Calculating and interpreting forest fire intensities

Alexander, Martin E.

doi:10.1139/b82-048

Cited by 351 publications

(254 citation statements)

References 12 publications

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“…Here, we present another proxy of fire intensity that accounts for fuel combustion: frontal fire intensity (I), calculated as the product of fire spread rate (r); net heat of combustion (H, kept constant for both plots); and the weight of fuel consumed by the fires (w) (I = Hwr) (25). In 2007, frontal fire intensity was (i) higher than in 2004 in both plots and (ii) higher in B3yr (edge: 820 kW·m −1 ; forest: 319 kW·m −1 ) than in B1yr (edge: 220 kW·m −1 ; forest: 141 kW·m −1 ).…”

Section: Resultsmentioning

confidence: 99%

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Abrupt increases in Amazonian tree mortality due to drought–fire interactions

Brando

Balch

Nepstad

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

647

710

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Interactions between climate and land-use change may drive widespread degradation of Amazonian forests. High-intensity fires associated with extreme weather events could accelerate this degradation by abruptly increasing tree mortality, but this process remains poorly understood. Here we present, to our knowledge, the first field-based evidence of a tipping point in Amazon forests due to altered fire regimes. Based on results of a large-scale, longterm experiment with annual and triennial burn regimes (B1yr and B3yr, respectively) in the Amazon, we found abrupt increases in fire-induced tree mortality (226 and 462%) during a severe drought event, when fuel loads and air temperatures were substantially higher and relative humidity was lower than long-term averages. This threshold mortality response had a cascading effect, causing sharp declines in canopy cover (23 and 31%) and aboveground live biomass (12 and 30%) and favoring widespread invasion by flammable grasses across the forest edge area (80 and 63%), where fires were most intense (e.g., 220 and 820 kW·m −1 ). During the droughts of 2007 and 2010, regional forest fires burned 12 and 5% of southeastern Amazon forests, respectively, compared with <1% in nondrought years. These results show that a few extreme drought events, coupled with forest fragmentation and anthropogenic ignition sources, are already causing widespread fire-induced tree mortality and forest degradation across southeastern Amazon forests. Future projections of vegetation responses to climate change across drier portions of the Amazon require more than simulation of global climate forcing alone and must also include interactions of extreme weather events, fire, and land-use change.forest dieback | fireline intensity | stable states | MODIS | fire mapping

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Section: Resultsmentioning

confidence: 99%

“…Details of these measurements can be found in Balch et al (21,26). Frontal fire intensity was calculated as the product of net heat of combustion, weight of fuel consumed, and rate of spread (25). Net heat of combustion was assumed to be 18,000 kJ·m −1 for both plots, following Alexander (25).…”

Section: Cumulative Treementioning

confidence: 99%

Abrupt increases in Amazonian tree mortality due to drought–fire interactions

Brando

Balch

Nepstad

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

647

710

View full text Add to dashboard Cite

show abstract

“…Fires were lit along the down-wind edge of a plot using a drip torch to create a single 15 m wide ignition line. Post-fire we re-surveyed plots to estimate burnt biomass thus allowing the calculation of fireline intensity as described by Alexander (1982). This paper focuses on understanding variation in rate of spread (RoS).…”

Section: Methodsmentioning

confidence: 99%

Developing shrub fire behaviour models in an oceanic climate: Burning in the British uplands

Davies

Legg

Smith

et al. 2006

Forest Ecology and Management

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Prescribed burning of moorland vegetation in the UK is used to provide habitat for red grouse, a game bird, and to improve grazing for sheep and deer. The peak time of fire risk corresponds to the normal legal burning period of 1 st November (1 st October in Scotland) to 15 th April rather than a meteorologically-defined fire season.Moorland fuels in the UK are unusual. They are dominated by Calluna vulgaris, which forms a dense, uniform canopy (though as stands age gaps become more frequent), and in which live material forms the majority of "available" fuel. The moisture content of live fuel plays a dominant role in determining fire behaviour. Weather in the UK uplands can vary rapidly from cold and wet, to sunny with drying winds and low atmospheric humidity. Frozen ground can prevent plants from replenishing water lost by transpiration. Fire behaviour can be difficult to predict and periods of significant wildfire activity can occur.Data from fifteen experimental fires were used to build empirical relationships between rate of spread, windspeed and vegetation structure. Fires in the high fuel-loads responded much more strongly to increased windspeed. The high density of the fuel-bed in younger Calluna stands may have a limiting effect on the rate of fire spread. Redundancy Analysis highlights the importance of fuel moisture content and stand structural heterogeneity.We tested the rate of spread predictions of BehavePlus and the Canadian Wildland Fire Information System (CWFIS). Predictions provided by BehavePlus were relatively good. The CWFIS was unable to predict rate of spread because the moisture content of live and dead Calluna was not accurately predicted by any of the moisture codes of the CWFIS. The system did detect a period of extreme risk associated with drought and wildfires during the spring of 2003. Multiple scales and causal factors of increased fire risk are discussed with reference to seasonal variation in the fuel moisture content of Calluna.

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“…Fire behaviour was monitored by a pair of observers on each side of the fire and walking parallel to its main direction of propagation. The observers timed (with stopwatches) the flame base arrival to reference points in order to estimate the rate of fire spread, and made visual estimates of flame height and flame tilt angle [5]. Flame height was estimated in 0.2-m and 0.5-m classes, respectively for flames shorter and taller than 2 m, and tilt angle was estimated to the nearest 5 o , assigning 0 o to vertical flames.…”

Section: Methodsmentioning

confidence: 99%

Fire behaviour and severity in a maritime pine stand under differing fuel conditions

2004

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-An experimental fire was conducted in the summer in a 28-year old maritime pine (Pinus pinaster) plantation in northeastern Portugal. Fuel conditions within the stand were age-dependent and comprised four situations: treated with prescribed fire at differing times, respectively 2, 3, and 13 years before the study, and undisturbed, where fuel accumulation time equalled stand age. The rate of fire spread did not respond to factors other than wind speed, in spite of the fuel-complex diversity. A high-intensity fire involving partially or totally the tree canopy and killing all trees was experienced in the older treatment area and in the untreated part of the stand, but the benefits of fuel management were still detectable in the former. Surface fire intensity, crown fire potential and fire severity (including tree mortality) were drastically reduced where prescribed fire had been carried recently. Fuel and fire management implications are discussed.fire behaviour / fire severity / experimental fire / fuel management / Pinus pinaster Résumé -Comportement et sévérité d'un feu dans un peuplement de pin maritime pour des conditions de végétation variées. Un feu expérimental a été réalisé pendant l'été dans une plantation de pin maritime (Pinus pinaster) âgé de 28 ans, situé au Nord-Est du Portugal. Les conditions du combustible dans le peuplement étaient dépendantes de la période d'accumulation, avec quatre situations; trois traitées avec brûlage dirigé en différents moments, respectivement 2, 3, et 13 ans avant l'étude, et une jamais traitée, où le temps d'accumulation de combustible était égal à l'âge du peuplement. Malgré la diversité des caractéristiques du combustible, la vitesse de propagation du feu n'a été influencée que par la vitesse du vent. La partie du peuplement traitée 13 ans auparavant et celle non traitée ont connu un feu d'une intensité élevée, qui a touché partiellement ou totalement le couvert arboré et tué tous les arbres, mais les effets bénéfiques du traitement furent encore décelables dans la partie brûlée antérieurement. En revanche, l'intensité du feu de surface, le potentiel à engendrer un feu de cime et la sévérité du feu (y compris la mortalité des arbres) ont été fortement réduits dans les zones où un brûlage dirigé avait été conduit récemment. Les conséquences en terme de gestion du combustible et du feu sont discutées. comportement du feu / sévérité du feu / feu experimental / gestion du combustible / Pinus pinaster

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Calculating and interpreting forest fire intensities

Cited by 351 publications

References 12 publications

Abrupt increases in Amazonian tree mortality due to drought–fire interactions

Abrupt increases in Amazonian tree mortality due to drought–fire interactions

Developing shrub fire behaviour models in an oceanic climate: Burning in the British uplands

Fire behaviour and severity in a maritime pine stand under differing fuel conditions

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