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

Bastien Romero,Anne Ganteaume

doi:10.3390/plants10102164

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.

Highlights

The flammability of a plant species can be considered a niche construction trait [1,2,3]
The principal component analyses (PCA) performed on the flammability variables measured for P. halepensis and P. sylvestris’ shoots showed that the three first components explained more than 75% of the total variance (77.43% and 79.99%, respectively, Figures 1a and 2a)
For P. halepensis, the flame height was split between the two first components while for P. sylvestris, it was best characterized by the first component

Summary

Introduction

The flammability of a plant species can be considered a niche construction trait [1,2,3]. Many plant traits are known to have a high impact on plant flammability such as the fuel moisture content (FMC), the leaves/needles structural characteristics (e.g., thickness, surface-to-volume ratio, etc.), and the fuel structure (e.g., the shoot or fuel bed bulk density) among others [23,25,26,27]. These traits differ among species that present different fire-adaptive strategies, but they can differ within the same species according to fire frequency [28,29]. These results are consistent with the hypothesis stated in [30] that suggests the possible heritability of flammability

Objectives

Methods

Results

Discussion

Conclusion