Background: Wildfires are a growing threat, especially in Mediterranean climate areas during periods of drought. The wildfire research community continues to investigate propagation mechanisms considering thermal transfer and fluid mechanics and sometimes a simplified chemistry taking into account the main combustion products such as CO, CO2, H2O, H2 and CH4. However, volatile organic compounds (VOCs) cannot be neglected and have a major role in vegetation ignition. Despite this, knowledge on the influence of wildfire on plant emissions remains lacking. Aims: This work addresses the effect of combined hydric and thermal stresses on the physiology and emissions of Rosmarinus officinalis and Cistus albidus, which are widely consumed in Mediterranean wildfires. Methods: Plants were submitted to hydric stress inside a greenhouse, then to thermal stress inside a heated hermetic enclosure while collecting emissions with adsorbent elements for analysis. Simultaneously, heating experiments were carried out with leaves sampled to analyse their emissions. Key results: The heating tests showed significant variations in monoterpene, fatty acid and alkane emissions between stressed and unstressed plants with different results between Rosmarinus officinalis and Cistus albidus. Conclusion/implication: Further experiments with other plant species and quantification of emissions may help to better know why Mediterranean wildfires are a particular threat and how to improve firefighting methods.

Flashover phenomena in wildfires have been reported by firefighters and have caused a number of fatalities among their ranks