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Fire regimes are changing across the globe in response to complex interactions between climate, fuel, and fire across space and time. Despite these complex interactions, research into predicting fire regime change is often unidimensional, typically focusing on direct relationships between fire activity and climate, increasing the chances of erroneous fire predictions that have ignored feedbacks with, for example, fuel loads and availability. Here, we quantify the direct and indirect role of climate on fire regime change in eucalypt dominated landscapes using a novel simulation approach that uses a landscape fire modelling framework to simulate fire regimes over decades to centuries. We estimated the relative roles of climate-mediated changes as both direct effects on fire weather and indirect effects on fuel load and structure in a full factorial simulation experiment (present and future weather, present and future fuel) that included six climate ensemble members. We applied this simulation framework to predict changes in fire regimes across six temperate forested landscapes in south-eastern Australia that encompass a broad continuum from climate-limited to fuel-limited. Climate-mediated change in weather and fuel was predicted to intensify fire regimes in all six landscapes by increasing wildfire extent and intensity and decreasing fire interval, potentially led by an earlier start to the fire season. Future weather was the dominant factor influencing changes in all the tested fire regime attributes: area burnt, area burnt at high intensity, fire interval, high-intensity fire interval, and season midpoint. However, effects of future fuel acted synergistically or antagonistically with future weather depending on the landscape and the fire regime attribute. Our results suggest that fire regimes are likely to shift across temperate ecosystems in south-eastern Australia in coming decades, particularly in climate-limited systems where there is the potential for a greater availability of fuels to burn through increased aridity.

Fire regimes are changing around the world raising important questions about the risks to biodiversity. Fire seasons are lengthening, high-severity fires are occurring more often and in unexpected places. Extensive research examines some of the fire related risks to life and property. However, in the fire risk research space there is often limited or simplified inclusion of ecological values. Future fire regimes, alongside climatic change, could have profound impacts on biodiversity conservation and ecosystem function. For example, plant population trajectories can be influenced by demographic traits, disturbance regimes and environmental variables such as climate. Climate change can affect all three and is likely to impact on plant populations through altering natural fire regimes as well as influencing species demographic traits. These changes are unlikely to be unidirectional with some plant types benefiting and others being disadvantaged. Here, we examine the impacts of climate change both on the shifts in fire regimes alone and combined with predicted climate-induced demographic shifts. We use two functional plant types (obligate seeder, facultative resprouter) in a number of case-study areas representing woodland-dominated landscapes of south-eastern Australia. We link a fire regime simulation tool with a spatially explicit population viability analysis model. We simulate fire regimes under six different future climates representing different temperature and precipitation shifts, and 16 demographic change scenarios, characterised by changes to individual or multiple plant demographic processes. Obligate seeder species were predicted to be less resilient to changes in demographic parameters. However, both resprouter and seeder species were found to be negatively affected by the combined impacts of changes to multiple demographic parameters or to a combination of a shifting fire regime and changes to demographic traits, particularly through simulated reductions in adult survival. To our knowledge this is the first study to integrate fire regime simulations with spatially explicit population viability analyses. Such an approach significantly increases our ability to identify which functional types are most at risk of population extinction under predicted fire regime and demographic changes. This flexible framework is an important first step in exploring the complex interactions that determine plant viability under a changing climate and will increase our ability to prioritise research and fire management for biodiversity into the future.