Effect of Fire Frequency on the Flammability of Two Mediterranean Pines: Link with Needle Terpene Content

Abstract

Flammability is a major factor involved in Mediterranean plant evolution that has led to the diversity of fire-related traits according to fire regimes and fire-adaptive strategies. With on-going climate change, new fire regimes are threatening plant species if they do not adapt or acclimate. Studying flammability and terpene content variation according to the different fire frequencies in the recent fire history represents a great challenge to anticipating the flammability of ecosystems in the near future. The flammability of shoots and litter as well as the needle terpene contents of two pine species with different fire adaptive strategies (Pinus halepensis and Pinus sylvestris) were measured according to two fire modalities (0 vs. 1–2 fire events over the last 60 years). Results showed that, regardless of the species and the fuel type, flammability was higher in populations having undergone at least one past fire event even when factors influencing flammability (e.g., structural traits and hydric content) were considered. The terpene content did not vary in P. sylvestris’ needles according to the fire modality, but that of sesqui- and diterpenes was higher in P. halepensis’ needles sampled in the “Fire” modality. In addition, associations made between flammability and terpene content using random forest analyses indicated that the terpene molecules differed between fire modalities for both species and fuel types. The same results were obtained with significant terpenes driving flammability as were highlighted in the PLS analyses, especially for P. halepensis for which enhanced shoot flammability in the “Fire” modality agreed with the adaptive strategy of this species to fire.

Rosin from Pinus pinaster Portuguese forests shows a regular profile of resin acids

“…This observation deserves focused examination in the future. Additional variability apart from that described in both ordinations can be explained by parameters that are not represented in the generated matrices, including genotype ( Rubini et al., 2022 ), pests ( Gaspar et al., 2020 ; Gonçalves et al., 2020 ; Kopaczyk et al., 2020 ; López-Goldar et al., 2020 ), and proximity of forest fires ( Cannac et al., 2009 ; Romero and Ganteaume, 2021 ), as suggested before. The impact of silvicultural conditions on resin composition, e.g., the resin tapping method, cannot be overlooked as well ( Rubini et al., 2022 ).…”

Natural forests for a safe climate: Enhancing ecosystem integrity, biodiversity and adaptive capacity for climate mitigation

“…Canopy depth and leaf area index are forest stand characteristics negatively correlated with ignitability, while clearcuts of former Scots pine stands showed the highest ignition probability; also the frequency of ignitions was lower for sites with higher canopy cover and leaf area index (Tanskanen, 2007). The flammability of pine stands was shown to be higher in stands that have burned previously considering flame height and residence, shoot flammability as well as time to ignition or higher combustibility (Romero and Ganteaume, 2021).…”

Shoot flammability patterns among plant species of the wildland–urban interface in the fire-prone Greater Blue Mountains World Heritage Area

“…We suggest that a candidate trait is the presence of volatile organic compounds (VOCs) such as terpenoids, particularly in species within the family Myrtaceae, a family well known for its VOCs (Whiffin and Ladiges 1992;Keszei et al 2008). Previous work has identified links between flammability and VOCs (Pausas et al 2016;Romero and Ganteaume 2021). Indeed, Della Rocca et al (2017) suggested that terpenoids should be included in physical models of the prediction and propagation of wildfire in mediterranean vegetation given their strong influence on plant flammability.…”