Fire form and function: evidence for exaptive flammability in the New Zealand flora

This study tests whether or not foliar flammability is related to resource-use and anti-herbivore defence strategies of plant species. We measured the flammability (at 400 °C) of 1640 dry and fresh leaves across 115 common native New Zealand woody and herbaceous species collected from sites throughout New Zealand. We used three indicators of foliar flammability—leaf temperature at smoke production and on ignition and the rate of increase in leaf temperature during the combustion process. We tested for relationships between these flammability measures, foliar morphological and chemical traits and growth form. All significant correlations showed increased foliar flammability with increasing foliar surface area:volume ratio (SAV) and nutrient content and decreasing tissue density, lignin and secondary metabolite concentrations. Coniferous trees were the growth form with the least flammable leaves due to leaf morphology associated low leaf SAV and high tissue density. This suggests there may be a general relationship between resource-use strategies and foliar flammability, via the influence of leaf morphology on both these aspects of plant function.