Dorian Gaboriau, Hugo Asselin, Adam Ali, Christelle Hely-Alleaume, Martin-Philippe Girardin. Drivers of extreme wildfire years in the 1965–2019 fire regime of the Tłı̨chǫ First Nation territory, Canada 2022. Ecoscience Online first
DOI : 10.1080/11956860.2022.2070342
Exceptionally large areas burned in 2014 in central Northwest Territories (Canada), leading members of the Tłı̨chǫ First Nation to characterize this year as ‘extreme’. Top-down climatic and bottom-up environmental drivers of fire behavior and areas burned in the boreal forest are relatively well understood, but not the drivers of extreme wildfire years (EWY). We investigated the temporal and spatial distributions of fire regime components (fire occurrence, size, cause, fire season length) on the Tłı̨chǫ territory from 1965 to 2019. We used BioSIM and data from weather stations to interpolate mean weather conditions, fuel moisture content and fire-weather indices for each fire season, and we described the environmental characteristics of burned areas. We identified and characterized EWY, i.e., years exceeding the 80th percentile of annual area burned for the study period. Temperature and fuel moisture were the main drivers of areas burned. Nine EWY occurred from 1965 to 2019, including 2014. Compared to non-EWY, EWY had significantly higher mean temperature (>14.7°C) and exceeded threshold values of Drought Code (>514), Initial Spread Index (>7), and Fire Weather Index (>19). Our results will help limit the effects of EWY on human safety, health and Indigenous livelihoods and lifestyles.
Alexandre Florent Nolin, Martin-Philippe Girardin, Jacques Tardif, Xiao Jing Guo, France Conciatori, Yves Bergeron. A 247-year tree-ring reconstruction of spring temperature
and relation to spring flooding in eastern boreal Canada. 2022. Int. J. Climatol. Online first
DOI : 10.1002/joc.7608
Few records of spring paleoclimate are available for boreal Canada, as biological proxies recording the beginning of the warm season are uncommon. Given the spring warming observed during the last decades, and its impact on snowmelt and hydrological processes, searching for spring climate proxies is receiving increasing attention. Tree-ring anatomical features and intra-annual widths were used to reconstruct the regional March to May mean air temperature from 1770 to 2016 in eastern boreal Canada. Nested principal component regressions calibrated on 116 years of gridded temperature data were developed from one Fraxinus nigra and 10 Pinus banksiana sites. The reconstruction indicated three distinct phases in spring temperature variability since 1770. Ample phases of multi-decadal warm and cold springs persisted until the end of the Little Ice Age (1850–1870 CE) and were gradually replaced since the 1940s by decadal to interannual variability associated with an increase in the frequency and magnitude of warm springs. Significant correlations with other paleotemperature records, gridded snow cover extent and runoff support that historical high flooding were associated with late, cold springs with heavy snow cover. Most of the high magnitude spring floods reconstructed for the nearby Harricana River also coincided with the lowest reconstructed spring temperature per decade. However, the last 40 years of observed and reconstructed mean spring temperature showed a reduction in the number of extreme cold springs contrasting with the last few decades of extreme flooding in the eastern Canadian boreal region. This result indicates that warmer late spring mean temperatures on average may contribute, among other factors, to advance the spring break-up and to likely shift the contribution of snow to rain in spring flooding processes.
Emmanuel Amoah Boakye, Daniel Houle, Yves Bergeron, Martin-Philippe Girardin, Igor Drobyshev. Insect defoliation modulates influence of climate on the growth
of tree species in the boreal mixed forests of eastern Canada 2022. Ecology and Evolution 12(3):e8656
DOI : 10.1002/ece3.8656
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.
Fougère Augustin, Martin-Philippe Girardin, Aurélie Terrier, Marie-Claude Lambert, Alain Leduc, Yves Bergeron, Pierre Grondin. Projected changes in fire activity and severity feedback in the spruce–Feather moss forest of western Quebec, Canada. 2022. Trees, Forests and People 8:100229
DOI : 10.1016/j.tfp.2022.100229
As a result of extreme weather conditions associated with anthropogenic climate change, fire regimes are expected to continue to change in the boreal forest over the 21st century and beyond. Consequently, changes in ecological attributes like stand composition, tree density and forest carbon stock can be expected. In the present study, we used an adjusted version of the CanFIRE model to project long-term (1971–2100) changes in burn rates, fire severity and fire-induced shifts in vegetation composition in response to anticipated scenarios of climate change, in the black spruce-feather moss subdomain of Western Quebec. The model provides decadal-scale estimates of the immediate physical effects of fire on forest communities by computing expected fire behavior and the resulting ecological effects. Changes in species composition of the forest is also computed based on mechanisms of succession in natural forest communities and fire-mediated vegetation transitions. Projections suggest an increase in potential burn rates across the study area under future weather conditions and also an overall reduction in percent tree mortality and total fuel consumption. This reduction is caused by negative feedback from vegetation composition that shifts to less-fire prone states. Although common forest communities will remain the same in the studied subdomain until 2100 (recurrence dynamics), significant losses of productive area (LPA) are projected, particularly in forest management units rich in forest communities dominated by black spruce or jack pine, as a result of regeneration failure due to very short intervals between successive fires. While remaining similar under moderate (RCP4.5) and high-end (RCP8.5) warming scenarios in all forest management units, LPA will vary from 25 to 36% of the percent cover by 2100 compared to 1970. These results provide insights to policy makers and land managers, and they attract attention to the pressing need to adjust management practices in the context of climate change.
Mathilde Pau, Sylvie Gauthier, Raphaël Chavardes, Martin-Philippe Girardin, William Marchand, Yves Bergeron. Site index as a predictor of the effect of climate warming on
boreal tree growth. 2021. Global Change Biology 28(5):1903-1918
DOI : 10.1111/gcb.16030
The boreal forest represents the terrestrial biome most heavily affected by climate change. However, no consensus exists regarding the impacts of these changes on the growth of tree species therein. Moreover, assessments of young tree responses in metrics transposable to forest management remain scarce. Here, we assessed the impacts of climate change on black spruce (Picea mariana [Miller] BSP) and jack pine (Pinus banksiana Lambert) growth, two dominant tree species in boreal forests of North America. Starting with a retrospective analysis including data from 2591 black spruces and 890 jack pines, we forecasted trends in 30-year height growth at the transitions from closed to open boreal coniferous forests in Québec, Canada. We considered three variables: (1) height growth, rarely used, but better-reflecting site potential than other growth proxies, (2) climate normals corresponding to the growth period of each stem, and (3) site type (as a function of texture, stoniness, and drainage), which can modify the effects of climate on tree growth. We found a positive effect of vapor pressure deficit on the growth of both species, although the effect on black spruce leveled off. For black spruce, temperatures had a positive effect on the height at 30 years, which was attenuated when and where climatic conditions became drier. Conversely, drought had a positive effect on height under cold conditions and a negative effect under warm conditions. Spruce growth was also better on mesic than on rocky and sub-hydric sites. For portions of the study areas with projected future climate within the calibration range, median height-change varied from 10 to 31% for black spruce and from 5 to 31% for jack pine, depending on the period and climate scenario. As projected increases are relatively small, they may not be sufficient to compensate for potential increases in future disturbances like forest fires.
Victor Danneyrolles, Martin-Philippe Girardin, Sylvie Gauthier, Hugo Asselin, Yves Bergeron, Dominic Cyr. Influences of climate fluctuations on northeastern North America’s burned areas largely outweigh those of European settlement since AD 1850. 2021. Environmental Research Letters 6(11):114007
DOI : 10.1088/1748-9326/ac2ce7
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.
Sylvie Gauthier, Martin-Philippe Girardin, Henrik Hartmann, William Marchand, Mathieu Lévesque, Yves Bergeron. Contrasting life-history traits of black spruce and jack pine influence their physiological response to drought and growth recovery in northeastern boreal Canada. 2021. Science of the Total Environment 794:148514
DOI : 10.1016/j.scitotenv.2021.148514
An increase in frequency, intensity and duration of drought events affects forested ecosystems. Trees react to these changes by adjusting stomatal conductance to maximize the trade-off between carbon gains and water losses. A better understanding of the consequences of these drought-induced physiological adjustments for tree growth could help inferring future productivity potentials of boreal forests. Here, we used samples from a forest inventory network in Canada where a decline in growth rates of black spruce (Picea mariana (Mill.) B.S.P.) and jack pine (Pinus banksiana Lamb.) occurred in 1988–1992, an exceptionally dry period, to verify if this growth decline resulted from physiological adjustments of trees to drought. We measured carbon and oxygen isotope ratios in growth rings of 95 spruces and 49 pines spanning 1985–1993. We used 13C discrimination (Δ13C) and 18O enrichment (Δ18O) as proxies for intrinsic water use efficiency and stomatal conductance, respectively. We studied how inter-annual variability in isotopic signals was linked to climate moisture index, vapor pressure deficit and annual snowfall amount. We found significantly lower Δ13C values over 1988–1990, and significantly higher Δ18O values in 1988–1989 and 1991 compared to the 1985–1993 averages. We also observed that a low climatic water balance and a high vapor pressure deficit were linked with low Δ13C and high Δ18O in the two study species, in parallel with low growth rates. The latter effect persisted into the year following drought for black spruce, but not for jack pine. These findings highlight that small differences in physiological parameters between species could translate into large differences in post-drought recovery. The stronger and longer lasting impact on black spruce compared to jack pine suggests a less efficient carbon use and a lower acclimation potential to future warmer and drier climate conditions.
Martin-Philippe Girardin, Johann Housset, Renzo Motta, Francine Tremblay, Endre Toth, Yves Bergeron, Christopher Carcaillet. Tree-rings, genetics and the environment: Complex interactions at the rear edge of species distribution range. 2021. Dendrochronologia 69:125863
DOI : 10.1016/j.dendro.2021.125863
Under climate change, modifications on plants’ growth are expected to be the strongest at species margins. Therein, tree acclimation could play a key role as migration is predicted to be too slow to track shifts of bioclimatic envelops. A requirement is, however, that intra-population genetic diversity be high enough for allowing such adaptation of tree populations to climate change. In this study, we tested for the existence of relationships between genetic diversity, site environmental conditions, and the response of annual tree growth to climate of Pinus cembra at its southern limit in the Alps. Site-specific climatic and environmental factors predominantly determined the response of trees along the precipitation gradient. The growth-climate interactions were chiefly linked to mean annual precipitation and temperature, slope and tree-size, and less to genetic diversity. We show that genetic background of Pinus cembra has exclusively indirect modulating power with limited effects on tree-ring formation, and within the southern limit in the Alps, genetic variability is not necessarily well expressed in the patterns of annual tree growth. Our results may imply little adaptive capacity of these populations to future changes in the water balance.
Yves Bergeron, Martin-Philippe Girardin, Emmanuel Amoah Boakye, Igor Drobyshev. Contrasting Growth Response of Jack Pine and Trembling Aspen to Climate Warming in Quebec Mixedwoods Forests of Eastern Canada Since the Early Twentieth Century 2021. JGR Biogeosciences 126(5):e2020JG005873
DOI : 10.1029/2020JG005873
Forest monitoring studies show contrasting trends in tree growth rates since the mid-twentieth century. However, due to their focus on annual and decadal dynamics, they provide limited insight into the effects of long-term climatic variability on tree growth. Here, we relied on a large tree-ring dataset (∼2,700 trees) of two common North American shade-intolerant tree species, trembling aspen (Populus tremuloides Michx.) and jack pine (Pinus banksiana Lambert), to assess their lifespan-long growth dynamics in the mixedwood forests of Québec. We also determined how the environmental conditions of the stands influenced tree growth. We observed a significant increase in the radial growth rate of trembling aspen during the study period, while the jack pine decline was not significant. Over the whole study region, the trees growing in sites with lower competition, and those at the lower sections of the terrain slope experienced more of the positive effects of temperature on growth rates. Our study suggests that the tree growth response to climate warming may be species-specific and will vary across the boreal mixedwoods.
Dorian Gaboriau, Cécile Remy, Martin-Philippe Girardin, Hugo Asselin, Christelle Hely-Alleaume, Yves Bergeron, Adam Ali. Temperature and fuel availability control fire size/severity in the
boreal forest of central Northwest Territories, Canada. 2020. Quaternary Science Review 250:106697
DOI : 10.1016/j.quascirev.2020.106697
The north-central Canadian boreal forest experienced increased occurrence of large and severe wildfires caused by unusually warm temperatures and drought events during the last decade. It is, however, difficult to assess the exceptional nature of this recent wildfire activity, as few long-term records are available in the area. We analyzed macroscopic sedimentary charcoal from four lakes and pollen grains from one of those lakes to reconstruct long-term fire regimes and vegetation histories in the boreal forest of central Northwest Territories. We used regional estimates of past temperature and hydrological changes to identify the climatic drivers of fire activity over the past 10,000 years. Fires were larger and more severe during warm periods (before ca. 5000 cal yrs. BP and during the last 500 years) and when the forest landscape was characterized by high fuel abundance, especially fire-prone spruce. In contrast, colder conditions combined with landscape opening (i.e., lower fuel abundance) during the Neoglacial (after ca. 5000 cal yrs. BP) were related with a decline in fire size and severity. Fire size and severity increased during the last five centuries, but remained within the Holocene range of variability. According to climatic projections, fire size and severity will likely continue to increase in central Northwest Territories in response to warmer conditions, but precipitation variability, combined with increased abundance of deciduous species or opening of the landscape, could limit fire risk in the future.
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Martin-Philippe Girardin, Jacques Tardif, Micheal Flannigan, Yves Bergeron. Reconstructing atmospheric circulation history using tree rings: one more step toward understanding temporal changes in forest dynamics.
3rd International Sustainable Forest Management Network Conference, Shaw Conference Centre, Edmonton, Alberta, Canada.
Martin-Philippe Girardin Multicentury reconstruction of the Canadian Drought Code, eastern Canada, and its relationships with atmospheric circulation.
6th International Conference on Dendrochronlogy, University Laval, Québec, Canada.
Martin-Philippe Girardin Synoptic scale atmospheric circulation and fire weather conditions of the past three centuries, Boreal Canada.
The Canadian Association of Geographers annual meeting, London, Ontario, Canada.
Martin-Philippe Girardin Population dynamics of Tamarack (Larix laricina (Du Roi) K. Koch) growing in wetlands from the southwestern Quebec boreal forest.
85th Annual Meeting of the Ecological Society of America, Snowbird, Utah, USA.
Martin-Philippe Girardin Caractère non-stationnaire et cyclique du climat de l’est canadien au cours des trois cent dernières années et son impact sur la forêt boréale mixte.
2e Colloque conjoint CRBF / GREFi - La forêt sous tout ses aspects. Pavillon La Laurentienne, Université Laval, Québec, Québec.
Martin-Philippe Girardin Dynamique des tourbières dominées par le mélèze (Larix laricina) dans la forêt boréale du sud-ouest québécois.
68ième congrès annuel de l’ACFAS. Université de Montréal, Québec, Canada.
Martin-Philippe Girardin, Jacques Tardif, Micheal Flannigan, Yves Bergeron. Synoptic scale atmospheric circulation and summer drought variability of the past three centuries, Boreal Canada.
90th Annual Meeting of the Ecological Society of America, Montreal, Quebec, Canada.