Quantifying the effect of mastication on flaming and smouldering durations in eucalypt forests and woodlands under laboratory conditions

Abstract

Mechanical mastication is growing in popularity as a wildfire mitigation technique. Yet few studies quantify its effects on fire behaviour. Such information is needed by fire managers to evaluate its efficacy. Our aim was to develop an understanding of how mastication alters flaming and smouldering durations and the longevity of any effects. Flaming and smouldering duration are important determinants of soil heating and smoke emissions. We used a paired sampling design, collecting litter bed (hereafter surface fuel) samples from 15 sites with masticated and untreated vegetation in shrub-encroached Eucalyptus woodlands. We measured a range of fuel bed properties and then burnt the samples in the laboratory. Average smouldering durations increased 88% from 25 to 47min in untreated v. masticated fuel; flaming durations increased 100% from 6 to 12min. These changes were attributable to higher fine and coarse fuel loads in the masticated fuel bed. However, fine and coarse fuel load declined significantly over 4 years, meaning the effects of mastication on combustion duration are likely to be short-lived. Despite being a laboratory study, the results assist with evaluating mastication as a fuel treatment by demonstrating the potential magnitude of changes to flaming and smouldering duration.

FLAMITS: A global database of plant flammability traits

“…Cui et al., 2020), because different flammability components have distinct implications for fire behaviour and ecological responses. Therefore, selecting the most relevant ones for a specific purpose has become a challenge, making the standardization of terminology and methodologies increasingly relevant (Cawson et al., 2023; Varner et al., 2015).…”

Long-Term Response of Fuel to Mechanical Mastication in South-Eastern Australia

“…However, the relocation of standing fuel to the ground results in larger amounts of fine (<6 mm diameter) and coarse (≥6 and ≤25 mm diameter) dead fuel particles on the forest floor. These can form a deep-surface fuel bed [10,13,14], with implications for increasing flaming and smouldering durations [15,16]. We need to understand how mastication changes fuel properties over short and longer timeframes to evaluate its effectiveness as a fuel treatment.…”

“…Furthermore, the results are typically contradictory among these few studies. For example, while most studies report declining surface fine fuel loads over time, the time to reach pre-treatment fuel levels varies between studies (e.g., within 4 years [15] to 8-16 years [17][18][19]). Similarly, surface coarse loads decrease quickly in some studies and slowly in others, e.g., 4 vs. 16 years [15,17], or can persist and remain unchanged, e.g., for up to ten years [8,19].…”

“…For example, while most studies report declining surface fine fuel loads over time, the time to reach pre-treatment fuel levels varies between studies (e.g., within 4 years [15] to 8-16 years [17][18][19]). Similarly, surface coarse loads decrease quickly in some studies and slowly in others, e.g., 4 vs. 16 years [15,17], or can persist and remain unchanged, e.g., for up to ten years [8,19]. There has been little explanation as to why the results are different between studies beyond the suggestion that the species being targeted for mastication could be a factor [8,14].…”

“…This information will enable us to fully evaluate the effectiveness of mastication against other fuel management strategies [37,38] and its potential to alter wildfire behaviour and risk [14]. Yet, there is relatively little known about the long-term efficacy of mastication in south-east Australian ecosystems as existing studies focus on shorter time periods post-mastication (e.g., 4 years) [12,15]. The aim of our study was to quantify the longer-term (9 years) effect of mastication on fuel across an aridity gradient.…”