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

Abstract

Background. Mitigation of wildfires at the wildland-urban interface (WUI) will be enhanced by understanding the flammability of plants growing in this zone. Aims. We aimed to: (1) compare shoot flammability among wildland native, and both urban native and urban exotic ornamental plants;(2) quantify relationships between shoot traits and flammability; and (3) establish flammability scores to distinguish low-from high-flammability species. Methods. Flammability and traits of field-collected shoots were measured and relationships quantified in 44 species from the Blue Mountains World Heritage Area, Australia. Key results. In our study area, urban exotic plants were less flammable than wildland and urban native plants. Slow-igniting shoots had high fuel moisture and bulk density; short-burning shoots had low bulk density and volume; shoots recording low maximum temperatures had high fuel moisture, low bulk density and volume; and shoots with low biomass consumed in flames had high fuel moisture and low volume. Our novel flammability scores distinguished low-flammability (e.g. Lophostemon confertus) from high-flammability native species (e.g. Callistemon citrinus). Conclusions and implications. Low-flammability plantings at the WUI should preferably use native species given potential ecological impacts of exotics. We suggest that future work should seek to identify broader suites of low-flammability native species.

A Review of Leaf-Level Flammability Traits in Eucalypt Trees

“…For example, our findings indicate that the most common methods to assess the flammability of eucalypt leaves include the use of a pilot flame, a muffle furnace, or a calorimeter (Table 1). Despite this, recent studies suggest there is a trend towards assessing the flammability of shoots, rather than individual leaves, using a grill [16,35,[73][74][75]. The proposed grill method allows the assessment of the effects of fuel arrangement (i.e., fuel continuity, density, and structure) on the flammability of the sample, which should better represent real-world scenarios but complicates comparison with leaf-level studies due to differences inherent in the experimental design, highlighting the need for standardised protocols and procedures (Figure 3, Table 1).…”

Shoot Flammability Patterns in Native and Exotic Street Tree Species at the Wildland–Urban Interface of Eastern Australia

“…We collected shoot samples from the exposed terminal branches of healthy, mature, and well-watered individuals, consistent with previous assessments of shoot flammability [29,30,44]. Shoots were sampled from nine replicate individual plants of each species [19,45]. Two representative and adjacent 50 cm shoot samples were collected from each plant.…”

“…However, tree ecosystem services can be offset by a range of disservices [16], including safety risks to residents from falling branches, and damage to infrastructure from tree roots [17,18]. The increase in vegetative fuel load from street tree plantings can also provide an ecosystem disservice, because high-flammability tree species contribute to risks of wildfire spread [19]. In contrast, despite increasing vegetative cover, plantings of low-flammability tree species could reduce wildfire risks, providing an ecosystem service in the form of opportunistic green firebreaks that help to slow or stop the spread of wildfires in urban regions [20][21][22][23][24][25][26][27].…”

“…The aims of this study were (1) to compare and rank the ten species based on their relative flammability to distinguish low-flammability from high-flammability species; (2) to quantify relationships between a range of shoot traits and shoot flammability; and (3) to determine whether shoot flammability differs between native and exotic tree species. There is a growing body of research exploring shoot flammability patterns among species in non-WUI areas (e.g., Argentina, [28]; Australia, [19,29]; New Zealand, [30][31][32]; South Africa, [33][34][35]). However, there have been no studies that specifically examine patterns of shoot flammability among species that are commonly planted as street trees in areas of the WUI, despite such information being of critical importance for understanding wildfire risks posed by street trees.…”

“…However, there have been no studies that specifically examine patterns of shoot flammability among species that are commonly planted as street trees in areas of the WUI, despite such information being of critical importance for understanding wildfire risks posed by street trees. Our identification of plant traits defining low-flammability species can be used to suggest other species worthy of further exploration as low-flammability species based on the traits that they possess [19,36].…”