Past fire shaping future fuel: influence of recent fire history on forest foliage chemistry

Background. Knowledge of how fire regimes influence flammability, and its role in shaping future fire regimes, exists mostly at species composition and ecosystem levels. The effect of fire regimes on fuel at the chemical level is poorly known. Aim. We aimed to empirically investigate the association between recent fire history and forest foliage chemistry; and to explore potential implications for forest fuel flammability. Methods. Using an orthogonal study design, we investigated the effects of fire frequency and time since fire on the chemical composition of Eucalyptus pilularis leaves from forest canopies and surface litter in south-eastern Australia. Key results. We found high fire frequency (fire-return interval 10–13 years) was associated with higher C:N, C:P, and C:K ratios in E. pilularis surface litter, and higher C:P in canopy leaves. Conclusions. Nutrients including nitrogen and phosphorous reduce flammability of plant tissues, and hence, the observed differences in leaf nutrients between high and low fire frequency sites could have important implications for future flammability of these forests. Implications. Our study has demonstrated a relationship between fire frequency and leaf nutrient stoichiometry, which may act as a mechanism through which repeated fires could increase fuel flammability. This warrants further investigation in other environments.