Does plant flammability differ between leaf and litter bed scale? Role of fuel characteristics and consequences for flammability assessment

Abstract

The increasing concern regarding fire in the wildland–urban interface (WUI) around the world highlights the need to better understand the flammability of WUI fuels. Research on plant flammability is rapidly increasing but commonly only considers a single fuel scale. In some cases, however, different fuel scales (e.g. leaf and litter bed) have greater influence on fire, for instance, when it spreads from the litter bed to the lower canopy. Examining fuel flammability at these different scales is necessary to better know the overall flammability but also provides insights into the drivers of flammability. To investigate if leaf and litter bed flammability differed, laboratory experiments were conducted on 15 species (native or exotic) commonly found in the WUI of south-eastern France. Species were ranked and the association of fuel characteristics with flammability sought at both scales. For most species, leaf and litter bed flammability differed because of strong fuel characteristics (e.g. leaf thickness or litter bulk density), entailing differences in rankings based on fuel scale and potentially leading to a misrepresentation of flammability of the species studied. Favouring species with lower flammability at both scales in the WUI, especially near housing, may help reduce undesired effects during wildfires.