Pine Species That Support Crown Fire Regimes Have Lower Leaf-Level Terpene Contents Than Those Native to Surface Fire Regimes

Rebecca A Dewhirst,Claire M Belcher,Nicholas Smirnoff

doi:10.3390/fire3020017

Abstract

Fire is increasingly being recognised as an important evolutionary driver in fire-prone environments. Biochemical traits such as terpene (volatile isoprenoid) concentration are assumed to influence plant flammability but have often been overlooked as fire adaptations. We have measured the leaf-level flammability and terpene content of a selection of Pinus species native to environments with differing fire regimes (crown fire, surface fire and no fire). We demonstrate that this biochemical trait is associated with leaf-level flammability which likely links to fire-proneness and we suggest that this contributes to post-fire seedling survival. We find that surface-fire species have the highest terpene abundance and are intrinsically the most flammable, compared to crown-fire species. We suggest that the biochemical traits of surface fire species may have been under selective pressure to modify the fire environment at the leaf and litter scale to moderate fire spread and intensity. We indicate that litter flammability is driven not only by packing ratios and bulk density, but also by terpene content.

Highlights

Plants have two distinctive relationships with fire; firstly, they provide the fuel that drives the dynamics of the fire itself, secondly, they can respond to the fire behaviour that they create in order to survive
Principal components analysis (PCA) analysis was carried out in MetaboAnalyst using the same data and groupings as Kruskal–Wallis analysis, with the aim of determining the factors that best described the differences between fire regimes
The needle litter of crown-fire species were this correlated with higher leaf-level flammability and corresponded with lab-formed litter-level found to have a lower peak heat release rate

Summary

Introduction

Plants have two distinctive relationships with fire; firstly, they provide the fuel that drives the dynamics of the fire itself, secondly, they can respond to the fire behaviour that they create in order to survive. Linkages between fire proneness and fire behaviour, and the development of fire related/adapted traits, have long been a source of major debate amongst ecologists (e.g., [1,2]). This is because of the requirement for such traits to confer a fitness advantage to the host species. Plant traits considered to enhance flammability include small leaves, presence of volatile organic compounds and retention of dead leaves and branches [1]. The presence of volatile compounds has often been considered as a flammability trait [3,4], this proposal has limited experimental evidence [5,6,7,8,9]

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