Comparison of flammability of undisturbed and disturbed litters sampled on limestone-derived soils in Provence (SE France)

M. Ganteaume (1) , M. Jappiot (1) , C. Lampin-Maillet (1) , T. Curt (1) , L. Borgniet (1)

1 UR EMAX - Ecosystèmes méditerranéens et risques

Knowledge about wildland fuel is essential to fire prevention and to both biodiversity conservation and reduction of the negative impacts of fire. Little is known of flammability of dead fuels, especially for non-reconstructed samples that are hypothesized to represent the field conditions. To assess the impact of the sampling method on the flammability, samples of litter were collected undisturbed (i.e. keeping intact the structure of litter layers, compactness and bulk-density) and disturbed (sample reconstructed using mainly the upper litter layer with a depth equal to the mean litter depth recorded on the plot) in limestone-derived soils in Provence. The sampling plan also comprised three types of vegetation among the most representative ecosystems of the study area: pure Pinus halepensis stands, mixed pine-oak stands and shrublands. At last, the sampling included four types of fire regime defined by the number of fires having occurred on each site since 1960 and the time interval since the last fire. Flammability experiments were carried out in laboratory using a glowing firebrand and a 10 kmh-1 wind. The main variables recorded were: time-to-ignition, flaming duration, flame rate of spread, flame propagation, mean flame temperature, mean flame height and rate of consumption in order to assess the ignitability, sustainability, combustibility and consumability of each litter sample. Results showed that there was no significant effect of the fire regime (time interval since the last fire and number of fires) on the flammability parameters. The type of vegetation had a significant effect on all the parameters except on flaming duration, flame temperature and flame height. Litter sampled in mixed stands and in pure pine stands were more flammable than litter sampled in shrublands and mixed stand litter was more ignitable than pine litter. The type of sampling had a significant effect on all the parameters except on time-to-ignition and flaming duration; undisturbed litter being more flammable than disturbed litter, with higher combustibility and consumability. The intact litter structure seemed to be a very important factor in the flammability, especially in the combustibility and consumability of litter samples and these parameters might be underestimated using reconstructed litter samples. The type of vegetation was a significant factor especially on the ignitability of the litter samples, the sampled collected under mixed stands being more ventilated than the compacted pine needle litter.

Mots clés: FORET MEDITERRANEENNE; PREVENTION DES FEUX DE FORETS; VEGETAL COMBUSTIBLE; COMBUSTIBLE; COMBUSTIBILITE; INFLAMMABILITE; REGIME D'INCENDIE; LITIERE VEGETALE

Domaines: Sciences de l'environnement

M. Ganteaume, M. Jappiot, C. Lampin-Maillet, T. Curt, L. Borgniet. Comparison of flammability of undisturbed and disturbed litters sampled on limestone-derived soils in Provence (SE France). VI International Conference on Forest Fire Research, Nov 2010, Coimbra, Portugal. 10 p. ⟨hal-00583414⟩