Every year worldwide some extraordinary wildfires occur, overwhelming suppression capabilities, causing substantial damages, and often resulting in fatalities. Given their increasing frequency, there is a debate about how to address these wildfires with significant social impacts, but there is no agreement upon terminology to describe them. The concept of extreme wildfire event (EWE) has emerged to bring some coherence on this kind of events. It is increasingly used, often as a synonym of other terms related to wildfires of high intensity and size, but its definition remains elusive. The goal of this paper is to go beyond drawing on distinct disciplinary perspectives to develop a holistic view of EWE as a social-ecological phenomenon. Based on literature review and using a transdisciplinary approach, this paper proposes a definition of EWE as a process and an outcome. Considering the lack of a consistent "scale of gravity" to leverage extreme wildfire events such as in natural hazards (e.g., tornados, hurricanes and earthquakes) we present a proposal of wildfire classification with seven categories based on measurable fire spread and behavior parameters and suppression difficulty. The categories 5 to 7 are labeled as EWE.

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© iForest -Biogeosciences and Forestry IntroductionThe general response of most countries to the problem of an increasing number of fires and burned areas has generally been to strengthen fire suppression capacity (Costa Alcubierre et al. 2011). France, Greece, Italy, Spain and Portugal spend a total of 2500 million Euros annually in the fight against forest fires, 60% of which allocated to cover costs related to suppressing fires, while only 40% is invested in activities targeted to prevention (EFIMED 2012).Despite the high investment to improve fire suppression resources, mainly through expenditure on important aerial fleets, such as in Spain, Greece or Italy, the phenomenon continues to be characterized by an aggressive trend, with a progressively reduced interval between dramatic years.Wildfires occurring during prolonged and severe heat waves (such as in 2003 for Portugal, 2006 for Spain, 2007 for Algeria, Italy, Spain and Portugal, 2010 for Russia, 2012 for all the Mediterranean countries including Algeria) demonstrate that a different approach must be considered for tackling the problem of forest fires. This means a shift from the short term policy, which is mainly based on huge investments for suppression measures, to a long term preventive policy (Birot 2009, Montiel & Herrero 2010.The key purpose of fire prevention measures is to reduce the number of fires through hazard reduction, education, and law enforcement. Improving prevention strategies seems mandatory if a further reduction in the mean yearly burnt area is to be pursued (Ruiz-Mirazo 2011). Fuel treatment and wildfire minimizationAn appropriate approach to wildfire prevention must be aimed at both lessening the possibility of a fire occurring and minimizing its spread should one occur. This can be achieved through fuel treatments for biomass reduction, which are paramount to wildfire abatement (Omi & Martinson 2002). To reduce fire damages, an infrastructure of roads and water supply should be constructed, firebreaks and fire detection systems established, an immediate and efficient intervention of ground crews ensured, but above all, fuel treatments should be timely executed (Leone et al. 2000).Fuel treatments are a key factor to decreasing wildfire risk (Omi & Joyce 2003): they target different fuel components in order to achieve both forest structures and fuel characteristics which are able to reduce the likelihood of fire spread.Fuel treatments are mainly aimed at eliminating the vertical and horizontal continuity of fuels, in order to disrupt the vertical progression of fire (passage from surface fuels to ladder fuels to canopy fuels), and its horizontal progression, especially from crown to crown (Scott & Reinhardt 2001, Graham et al. 2004.Activities aimed at reducing surface fuels (low vegetation, woody fuel, shrub layer) decrease the chances of surface fires igniting ladder fuels and canopy fuels (Pollet & Omi 2002, Fernandes & Botelho 2003.The range of possible treatments to modify forest fuels is rather wide, varying from pruning (Le...

Pinus halepensis Mill., a widespread, low elevation conifer common in Mediterranean Basin, shows a dual reproductive strategy: post-fire obligate seeder (from serotinous cones) and an early coloniser (from non-serotinous cones). Release of seeds encased in serotinous cones is induced either by fire (pyriscence, serotiny or bradychory) or by drying (xeriscence). Morphological differences in serotinous and non-serotinous cones in natural populations of P. halepensis in Southeastern Italy were analyzed. Relationships between tree size (diameter class) and serotiny were checked by counting and sampling serotinous and non-serotinous cones. The macro and microscopic characteristics that could affect cones' opening were measured in sampled cones. Protection against high temperatures offered by wood scales was also evaluated by applying different temperatures and time exposures, and following the inner thermal raise. Results showed that nonserotinous cones had bigger resin ducts and more separate scales. Also it was highlighted that ovuliferous scales of serotinous cones were bigger and thicker. These scales had more lamellated (multilayered) sclereid cells, and were significantly thinner with a shorter lumen diameter. Continuous temperature-monitoring heat tests inside cones showed that temperatures close to the cone axis were rather low, so seed germination was not influenced. Results confirm that serotinous cones are more compact, rigid and consistent than non-serotinous cones. These characteristics explain the lower insulation, seed protection and the ease opening of non-serotinous cones as well. In conclusion, opening mechanism of pinecone scales under the effect of fire or dry conditions seem related to anatomic differences and it provides seeds with an efficient protection against heat.

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