Plant traits and their effect on fire and decomposition

Wildfires are a major disturbance worldwide with large effects on ecosystem functioning, species composition and nutrient cycling. A fundamental factor in wildfires is the fuel, namely, live and dead plant material. Plant species differ in their flammability, but the role of plant traits in this remains largely unknown. The decomposition rates of different plant materials (and species) can strongly affect the availability of fuel for potential wildfires.While the influence of leaf traits on litter decomposability is reasonably well studied, it has never been compared to the drivers of litter flammability. In this thesis I focused on these two important turnover processes of plant material, i.e., fire and decomposition. By comparing a wide range of species from south-eastern Australia, I investigated theexistence of general relationships between plant traits, flammability and litter decomposability. In experiments on individual leaves (Chapter 2) I found that morphological leaf traits (such as specific leaf area or dry mass) were most strongly correlated with interspecific variation in flammability, while decomposability was mainly driven by chemical traits. Similar results were found for bark, another important litter component of the Australian forests (Chapter 4). Bark ignitibility of smooth bark species was driven by bark mass per area, while decomposition was strongly associated with initial lignin concentration. Consequently, fire and decomposition, as two alternative fates for leaves or bark, were unrelated. Next, I demonstrated that leaf traits which affect the flammability of individual leaves (e.g. specific leaf area) continue to affect flammability when scaling up to fuel beds (Chapter 3). Can we use these findings on interspecific variation in leaf trait – flammability relationships to improve predictions of fire behaviour? In Chapter 5 I showed that the inclusion of leaf traits (especially leaf thickness) improved the prediction of individual leaf ignitibility. Altogether, this suite of studies increased our understanding of trait-effects on leaf and bark flammability and decomposability. Including plant traits in future analyses could improve the estimation of fuel loads and the prediction of wildfires.