais augmente aussi avec le temps depuis la dernière perturbation majeure. La dynamique de perturbation secondaire de ces écosystèmes gagne aussi en complexité au fur et à mesure que la première cohorte, apparue suite à la dernière perturbation majeure, est remplacée par de nouvelles cohortes, renforçant cette diversité structurelle. Au début du processus de transition vers l’état de vieille forêt, les perturbations de sévérité faible dominent mais les perturbations de sévérité modérée gagnent progressivement en importance, jusqu’à atteindre un niveau similaire à celui des perturbations de sévérité faible. Les épidémies de tordeuse des bourgeons de l’épinette (Choristoneura fumiferana, Clemens) apparaissent alors comme un élément clé de cette dynamique de perturbations secondaires, indépendamment de leur sévérité. En comparaison des feux de forêt, l’aménagement forestier a récolté une plus grande proportion de vieilles forêts (se définissant ici par un âge supérieur à 100 ans) sur ce territoire, notamment caractérisées par un volume de bois marchand plus important. L’influence de l’exploitation forestière sur la diversité structurelle du territoire diffère donc de celle du feu. Par ailleurs, le plus récent inventaire photographique aérien réalisé par le gouvernement du Québec sous-estimait fortement l’abondance des vieilles forêts sur le territoire d’étude. La majorité de ces peuplements, se définissant sur le terrain par une structure complexe, étaient identifiés comme des peuplements équiens (c’est- à-dire structurellement simples) par l’inventaire aérien. Des seuils inadaptés à la forêt boréale ainsi que l’absence d’éléments de vieilles forêts particulièrement visibles par télédétection ou suivant une observation superficielle du peuplement peuvent expliquer ces résultats. Une fois le stade de vieille forêt atteint, les peuplements forestiers boréaux continuent donc de suivre une dynamique complexe, ce qui peut mener à de nombreux changements structuraux dans le temps. La diversité des vieilles forêts boréales doit donc être reconnue dans l’aménagement forestier, car impliquant la présence de nombreux types d’habitats nécessaires à la biodiversité. Nos résultats montrent cependant que les peuplements récoltés en priorité sont les vieilles forêts avec la plus forte valeur marchande. Ignorer cette diversité – par exemple en se retreignant à un simple pourcentage de vieilles forêts à conserver, qu’importe leur type – pourrait donc mener à une réduction de la diversité structurelle des vieilles forêts en territoire aménagé, causant à terme une perte d’habitat. Dans l’état actuel des choses, les inventaires photographiques aériens ne permettent pas de reconnaître la diversité des vieilles forêts, ce qui empêche la mise en place de stratégies efficaces. Intégrer de manière durable les vieilles forêts boréales dans l’aménagement forestier demande par conséquent non-seulement la reconnaissance de la richesse et de la complexité de ces écosystèmes, mais aussi le développement d’outils permettant d’assurer l’identification des nombreuses formes sous lesquelles elles peuvent se présenter. Maintaining old-growth forests, i.e. stands driven by gap-dynamics, in managed boreal landscapes is a major environmental issue. The efficacy of old-growth forests conservation strategies depends however on an adequate knowledge about these ecosystems. The objective of this thesis is therefore to improve our knowledge about the diversity, the dynamics and the conservation values of boreal old-growth forests in manged landscapes. This study focuses on a 2200km2 territory situated in Québec’s black spruce – feathermoss bioclimatic domain, Canada. We sampled the structural characteristics of 74 stands that were mature to very old. We also performed dendrochronological analysis on 21 of these sites. Finally, we also used Québec’s decadal forest surveys data sampled since the 1960’s to observe the evolution of old-growth forest characteristics on the study territory, as well as the accuracy of these surveys in identifying old-growth stands. According to our results, boreal old-growth forests are structurally diversified. 11 different old-growth forests structures have been identified. This diversity is in part a result of topography but also of time since the last stand-replacing disturbance. Secondary disturbances dynamics increase in complexity while the first cohort, which appeared following the last stand-replacing disturbance, is replaced by new cohorts. At the beginning of the transition process toward the old-growth stage, a low severity defines most of the secondary disturbances but moderate severity disturbances progressively gain in importance. When the true old-growth stage is reached, low and moderate severity disturbances are equal in importance in stand dynamics. Most of these disturbances seems to result from spruce budworm (Choristoneura fumiferana, Clemens) outbreaks, independently of disturbance severity. In comparison to forest fires, most of the stands logged on the study territory were old-growth stands (here defined by an age superior to 100 years) characterized by higher merchantable wood volume. Logging activities have therefore an influence on landscape structural diversity which differs from that of fire. Moreover, the most recent photographic aerial survey performed by Québec’s government significantly underestimated old-growth forests abundance on this territory. Most of these stands, defined by a complex structure based on field surveys, were identified as even-aged (i.e. structurally simple) by the aerial survey. Unsuitable thresholds for boreal forests as well as the absence of particularly visible old-growth attributes were the main factors that may explain the low accuracy of aerial surveys. The dynamics of boreal old-growth forests is complex, especially once the true old-growth stage reached. For this reason, the structure of old-growth stands may significantly change over time. Boreal old-growth forest structural diversity must be explicitly acknowledged by forest managers, because it implies the presence of different habitats among old-growth stands and therefore different species. However, logging activities cut in priority old-growth forests with the highest economic value, as indicated by our results. Ignoring this diversity (e.g. by only defining a given percentage of old-growth forests that must be maintained in managed landscapes, regardless of their structure) could therefore lead to the erosion of boreal old-growth forest diversity, causing biodiversity issues because of the disappearance of specific habitats. In addition, orthographic forest surveys are currently not accurate enough to identify boreal old-growth forests and discriminate their structures, hence limiting the development of efficient management strategies. The integration of boreal old-growth forests in sustainable forest management therefore requires first the acknowledgement of the diversity and the complexity of these ecosystems and second, the development of accurate tools capable of identifying all the forms of boreal old-growth forests

Une seule manière d'utiliser les exceptions ? Une étude empirique de 21 applications Java

International audienceLe langage Java offre un puissant système de gestion des exceptions et de traitement des erreurs. L'étude de différentes applications Java peut permettre de distinguer différentes utilisations de ce système. Ce papier étudie les utilisations des exceptions pour constater les différences ou similitudes entre 21 applications. Les résultats permettent de constater de fortes différences entre les applications et dans l'ensemble une gestion très variée des exceptions

Boreal old-growth forest structural diversity challenges aerial photographic survey accuracy

The erosion of old-growth forests in boreal managed landscapes is a major issue currently faced by forest managers; however, resolving this problem requires accurate surveys. The intention of our study was to determine if historic operational aerial forest surveys accurately identified boreal old-growth forests in Quebec, Canada. We first compared stand successional stages (even-aged vs. old-growth) in two aerial surveys performed in 1968 (preindustrial aerial survey) and 2007 (modern aerial survey) on the same 2200 km2 territory. Second, we evaluated the accuracy of the modern aerial survey by comparing its results with those of 74 field plots sampled in the study territory between 2014 and 2016. The two aerial surveys differed significantly; 80.8% of the undisturbed stands that were identified as “old-growth” in the preindustrial survey were classified as “even-aged” in the modern survey, and 60% of the stands identified as “old-growth” by field sampling were also erroneously identified as “even-aged” by the modern aerial survey. The scarcity of obvious old-growth attributes in boreal old-growth forests, as well as poorly adapted modern aerial survey criteria (i.e., criteria requiring high vertical stratification and significant changes in tree species composition along forest succession), were the main factors explaining these errors. It is therefore likely that most of Quebec’s boreal old-growth forests are currently not recognized as such in forest inventories, challenging the efficacy of sustainable forest management policies. L’érosion des superficies des vieilles forêts boréales est actuellement un enjeux majeurs pour les gestionnaires forestier. Répondre efficacemment à cette problématique demande néanmoins l’accès à des données d’inventaires fiables. Ainsi, l’objectif de cette étude était de déterminer si les inventaires forestiers aériens identifient correctement les vieilles forêts dans les paysages boréaux du Québec, Canada. Nous avons comparé les stades de succession (forêt équienne ou vieille forêt) de deux inventaires aériens réalisés en 1968 (inventaire aérien préindustriel) et en 2007 (inventaire aérien moderne) sur un territoire de 2200 km2. Nous avons aussi comparé les résultats de l’inventaire aérien moderne avec ceux obtenus à partir de 74 placettes de terrain échantillonnés entre 2014 et 2016. Les deux inventaires aériens étaient très incohérents : 80.8% des peuplements non-perturbés identifiés comme « vieilles forêts » par l’inventaire préindustriel étaient classés comme « équiens » par l’inventaire moderne. 60% des placettes de terrain identifiées comme vieilles forêts étaient aussi classées « équiens » par l’inventaire aérien moderne. Le manque d’attributs de vieilles forêts évidents ainsi que l’utilisation de critères inadaptés (c’est-à-dire nécessitant une forte complexité verticale et d’importants changements de composition en espèces arborescentes durant la succession forestière) étaient les principaux éléments expliquant ces erreurs. Il est ainsi possible que la majorité des vieilles forêts boréales du Québec ne soient pas identifiés comme telles, limitant l’efficacité des stratégies de gestion durable

Unveiling the diversity of tree growth patterns in boreal old-growth forests reveals the richness of their dynamics

Research Highlights: Radial growth patterns of trees growing in old-growth boreal forests in eastern Canada can be grouped into a small number of simple patterns that are specific to different old-growth forest types or successional stages. Background and Objectives: Identifying the main radial growth trends in old-growth forests could help to develop silvicultural treatments that mimic the complex dynamics of old-growth forests. Therefore, this study aimed to identify the main radial growth patterns and determine how their frequencies change during forest succession in old-growth forests, focusing on boreal landscapes in eastern Canada. Materials and Methods: We used dendrochronological data sampled from 21 old-growth stands in the province of Quebec, Canada. Tree-ring chronologies were simplified into chronologies of equal length to retain only primary growth trends. We used k-means clustering to identify individual growth patterns and the difference in growth-pattern frequency within the studied stands. We then used non-parametric analyses of variance to compare tree or stand characteristics among the clusters. Results: We identified six different growth patterns corresponding to four old-growth forest types, from stands at the canopy breakup stage to true old-growth stands (i.e., when all the pioneer cohort had disappeared). Secondary disturbances of low or moderate severity drove these growth patterns. Overall, the growth patterns were relatively simple and could be generally separated into two main phases (e.g., a phase of limited radial increment size due to juvenile suppression and a phase of increased radial increment size following a growth release). Conclusions: The complexity of old-growth forest dynamics was observed mainly at the stand level, not at the tree level. The growth patterns observed in true old-growth forests were similar to those observed following partial or stem-selection cuts in boreal stands; thus, these silvicultural treatments may be effective in mimicking old-growth dynamics

10-W-level monolithic dysprosium-doped fiber laser at 3.24 μm

We report, to the best of our knowledge, the first entirely monolithic dysprosium (Dy)-doped fluoride fiber laser operating in the mid-IR region. The system delivers 10.1 W at 3.24 μm in continuous operation, a record for fiber oscillators in this range of wavelengths. The Dy3+ fiber is pumped in-band using an erbium-doped fiber laser at 2.83 μm made in-house and connected through a fusion splice. Two fiber Bragg gratings directly written in the Dy-doped fiber form the 3.24 μm laser cavity to provide a spectrally controlled laser output. This substantial increase of output power in the 3.0 3.3 μm spectral range–could open new possibilities for applications in spec-troscopy and advanced manufacturing

Long-Term Impacts of Forest Management Practices under Climate Change on Structure, Composition, and Fragmentation of the Canadian Boreal Landscape

Forest harvesting and fire are major disturbances in boreal forests. Forest harvesting has modified stand successional pathways, which has led to compositional changes from the original conifer-dominated forests to predominantly mixed and hardwood forests. Boreal fire regimes are expected to change with future climate change. Using the LANDIS-II spatially explicit landscape model, we evaluated the effects of forest management scenarios and projected fire regimes under climate change in northeastern Canadian boreal forests, and we determined the subsequent alteration in stand- and landscape-level composition, succession, and spatial configuration of boreal forests. We observed that, in contrast to successional pathways that followed fire, successional pathways that followed forest harvesting favored mixed forests with a prevalence of shade-intolerant hardwoods for up to 300 y after harvesting. This trend was exacerbated under climate change scenarios where forests became dominated by hardwood species, particularly in ecoregions where these species were found currently in low abundance. Our results highlight the failure of existing forest management regimes to emulate the effects of natural disturbance regimes on boreal forest composition and configuration. This illustrates the risks to maintaining ecosystem goods and services over the long term and the exacerbation of this trend in the context of future climate change.Funding: Natural Sciences and Engineering Research Council of Canada (Grant number 125559117), GreenFirst, and West Fraser Timber Co. Ltd. Acknowledgments: We would like to thank the Quebec Ministère des Forêts, de la Faune et des Parcs (Ministry of Forests, Wildlife and Parks) and its forest inventory department for providing the digital inventory data to calibrate LANDIS-II. The Sustainable Forest Management UQAT/UQAM Chair (SFM Chair) also helped this project by providing all technical support. We thank Dominic Cyr for their helpful comments and suggestions for this study. We are also grateful to Johana Herrera and Javier Peinado for the compilation and construction of some of the input data sets and to Thomas A. Gavin and Murray Hay for the English revision. This manuscript is part of the Ph.D. thesis of Eliana Cristina Molina at the University of Quebec in Abitibi-Témiscamingue. A version of this manuscript is available online at depositium.uqat.ca

Une seule manière d'utiliser les exceptions ? Une étude empirique de 21 applications Java

International audienceLe langage Java offre un puissant système de gestion des exceptions et de traitement des erreurs. L'étude de différentes applications Java peut permettre de distinguer différentes utilisations de ce système. Ce papier étudie les utilisations des exceptions pour constater les différences ou similitudes entre 21 applications. Les résultats permettent de constater de fortes différences entre les applications et dans l'ensemble une gestion très variée des exceptions

Structural diversity and dynamics of boreal old-growth forests case study in Eastern Canada

Old-growth stands are considered as key components of boreal forest diversity and their preservation is largely integrated into management plans. However, while the differences between old-growth and young forests have largely been studied, little is known about the diversity of boreal old-growth forests. In managed landscapes, the efficacy of old-growth conservation plans may be reduced depending on how these old-growth forests are considered: as a single, homogeneous and steady-state forest type or as multiple, diverse and dynamic forest types. To fulfil this gap, our objectives were: (1) to create a typology of old-growth boreal structures; (2) to observe how these structures are influenced by environmental and temporal parameters; and (3) to elaborate a succession model of old-growth structural dynamics along temporal and environmental gradients. Seventy-one mature and overmature stands were sampled within a 2200 km2 territory situated in Eastern Canada. Cluster analysis divided the sampled stands into two even-aged types, three transition old-growth types and six true old-growth types. Slope, minimum time since last fire and organic horizon depth were the three environmental and temporal parameters influencing the old-growth structures. Paludification-related productivity decline was present in only one old-growth forest type, while the other sites remained productive. These results allowed the creation of three succession models of the dynamics of old-growth stands in the boreal forest of eastern Canada. Boreal stands can undergo numerous structural changes once the old-growth succession process is initiated. An increase in structural diversity when the true old-growth stage is reached, coupled with a variety of secondary disturbance characteristics, favours multiple pathways of structural evolution of these ecosystems over time. Therefore, forest management planning should incorporate this complexity to improve the preservation of old-growth forests in managed territories

Secondary disturbances of low and moderate severity drive the dynamics of eastern Canadian boreal old-growth forests

Key message Both low- and moderate-severity secondary disturbances are drivers of eastern Canadian boreal old-growth forests dynamics. Moderate-severity disturbances reflect mainly spruce budworm outbreaks. Low-severity disturbances are produced by both spruce budworm outbreaks and random events such as windthrow. Each level of disturbance severity has a specific impact on stand dynamics, and both shape the diversity of boreal old-growth forests. Context A regular succession of low-severity disturbances is seen as determining the dynamics of the old-growth stage (gap dynamics); however, recent studies suggest that moderate-severity secondary disturbances also play an important role in the dynamics of eastern Canadian boreal forests. Aims This study aims to determine if eastern Canadian boreal old-growth forests are driven by a combination of low- and moderate-severity secondary disturbances. Methods We reconstructed the 200-year disturbance history of 20 boreal old-growth stands using dendrochronological analysis. We discriminated low- from moderate-severity disturbances based on their respective influence on mean stand growth. Results The secondary disturbance regime of eastern Canadian boreal old-growth forests varies highly over time, reflected by disturbance peaks in the chronological record. Most peaks occurred during spruce budworm outbreaks related to both low- and moderate-severity disturbances. Between each peak, low-severity disturbances dominate. Each level of disturbance severity has specific consequences for stand dynamics. Conclusion Both low and moderate secondary disturbances are drivers of forest dynamics in eastern Canadian boreal old-growth stands and shape the structural diversity of these stands. The complexity of these dynamics should be recognized in management planning to ensure the efficiency of old-growth forest conservation policies