Evaluating the Fire Retardance of Callicarpa americana, Ilex glabra, and Ilex vomitoria Using the Composite Plant Flammability Index (CPFI)

The flammability of three distinct native southeastern U.S. species was examined: Callicarpa americana, Ilex glabra, and Ilex vomitoria. Ignition temperature, burn duration, flame height, and estimated volatile organic compound (VOC) emissions were combined into a single numerical value, the Composite Plant Flammability Index (CPFI). Two leaves of each species were dried in a drying oven, and 120 burn trials were conducted. Three flammability metrics were examined: ignition temperature (°C), burn duration (s), and flame height (cm). VOC emissions were estimated from published literature. These metrics were converted into standardized values and combined using the CPFI formula. One-way ANOVA results showed large intraspecific differences across ignition temperature (F(3, 116) = 57.24, p < 0.001), flame duration (F(3, 117) = 152.58, p < 0.001), and flame height (F(3, 116) = 11.21, p < 0.001). Ilex vomitoria had the highest mean ignition temperatures and longest burn durations, therefore, having the lowest CPFI value and the greatest fire resistance. Callicarpa americana had the lowest ignition temperatures and the shortest burn times, resulting in the highest CPFI numerical value and the highest flammability. Ilex glabra’s results has median values across all of the metrics being analyzed. The ANOVA tests and the post-hoc tests revealed intraspecific variation among the groups. These findings suggest that Ilex vomitoria is the most fire-retardant species and show the effectiveness of tools like the CPFI for evaluating plant flammability.