La saison des feux de forêt de 2023 au Québec, marquée par des conditions extrêmement chaudes et sèches, a établi de nouveaux records en brûlant 4,5 millions d'hectares. Cette situation est directement liée aux impacts persistants et en augmentation du changement climatique. Cette étude examine les conditions météorologiques exceptionnelles ayant mené aux feux et évalue leurs impacts significatifs sur le secteur forestier, la gestion des feux, les habitats du caribou boréal, et met particulièrement en lumière les répercussions profondes sur les communautés des Premières Nations. Les feux ont entraîné une baisse significative de la productivité des forêts et de l'approvisionnement en bois, submergeant les équipes de gestion des feux et nécessitant des évacuations massives. Le territoire et les communautés des Premières Nations ont été profondément affectés, confrontés à de graves problèmes de qualité de l'air et à des bouleversements considérables. Si l'impact sur l?habitat du caribou a été modeste dans l'ensemble de la province, les répercussions écologiques, économiques et sociales ont été considérables. Pour atténuer les impacts à venir des prochaines saisons de feux de forêt extrêmes, une avenue suggérée serait de modifier les pratiques d?aménagement forestier afin d'accroître la résilience et la résistance des forêts, d'adapter les structures industrielles aux nouvelles sources d'approvisionnement en bois et d'améliorer les stratégies de lutte contre les feux et la gestion des risques. De même, une approche globale

Les caractéristiques des forêts préindustrielles permettent d?établir des états de référence pour l'aménagement durable des forêts. Cette approche historique est particulièrement pertinente pour les régions soumises à une forte influence humaine, dans lesquelles les forêts naturelles sont rares. C'est le cas de la région de Rouyn-Noranda, à l'ouest du Québec. Nous avons utilisé les archives d'arpentage disponibles pour reconstituer la composition préindustrielle des forêts boréales mixtes de cette région. ? partir d'une base de données comportant 3621 observations sur la composition historique des forêts (1909?1940), nous dressons un portrait des forêts préindustrielles et des changements survenus dans la région. ? l?époque préindustrielle, les épinettes représentaient les espèces les plus abondantes: elles étaient présentes dans 85,5 % des observations, et étaient identifiées comme dominantes (c.-à-d., les plus abondantes localement) dans 63,9 % des observations. Les épinettes tendaient à être abondantes sur l'ensemble du territoire et des types de dépôts de surface. Entre les époques préindustrielle et moderne (1980?2020), nos résultats montrent une augmentation de la fréquence des feuillus de début de succession, dont principalement le peuplier faux tremble (+28 %). Ces changements de composition semblent attribuables à la combinaison de perturbations (feux, coupes, agriculture, etc.). Nous discutons finalement des implications de ces résultats pour les stratégies d'aménagement écosystémique dans la région.

Warning: This article contains terms, descriptions, and opinions used for historical context that may be culturally sensitive for some readers.Background: Understanding drivers of boreal forest dynamics supports adaptation strategies in the context of climate change.Aims: We aimed to understand how burn rates varied since the early 1700s in North American boreal forests.Methods: We used 16 fire-history study sites distributed across such forests and investigated variation in burn rates for the historical period spanning 1700-1990. These were benchmarked against recent burn rates estimated for the modern period spanning 1980-2020 using various data sources.Key results: Burn rates during the historical period for most sites showed a declining trend, particularly during the early to mid 1900s. Compared to the historical period, the modern period showed less variable and lower burn rates across sites. Mean burn rates during the modern period presented divergent trends among eastern versus northwestern sites, with increasing trends in mean burn rates in most northwestern North American sites.Conclusions: The synchronicity of trends suggests that large spatial patterns of atmospheric conditions drove burn rates in addition to regional changes in land use like fire exclusion and suppression.Implications: Low burn rates in eastern Canadian boreal forests may continue unless climate change overrides the capacity to suppress fire.

Increase in forest disturbance due to land use as well as climate change has led to an expansion of young forests worldwide, which drives global carbon dynamics and timber allocation. This study presents a method that combines a single airborne LiDAR acquisition and time since harvest maps to model height growth of post-logged black spruce-dominated forests in a 1700 km2 eastern Canadian boreal landscape. We developed a random forest model in which forest height at a 20 m × 20 m pixel resolution is a function of stand age, combined with environmental variables (e.g., slope, site moisture, surface deposit). Our results highlight the model's strong predictive power: least-square regression between predicted and observed height of our validation dataset was very close to the 1:1 relation and strongly supported by validation metrics (R2 = 0.74; relative RMSE = 19%). Environmental variables thus allowed to accurately predict forest productivity with a high spatial resolution (20 m × 20 m pixels) and predicted forest height growth in the first 50 years after logging ranged between 16 and 27 cm·year−1 across the whole study area, with a mean of 20.5 cm·year−1. The spatial patterns of potential height growth were strongly linked to the effect of topographical variables, with better growth rates on mesic slopes compared to poorly drained soils. Such models could have key implications in forest management, for example to maintain forest ecosystem services by adjusting the harvesting rates depending on forest productivity across the landscapes.

There is a pressing need for a better understanding of changing forest fire regimes worldwide, especially to separate the relative effects of potential drivers that control burned areas. Here we present a meta-analysis of the impacts of climate fluctuation and Euro-Canadian settlement on burned areas from 1850 to 1990 in a large zone (>100 000 km2) in northern temperate and boreal forests of eastern Canada. Using Cox regression models, we tested for potential statistical relationships between historical burned areas in 12 large landscapes (reconstructed with dendrochronological data) with climate reconstructions, changes in the Euro-Canadian population, and active suppression (all reconstructed at the decadal scale). Our results revealed a dominant impact of climate fluctuations on forest burned areas, with the driest decades showing fire hazards between 5 to 15 times higher than the average decades. Comparatively, the Euro-Canadian settlement had a much weaker effect, having increased burned areas significantly only during less fire-prone climate conditions. During periods of fire-prone climate, burned areas were maximum independent of fluctuations in Euro-Canadian populations. Moreover, the development of active fire suppression did not appear to reduce burned areas. These results suggest that a potential increase in climate moisture deficit and drought may trigger unprecedented burned areas and extreme fire events no matter the effects of anthropogenic ignition or suppression.

1. A better understanding of how disturbance impacts tree diversity at different scales is essential for our ability to conserve and manage forest ecosystems in the context of global changes. Here we test the impacts of land use?related disturbances on tree diversity since the 19th century across a broad region (>150,000 km2) of northern temperate forests in eastern Canada.
2. We used a large and unique dataset of early land surveys conducted during the 19th century (>130,000 species lists), along with modern forest inventories (>80,000 plots), to analyse long?term changes in taxonomic and functional tree diversity at several scales (grid cell resolutions ranging from 12.5 to 1,600 km2; we refer to one grid cell as a ‘landscape’).
3. Our results show that land use?related disturbances have led simultaneously to (a) increased diversity within landscapes and a (b) homogenization at the regional scale (i.e. decreased composition dissimilarity among landscapes). These trends were found for both taxonomic diversity and functional diversity, with temporal changes more pronounced for taxonomic than functional diversity. We also found an increase over time in the strength of correlations between environmental variables and diversity both within and among landscapes.
4. Synthesis. Our results support the idea that human?induced impacts on biodiversity are strongly scale?dependent and not necessarily associated with biodiversity loss. This highlights possible ways that human?driven changes in tree diversity might impact forest resistance and resilience to future global changes.

Forest fires are a key driver of boreal landscape dynamics and are expected to increase with climate change in the coming decades. A profound understanding of the effects of fire upon boreal forest dynamics is thus critically needed for our ability to manage these ecosystems and conserve their services. In the present study, we investigate the long-term post-fire forest dynamics in the southern boreal forests of western Quebec using historical aerial photographs from the 1930s, alongside with modern aerial photographs from the 1990s. We quantify the changes in forest cover classes (i.e., conifers, mixed and broadleaved) for 16 study sites that were burned between 1940 and 1970. We then analyzed how interactions between pre-fire forest composition, site characteristics and a fire severity weather index (FSWI) affected the probability of changes in forest cover. In the 1930s, half of the cover of sampled sites were coniferous while the other half were broadleaved or mixed. Between the 1930s and the 1990s, 41% of the areas maintained their initial cover while 59% changed. The lowest probability of changes was found with initial coniferous cover and well drained till deposits. Moreover, an important proportion of 1930s broadleaved/mixed cover transitioned to conifers in the 1990s, which was mainly associated with high FSWI and well-drained deposits. Overall, our results highlight a relatively high resistance and resilience of southern boreal coniferous forests to fire, which suggest that future increase in fire frequency may not necessarily result in a drastic loss of conifers. View Full-Text

Predicting future ecosystem dynamics depends critically on an improved understanding of how disturbances and climate change have driven long-term ecological changes in the past. Here we assembled a dataset of >100,000 tree species lists from the 19th century across a broad region (>130,000km2) in temperate eastern Canada, as well as recent forest inventories, to test the effects of changes in anthropogenic disturbance, temperature and moisture on forest dynamics. We evaluate changes in forest composition using four indices quantifying the affinities of co-occurring tree species with temperature, drought, light and disturbance. Land-use driven shifts favouring more disturbance-adapted tree species are far stronger than any effects ascribable to climate change, although the responses of species to disturbance are correlated with their expected responses to climate change. As such, anthropogenic and natural disturbances are expected to have large direct effects on forests and also indirect effects via altered responses to future climate change.