@article {bnh-8328, title = {Post-fire impact assessment of Tasmanian sphagnum bogs}, number = {724}, year = {2022}, month = {03/2022}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

In the summer of 2015-2016 several large dry lightning storms ignited wildfires that burned across Western Tasmanian landscapes desiccated by the combination of severe spring drought and above average summer temperatures. Approximately 20 000 ha of the Tasmanian Wilderness World Heritage Area burnt including Sphagnum moss communities, or {\textquoteleft}sphagnum bogs{\textquoteright}, and other significant areas of high conservation value Gondwanan refugia. The scale of the fires prompted the Tasmanian government to fund research in techniques to rehabilitate fire-impacted Gondwanan refugia, including sphagnum bogs, in the Lake Mackenzie area of the Northern Central Plateau. A key step in sphagnum bog restoration is the development of rapid, broad-scale, cost-effective and low impact survey techniques to identify sites in need of rehabilitation. We trialled unmanned aerial systems (UAS) with visible spectrum sensor technology to map fire extent and severity.\  Three sphagnum bogs were used to develop an ENVI classification workflow based on a training data set of burn severity categories and other ecological surface cover measurements to map burn severity.\  These maps were validated using ocular assessments of ground cover and burn severity in pre-existing permanently marked quadrats. We found poor to moderate agreement between the UAS and field fire severity with considerable variation amongst the sampled bogs. Total burnt area sphagnum bog maps were then produced by combining burnt severity categories for five bogs, including the three used for fire severity mapping, The congruence between Sphagnum burn extent maps with field data collected by differential Global Positioning System was found to range from substantial to poor according to Cohen{\textquoteright}s Kappa index. Multivariate analysis of the quadrat ground cover assessments showed that high grass cover was most strongly associated with poor field validation agreement (low Kappa scores), whereas acceptable field validation agreement (high Kappa scores), were associated with high cover of Sphagnum. A major constraint of this study was the two-year time gap between the fire and remote sensing mapping and field survey. Higher accuracy fire severity mapping and area burned mapping would be possible if imagery was acquired immediately after a fire event. In light of our findings, we provide recommendations for future UAS surveys of fire impacted sphagnum bogs, the most critical of which is acquiring remote sensing and field data in the same growing season as the fire.

}, keywords = {bogs, impact assessment, post-fire, sphagnum, Tasmanian}, issn = {724}, author = {Morgan Harding and Darren Turner and Grant Williamson and Scott Nichols and David Bowman} } @article {bnh-7977, title = {Bioclimatic drivers of fire severity across the Australian geographical range of giant Eucalyptus forests}, journal = {Journal of Ecology}, year = {2021}, month = {04/2021}, abstract = {

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.

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.

We found that surface fuels in cooler, moister regions were available to burn 1{\textendash}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{\textendash}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.

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{\textquoteright}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.

}, keywords = {biogeography, Climate change, ecological disturbance, fire ecology, fire severity, macroecology, mixed-severity fires, tall wet Eucalyptus forests}, doi = {https://doi.org/10.1111/1365-2745.13663}, url = {https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.13663}, author = {Furlaud, James M. and Lynda Prior and Grant Williamson and David Bowman} } @article {bnh-6392, title = {Evolution of an extreme Pyrocumulonimbus-driven wildfire event in Tasmania, Australia}, journal = {Natural Hazards and Earth System Sciences}, year = {2019}, month = {12/2019}, abstract = {

Extreme fires have substantial adverse effects on society and natural ecosystems. Such events can be associated with intense coupling of fire behaviour with the atmosphere, resulting in extreme fire characteristics such as pyrocumulonimbuscloud (pyroCb) development. Concern that anthropogenic climate change is increasing the occurrence of pyroCbs globally is driving more focused research into these meteorological phenomena. Using 6-minute scans from a nearby weather radar, we describe the development of a pyroCb during the afternoon of 4 January 2013 above the Forcett-Dunalley fire in south-eastern Tasmania. We relate storm development to: (1) near-surface weather using the McArthur Forest Fire Danger Index (FFDI), and the C-Haines Index, a measure of the vertical atmospheric stability and dryness both derived from gridded weather reanalysis for Tasmania (BARRA-TA), and (2) a chronosequence of fire severity derived from remote sensing. We show that the pyroCb rapidly developed over a 24-minute period in the afternoon of 4 January, with the cloud top reaching a height of 15 km. The pyroCb was associated with a highly unstable atmosphere (C-Haines 10-11) and Severe-marginally Extreme (FFDI 60-75) near-surface fire weather, and formed over an area of forest that was severely burned (total crown defoliation). We use spatial patterns of elevated fire weather in Tasmania, and fire weather during major runs of large wildfires in Tasmania for the period 2007-2016 to geographically and historically contextualise this pyroCb event. Although the Forcett-Dunalley fire is the only known record of a pyroCb in Tasmania, our results show that eastern and south-eastern Tasmania are prone to the conjunction of high FFDI and C-Haines values that have been associated with pyroCb development. Our findings have implications for fire weather forecasting and wildfire management, and highlight the vulnerability of southeast Tasmania to extreme fire events.

}, keywords = {C-Haines, extreme fire, fire severity, Fire weather, McArthur Forest Fire Danger Index, pyrocumulonimbus, smoke plume injection, Tasmania, wildland fire}, doi = {https://doi.org/10.5194/nhess-2019-354}, url = {https://www.nat-hazards-earth-syst-sci-discuss.net/nhess-2019-354/}, author = {Mercy Ndalila and Grant Williamson and Paul Fox-Hughes and Jason J. Sharples and David Bowman} } @article {bnh-5259, title = {Can air quality management drive sustainable fuels management at the temperate wildland{\textendash}urban interface?}, journal = {Fire}, volume = {1}, year = {2018}, month = {08/2018}, abstract = {

Sustainablefiremanagementhaseludedallindustrialsocieties. Giventhegrowingnumber and magnitude of wildfire events, prescribed fire is being increasingly promoted as the key to reducing wildfire risk. However, smoke from prescribed fires can adversely affect public health. We propose that the application of air quality standards can lead to the development and adoption of sustainable fire management approaches that lower the risk of economically and ecologically damagingwildfireswhileimprovingairqualityandreducingclimate-forcingemissions. Forexample, green fire breaks at the wildland{\textendash}urban interface (WUI) can resist the spread of wildfires into urban areas. These could be created through mechanical thinning of trees, and then maintained by targeted prescribedfiretocreatebiodiverseandaestheticallypleasinglandscapes. Theharvestedwoodydebris could be used for pellets and other forms of bioenergy in residential space heating and electricity generation. Collectively, such an approach would reduce the negative health impacts of smoke pollutionfromwildfires,prescribedfires,andcombustionofwoodfordomesticheating. Weillustrate such possibilities by comparing current and potential fire management approaches in the temperate and environmentally similar landscapes of Vancouver Island in British Columbia, Canada and the island state of Tasmania in Australia.

}, url = {https://www.researchgate.net/profile/Sarah_Henderson4/publication/326955566_Can_Air_Quality_Management_Drive_Sustainable_Fuels_Management_at_the_Temperate_Wildland-Urban_Interface/links/5b6db08245851546c9fa2dab/Can-Air-Quality-Management-Drive-Sustainable}, author = {David Bowman and Lori Daniels and Fay Johnston and Grant Williamson and Matt Jolly and Sheryl Magzamen and Ana Rappold and Michael Brauer and Sarah Henderson} } @article {bnh-6321, title = {Geographic Patterns of Fire Severity Following an Extreme Eucalyptus Forest Fire in Southern Australia: 2013 Forcett-Dunalley Fire }, journal = {Fire}, volume = {1}, year = {2018}, month = {10/2018}, abstract = {

Fire severity is an important characteristic of fire regimes; however, global assessments of fire regimes typically focus more on fire frequency and burnt area. Our objective in this case study is to use multiple lines of evidence to understand fire severity and intensity patterns and their environmental correlates in the extreme 2013 Forcett-Dunalley fire in southeast Tasmania, Australia. We use maximum likelihood classification of aerial photography, and fire behavior equations, to report on fire severity and intensity patterns, and compare the performance of multiple thresholds of the normalised burn ratio (dNBR) and normalized difference vegetation index (dNDVI) (from pre- and post-fire Landsat 7 images) against classified aerial photography. We investigate how vegetation, topography, and fire weather, and therefore intensity, influenced fire severity patterns. According to the aerial photographic classification, the fire burnt 25,950 ha of which 5\% burnt at low severities, 17\% at medium severity, 32\% at high severity, 23\% at very high severities, while 22\% contained unburnt patches. Generalized linear modelling revealed that fire severity was strongly influenced by slope angle, aspect, and interactions between vegetation type and fire weather (FFDI) ranging from moderate (12) to catastrophic (\>100). Extreme fire weather, which occurred in 2\% of the total fire duration of the fire (16 days), caused the fire to burn nearly half (46\%) of the total area of the fireground and resulted in modelled extreme fireline intensities among all vegetation types, including an inferred peak of 68,000 kW{\textperiodcentered}m-1 in dry forest. The best satellite-based severity map was the site-specific dNBR (45\% congruence with aerial photography) showing dNBR potential in Eucalyptus forests, but the reliability of this approach must be assessed using aerial photography, and/or ground assessment.

}, keywords = {aerial photography, Eucalyptus forest, fire intensity, fire severity mapping, generalized linear modelling, geospatial validation, normalized burn ratio, Tasmania}, doi = {https://doi.org/10.3390/fire1030040}, url = {https://www.mdpi.com/2571-6255/1/3/40}, author = {Mercy Ndalila and Grant Williamson and David Bowman} } @article {bnh-4361, title = {Simulating the effectiveness of prescribed burning at altering wildfire behaviour in Tasmania, Australia}, journal = {International Journal of Wildland Fire}, year = {2017}, month = {12/2017}, abstract = {

Prescribed burning is a widely accepted wildfire hazard reduction technique; however, knowledge of its effectiveness remains limited. To address this, we employ simulations of a widely used fire behaviour model across the ecologically diverse Australian island state of Tasmania. We simulate three broad scenarios: (1) no fuel treatment, (2) a maximal treatment, with the most possible prescribed burning within ecological constraints, and (3) 12 hypothetically more implementable state-wide prescribed-burning plans. In all simulations, we standardised fire-weather inputs to represent regionally typical dangerous fire-weather conditions. Statistical modelling showed that an unrealistically large maximal treatment scenario could reduce fire intensity in three flammable vegetation types, and reduce fire probability in almost every vegetation type. However, leverage analysis of the 12 more-realistic implementable plans indicated that such prescribed burning would have only a minimal effect, if any, on fire extent and that none of these prescribed-burning plans substantially reduced fire intensity. The study highlights that prescribed burning can theoretically mitigate wildfire, but that an unrealistically large area would need to be treated to affect fire behaviour across the island. Rather, optimisation of prescribed burning requires careful landscape design at the local scale. Such designs should be based on improved fire behaviour modelling, empirical measurement of fuels and analysis of actual wildfires.

}, doi = {https://doi.org/10.1071/WF17061}, url = {http://www.publish.csiro.au/wf/WF17061}, author = {Furlaud, James M. and Grant Williamson and David Bowman} }