Alexis Schab, Jesus Pascual Puigdevall, Yves Bergeron, Sylvie Gauthier, Frédérick Raulier , Osvaldo Valeria. Modeling paludification and fire impacts on the forest productivity of a managed landscape using valuable indicators: the example of the Clay Belt 2021. Can. J. For. Res. 51(9):1347–1356
DOI : 10.1139/cjfr-2020-0386
In areas sensitive to forest management, paludification and successive disturbances in boreal forest can affect forest regeneration negatively, sometimes resulting in stand opening. As these negative effects on forest productivity are not fully considered in strategic management planning, a new landscape dynamics model integrating fire, paludification, forest harvesting, and regeneration failure was used to assess these impacts in a large forest management unit (10,828 km2) of northwestern Québec. Two reforestation scenarios, one based on the accessibility of the areas to be treated and the other aimed at restoring all burned and paludified areas to production were compared to one with no intervention. The success of the scenarios was evaluated using the predicted volume harvested, the proportion of closed or opened stands areas, an indicator of productivity; the cost of reforestation and the royalties associated with harvesting. Harvesting the paludified areas without reforesting would lead to a sharp increase in open stands areas (+17.3%). The strategy of reforesting accessible areas is the most promising for achieving sustainable forest management targets. The monitoring of maximum potential volume (MPV) and the closed forest area as indicators of landscape productivity provides the ability to anticipate problems earlier than with the conventional forest planning indicators.
Baburam Rijal, David L. Martell, Sylvie Gauthier, Frédérick Raulier . The economic impact of fire management on timber production in the boreal forest region of Quebec, Canada. 2018. International Journal of Wildland Fire 27(12):831-844
DOI : 10.1071/WF18041
Wildfire is an important component of the dynamics of boreal-forest ecosystems, but it can also contribute to the loss of forest resources, especially when fires escape initial attack and become large. Annual fire management costs in the province of Quebec are substantial (annual average of C$69 million for 1994–2014). The main objective of this study was to evaluate the financial impact of fire management on forest resources in Quebec. Our study includes cost–benefit analyses of nine fire management presuppression expenditure scenarios using forest and fire data for three commercially managed forest management units in the province of Quebec that experience varying mean annual burn rates (0.06–0.56%?year?1). The reduction in the burn rate attributed to fire management increased the revenue from the sale of primary-processed wood product and reduced fire suppression expenditure. The combined effects of reduced suppression expenditure and increased revenue from value-added timber harvest and wood processing with a lower fire risk compensated for increased fire presuppression expenditure.
Baburam Rijal, Luc Lebel, David L. Martell, Jean-Martin Lussier, Frédérick Raulier , Sylvie Gauthier. Value-added forest management planning: A new perspective on old-growth forest conservation in the fire-prone boreal landscape of Canada. 2018. For. Ecol. Manage.
DOI : 10.1016/j.foreco.2018.06.045
The maintenance of old-growth stands is important for sustaining natural forest ecosystems, but fire disturbances and commonly-used timber harvest practices exert adverse impacts on the retention of old-growth forests. Forest management planning prescribes harvest levels based on the planning policy and models, but the impact of the management strategies on the retention of old-growth forests has not been well studied. The objectives of this study were to examine: a) the impact of implementing three different harvest policies on the retention of old-growth forest and b) the impact of implementing a policy of maintaining a targeted minimum of 20% old-growth area on the harvest revenue that would be generated over a long planning horizon. To simulate the implementation of these policies, we developed three strategic timber harvest-scheduling models. The first model (Model 1) maximizes harvest timber volume; Model 2 maximizes the net present value (NPV) of the timber harvested; and Model 3 maximizes the NPV of value-added products at the primary processing mills. The value-added products we considered were lumber, chips and sawdust. The models were solved for three forest management units with different fire regimes. Solutions to models that did not include a strict constraint on old-growth forest area retention did not retain the targeted level of old-growth forest over a 150-year planning horizon. When an old-growth constraint was implemented, Model 3 produced the greatest revenue with the least variation by 5-year period over the planning horizon. The probability of finding a feasible solution to our optimization Model 3 with an old-growth forest constraint increased to 0.87–1.0 compared with 0.71–0.83 using Model 1, and 0.78–0.87 using Model 2. We conclude that the value-added policy model increases the probability of sustaining the bioeconomy while preserving forest ecosystems initiated by disturbance.
Dinesh Babu Irulappa Pillai Vijayakumar, Yves Bergeron, David Pothier, Sylvie Gauthier, Pierre Bernier, Frédérick Raulier . Fire disturbance data improves the accuracy of remotely sensed estimates of
aboveground biomass for boreal forests in eastern. 2017. Remote Sensing Application : Society and Environment 9:71-82
DOI : 10.1016/j.rsase.2017.07.010
Accurate estimation of aboveground biomass (AGB) using remote sensing data is still challenging and an approach based on an understanding of forest disturbance and succession could help improve AGB estimation. In the boreal forest of North America, time since last fire (TSLF) is seen as a useful variable to explain post-fire successional change and aboveground biomass (AGB). Within a large study area (>200 000 km2) located in the northeastern American boreal forest, we compared remotely sensed biomass estimates of MODIS (Moderate Resolution Imaging Spectroradiometer), GLAS (Geoscience Laser Altimeter System) and ASAR (Advanced Synthetic Aperture Radar) with inventory-based estimates derived from ground plots, and forest maps at a spatial resolution of 2-km2. We identified that TSLF could explain the error observed in remotely sensed AGB estimates (MODIS (45%), GLAS (47%) or ASAR (23%)) when associated with surficial geological substrate information at that scale. Our results therefore show the importance of TSLF as a potential ancillary variable for improving the accuracy of remotely sensed AGB estimates in North American boreal forests.
Dinesh Babu Irulappa Pillai Vijayakumar, Hakim Ouzennou, Sylvie Gauthier, Yves Bergeron, Alain Leduc, Frédérick Raulier . Projections of future forest age class structure under the influence of fire and harvesting: implications for forest management in the boreal forest of eastern Canada. 2017. Forestry 90(4):485-495
DOI : 10.1093/forestry/cpx022
In northeastern Canadian boreal forests, a coarse-filter approach was adopted to provide sustainable ecosystem services in order to maintain a balance between biodiversity, ecosystem function and timber production. An old forest (>100 years) maintenance target was established considering the range of historical variability in the proportion of this forest stage. However, the estimation of the harvesting rate that maintains the target level in old forests did not consider explicitly the impact of current and future, i.e. possibly higher, fire frequency. In this context, we compared historical, current, and future age structures according to recorded or projected fire activity and the current level of harvesting in western Quebec's boreal forest. Results show that under the current rates of harvesting and fire, the proportion of old forests could reach a minimum level rarely seen in the natural landscape in the past. The situation could become even more critical with the projected increase in fire activity under climate change. Numerous forest and fire management solutions exist, such as increasing rotation length, implementing a diversified silviculture, using a fire-smart approach or reaching a better balance between intensive management and conservation. We advocate their rapid implementation to reverse the projected decrease in the proportion of old forests.
Georgina-Renee Rodriguez-Baca, Alain Leduc, Frédérick Raulier . Rating a Wildfire Mitigation Strategy with an Insurance Premium: A Boreal Forest Case Study. 2016. Forests 7(5):107
DOI : 10.3390/f7050107
Risk analysis entails the systematic use of historical information to determine the frequency, magnitude and effects of unexpected events. Wildfire in boreal North America is a key driver of forest dynamics and may cause very significant economic losses. An actuarial approach to risk analysis based on cumulative probability distributions was developed to reduce the adverse effects of wildfire. To this effect, we developed spatially explicit landscape models to simulate the interactions between harvest, fire and forest succession over time in a boreal forest of eastern Canada. We estimated the amount of reduction of timber harvest necessary to build a buffer stock of sufficient size to cover fire losses and compared it to an insurance premium estimated in units of timber volume from the probability of occurrence and the amount of damage. Overall, the timber harvest reduction we applied was much more costly than the insurance premium even with a zero interest rate. This is due to the fact that the insurance premium is directly related to risk while the timber harvest reduction is not and, as a consequence, is much less efficient. These results, especially the comparison with a standard indicator such as an insurance premium, have useful implications at the time of choosing a mitigation strategy to protect timber supplies against risk without overly diminishing the provision of services from the forest. They are also promoting the use of insurance against disastrous events in forest management planning.
Rija Rapanoela, Sylvie Gauthier, Frédérick Raulier . Regional Instability in the Abundance of Open Stands in the Boreal Forest of Eastern Canada. 2016. Forests 7(5):103
DOI : 10.3390/f7050103
Fires are a key disturbance of boreal forests. In fact, they are the main source of renewal and evolution for forest stands. The variability of fire through space and time results in a diversified forest mosaic, altering their species composition, structure and productivity. A resilient forest is assumed to be in a state of dynamic equilibrium with the fire regime, so that the composition, age structure and succession stages of forests should be consistent with the fire regime. Dense spruce-moss stands tend, however, to diminish in favour of more open stands similar to spruce-lichen stands when subjected to more frequent and recurring disturbances. This study therefore focused on the effects of spatial and temporal variations in burn rates on the proportion of open stands over a large geographic area (175,000 km2) covered by black spruce (Picea mariana (Mill.) Britton, Sterns, Poggenb.). The study area was divided into 10 different zones according to burn rates, as measured using fire-related data collected between 1940 and 2006. To test if the abundance of open stands was unstable over time and not in equilibrium with the current fire regime, forest succession was simulated using a landscape dynamics model that showed that the abundance of open stands should increase progressively over time in zones where the average burn rate is high. The proportion of open stands generated during a specific historical period is correlated with the burn rate observed during the same period. Rising annual burn rates over the past two decades have thereby resulted in an immediate increase in the proportion of open stands. There is therefore a difference between the current proportion of open stands and the one expected if vegetation was in equilibrium with the disturbance regime, reflecting an instability that may significantly impact the way forest resources are managed. It is apparent from this study that forestry planning should consider the risks associated with the temporal variability of fire regimes on the forest ecosystem, as the resulting changes can have a significant impact on biodiversity and allowable cut estimates.
Dinesh Babu Irulappa Pillai Vijayakumar, Sylvie Gauthier, Yves Bergeron, David Pothier, Pierre Bernier, Frédérick Raulier , David Paré. Cover density recovery after fire disturbance controls landscape aboveground biomass carbon in the boreal forest of eastern Canada. 2016. For. Ecol. Manage. 360:170-180
DOI : 10.1016/j.foreco.2015.10.035
In existing carbon budget models, carbon stocks are not explicitly related to forest successional dynamics and environmental factors. Yet time-since-last-fire (TSLF) is an important variable for explaining successional changes and subsequent carbon storage. The objective of this study was to predict the spatial variability of aboveground biomass carbon (ABC) as a function of TSLF and other environmental factors across the landscape at regional scales. ABC was predicted using random forest models, both at the sample-plot level and at the scale of 2-km2 cells. This cell size was chosen to match the observed minimum fire size of the Canadian large fire database. The percentage variance explained by the empirical sample-plot level model of ABC was 50%. At that scale, TSLF was not significantly related to ABC. At the 2-km2 scale, ABC was influenced mainly by the proportions of cover density classes, which explained 83% of the variance. Changes in cover density were related to TSLF at the same 2-km2 scale, indicating that the increase in cover density following fire disturbance is a dominant mechanism through which TSLF acts upon ABC at the scale of landscapes.
Hakim Ouzennou, Jean-Pierre Saucier, Sylvie Gauthier, Frédérick Raulier . Strategic analysis of forest vulnerability to risk related to fire: an example from the coniferous boreal forest of Quebec. 2015. Can. J. For. Res. 45(5): 553-565
DOI : 10.1139/cjfr-2014-0125
Le feu est considéré comme étant une perturbation majeure en forêt boréale. Il importe donc d’en tenir compte dans le processus de planification de l’aménagement forestier. De plus, comme le temps d’exposition des peuplements au feu est relié à leur productivité, le fait de combiner des données sur la productivité à celle du risque lié au feu devrait nous aider à évaluer le potentiel d’un territoire pour y pratiquer un aménagement forestier durable. Dans cet article, nous présentons une méthode qui permet d’évaluer la vulnérabilité potentielle d’une région au risque relié aux feux de forêt et nous l’illustrons en l’appliquant à la forêt boréale coniférienne du Québec. Cette méthode prend en compte quelques éléments d’incertitude liés à la productivité et à l’activité des feux. Nous avons spatialisé la productivité des peuplements pour l’ensemble du territoire à l’étude, à partir des tables de rendement, de manière à estimer, pour chaque secteur, la superficie occupée par des forêts productives, en considérant ou non le risque relié au feu. Les résultats indiquent que la superficie des peuplements productifs décroît généralement avec une diminution du nombre de degrés-jours et une augmentation de l’altitude ou selon les dépôts de surface. De plus, même les secteurs ayant une productivité de moyenne à bonne sont jugés comme étant vulnérables au feu lorsque leur taux de brûlage excèdent 0,333 %·année–1. Notre approche innovatrice a permis d’évaluer le degré de vulnérabilité des différents secteurs par rapport au feu. Elle pourra aussi être utile dans plusieurs régions où, en raison des changements climatiques, nous pouvons prévoir un accroissement des superficies annuelles brûlées.
Rik Van Bogaert, Jean-Pierre Saucier, Yves Bergeron, André Robitaille, Dominique Boucher, Sylvie Gauthier, Frédérick Raulier . Exploring forest productivity at an early age after fire: a case study at the northern limit of commercial forests in Quebec. 2015. Can. J. For. Res. 45(5): 579-593
DOI : 10.1139/cjfr-2014-0273
Avec l’intérêt croissant à travers le monde envers les forêts du nord tant pour la production de fibre que pour l’atténuation des changements climatiques, des travaux explorant la productivité forestière peu après le feu et les facteurs qui la déterminent sont requis. Nous avons étudié la productivité des forêts, définie en termes de qualité du coefficient de distribution (stocking) et de la croissance, dans 116 sites de 10–30 années après feu distribués dans une zone de 90 000 km2 au nord de la limite d’attribution des forêts commerciales du Québec et dominé par Picea mariana (Mill.) B.S.P. et Pinus banksiana Lamb. Soixante-douze pour cent des sites ont été classés comme improductifs, principalement en raison de la faible croissance. Puisque la croissance est fortement liée à des facteurs climatiques, le boisement seul ne serait pas suffisant pour augmenter la productivité des peuplements dans notre zone d’étude. En outre, nos résultats montrent que P. banksiana sur des sites secs pourrait être moins résilient au feu qu’on ne le pensait, probablement à cause de mauvaises conditions de sites et du climat. Finalement, notre étude est l’une des premières à explorer les enjeux de productivité en bas âge dans les forêts naturelles du nord. Le schéma d’analyse proposé, en définissant la productivité des peuplements sur la base de la croissance et du coefficient de distribution, pourrait fournir un outil intéressant pour évaluer des problèmes similaires de manière précoce dans d’autres systèmes.
Rija Rapanoela, Hakim Ouzennou, Yves Bergeron, Jean-Pierre Saucier, Sylvie Gauthier, Frédérick Raulier . Contrasting current and potential productivity and the influence of fire and species composition in the boreal forest: a case study in eastern Canada. 2015. Can. J. For. Res. 45(5): 541-552
DOI : 10.1139/cjfr-2014-0124
La capacité d’une forêt à produire du bois est en relation avec les interactions existant entre sa capacité de régénération, les caractéristiques physiques du site (climat, dépôt de surface, drainage) et les perturbations. De façon minimale, pour que son aménagement soit durable, une forêt doit être suffisamment productive et capable de se régénérer après une perturbation de façon telle à ce que sa capacité de production soit maintenue ou améliorée. À cet égard, nous avons évalué la productivité en bois d’une vaste région (175?000 km2) qui recouvre l’étendue latitudinale de la pessière noire fermée (Picea mariana (Mill.) B.S.P). L’indice de qualité de station et l’indice de densité relative ont été utilisés pour identifier les peuplements qui ne peuvent atteindre un volume minimal de bois et des dimensions minimales d’arbres en une révolution. Une méthode non paramétrique a été utilisée pour estimer leur valeurs pour tous les peuplements de l’aire d’étude. Cette imputation a été faite en utilisant soit uniquement les attributs physiques du site pour estimer une productivité potentielle indépendante de l’historique du peuplement, soit une combinaison d’attributs physiques et de végétation pour estimer une productivité actuelle. La proportion de peuplements productifs a ensuite été estimée à l’échelle de paysages de taille variant entre 39 et 2491 km2. Les facteurs physiques du site expliquent à eux seuls 84 % de la variabilité dans le pourcentage potentiel de peuplements productifs (78 % pour le pourcentage actuel de peuplement productifs) et leur combinaison cause une transition abrupte de la productivité dans l’aire d’étude. Toutefois, le taux de brûlage, lorsque considéré seul, explique 63 % de la variabilité de la proportion de peuplements actuellement productifs et 41 % de la différence relative entre les pourcentages actuels et potentiels de peuplements productifs. Ces résultats ont des implications pour la planification stratégique de l’aménagement au moment de la stratification du territoire, puisque il est supposé que la superficie productive reste constante dans le temps alors qu’elle semble être en lien avec le taux de perturbation.
Robert Jobidon, Yves Bergeron, Sylvie Gauthier, André Robitaille, Jean-Pierre Saucier, Catherine Boudreault, Louis Imbeau, Frédérick Raulier . A biophysical approach to delineate a northern limit to commercial forestry: the case of Quebec’s boreal forest. 2015. Can. J. For. Res. 45(5): 515-528
DOI : 10.1139/cjfr-2014-0260
La forêt boréale est l’une des plus grandes forêts naturelles du monde et fournit de nombreux services écologiques à la société. La forêt boréale est également économiquement importante, mais la récolte du bois et son aménagement deviennent de plus en plus difficiles à mesure que l’on progresse du sud vers le nord. Une approche a donc été développée pour évaluer l’adéquation de districts écologiques pour la production de bois dans un contexte d’aménagement durable des forêts (ADF) dans la forêt boréale du nord de la province de Québec (Canada). Cette région inclut l’entièreté du domaine de la pessière noire à mousses (forêt fermée) ainsi que la portion sud de la pessière noire à lichens (forêt ouverte). Quatre critères spécifiques aux aspects biophysiques de l’ADF ont été évalués dans 1114 districts écologiques : l’environnement physique, la capacité de production de bois, la vulnérabilité de la forêt au feu (e.g., la probabilité qu’elle arrive à maturité) et la conservation de la biodiversité. Des indicateurs et des valeurs seuils ont été déterminés pour chaque critère et une analyse séquentielle a été développée pour évaluer si un district a le potentiel d’être aménagé de manière durable. Ce processus analytique a permis la classification de ces districts en trois catégories, soit légèrement sensibles (ADF possible), modérément sensibles (ADF possible sous certaines conditions) et fortement sensibles (ADF impossible). Les résultats montrent que 354 districts sont très sensibles, 62 du fait de contraintes physiques (7.5 % de la superficie), 130 du fait d’une productivité insuffisante (15.4 % de la superficie), 92 du fait d’une productivité potentielle insuffisante pour permettre de tenir compte du risque de feu (13.8 % de la superficie) et 70 du fait d’une insuffisance de peuplements denses et hauts (7.7 % de la superficie — critère de la biodiversité). Ce travail fournit une assise scientifique pour proposer une limite nordique des activités d’aménagement forestier au Québec. L’approche proposée pourrait être utile à d’autres juridictions pour aborder des questions similaires.
Pierre Bernier, Sylvie Gauthier, Yves Bergeron, Nicolas Mansuy, Frédérick Raulier , Alain Leduc. Using salvage logging and tolerance to risk to reduce the impact of forest fires on timber supply calculations. 2015. Can. J. For. Res. 45(4): 480-486
DOI : 10.1139/cjfr-2014-0434
Il est reconnu que les feux de forêt d’origine naturelle ne peuvent pas et même ne doivent pas être éliminés de la forêt boréale nord-américaine. Les feux de forêt occasionnent des pertes immédiates de volume de bois, perturbent la conversion de la structure courante d’âge de la forêt vers une structure cible et empêchent l’approvisionnement planifié en bois (APB) d’être atteint de manière constante. Dans cet article, nous explorons dans quelle mesure les déficits périodiques en bois disponible causés par divers risques de feux peuvent être atténués par la coupe de récupération et par le degré de tolérance des gestionnaires forestiers face à ces déficits, et ceci en fonction de la structure d’âge des forêts. Les simulations sont faites en utilisant une représentation temporelle déterministe et stochastique des feux. Les résultats montrent que la fréquence des périodes en déficit de bois peut être réduite par la coupe de récupération et par l’introduction de mesures de tolérance à ces déficits, et que ce potentiel d’atténuation est influencé par la structure d’âge de la forêt initiale et par le niveau de pertes par le feu. Les résultats montrent également que même un taux de coupe de récupération à 100 % ne peut pas compenser entièrement les pertes de bois par le feu et éliminer les déficits périodiques qui en résultent. En outre, l’ajout de la variabilité interannuelle des feux réduit l’efficacité des deux mesures d’atténuation. Enfin, puisque l’APB n’est en fait jamais réalisé dans les forêts sujettes aux feux, le coût réel d’une réduction l’APB doit être estimé non pas par la différence l’APB, mais plutôt par la différence plus réaliste de récolte de bois réalisée.q
Dinesh Babu Irulappa Pillai Vijayakumar, Yves Bergeron, David Pothier, Pierre Bernier, Frédérick Raulier , Sylvie Gauthier. Lengthening the historical records of fire history over large areas
of boreal forest in eastern Canada using empirical relationships. 2015. For. Ecol. Manage. 347:30-39
DOI : 10.1016/j.foreco.2015.03.011
Fire plays an important role for boreal forest succession, and time since last fire (TSLF) is therefore seen as a useful covariate to devise forest management strategies, but TSLF information is currently either spatially or temporarily limited. We therefore developed a TSLF map for an extensive region in eastern Canada (217,000 km2) by generalizing the empirical relationships that exist between regional historical records of fire (1880–2000) with forest inventory data and biophysical variables. Two random forest models were used to predict TSLF at the scale of 2-km2 cells. These cells were first classified into TSLF ? 120 years and >120 years and TSLF was then estimated by decade for cells classified as younger than 120 years. Overall, both models showed a substantial agreement at the scale of both the study area and landscape units, but the accuracy remained fairly low at the scale of individual cells. Results show that the decades between 1920 and 1940 were characterized by widespread fire activity covering approximately 28% of the study region. Studies have reported a doubling of the burn rate from 1970 to 2000, but our longer-term analysis suggests that the 1970–2000 burn rate (4.3% decade?1) is lower than the one detected between 1920 and 1940 (16.4% decade?1) and provides a relevant context for interpreting the recent increases in area burned observed since 1970. These results highlight the importance of lengthening the historical records of fire history maps in order to provide a better perspective of the actual changes of fire regime.
Narayan Prasad Dhital, Marie-Pierre Lapointe-Garant, Yves Bergeron, Pierre Bernier, Frédérick Raulier , Frank Berninger. Adaptation potential of ecosystembased
management to climate change
in the eastern Canadian boreal forest. 2015. Journal of of Environmental Planning and Management
DOI : 10.1080/09640568.2014.978079
Ecosystem-based management (EBM) of forests is gaining acceptance for its focus on the maintenance of the long-term integrity of ecosystem processes, but climate change challenges this view because of its impacts on these very processes. We have therefore evaluated the robustness of EBM to projected climate change, considering the role of climate on forest growth and fire regime in a boreal forest of eastern Canada. A climate sensitive growth index model was calibrated for three commercial species and used to project the evolution of merchantable volume for two climate scenarios (B1 and A2) under conventional and EBM strategies. Current burn rate and burn rates under future climate scenarios were also considered. Under the most extreme projected climate scenario, the periodic timber supply could be reduced by up to 79% through direct (growth reduction) and indirect (fire) effects. However, ecological indicators show that EBM is a more robust forest management strategy than conventional one demonstrating its adaptation potential to climate change at least in the short term.
Yves Bergeron, Kenneth Anyomi, Frédérick Raulier , Daniel Mailly, Martin-Philippe Girardin. Spatial and temporal heterogeneity of forest site productivity drivers: a case study within the eastern boreal forests of Canada. 2014. Landscape Ecology 29(5):905-918
DOI : 10.1007/s10980-014-0026-y
Forest productivity is driven by a suite of direct climatic and non-climatic factors that are transient or permanent. The kind of productivity driver and the nature of their effects vary by species, and scale dependencies potentially complicate these relationships. This study explored productivity-driver relations in eastern Boreal Canada and determined spatial effects in productivity control when expressed with stand dominant height at a reference age (site index). Data from 4,217 temporary sample plots obtained from boreal mixedwood and conifer bioclimatic domains, and with varied species composition, were used in this study. A single-level global model that assumes equal sensitivities across spatial scales was calibrated and compared with three alternative models reflecting different hypotheses on possible spatial heterogeneities. Alternative models were calibrated by plot-level soil deposit types (microscale), landscape dominant deposits (mesoscale) and bioclimatic domains (macroscale). A marked difference between the global and alternative models was observed, suggesting that a single global model does not sufficiently reflect existing heterogeneity in productivity-driver relationships. A combination of macro- and microscale models provided the best explanation of site index. Results further showed that site index is mainly driven by species composition (complementarity effects of aspen and jack pine compositions) and stand diameter structural diversity effects. It is concluded that successional changes, more than direct climatic effects, drive productivity.
Xiao Jing Guo, Rogier De Jong, Christophe Kinnard, Frédérick Raulier , Pierre Bernier, Martin-Philippe Girardin. Unusual forest growth decline in boreal North America covaries with the retreat of Arctic sea ice. 2014. Global Change Biology 20(3):851-866
DOI : 10.1111/gcb.12400
The 20th century was a pivotal period at high northern latitudes as it marked the onset of rapid climatic warming brought on by major anthropogenic changes in global atmospheric composition. In parallel, Arctic sea ice extent has been decreasing over the period of available satellite data records. Here, we document how these changes influenced vegetation productivity in adjacent eastern boreal North America. To do this, we used normalized difference vegetation index (NDVI) data, model simulations of net primary productivity (NPP) and tree-ring width measurements covering the last 300 years. Climatic and proxy-climatic data sets were used to explore the relationships between vegetation productivity and Arctic sea ice concentration and extent, and temperatures. Results indicate that an unusually large number of black spruce (Picea mariana) trees entered into a period of growth decline during the late-20th century (62% of sampled trees; n = 724 cross sections of age >70 years). This finding is coherent with evidence encoded in NDVI and simulated NPP data. Analyses of climatic and vegetation productivity relationships indicate that the influence of recent climatic changes in the studied forests has been via the enhanced moisture stress (i.e. greater water demands) and autotrophic respiration amplified by the declining sea ice concentration in Hudson Bay and Hudson Strait. The recent decline strongly contrasts with other growth reduction events that occurred during the 19th century, which were associated with cooling and high sea ice severity. The recent decline of vegetation productivity is the first one to occur under circumstances related to excess heat in a 300-year period, and further culminates with an intensifying wildfire regime in the region. Our results concur with observations from other forest ecosystems about intensifying temperature-driven drought stress and tree mortality with ongoing climatic changes.
Narayan Prasad Dhital, Yves Bergeron, Frédérick Raulier , Osvaldo Valeria, Louis Imbeau, Hugo Asselin. Emulating boreal forest disturbance dynamics: Can we maintain timber supply, aboriginal land use, and woodland caribou habitat? 2013. For. Chron. 89(1):54-65
DOI : 10.5558/tfc2013-011
Les effets sur l’approvisionnement en matière ligneuse découlant de l’implantation d’une stratégie d’aménagement écosystémique ont été analysés dans le cas d’une unité de la forêt boréale sous aménagement forestier dans l’est du Canada. Une programmation linéaire standard a été utilisée pour évaluer les effets de quatre principales politiques : (1) chercher à établir une structure d’âge cible de la forêt découlant du cycle naturel des feux de forêts et de la dynamique forestière (approche avec plusieurs cohortes), (2) rapprocher les blocs de coupe dans les zones exploitées afin de reproduire les patrons de perturbation naturelle à l’échelle du paysage, (3) maintenir les niveaux cumulatifs de coupe à blanc et de perturbations naturelles à l’intérieur de l’intervalle habituel de variabilité et (4) exclure les coupes d’exploitation dans les zones d’intérêt potentiel pour les peuples autochtones. La structure d’âge cible de la forêt a été atteinte suite à une réduction minime de l’approvisionnement périodique en matière ligneuse, mais seulement après 50 ans. Comparativement au scénario « usuel », l’inclusion des trois premières politiques a entraîné une réduction de 3% à 11% de l’approvisionnement planifié en matière ligneuse et une période de restauration nécessitant que 43% à 67% du territoire productif soit exclu des activités de coupe pour les 50 prochaines années. De tels résultats impliquent que les coupes partielles ne soient pas confinées dans les zones d’opération retenues pour la coupe à blanc. L’exclusion additionnelle du territoire forestier ayant un intérêt potentiel pour les peuples autochtones a provoqué une réduction supplémentaire de 4% à 10% de l’approvisionnement planifié en matière ligneuse. La validation des trois critères de base utilisés dans cette étude (les trois premières politiques) a été effectuée au moyen des exigences en matière d’habitat du caribou des bois (Rangifer tarandus caribou). Presque tous les scénarios ont engendré un niveau de perturbation permettant vraisemblablement le maintien des populations de caribou des bois en moins de 25 ans.
Kenneth Anyomi, Yves Bergeron, Frédérick Raulier , Daniel Mailly. The predominance of stand composition and structure over direct climatic and site effects in explaining aspen (Populus tremuloides Michaux) site index within boreal and temperate forests of western Quebec, Canada. 2013. For. Ecol. Manage. 302:390-403
DOI : 10.1016/j.foreco.2013.03.035
Existing models that use the site-index concept (dominant canopy height of a tree species at a reference stand age) are fundamentally stand-level models that do not account for stand dynamics, limiting their use to only a part of successional trajectories. Given that stand dynamics is influenced by both large and fine scale processes, we took a multi-level look at aspen (Populus tremuloides Michaux) productivity by determining landscape- and plot-level factors related to productivity as rated with site index. The study area extends from latitude 45° to 50°N in western Québec, from which were sampled 62 landscapes made up of 4948 plots, 25% of which had aspen as dominant and/co-dominants in the canopy. There, aspen is most often found in mixed stands. A stepwise procedure with forward selection was used in building landscape- and plot-level models and models were then arranged hierarchically such that (a) predicted estimates of the landscape model were inputs to the plot-level model (top-down) and (b) significant landscape variables were added to selected plot level variables (bottom-up). For the plot-level model, none of the climate variables considered were selected but at the landscape level, annual sum of degree–days was only the third to enter. In both cases, aspen site index was more related to the proportion of spruce (Picea mariana (Mill.) B.S.P. and Picea glauca (Moench.) Voss). At the level of landscapes, this observation might be due to the existence of particular vegetation mosaics, of which spruce proportion could be a surrogate. At the level of plots, influence of spruce on aspen site index is probably indicative of niche sharing with aspen. A high random variability was associated with the plot-level model but not with the landscape-level model. The similarity in drivers of aspen site index at both levels and the fact that both top-down and bottom-up approaches provided the same information, suggest that the use of landscape variables when modelling site index in mixed stands may help distinguish peculiarities shared by plots located in a landscape and improve the signal between site index and explanatory variables by reducing the random noise observed at the level of plots.
Narayan Prasad Dhital, Frédérick Raulier , Yves Bergeron, Osvaldo Valeria, Louis Imbeau, Hugo Asselin. Emulating boreal forest disturbance dynamics: Can we maintain
timber supply, aboriginal land use, and woodland caribou habitat? 2013. For. Chron. 89(1):54-65
DOI : 10.5558/tfc2013-011
The effects on timber supply incurred by implementing an ecosystem-based management strategy were evaluated in an eastern Canadian boreal forest management unit. Standard linear programming was used to test the effects of four key policy issues: (1) aim for a targeted forest age structure inspired by natural fire regime and forest dynamics (multi-cohort approach), (2) agglomerate harvest blocks in operating areas to reproduce natural disturbance patterns at the landscape scale, (3) maintain cumulated clearcutting and natural disturbance rates inside the historical range of variability, and (4) exclude from harvest areas of potential interest to aboriginal people. The targeted forest age structure was achieved with a minimum reduction of periodic timber supply, but only after 50 years. Compared to a "business-as-usual" scenario, inclusion of the first three policy issues resulted in a 3% to 11% reduction in planned timber supply and a restoration period requiring that 43% to 67% of the productive area be excluded from clearcutting activities for the next 50 years. Such results require that partial cutting not be confined to operating areas eligible for clearcutting. Further exclusion of forest areas of potential interest to aboriginal people resulted in an additional 4% to 10% decrease in planned timber supply. Validation of the coarse filters used in this study (first three policy issues) was done using habitat requirements of woodland caribou (Rangifer tarandus caribou). Almost all scenarios induced a disturbance rate likely to allow a self-sustaining woodland caribou population within 25 years.
Frédérick Raulier , Rija Rapanoela, Yves Bergeron, Héloïse Le Goff, Sylvie Gauthier. Introducing two indicators for fire risk consideration in the management of boreal forests. 2013. Ecological Indicator 24:451-461
DOI : 10.1016/j.ecolind.2012.07.023
When forest fires are taken into account during timber supply analyses, planned harvest rates are necessarily reduced to prevent potential timber shortages due to future forest fires. Because fire events are highly unpredictable, forest managers are reluctant to proactively reduce harvest targets, as it results in an immediate revenue loss. We explored a simple but proactive way of including the risks and uncertainties of fire in forest management planning through the identification of low productivity forest areas most vulnerable to fire in two different boreal forest zones. Site index and relative density index were used to estimate the time required to reach different harvesting thresholds based on stem size and tree density. We varied the production objective by using three different thresholds of minimum stem size (dm3/tree) and stand yield (m3/ha) (50 dm3/tree – 50 m3/ha, 70 dm3/tree – 70 m3/ha, 90 dm3/tree – 90 m3/ha). We estimated the time required to reach these thresholds and the proportion of forest zone that could exceed them. Fire cycle length was then used to assess the survival likelihood (probability of reaching the threshold at the stand scale when considering fire risk). An alternative rate of return was also used as an indicator of profit exposure to fire risk. When survival likelihood and alternative rate of return are considered jointly with time-declining interest rates, minimum survival likelihoods need to be higher for longer fire cycles. The proportion of stands vulnerable to fire served to decide whether or not to include fire risk into strategic planning. The identification of major break points in the vulnerability assessment also helped to decide which minimum harvesting threshold is appropriate as a function of the productivity characteristics and fire cycle of the forest under management.
Xiao Jing Guo, Pierre Bernier, Martin-Philippe Girardin, Sylvie Gauthier, Frédérick Raulier . Changes in growth of pristine boreal North American forests from 1950 to 2005 driven by landscape demographics and species traits. 2012. Biogeosciences 9:2523-2536
DOI : 10.5194/bg-9-2523-2012
In spite of the many factors that are occurring and known for positively affecting the growth of forests, some boreal forests across North America have recently felt the adverse impacts of environmental changes. Knowledge of causes for productivity declines in North American boreal forests remains limited, and this is owed to the large spatial and temporal scales involved, and the many plant processes affected. Here, the response of pristine eastern boreal North American (PEBNA) forests to ongoing climatic changes is examined using in situ data, community ecology statistics, and species-specific model simulations of carbon exchanges forced by contemporary climatic data. To examine trends in forest growth, we used a recently acquired collection of tree-ring width data from 252 sample plots distributed in PEBNA forests dominated by black spruce (Picea mariana [Mill.] B.S.P.) and jack pine (Pinus banksiana Lamb.). Results of linear trend analysis on the tree growth data highlight a dominating forest growth decline in overmature forests (age > 120 years) from 1950 to 2005. In contrast, improving growth conditions are seen in jack pine and mature (70–120 years) black spruce stands. Multivariate analysis of climate and growth relationships suggests that responses of PEBNA forests to climate are dependent on demographic and species traits via their mediation of temperature and water stress constraints. In support of this hypothesis, the simulation experiment suggests that in old-growth black spruce stands the benefit to growth brought on by a longer growing season may have been low in comparison with the increasing moisture stress and respiration losses caused by warmer summer temperatures. Predicted increases in wildfire frequency in PEBNA forests will likely enhance the positive response of landscape-level forest growth to climate change by shifting the forest distribution to younger age classes while also enhancing the jack pine component.
Kenneth Anyomi, Frédérick Raulier , Daniel Mailly, Yves Bergeron, Martin-Philippe Girardin. Using height growth to model local and regional response of trembling aspen (Populus tremuloides Michx.) to climate within the boreal forest of western Québec. 2012. Ecological Modelling 243( 123-132)
DOI : 10.1016/j.ecolmodel.2012.06.020
Studies relating site index to climatic variables basically assume that the sensitivity of a species to climate remains stable across the geographic range of their study area. Yet, provenance trials speak to the contrary and show that populations are adapted to their local climatic conditions and tend to respond differently to climate. Spatial and temporal complexity of forest productivity and climate-relationships has been globally reported and recent studies have emphasized the necessity for regional studies on forest growth dynamics of current and future populations. The objective of this study was to determine whether the main climatic and non-climatic drivers of trembling aspen (Populus tremuloides Michx.) growth in Québec should be treated as regional (the study area reacts as a unique population) or local factors (the area is composed of different populations) when modeling the spatio-temporal variability of aspen productivity as measured with site index. Stem analysis data was collected from 124 trees (32 stands) that span a north-south (latitude 46–51°N) transect in western boreal Québec. Most stands were dense with cover density above 60%, even-aged, 50–90 years old, and very often mixed. The northernmost regions (latitude 48–51°N) are characterized by either organic or clay deposits, while in the south (latitude 46–48°N) till or clay deposits predominate. Climate variables that met selection criteria as major regional or local factors that influence aspen productivity were selected. A mixed modeling approach was subsequently employed to identify the categorization unit that could be defined as a population. We then predicted variation in the random error with prior information obtained at stand level. Our results show that aspen height growth is mainly driven by annual sums of degree days and stand age. Surface deposit type, which is an indicator of soil nutritive status and moisture potential, was found to have modulated climate influence. Finally, aspen productivity is better explained with a model that assumes that specific populations have a different response function to climate and are adapted to their local climatic conditions. This has implications when predicting the response to climatic change for forest growth models that assume that conspecifics respond to climate similarly.
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