Assessing the flammability of surface fuels beneath ornamental vegetation in wildland–urban interfaces in Provence (south-eastern France)

Abstract

The objectives of this paper are to assess in laboratory conditions the flammability of undisturbed litter sampled beneath plants of seven species that are among those most frequently planted in hedges in Provence (south-eastern France). The variability in litter flammability recorded during burning experiments was partly explained by the proportions of the different litter components of each species. Phyllostachys sp. and Nerium oleander litters were the quickest to ignite whereas Prunus laurocerasus litter had the lowest bulk density and long time-to-ignition, but high flame-propagation. Photinia fraseri litter ignited frequently and had a high flame spread whereas Pittosporum tobira litter ignited the least frequently and for the shortest duration. Cupressus sempervirens litter had the highest bulk density and the longest flaming duration but the lowest flame propagation. Pyracantha coccinea litter was the slowest to ignite and flame propagation was low but lasted a long time. Co-inertia analysis identified species with the same flammability characteristics according to the composition of their litter. Hierarchical cluster analysis ranked the seven species in four distinct clusters from the most flammable (Photinia fraseri and Prunus laurocerasus) to the least flammable (Pittosporum tobira), the other species displaying two groups of intermediate flammability. These latter species should not be used in hedges planted in wildland–urban interfaces in south-eastern France.

Possible land management uses of common cypress to reduce wildfire initiation risk: a laboratory study

“…In nature, C. sempervirens litter has a high bulk density (Ganteaume et al, 2013b), as the small segments accumulate in thick layers, also due to a low mineralisation rate (Della Rocca et al, 2006). These traits reduce the circulation of air in the litter, which may act like a sponge and retain humidity, thus hampering ignition.…”

“…The flammability of plants is usually assessed by means of laboratory assays in which several methods and devices are used (Etlinger and Beall, 2004;Weise et al, 2005;Madrigal et al, 2012;Ganteaume et al, 2013aGanteaume et al, , 2013b. The epiradiator, or radiant heater, has been used to evaluate flammability parameters in many studies (Valette, 1990;Hernando, 2000;Dimitrakopoulos and Papioannou, 2001;Alessio et al, 2008;Ganteaume et al, 2013a).…”

Testing Vegetation Flammability: The Problem of Extremely Low Ignition Frequency and Overall Flammability Score

“…If ignition source has low heat flux (e.g., cigarette butt, sparks, firebrands, not completely extinguished grilling amber, etc. ), flammability together with other material properties can have a relevant role in determining whether or not ignition occurs and how fast initial combustion process proceeds, as shown in research made by Ganteaume et al on reconstructed [22] and undisturbed [39] leaf litters tested with standardised firebrand. (Table 1), with the highest level of significance obtained for ignition related parameters: ID and IT.…”

“…In a different study which tested flammability of undisturbed leaf litters Ganteaumne et al [39] also performed hierarchical cluster analysis based on four parameters (ignition frequency: IF, time to ignite: TTI, flaming duration: FD, and number of sides reached by the flame/flame spread: S). Even though we acknowledge the remarkable quality of the gathered data we disagree with its interpretation.…”

“…If ignition frequency is lower than 50%, material can be assigned only 0 and 1 flammability score regardless of ignition delay. Even when alternative interpretation of data is given [26,32] or alternative testing method is used [39], its final intention is to give a single flammability score.…”