Long distance spotting potential of messmate stringybark

Background Messmate stringybark (Eucalyptus obliqua, L’Her) is notorious for causing mass spotting near the fire front and up to several kilometres ahead. However, its contribution to longer distance spotting (5–30 km ahead of the fire) is unclear. Messmate is widespread in the forests of southeastern Australia making the study of its spotting potential particularly important. Aim This study seeks to quantify the intermediate and long-distance spotting potential of large stringybark firebrands by examining how firebrand size influences terminal velocity and burnout time. Methods Firebrand samples of three lengths (10, 15 and 20 cm) were introduced to a vertical wind tunnel and ignited at one end or across the entire outer layer. Combustion time and burnout mass were measured. Key results No strong correlation was found between firebrand length, sap content, or ignition method and flameout time. Extended burnout times exceeding 200 s were recorded in 11% of the samples, with reflaming observed in 35% of all samples. Conclusions Messmate has the potential to cause spotting up to several kilometres but spotting beyond 10 km is unlikely. Implications Spotting models can assume spotting distances of less than 10 km for stringybark eucalypts.