Large wildfires are common in spinifex grasslands of arid Australia. Threat mitigation measures including fire preparedness, prescribed burning and wildfire suppression are greatly enhanced by the ability to predict fire behaviour. The new spinifex fire behaviour model presented here was developed and validated from 186 experimental fires across a wide range of fuel and weather conditions. Because spinifex fuels are discontinuous, modelling is a two-step process; once ignition is achieved, the first step is to determine the likelihood of fire spread, which is dependent on conditions of wind speed, fuel cover and fuel moisture content. If spread thresholds are met, the second step is to predict rate of spread and flame height using the same three independent variables. Thirty-six of the 186 experimental fires not used in modelling were used to validate the model, which proved to be reasonably accurate and an improvement on the previous model.

Development and validation of a model for predicting fire behaviour in spinifex grasslands of arid Australia

Fire intensity is recognised as an important driver of regeneration dynamics in forest and shrubland vegetation types, but its effects on recruitment processes in arid grasslands are poorly understood Here, we used fire severity as a surrogate measure of fire intensity, and compared post-fire seedling recruitment from arid Triodia pungens (soft spinifex) plots burnt by low-severity experimental fires against those burnt by a high-severity wildfire To explain T pungens recruitment patterns, we also: (1) conducted a longitudinal depth distribution study of soil seedbank densities, and (2) carried out a lethal-temperature experiment on T pungens seeds High-severity burning was associated with reduced T pungens recruitment compared with low-severity fire, and this relationship was attributed to the low lethal temperature thresholds of seeds and the adverse impacts of elevated soil temperatures during high-severity fire on the shallow soil seedbank Among other species in the community, there were varied recruitment responses to fire severity Overall, our results indicate that a strong link exists between fire severity and recruitment in arid spinifex grassland, though the association is variable among species, and dependent on the seedbank attributes, germination biologies and lethal-temperature thresholds of seeds of individual species

Relationships between fire severity and recruitment in arid grassland dominated by the obligate-seeding soft spinifex (Triodia pungens)

Although fire is a widespread phenomenon and major ecosystem disturbance at the global scale, fire is a relatively rare event in much of the arid lands as rainfall and productivity are generally too low to support the dense vegetation and continuous fuel needed to sustain fires (Pausas and Bradstock 2007; Pausas and Ribeiro 2013). There are exceptions to this, such as landscapes dominated by xerophytic perennial grasses, where infrequent periods with above-average rainfall can result in exceptional grass and herb growth or where invasive species, particularly alien grasses, enhance fuel loads (Greenville et al. 2009; Keeley et al. 2012; Balch et al. 2013). Changes in land management (e.g. reduction in grazing, land abandonment), climate change and increased atmospheric CO2 concentrations have also been linked to increased fire activity in arid zones across the globe (Bond and Midgley 2012; Pausas and Fernandez-Munoz 2012; Bachelet et al. 2016).

On the Ecology of Australia’s Arid Zone: ‘Fire Regimes and Ecology of Arid Australia’

Incentivising fire management in Pindan (Acacia shrubland): A proposed fuel type for Australia's Savanna burning greenhouse gas emissions abatement methodology

https://link.springer.com/content/pdf/10.1007/s10980-021-01373-w.pdf

Indigenous burning shapes the structure of visible and invisible fire mosaics

Unplanned, unmanaged wildfires are a significant threat to people, infrastructure and ecosystems around the world. Managed, planned burning is widely used for reducing the incidence, extent or intensity of wildfires. Fire weather and the season of burning are recognised as crucial factors influencing fire behaviour but the demonstrated influence of ignition technique on fire behaviour is not as prominently discussed in relation to planned fires. We found wildfires, irrespective of season, burnt the ground layer more completely (i.e. were less patchy) and produced greater crown scorch severity than did planned fires in a spinifex (Triodia spp.)-dominated open woodland. Fires ignited with a 50-m line burning with the wind produced significantly higher intensities than did line ignition against the wind, and spot ignitions with or against the wind. These data suggest that the higher severity of wildfires in spinifex-dominated habitats is strongly influenced by long fire fronts, in addition to fire season and weather conditions. This study supports the value of planned burning for reducing fire severity and highlights the value of spot ignitions in ecological burning to create a patchily burnt landscape, with limited canopy severity.

The influence of ignition technique on fire behaviour in spinifex open woodland in semiarid northern Australia

Introduced grasses, such as buffel, alter the dynamics of grassy ecosystems by replacing native species and influencing recruitment. Several different smoke-derived chemicals are separately responsible for the promotion and inhibition of germination of various plant species. We tested whether smoke derived from the introduced buffel grass (Cenchrus ciliaris) produced the same density of germination as provided by smoke derived from a native spinifex grass (Triodia brizoides). Smoke from both spinifex and buffel grass significantly enhanced the germination of a native lemon grass (Cymbopogon obtectus) in comparison to untreated seed, reflecting the significant role of fire in woodlands across northern Australia. This is the first record of smoke-promoted germination in a species of Cymbopogon. However, smoke from the exotic buffel grass provided the same level of germination as that from the native spinifex, suggesting similarity in smoke chemicals involved. Further research is required to test the effect of buffel smoke on the germination of other species and whether exotics such as buffel grass provide the same temperature profile in the topsoil as does spinifex, and therefore equivalent germination cues to heat-shock responsive native plants.

Lauren Colless

Papers

The influence of ignition technique on fire behaviour in spinifex open woodland in semiarid northern Australia

Introduced and native grass-derived smoke effects on Cymbopogon obtectus germination