Le régime des incendies de forêt en Valais: influences climatiques et anthropiques | Forest fire regimes in Valais: climatic and human influences

Forest fire regimes are particularly sensitive to variations in the climate and to human influences. In the Alps both the manner in which the land is used and climatic changes, in particular rises in temperature and the frequency of drought periods, are probably going to bring about considerable modifications in fire regimes. The history of these fires in Valais in the 20th century is however still little known, as is the influence of the different determining factors. From a study of documentary archives we have therefore reconstituted the history of forest fires in Valais from 1904 to 2008. We then tried to establish whether or not the fire regime had evolved during this time by comparing descriptive statistics from the first and the second halves of the period under study. By means of correlation analyses we could then find what factors had a significant influence on the occurrence of fires. What emerges is that forest fire activity moved towards the plain in the course of the 20 century, probably on account of the increase in population density at lower altitudes. The seasonality of the fires also evolved: there was an outbreak of fires in the spring during the second half of the period under study, whereas in the first half fires mostly occurred in summer. On the other hand the frequency of the fires and the surface area burned annually did not differ significantly in the periods before and after 1955. As for the balance between factors determining the frequency of fires and the surface burned annually, there has been a modification in the period under study. Although drought was a decisive factor in the first decades of the 20 century, afterwards it seems to have declined in importance, being supplanted by other factors, notably the availability of combustible material. The fact that at present the forest fire regime is apparently regulated by factors other than the climate means it is possible to envisage concrete measures in order to limit fire risks.

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Historical fire records at the two ends of Iberian Central Mountain System: Estrela massif and Ayllón massif

Investigaciones Geográficas ◽

10.14198/ingeo2019.72.02 ◽

2019 ◽

pp. 31

Author(s):

Catarina Romão Sequeira ◽

Cristina Montiel-Molina ◽

Francisco Castro Rego

Keyword(s):

Fire Regime ◽

Fire Regimes ◽

Historical Record ◽

Multiscale Approach ◽

Natural Region ◽

Fire Use ◽

Prone Area ◽

Mountain System ◽

History Of ◽

In Fire

The Iberian Peninsula has a long history of fire, as the Central Mountain System, from the Estrela massif in Portugal to the Ayllón massif in Spain, is a major fire-prone area. Despite being part of the same natural region, there are different environmental, political and socio-economic contexts at either end, which might have led to distinct human causes of wildfires and associated fire regimes. The hypothesis for this research lies in the historical long-term relationship between wildfire risks and fire use practices within a context of landscape dynamics. In addition to conducting an analysis of the statistical period, a spatial and temporal multiscale approach was taken by reconstructing the historical record of prestatistical fires and land management history at both ends of the Central Mountain System. The main result is the different structural causes of wildland fires at either end of the Central Mountain System, with human factors being more important than environmental factors in determining the fire regimes in both contexts. The study shows that the development of the fire regime was non-linear in the nineteenth and twentieth centuries, due to broader local human context factors which led to a shift in fire-use practices.

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Forest fire occurrence and climate change in Canada

International Journal of Wildland Fire ◽

10.1071/wf09002 ◽

2010 ◽

Vol 19 (3) ◽

pp. 253 ◽

Cited By ~ 226

Author(s):

B. M. Wotton ◽

C. A. Nock ◽

M. D. Flannigan

Keyword(s):

Climate Change ◽

Boreal Forest ◽

Forest Fire ◽

Forest Fires ◽

General Circulation ◽

Fire Regime ◽

General Circulation Models ◽

Fire Occurrence ◽

Fire Activity ◽

In Fire

The structure and function of the boreal forest are significantly influenced by forest fires. The ignition and growth of fires depend quite strongly on weather; thus, climate change can be expected to have a considerable impact on forest fire activity and hence the structure of the boreal forest. Forest fire occurrence is an extremely important element of fire activity as it defines the load on suppression resources a fire management agency will face. We used two general circulation models (GCMs) to develop projections of future fire occurrence across Canada. While fire numbers are projected to increase across all forested regions studied, the relative increase in number of fires varies regionally. Overall across Canada, our results from the Canadian Climate Centre GCM scenarios suggest an increase in fire occurrence of 25% by 2030 and 75% by the end of the 21st century. Results projected from fire climate scenarios derived from the Hadley Centre GCM suggest fire occurrence will increase by 140% by the end of this century. These general increases in fire occurrence across Canada agree with other regional and national studies of the impacts of climate change on fire activity. Thus, in the absence of large changes to current climatic trends, significant fire regime induced changes in the boreal forest ecosystem are likely.

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Fire regime shift linked to increased forest density in a piñon–juniper savanna landscape

International Journal of Wildland Fire ◽

10.1071/wf13053 ◽

2014 ◽

Vol 23 (2) ◽

pp. 234 ◽

Cited By ~ 17

Author(s):

Ellis Q. Margolis

Keyword(s):

Regime Shift ◽

Fire History ◽

Fire Regime ◽

Fire Regimes ◽

Fire Frequency ◽

Climatic Conditions ◽

Tree Density ◽

High Severity ◽

Wide Range ◽

In Fire

Piñon–juniper (PJ) fire regimes are generally characterised as infrequent high-severity. However, PJ ecosystems vary across a large geographic and bio-climatic range and little is known about one of the principal PJ functional types, PJ savannas. It is logical that (1) grass in PJ savannas could support frequent, low-severity fire and (2) exclusion of frequent fire could explain increased tree density in PJ savannas. To assess these hypotheses I used dendroecological methods to reconstruct fire history and forest structure in a PJ-dominated savanna. Evidence of high-severity fire was not observed. From 112 fire-scarred trees I reconstructed 87 fire years (1547–1899). Mean fire interval was 7.8 years for fires recorded at ≥2 sites. Tree establishment was negatively correlated with fire frequency (r=–0.74) and peak PJ establishment was synchronous with dry (unfavourable) conditions and a regime shift (decline) in fire frequency in the late 1800s. The collapse of the grass-fuelled, frequent, surface fire regime in this PJ savanna was likely the primary driver of current high tree density (mean=881treesha–1) that is >600% of the historical estimate. Variability in bio-climatic conditions likely drive variability in fire regimes across the wide range of PJ ecosystems.

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Production of peroxy nitrates in boreal biomass burning plumes over Canada during the BORTAS campaign

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-3485-2016 ◽

2016 ◽

Vol 16 (5) ◽

pp. 3485-3497 ◽

Cited By ~ 3

Author(s):

Marcella Busilacchio ◽

Piero Di Carlo ◽

Eleonora Aruffo ◽

Fabio Biancofiore ◽

Cesare Dari Salisburgo ◽

...

Keyword(s):

Boreal Forest ◽

Forest Fire ◽

Biomass Burning ◽

Forest Fires ◽

Chemical Mechanism ◽

Fire Emissions ◽

Fire Plumes ◽

Peroxy Nitrates ◽

In Fire ◽

The Impact

Abstract. The observations collected during the BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS) campaign in summer 2011 over Canada are analysed to study the impact of forest fire emissions on the formation of ozone (O3) and total peroxy nitrates ∑PNs, ∑ROONO2). The suite of measurements on board the BAe-146 aircraft, deployed in this campaign, allows us to calculate the production of O3 and of ∑PNs, a long-lived NOx reservoir whose concentration is supposed to be impacted by biomass burning emissions. In fire plumes, profiles of carbon monoxide (CO), which is a well-established tracer of pyrogenic emission, show concentration enhancements that are in strong correspondence with a significant increase of concentrations of ∑PNs, whereas minimal increase of the concentrations of O3 and NO2 is observed. The ∑PN and O3 productions have been calculated using the rate constants of the first- and second-order reactions of volatile organic compound (VOC) oxidation. The ∑PN and O3 productions have also been quantified by 0-D model simulation based on the Master Chemical Mechanism. Both methods show that in fire plumes the average production of ∑PNs and O3 are greater than in the background plumes, but the increase of ∑PN production is more pronounced than the O3 production. The average ∑PN production in fire plumes is from 7 to 12 times greater than in the background, whereas the average O3 production in fire plumes is from 2 to 5 times greater than in the background. These results suggest that, at least for boreal forest fires and for the measurements recorded during the BORTAS campaign, fire emissions impact both the oxidized NOy and O3, but (1 ∑PN production is amplified significantly more than O3 production and (2) in the forest fire plumes the ratio between the O3 production and the ∑PN production is lower than the ratio evaluated in the background air masses, thus confirming that the role played by the ∑PNs produced during biomass burning is significant in the O3 budget. The implication of these observations is that fire emissions in some cases, for example boreal forest fires and in the conditions reported here, may influence more long-lived precursors of O3 than short-lived pollutants, which in turn can be transported and eventually diluted in a wide area.

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Forest Fire Regime in a Mediterranean Ecosystem: Unraveling the Mutual Interrelations between Rainfall Seasonality, Soil Moisture, Drought Persistence, and Biomass Dynamics

Fire ◽

10.3390/fire3030049 ◽

2020 ◽

Vol 3 (3) ◽

pp. 49

Author(s):

Nunzio Romano ◽

Nadia Ursino

Keyword(s):

Climate Change ◽

Soil Water ◽

Forest Fires ◽

Fire Regime ◽

Fire Regimes ◽

Mediterranean Ecosystem ◽

Water Retention Capacity ◽

Soil Water Retention ◽

Retention Capacity ◽

Rainfall Frequency

Frequent and severe droughts typically intensify wildfires provided that there is enough fuel in situ. The extent to which climate change may influence the fire regime and long time-scale hydrological processes may soften the effect of inter-annual climate change and, more specifically, whether soil-water retention capacity can alleviate the harsh conditions resulting from droughts and affect fire regimes, are still largely unexplored matters. The research presented in this paper is a development of a previous investigation and shows in what way, and to what extent, rainfall frequency, dry season length, and hydraulic response of different soil types drive forest fires toward different regimes while taking into consideration the typical seasonality of the Mediterranean climate. The soil-water holding capacity, which facilitates biomass growth in between fire events and hence favors fuel production, may worsen the fire regime as long dry summers become more frequent, such that the ecosystem’s resilience to climate shifts may eventually be undermined.

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Mapping fire regime ecoregions in California

International Journal of Wildland Fire ◽

10.1071/wf19136 ◽

2020 ◽

Vol 29 (7) ◽

pp. 595 ◽

Cited By ~ 1

Author(s):

Alexandra D. Syphard ◽

Jon E. Keeley

Keyword(s):

Fire Regime ◽

Fire Severity ◽

Fire Regimes ◽

Unsupervised Classification ◽

Fire Frequency ◽

The State ◽

Reduction Strategies ◽

Lower Variability ◽

Fire Characteristics ◽

In Fire

The fire regime is a central framing concept in wildfire science and ecology and describes how a range of wildfire characteristics vary geographically over time. Understanding and mapping fire regimes is important for guiding appropriate management and risk reduction strategies and for informing research on drivers of global change and altered fire patterns. Most efforts to spatially delineate fire regimes have been conducted by identifying natural groupings of fire parameters based on available historical fire data. This can result in classes with similar fire characteristics but wide differences in ecosystem types. We took a different approach and defined fire regime ecoregions for California to better align with ecosystem types, without using fire as part of the definition. We used an unsupervised classification algorithm to segregate the state into spatial clusters based on distinctive biophysical and anthropogenic attributes that drive fire regimes – and then used historical fire data to evaluate the ecoregions. The fire regime ecoregion map corresponded well with the major land cover types of the state and provided clear separation of historical patterns in fire frequency and size, with lower variability in fire severity. This methodology could be used for mapping fire regimes in other regions with limited historical fire data or forecasting future fire regimes based on expected changes in biophysical characteristics.

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Holocene history of fire, vegetation and land use from the central Pyrenees (France)

Quaternary Research ◽

10.1016/j.yqres.2011.09.009 ◽

2012 ◽

Vol 77 (1) ◽

pp. 54-64 ◽

Cited By ~ 38

Author(s):

Damien Rius ◽

Boris Vanniére ◽

Didier Galop

Keyword(s):

Land Use ◽

Late Holocene ◽

Landscape Management ◽

Fire Regimes ◽

Fire Frequency ◽

Subsequent Reduction ◽

Human Land Use ◽

History Of ◽

In Fire ◽

Central Pyrenees

Located on a mountain pass in the west-central Pyrenees, the Col d'Ech peat bog provides a Holocene fire and vegetation record based upon nine 14C (AMS) dates. We aim to compare climate-driven versus human-driven fire regimes in terms of frequency, fire episodes distribution, and impact on vegetation. Our results show the mid-Holocene (8500–5500 cal yr BP) to be characterized by high fire frequency linked with drier and warmer conditions. However, fire occurrences appear to have been rather stochastic as underlined by a scattered chronological distribution. Wetter and colder conditions at the mid-to-late Holocene transition (4000–3000 cal yr BP) led to a decrease in fire frequency, probably driven by both climate and a subsequent reduction in human land use. On the contrary, from 3000 cal yr BP, fire frequency seems to be driven by agro-pastoral activities with a very regular distribution of events. During this period fire was used as a prominent agent of landscape management.

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Current and future estimates for the fire frequency and the fire rotation period in the main woodland types of peninsular Spain: a case-study approach

Forest Systems ◽

10.5424/fs/2015242-06454 ◽

2015 ◽

Vol 24 (2) ◽

pp. e031 ◽

Cited By ~ 11

Author(s):

Antonio Vázquez ◽

José M. Climent ◽

Luis Casais ◽

José R. Quintana

Keyword(s):

Forest Fires ◽

Fire Regime ◽

Rotation Period ◽

Fire Frequency ◽

Large Variability ◽

Rotation Periods ◽

In Fire ◽

Climatic Scenario ◽

Peninsular Spain ◽

Reference Areas

Aim of study. Fire regimes are frequently dynamic and change as a function of the interactions between the three main fire drivers: fuels, ignitions and climatic conditions. We characterized the recent period (1974-2005) and performed estimates for the future fire regimeArea of study. We have considered five pine and another four woodland types by means of the analyses of 100 reference areas in peninsular Spain.Material and methods. The estimates of the expected alterations in fire frequency and the fire rotation period were based on models previously developed for the climatic scenarios SRES A2 and B2.Main results. The results point to the large variability in fire frequency and rotation periods between the woodland types as defined, and also among the reference areas delimited for each of them. Fire frequencies will increase for all woodland types while very relevant shortenings of the fire rotation periods are expected. For the 32 yr period analysed, rotation periods longer than 500 yr were obtained in 54% of the reference areas while this percentage would decrease to 31% in the B2 and to 29% in the A2 climatic scenario. In the most affected woodland type, P. pinaster, from a median rotation period of 83 yr it would decrease to 26 yr in the B2 and to 20 yr in the A2 climatic scenario.Research highlights. We conclude that the predicted increases in fire activity will have adverse effects on some of the main Spanish woodland types due to the expected future disruptions in the fire regime. Keywords: Forest fires; fire regime; fire frequency; fire rotation period; climatic change.Abbreviations used: SRES: Special Report on Emissions Scenarios; IPCC: Intergovernmental Panel on Climate Change; RA: Reference Areas.

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Fire History of the Lamar River Drainage, Yellowstone National Park, Wyoming

The UW National Parks Service Research Station Annual Reports ◽

10.13001/uwnpsrc.1989.2821 ◽

1989 ◽

Vol 13 ◽

pp. 169-173

Author(s):

Stephen Barrett ◽

Stephen Arno

Keyword(s):

Yellowstone National Park ◽

National Park ◽

Fire History ◽

Fire Regime ◽

Lodgepole Pine ◽

Fire Regimes ◽

Pine Forests ◽

River Drainage ◽

Tree Ring Data ◽

History Of

This study's goal is to document the fire history of the Lamar River drainage, southeast of Soda Butte Creek in the Absaroka Mountains of northeastern Yellowstone National Park (YNP). Elsewhere in YNP investigators have documented very long-interval fire regimes for lodgepole pine forests occurring on rhyolitic derived soils (Romme 1982, Romme and Despain 1989) and short-interval fire regimes for the Douglas-fir/grassland types (Houston 1973). No fire regime information was available for lodgepole pine forests on andesitic derived soils, such as in the Lamar drainage. This study will provide managers with a more complete understanding of YNP natural fire history, and the data will supplement the park's Geographic Information System (GIS) data base. Moreover, most of the study area was severely burned in 1988 and historical tree ring data soon will be lost to attrition of potential sample trees.

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The status and challenge of global fire modelling

10.5194/bg-2016-17 ◽

2016 ◽

Cited By ~ 1

Author(s):

S. Hantson ◽

A. Arneth ◽

S. P. Harrison ◽

D. I. Kelley ◽

I. C. Prentice ◽

...

Keyword(s):

Atmospheric Chemistry ◽

Fire Regime ◽

Fire Regimes ◽

Climate Projections ◽

Data Sets ◽

Predictive Skill ◽

Current State ◽

Fire Modelling ◽

The Status ◽

In Fire

Abstract. Biomass burning impacts vegetation dynamics, biogeochemical cycling, atmospheric chemistry, and climate, with sometimes deleterious socio-economic impacts. Under future climate projections it is often expected that the risk of wildfires will increase. Our ability to predict the magnitude and geographic pattern of future fire impacts rests on our ability to model fire regimes, either using well-founded empirical relationships or process-based models with good predictive skill. A large variety of models exist today and it is still unclear which type of model or degree of complexity is required to model fire adequately at regional to global scales. This is the central question underpinning the creation of the Fire Model Intercomparison Project – FireMIP, an international project to compare and evaluate existing global fire models against benchmark data sets for present-day and historical conditions. In this paper we summarise the current state-of-the-art in fire regime modelling and model evaluation, and outline what lessons may be learned from FireMIP.

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