Hidden fuels: exploring the association between cuticular waxes and leaf flammability in a mediterranean-type forest.

Understanding the chemical drivers of plant flammability is essential for predicting fire behavior in fire-prone ecosystems. While previous research has largely focused on the role of terpenes, the contribution of cuticular waxes to foliar flammability remains poorly understood. In this study, we explored foliar flammability in six native species of the Chilean sclerophyllous forest, five of which were successfully characterized for cuticular wax chemistry. Foliar flammability was characterized by measuring ignition probability, ignition time, flame duration, and combustion time of foliar samples, and it was related to the chemical profile of cuticular waxes, including compound composition and concentrations. Results showed that higher total wax loads were associated with increased flammability, particularly through shorter ignition times and prolonged combustion. Non-alkane compounds, especially ketones and terpenoids, emerged as the main components associated with flammability. In particular, 16-hentriacontanone was consistently associated with highly flammable species, suggesting a potential association with ignition-related flammability. Among alkanes, nonacosane was correlated with flame duration. Our results highlight the importance of exploring the relationships among chemical compound classes potentially associated with flammability. This study provides the first evidence that non-alkane constituents of cuticular waxes appear to be more strongly associated with flammability than alkanes. By expanding the focus beyond terpenes, our findings offer a novel perspective on the chemical basis of plant foliar flammability and contribute to improving fire-risk assessment in Mediterranean-type ecosystems under increasing drought and fire activity.