Quercus Suber Cork As a Keystone Trait for Fire Response: A Flammability Analysis Using Bench and Field Scales

Quercus suber (cork oak tree) is an excellent epicormic resprouter that can keep cambium alive after high intensity fires because of its plan traits, mainly its thick cork. Although tree bark harvesting is an important source of income, it may reduce protection against wildfires. This study aims to identify stem and cork characteristics that affect the probability of reaching lethal cambial temperature and hence the probability of survival of living tissues. Cork flammability was analyzed using a sample set comprised of 120 cork specimens and 120 cork pieces. Five experimental fires were used to test the results obtained at bench scale. Bench-scale flammability experiments could not simulate the real heat spread and presence of highly volatile isoprenoids. The results revealed differences in cambial temperature and lethal temperature rate (LTR) at both scales according to corkback roughness and cork quality. Peak cambial temperature and LTR show an increase in stems characterized by maximum roughness and worse cork quality. The LTR measurements showed a 30% difference between bench and field scales (0.35 mm s(-1) and 0.5 mm s(-1), respectively). The findings indicate that corkback roughness, cork thickness, cork porosity and cork quality could influence the vulnerability of cork oak forests to wildfires. A negative correlation was found between total thickness and cambial temperature. A total thickness of over 3.7 cm prevented reaching lethal cambial temperature. Forest managers can use this information to define silviculture and design forest treatments with a view to reducing fire severity and mitigating the ecological and socioeconomic impacts of fire in cork oak forests.