Moderator: Ben Miller (WA Department of Biodiversity, Conservation and Attractions)

Fire has shaped the ecology and evolution of Australian biodiversity over millions of years. Most Australian ecosystems experience fire, regularly or infrequently, and their responses depend on the traits of their constituent species, the nature of the fire regime, and other conditions in the environment.

Fire science’s ‘fire regime’ concept includes season, interval, severity (and/or intensity) and type of fire, plus a spatial component (extent, edge complexity, number, size and distances between unburned patches…). Variance in intervals, and heterogeneity in severity within and between events add to complexity, and all this exists in a landscape mosaic of areas with different times since last fire, severity of last fire, previous interval, etc. Interactions and feedbacks between these elements are also mediated through the effects of time since last fire on fuel attributes that influence fire behaviour: for instance, low severity, patchy fires are more likely when fire intervals are short.

The demographic and ecological attributes, and resource and habitat needs of plant and animal species interact to define their fire response strategies. Plant fire response traits include resprouting ability, longevity, and maturation time, plus seed longevity, storage mode and dispersal capability. For instance ‘fire ephemerals’ germinate following fire and have a lifespan shorter than usual fire intervals, they mature quickly and produce seeds that survive in a soil seedbank awaiting the next fire. Resprouting shrubs or trees may survive many fire events and have very low fecundity, while long-lived, slow-maturing and non-resprouting trees can only persist in environments with very long fire intervals.

Plant population responses vary with species fire response syndrome. Some are favoured by short intervals, others by longer intervals, but all have a characteristic shape with time since fire, often with some climate-driven variance. Fire recurrence at a point forms a sequence of intervals which sample an underlying fire likelihood distribution. Weather conditions and climate influence this system – seedbank accumulation rates, fuel accumulation rates (fire hazard), ignition likelihood, fire behaviour and spread, post fire recovery of populations. As such, in a patch, the relative abundance of plant species with different response curves, time since last fire and current and recent weather conditions largely determine future plant community composition if there was a fire. Likewise the mosaic of fire histories and spatial expression of patterns of local fire sequence determine the state and distribution of species, across a landscape. The arrangement of fuel states in the mosaic also influences likelihood and spread of landscape fires.

Land managers, such as Western Australia’s Department of Biodiversity Conservation and Attractions (DBCA), seek to minimise wildfire risk and impacts on people and economic, social, and biodiversity values. DBCA seeks to reduce the likelihood and spread of damaging wildfires by managing different zones in the landscape (e.g. defined by distance from settlements) to maintain target proportions of the landscape with fuel age below a threshold relevant for the fuel type. Prescribed burning, the primary tool for fire risk management, involves carefully planned introduction of fire under conditions resulting in patchy fire with mild, easily-managed behaviour.

WA fire history data shows the severity and frequency of wildfires and prescribed burning in fuels with different times since last treatment, and ecological models indicate the range of likely species response curves. This MISG aims to use these to explore the range of conditions under which commonplace fire management statements may be valid: that no single fire regime can support all species in a landscape; that the richness and diversity of species is best supported by maintaining a diverse landscape with a range of times since fire and past fire experiences; and that maintaining a mosaic supports resilience against future fire and climate change impacts.

Burrows (2008) Linking fire ecology and fire management in south-west Australian forest landscapes. Forest Ecology and Management 255:2394-2406

Cruz et al. (2022) An empirical-based model for predicting the forward spread rate of wildfires in eucalypt forests. International Journal of Wildland Fire 31:81–95

Enright et al. (2014) Resistance and resilience to changing climate and fire regime depend on plant functional traits. Journal of Ecology 102:1572-1581.

Enright et al. (2015) Interval squeeze: altered fire regimes and demographic responses interact to threaten woody species persistence as climate changes.  Frontiers in Ecology and the Environment 13:265-272. 

McCarthy et al. (2001) Theoretical fire-interval distributions.  International Journal of Wildland Fire 10:73–77