Pathways of change: Predicting the effects of fire on flammability

Impacts of wildfire on humans are increasing as urban populations continue to expand into fire prone landscapes. Effective fire risk management can only be achieved if we understand and quantify how ecosystems change in response to fire and how these changes affect flammability. However, there have been limited studies to this effect with the dominant paradigm being the assumption that recently burnt vegetation is less flammable than older vegetation. To better quantify changes in flammability, we first need to quantify trajectories of changes in response to fire within individual vegetation communities. Second, we need to examine the extent to which these changes alter flammability. Here, we quantify the flammability pathways with increasing time since fire for five vegetation communities in south-eastern Australia. A total of 116 sites were measured across a range of heathland, woodland and forest ecosystems. Flammability was measured using an ecological point based mechanistic fire behaviour model that estimates three measures of flammability relevant to both fire management and research. Predicted changes in flammability varied between vegetation types with heathland and wet forests generally increasing in flammability with time since fire and tall mixed, foothills and forby forests decreasing or showing limited changes with time since fire. Variations in flammability pathways suggest fire management activities that alter fuel structure, such as prescribed burning, may only reduce flammability in a limited set of ecosystems. Incorporating these results into a landscape analysis will improve the quantification of fire risk.