Morphological drivers of flammability in canopy and litter contexts across conifer families

Wildfires have shaped ecosystems for millions of years, with plant functional traits playing a key role in fire behaviour and severity. Morphological and physiological traits, particularly at the leaf and shoot levels, influence flammability by determining fuel composition and structure within both canopy and litter layers. These traits are hypothesized not only to affect critical fire dynamics, such as the likelihood of surface fires transitioning into crown fires, with significant consequences for fire intensity and ecosystem impacts, but also influence the evolution of fire-related traits.

This study investigates how leaf- and shoot-level morphology influences flammability in canopy and litter contexts across six dominant conifer families: Araucariaceae, Cupressaceae, Pinaceae, Podocarpaceae, Taxaceae, and Taxodiaceae. Flammability properties were assessed using fire calorimetry to measure ignitability, flame spread, and variability in the rate of energy release from combustion. Results indicate that while shed plant parts (e.g., leaves and shoots) shape fire behaviour by influencing bulk density, aeration, and flame spread rate—ultimately affecting burn sustainability and total energy release—shoot-level traits in isolation, including leaf shape and the arrangement of leaves within shoots, do not consistently predict flammability in canopy material.

Our findings highlight the dynamic interplay between plant morphology, fire regimes, and evolutionary pressures. Traits such as leaf size, shape, and arrangement contribute to fuel structure, driving patterns of fire behaviour that influence long-term plant fitness and survival. This underscores the importance of reconciling fire behaviour, plant functional traits, and the evolutionary history of fire adaptations across phylogenies.

With global change drivers intensifying fire regimes, understanding the relationship between plant flammability, fire regimes, and the acquisition of fire-related traits is increasingly critical. Non-fire-adapted species may face heightened extinction risks, threatening ecosystem stability. Quantifying the intrinsic flammability of plant traits is therefore essential for informing fire management, guiding conservation strategies, and ensuring the long-term sustainability of vegetative communities in a changing climate.