33 research outputs found
Global warming reshapes European pyroregions
Wildland fire is expected to increase in response to global warming, yet little is known about future changes to fire regimes in Europe. Here, we developed a pyrogeography based on statistical fire models to better understand how global warming reshapes fire regimes across the continent. We identified five large-scale pyroregions with different levels of area burned, fire frequency, intensity, length of fire period, size distribution, and seasonality. All other things being equal, global warming was found to alter the distribution of these pyroregions, with an expansion of the most fire prone pyroregions ranging respectively from 50% to 130% under 2° and 4°C global warming scenarios. Our estimates indicate a strong amplification of fire across parts of southern Europe and a subsequent shift toward new fire regimes, implying substantial socio-ecological impacts in the absence of mitigation or adaptation measures
Les effets du passage dâun feu dans un peuplement arborĂ© : synthĂšse des connaissances et applications pour le gestionnaire forestier mĂ©diterranĂ©en
Lâincendie de forĂȘt constitue la premiĂšre perturbation des Ă©cosystĂšmes forestiers mĂ©diterranĂ©ens. Il existe de fortes interactions entre lâĂ©cosystĂšme, les pratiques sylvicoles et les rĂ©gimes de feu associĂ©s. Cet article constitue une synthĂšse des connaissances disponibles et les appliquent aux problĂ©matiques rencontrĂ©es par le gestionnaire forestier mĂ©diterranĂ©en
Simulation numĂ©rique du couplage surface/canopĂ©e lors de la propagation d'un feu de cime en forĂȘt borĂ©ale
Cette Ă©tude concerne la modĂ©lisation numĂ©rique de l'ignition et de la propagation d'un feu de cime dans une forĂȘt de type borĂ©ale. La formulation mathĂ©matique est basĂ©e sur une approche multi-phasique, construite Ă partir des Ă©quations de conservation (masse, quantitĂ© de mouvement, Ă©nergie) gouvernant l'Ă©volution du systĂšme couplĂ© formĂ© par la vĂ©gĂ©tation et l'atmosphĂšre ambiant. Le modĂšle a prĂ©alablement Ă©tĂ© testĂ© Ă petite Ă©chelle, sur des feux de litiĂšre homogĂšne et Ă plus grande Ă©chelle, sur des feux de prairie et en garrigue MĂ©diterranĂ©enne. Les rĂ©sultats ont Ă©tĂ© comparĂ©s avec des donnĂ©es expĂ©rimentales de la littĂ©rature, et les prĂ©dictions des modĂšles empiriques opĂ©rationnels dĂ©veloppĂ©s en Australie (MkV) et aux Etats Unis (BEHAVE). Le modĂšle a Ă©tĂ© Ă©tendu Ă un profil de vĂ©gĂ©tation composĂ© d'une couche arbustive et d'une canopĂ©e. Les rĂ©sultats mettent en Ă©vidence le rĂŽle jouĂ© par le combustible de surface sur la dynamique gĂ©nĂ©rale du feu de cime. Les rĂ©sultats numĂ©riques ont Ă©tĂ© confrontĂ©s aux donnĂ©es collectĂ©es Ă l'occasion de campagnes expĂ©rimentales internationales rĂ©alisĂ©es au Canada
SurEau-Ecos v2.0: a trait-based plant hydraulics model for simulations of plant water status and drought-induced mortality at the ecosystem level
A widespread increase in tree mortality has been observed
around the globe, and this trend is likely to continue because of ongoing
climate-induced increases in drought frequency and intensity. This raises
the need to identify regions and ecosystems that are likely to experience
the most frequent and significant damage. We present SurEau-Ecos, a trait-based,
plant hydraulic model designed to predict tree desiccation and mortality at
scales from stand to region. SurEau-Ecos draws on the general principles of the SurEau model
but introduces a simplified representation of plant architecture and
alternative numerical schemes. Both additions were made to facilitate model
parameterization and large-scale applications. In SurEau-Ecos, the water fluxes from
the soil to the atmosphere are represented through two plant organs (a leaf
and a stem, which includes the volume of the trunk, roots and branches) as
the product of an interface conductance and the difference between water
potentials. Each organ is described by its symplasmic and apoplasmic
compartments. The dynamics of a plant's water status beyond the point of
stomatal closure are explicitly represented via residual transpiration flow,
plant cavitation and solicitation of plants' water reservoirs. In addition
to the âexplicitâ numerical scheme of SurEau, we implemented a âsemi-implicitâ
and âimplicitâ scheme. Both schemes led to a substantial gain in computing
time compared to the explicit scheme (>10â000 times), and
the implicit scheme was the most accurate. We also observed similar plant
water dynamics between SurEau-Ecos and SurEau but slight disparities in infra-daily
variations of plant water potentials, which we attributed to the differences
in the representation of plant architecture between models. A global model's
sensitivity analysis revealed that factors controlling plant desiccation
rates differ depending on whether leaf water potential is below or above the
point of stomatal closure. Total available water for the plant, leaf area
index and the leaf water potential at 50â% stomatal closure mostly drove
the time needed to reach stomatal closure. Once stomata are closed,
resistance to cavitation, residual cuticular transpiration and plant water
stocks mostly determined the time to hydraulic failure. Finally, we
illustrated the potential of SurEau-Ecos to simulate regional drought-induced mortality
over France. SurEau-Ecos is a promising tool to perform regional-scale predictions of
drought-induced hydraulic failure, determine the most vulnerable areas and
ecosystems to drying conditions, and assess the dynamics of forest
flammability.</p
Plant hydraulics at the heart of plant, crops and ecosystem functions in the face of climate change
16 pĂĄginas.- 5 figuras.- 179 referencias.- Additional Supporting Information may be found online in theSupporting Information section at the end of the article.Plant hydraulics is crucial for assessing the plants' capacity to extract and transport water from the soil up to their aerial organs. Along with their capacity to exchange water between plant compartments and regulate evaporation, hydraulic properties determine plant water relations, water status and susceptibility to pathogen attacks. Consequently, any variation in the hydraulic characteristics of plants is likely to significantly impact various mechanisms and processes related to plant growth, survival and production, as well as the risk of biotic attacks and forest fire behaviour. However, the integration of hydraulic traits into disciplines such as plant pathology, entomology, fire ecology or agriculture can be significantly improved. This review examines how plant hydraulics can provide new insights into our understanding of these processes, including modelling processes of vegetation dynamics, illuminating numerous perspectives for assessing the consequences of climate change on forest and agronomic systems, and addressing unanswered questions across multiple areas of knowledge.This article is an output of the international network âPsiHubâ funded and supported by the ECODIV department of INRAE.This review was partly supported by the H2020 Project FORGENIUS (Improving access to FORest GENetic resourcesInformation and services for end-USers) #862221Peer reviewe
Coupled slope and wind effects on fire spread with influences of fire size: a numerical study using FIRETEC
Effets de la récurrence des incendies sur le comportement du feu dans des suberaies (Quercus suber L.) et maquis méditerranéens sur les cinquante derniÚres années
International audiencePast fire recurrence impacts the vegetation structure, and it is consequently hypothesized to alter its future fire behaviour. We examined the fire behaviour in shrubland-forest mosaics of southeastern France, which were organized along a range of fire frequency (0 to 3â4 fires along the past 50 years) and had different time intervals between fires. The mosaic was dominated by Quercus suber L. and EricaâCistus shrubland communities. We described the vegetation structure through measurements of tree height, base of tree crown or shrub layer, mean diameter, cover, plant water content and bulk density. We used the physical model Firetec to simulate the fire behaviour. Fire intensity, fire spread, plant water content and biomass loss varied significantly according to fire recurrence and vegetation structure, mainly linked to the time since the last fire, then the number of fires. These results confirm that past fire recurrence affects future fire behaviour, with multi-layered vegetation (particularly high shrublands) producing more intense fires, contrary to submature Quercus woodlands that have not burnt since 1959 and that are unlikely to reburn. Further simulations, with more vegetation scenes according to shrub and canopy covers, will complete this study in order to discuss the fire propagation risk in heterogeneous vegetation, particularly in the Mediterranean area, with a view to a local management of these ecosystems.La combustibilitĂ© de 51 placettes correspondant Ă diffĂ©rentes rĂ©currences dâincendies depuis 1959 (0 Ă 4 feux) a Ă©tĂ© analysĂ©e en Provence siliceuse. Les Ă©cosystĂšmes Ă©tudiĂ©s sont des suberaies dominĂ©es par Quercus suber L., et des maquis Ă Erica arborea L. et Ă cistes. Les donnĂ©es descriptives de la vĂ©gĂ©tation combustible (composition, biomasse, recouvrement, hauteur) ont Ă©tĂ© entrĂ©es dans un modĂšle physique du feu (Firetec) afin dâobtenir des variables descriptives du comportement de feu. Les pertes en masse et en eau de la vĂ©gĂ©tation, la vitesse de propagation et lâintensitĂ© du feu augmentent de façon significative avec la continuitĂ© verticale du combustible, qui dĂ©pend principalement du temps depuis le dernier feu, puis du nombre de feux. Les rĂ©sultats confirment lâhypothĂšse selon laquelle le feu est particuliĂšrement intense et rapide dans des peuplements multi-stratifiĂ©s Ă forte charge en Ă©lĂ©ments fins et forte connexion spatiale entre les individus, tels que les maquis hauts dĂ©veloppĂ©s aprĂšs un seul feu intense en cinquante ans. Au contraire, le feu ne se propage pas dans les forĂȘts de chĂȘnes submatures nâayant pas brĂ»lĂ© depuis au moins cinquante ans et caractĂ©risĂ©es par une faible connectivitĂ© verticale entre la canopĂ©e et le sous-Ă©tage, favorisant ainsi un effet « auto-protecteur » contre les incendies futurs. Ces informations permettent de discuter de la gestion de la vĂ©gĂ©tation, en particulier la surveillance ou le dĂ©broussaillement local des maquis hauts grandement combustibles, pour diminuer le risque de propagation des feux Ă lâĂ©chelle de la parcelle
Exploring three-dimensional coupled fireâatmosphere interactions downwind of wind-driven surface fires and their influence on backfires using the HIGRAD-FIRETEC model
Fuel bulk density and fuel moisture content effects on fire rate of spread A comparison between FIRETEC model predictions and experimental results in shrub fuels
Fuel bulk density and fuel moisture content effects on fire rate of spread were assessed in shrub fuels, comparing experimental data observed in outdoor wind tunnel burns and predictions from the physically-based model FIRETEC. Statistical models for the combined effects of bulk density and fuel moisture content were fitted to both the experimental and the simulated rate of spread values using non-linear regression techniques. Results confirmed a significant decreasing effect of bulk density on rate of spread in a power law in both laboratory burns and simulations. However, experimental data showed a lesser effect than simulations, suggesting a difference in the effective drag. Fuel moisture content effect was highly consistent, showing a similar exponential relationship with rate of spread in laboratory and in simulations. FIRETEC simulations showed similar orders of magnitude with predictions of two field-based empirical models, finding a significant correlation between rate of spread values. The study confirms the efficacy of the combined approach through experimental data and simulations to study fire behaviour. © The Author(s) 2012
A Bioeconomic Projection of ClimateâInduced Wildfire Risk in the Forest Sector
International audienceUnder the influence of climate change, wildfire regimes are expected to intensify and expand to new areas, increasing threats to natural and socioeconomic assets. We explore the environmental and economic implications for the forest sector of climate-induced changes in wildfire regimes. To retain genericity while considering local determinants, we focus on the regional level and take Mediterranean France as an example. Coupling a bioeconomic forest sector model and a model of wildfire activity, we perform spatially explicit simulations under various levels of radiative forcing. By using a probabilistic framework, we also assess the propagation of several sources of uncertainty to the forest sector, considering both climate-induced uncertainty and the intrinsic stochasticity of the fire process. By the end of the century, summer burned areas increase by up to 55%, causing moderate losses of merchantable timber and forest carbon stocks, with cascading impacts for industrial activities and climate mitigation in the forest sector. Implications for industries remain limited, but we observe price increases, especially for softwoods, as well as spatially differentiated changes in producer welfare. Inter-annual fluctuations explain most of uncertainty in wildfire activity, but their impacts on the forest sector are quickly dampened. Over time, owing to the cumulative nature of wildfire impacts on forest resources, uncertainty related to climate warming, climate modelsâ response and stochasticity intrinsic to the wildfire phenomenon strongly increase in relative importance. Results reassert the need to consider multiple futures in prospective assessments, including uncertainty inherent to natural processes, often omitted in large-scale economic assessments.maint