The relationship between terpenes and flammability of leaf litter

Many studies have assumed that plant terpenes favor fire due to their enormous flammability. However, only a few of them, all performed on green leaves, have demonstrated this. In the present work we investigated the question of whether litter terpene content can be used to estimate flammability and temperatures reached during fire. Epiradiator and burn table tests were used to compare flammability of leaf litter of P. pinaster, P. halepensis, P. pinea, C. albidus, C. ladanifer, C. laurifolius and the mixture of litter of P. pinaster with that of the other five species (e.g. P. pinaster + P. halepensis). Tests with burn table showed increasing spread rates and shorter combustion times under higher terpene contents. Flame height was triggered both with higher a terpene content and bed thickness, whereas the percentage of burned biomass was only significantly correlated to bed height. Epiradiator tests indicated that terpene concentration in leaf litter was positively correlated to flame height and negatively correlated to both flame residence time and ignition delay. Flammability was high for P. pinaster, P. halepensis, and hence for P. pinaster + P. halepensis, intermediate for C. albidus, P. pinea and P. pinaster combined with each of these species, and low for C. laurifolius, C. ladanifer and P. pinaster combined with them. Accordingly, their terpene content was high, intermediate and low. We concluded that plants might influence fire intensity, by having stored terpenes in their dead leaves, in addition to having developed traits to survive fire. Thus, a correct management of dead aboveground fuels rich in terpene concentrations, such as those of P. pinaster and P. halepensis, could prove helpful in reducing the hazard of fire.