Laboratory Assessment of Post-Treatment Vegetation Flammability According to Treatment Methods Used in Southeastern France

Fuel reduction, through various methods, is commonly used in fire prevention, but its effect on mitigating the flammability of the treated vegetation is rarely studied. This work aimed, therefore, to assess, at the laboratory scale, how flammability changed from untreated to treated vegetation, which would give an initial estimate of the efficiency of these treatments implemented in southeastern France, as in other countries. The methods studied were mechanical shredding and prescribed burning for woody plants as well as mechanical (with or without residues left) and manual mowing (with residues) for roadside grasses. We investigated their effects, comparing the treated vegetation’s flammability to that of a control during laboratory burnings, and testing both ignition capacity and flame front propagation. Mechanical shredding, and especially prescribed burning, led to a decrease in the treated vegetation flammability mainly due to the reduction in fuel load. Surprisingly, mechanical mowing resulted in an overall increase in flammability in contrast to manual mowing. The structure of the treated grass, which was more conducive to fire after mechanical mowing, mainly explained this difference. This study provided new insights on the effectiveness of fuel treatment methods, highlighting a more significant effect on flammability mitigation with prescribed burning at the laboratory scale. Moreover, the inability of mechanical mowing to decrease treated grass flammability should be accounted for. These laboratory results, mostly in line with those of similar previous studies, have to be combined with data obtained at a larger scale in the field to confirm or refute the tendencies highlighted in the current work.