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Bushfires

Experiments on the influence of spot fire and topography interaction on fire rate of spread

Spotting is thought to increase wildfire rate of spread (ROS) and in some cases become the main mechanism for spread. The role of spotting in wildfire spread is controlled by many factors including fire intensity, number of and distance between spot fires, weather, fuel characteristics and topography. Through a set of 30 laboratory fire experiments on a 3 m x 4 m fuel bed, subject to air flow, we explored the influence of manually ignited spot fires (0, 1 or 2), the presence or absence of a model hill and their interaction on combined fire ROS (i.e. ROS incorporating main fire and merged spot fires). During experiments conducted on a flat fuel bed, spot fires (whether 1 or 2) had only a small influence on combined ROS. Slowest combined ROS was recorded when a hill was present and no spot fires were ignited, because the fires crept very slowly downslope and downwind of the hill. This was up to, depending on measurement interval, 5 times slower than ROS in the flat fuel bed experiments. However, ignition of 1 or 2 spot fires (with hill present) greatly increased combined ROS to similar levels as those recorded in the flat fuel bed experiments (depending on spread interval). The effect was strongest on the head fire, where spot fires merged directly with the main fire, but significant increases in off-centre ROS were also detected. Our findings suggest that under certain topographic conditions, spot fires can allow a fire to overcome the low spread potential of downslopes. Current models may underestimate wildfire ROS and fire arrival time in hilly terrain if the influence of spot fires on ROS is not incorporated into predictions.

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Bushfires, Climate Change, Flora and Fauna

Limits to post‐fire vegetation recovery under climate change.

Record-breaking fire seasons in many regions across the globe raise important questions about plant community responses to shifting fire regimes (i.e., changing fire frequency, severity and seasonality). Here, we examine the impacts of climate-driven shifts in fire regimes on vegetation communities, and likely responses to fire coinciding with severe drought, heatwaves and/or insect outbreaks. We present scenario-based conceptual models on how overlapping disturbance events and shifting fire regimes interact differently to limit post-fire resprouting and recruitment capacity. We demonstrate that, although many communities will remain resilient to changing fire regimes in the short-term, longer-term changes to vegetation structure, demography and species composition are likely, with a range of subsequent effects on ecosystem function. Resprouting species are likely to be most resilient to changing fire regimes. However, even these species are susceptible if exposed to repeated short-interval fire in combination with other stressors. Post-fire recruitment is highly vulnerable to increased fire frequency, particularly as climatic limitations on propagule availability intensify. Prediction of community responses to fire under climate change will be greatly improved by addressing knowledge gaps on how overlapping disturbances and climate change-induced shifts in fire regime affect post-fire resprouting, recruitment, growth rates, and species-level adaptation capacity.

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Cultural burning

Grandmother trees, Aboriginal women and fire

Cavanagh, V. (2020). Grandmother trees, Aboriginal women and fire. In S. Gardner, P. Anderson, P. James & P. Komesaroff (Eds.), Continent aflame: responses to an Australian catastrophe (pp. 44-48). Melbourne, VIC: Palaver.

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Uncategorized

Igniting a conversation: Indigenous intercultural doctoral supervision

Cavanagh, V., Hammersley, L., & Adams, M. Igniting a conversation: Indigenous intercultural doctoral supervision. Geographical Research.

The importance of higher degree research supervision is well studied and understood. There is also an increasing body of literature examining cross-cultural and intercultural supervision. Much less research, however, focuses on supervision experiences with Indigenous postgraduate students and their non-Indigenous supervisors. High-quality, culturally appropriate, and safe supervision is even more significant for Indigenous postgraduate students, who also have to deal with the ongoing inequities of colonialism in both higher education and broader society. The doctoral research at the centre of this article is undertaken by an Indigenous person who is supervised by two non-Indigenous settler academics in geography. Drawing on Indigenous and non-Indigenous scholarly research, we provide narrative examples of some of the complexities and possibilities experienced through the research process and supervisory relationship. The article does not present an argument for a best practice model in intercultural supervision, nor does it make recommendations or argue for standardised practices in geography. Instead, we seek to contribute to emerging discussions on Indigenous doctoral supervision in settler colonial contexts and, in doing so, highlight spaces of resistance as we challenge conventional supervisory relationships and knowledge making practices.

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Bushfires, Drought

The severity and extent of the 2019-20 Eucalyptus forest fires are not the legacy of forest management.

The 2019–20 wildfires in eastern Australia presented a globally important opportunity to evaluate the respective roles of climatic drivers and natural and anthropogenic disturbances in causing high-severity fires. Here, we show the overwhelming dominance of fire weather in causing complete scorch or consumption of forest canopies in natural and plantation forests in three regions across the geographic range of these fires. Sampling 32% (2.35 Mha) of the area burnt we found that >44% of the native forests suffered severe canopy damage. Past logging and wildfire disturbance in natural forests had a very low effect on severe canopy damage, reflecting the limited extent logged in the last 25 years (4.5% in eastern Victoria, 5.3% in southern New South Wales (NSW) and 7.8% in northern NSW). The most important variables determining severe canopy damage were broad spatial factors (mostly topographic) followed by fire weather. Timber plantations affected by fire were concentrated in NSW and 26% were burnt by the fires and >70% of the NSW plantations suffered severe canopy damage showing that this intensive means of wood production is extremely vulnerable to wildfire. The massive geographic scale and severity of these Australian fires is best explained by extrinsic factors: an historically anomalous drought coupled with strong, hot dry westerly winds that caused uninterrupted, and often dangerous, fire weather over the entire fire season.

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Air Quality, Bushfires, Health, Prescribed Burning

Smoke health costs change the calculus for wildfires fuel management.

Background

Smoke from uncontrolled wildfires and deliberately set prescribed burns has the potential to produce substantial population exposure to fine particulate matter (PM2·5). We aimed to estimate historical health costs attributable to smoke-related PM2·5 from all landscape fires combined, and the relative contributions from wildfires and prescribed burns, in New South Wales, Australia.

Methods

We quantified PM2·5 from all landscape fire smoke (LFS) and estimated the attributable health burden and daily health costs between July 1, 2000, and June 30, 2020, for all of New South Wales and by smaller geographical regions. We combined these results with a spatial database of landscape fires to estimate the relative total and per hectare health costs attributable to PM2·5 from wildfire smoke (WFS) and prescribed burning smoke (PBS).

Findings

We estimated health costs of AU$ 2013 million (95% CI 718–3354; calculated with the 2018 value of the AU$). $1653 million (82·1%) of costs were attributable to WFS and $361 million (17·9%) to PBS. The per hectare health cost was of $105 for all LFS days ($104 for WFS and $477 for PBS). In sensitivity analyses, the per hectare costs associated with PBS was consistently higher than for WFS under a range of different scenarios.

Interpretation

WFS and PBS produce substantial health costs. Total health costs are higher for WFS, but per hectare costs are higher for PBS. This should be considered when assessing the trade-offs between prescribed burns and wildfires.

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Bushfires, Health

Unprecedented smoke‐related health burden associated with the 2019–20 bushfires in eastern Australia.

Weather conditions conducive to extreme bushfires are becoming more frequent as a consequence of climate change. Such fires have substantial social, ecological, and economic effects, including the effects on public health associated with smoke, such as premature mortality and exacerbation of cardio‐respiratory conditions., During the final quarter of 2019 and the first of 2020, bushfires burned in many forested regions of Australia, and smoke affected large numbers of people in New South Wales, Queensland, the Australian Capital Territory and Victoria. The scale and duration of these bushfires was unprecedented in Australia. We undertook a preliminary evaluation of the health burden attributable to air pollution generated by bushfires during this period.

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Bushfires, Flammability

Patterns of flammability after a sequence of mixed-severity wildfire in dry eucalypt forests of southern Australia

Fire severity is the impact of a fire on the landscape, particularly the physical impact on vegetation. Previous studies have established that the severity of a fire can be influenced by the severity of previous fires. Many of these studies were conducted in mixed-conifer forests, while little is known of this process in temperate eucalypt forests. Barker and Price in their 2018 publication (“Positive severity feedback between consecutive fires in dry eucalypt forests of southern Australia,” Ecosphere 9:e02110) found that high severity fire promotes high severity fire in eucalypt forests, but how is the severity of a fire in these systems affected by the severity of two sequential previous fires? This was investigated using remotely sensed and mapped fire severity data. We found that high severity fire is more likely after at least one previous high severity fire, regardless of its position in the sequence. A sequence of low or moderate severity fire followed by low severity fire resulted in the lowest proportion of high severity in the response fire. Our results suggest that low severity fire maintains the structure of forest fuels, so flammability remains relatively constant. A single high severity fire drives change, altering the structure and flammability of the vegetation and promoting more severe fire. However, the effects were small, so a cycle of high severity fire may be easily broken due to the influence of other variables, such as weather. Repeated high severity fire may also result in a decline in the ability of plants to recover from fire, leading to a compositional and structural change and potentially reducing the flammability of a forest.

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Bushfires, Flora and Fauna, Prescribed Burning

Bioclimatic drivers of fire severity across the Australian geographical range of giant Eucalyptus forests

  1. The relationships between productivity, fire frequency and fire severity shape the distribution of plant communities globally. Dry forests are expected to burn frequently and wet forests to burn infrequently. However, the effect of productivity on intensity and severity of wildfire is less consistent and poorly understood. One productive ecosystem where this is especially true is the Australian tall wet Eucalyptus-dominated forest (TWEF), which spans wet areas across the continent. This study aims to characterise how climate shapes the likelihood of low- and high-severity wildfire across Australian TWEF.
  2. We performed a continental-scale analysis of fuels in 48 permanent plots in early-mature stage TWEF across four climate regions in Australia. We estimated fuel loads and measured understorey microclimate. We then obtained historical fire-weather observations from nearby meteorological stations and used fuel moisture and fire behaviour equations to predict the historical frequency with which TWEF could burn and what fire severities were expected. We investigated how this varies across the different TWEF climate regions. Lastly, we validated our approach by remeasuring eight plots that burned unexpectedly post-measurement.
  3. We found that surface fuels in cooler, moister regions were available to burn 1–16 days per year historically, with only low-severity, surface fire possible most of these days: high-severity fire was only possible under rare, extreme fire-weather conditions. However, in warmer, drier regions, fuels were available to burn 23–35 days annually, and high-severity fire was more likely than low-severity fire. Validation showed that we slightly overestimated flame heights, inflating high-severity risk estimates. If we used elevated fuel loads to predict flame heights, however, high-severity fire was more likely than low-severity fire everywhere. Lastly, the likelihood of high-severity fire increased with increasing temperature and worsening fire weather.
  4. Synthesis. Fire activity in early-mature TWEF is limited by climatic constraints on fire weather and availability to burn, with high-severity fire more likely in warmer, drier regions than in cooler, wetter ones. This indicates a particularly worrisome vulnerability to climate change, given TWEF's diminished ability to recover from disturbance in a warmer world. The occurrence of both low- and high-severity fire means the fire regimes of TWEF are best described as mixed severity.

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Bushfires, Flora and Fauna

Fire‐triggered flowering is the dominant post‐fire strategy in a tropical savanna.

Questions

In fire-prone ecosystems, fire can enhance the flowering and fruiting of many species, a strategy assumed to be well represented in savanna. Despite this, there are surprisingly few studies assessing how prevalent fire-stimulated flowering is. Thus, we asked: (a) are there differences in the reproductive phenology of Cerrado plants between recently burned and unburned areas; (b) how does fire affect the speed of flowering and how does this differ between growth forms; and (c) what are the post-fire flowering (PFF) strategies of Cerrado species and is there evidence for high proportions of obligate PFF?

Location

Open savannas (campo sujo in the Cerrado) in Central Brazil (Reserva Natural Serra do Tombador — RNST, 13°35–13°38' S and 47°45'–47°51' W).

Methods

We established six plots, three recently and frequently burned (FB) and three excluded from fire for six years (E). In all treatments, the number of species flowering and fruiting was counted every 15 days for three months, and then at six, nine and 12 months after fire. We also counted the number of reproductive and vegetative shoots in 10 subplots (1 m × 1 m) per plot.

Results

Approximately 66% of species studied were fire-stimulated, with half of these only flowering after fire (obligate PFF). Fire-enhanced flowering was rapid, with the clearest differences between burned and unburned plots seen in the first 30 days, and up to three months after fire, where there were up to two times more species flowering in the FB than E areas.

Conclusions

The extremely high proportion of PFF species, at least five times that reported for heathlands and other shrub communities, highlights the role that short-interval fire regimes have in savanna ecosystems, selecting for resprouting life forms and PFF dominance, particularly in herbaceous species. Rapid post-fire reproduction may be a strategy to disperse large quantities of seed into an environment with a small recruitment window.

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