Frequent mild fire regimes have been associated with healthy and bushfire-safe forests, particularly under traditional Aboriginal management in Australia and the New World. In this study, we tested the hypothesis that karri (Eucalyptus diversicolor) forest tree canopy health (TCH) declines with time since fire (TSF) due to changes in soil chemistry that adversely impacts tree roots. We visually assessed the TCH of dominant and co-dominant trees at 66 sites in mature karri forests based on the extent and density of foliage, the extent of epicormic growth, and the extent of branch death. TSF ranged from two to 94 years. Fire regimes can influence tree health via soil chemistry conditions, so we sampled topsoil at each site. A model based on TSF and soil exchangeable potassium content explained 63.9

Indigenous Australians used fire in spinifex deserts for millennia. These practices mostly ceased following Eu-ropean colonisation, but many contemporary Indigenous groups seek to restore 'right-way fire' practices, to meet inter-related social, economic, cultural and biodiversity objectives. However, measuring and reporting on the fire pattern outcomes of management is challenging, because the spatio-temporal patterns of right-way fire are not clearly defined, and because spatio-temporal variability in rainfall makes fire occurrence highly variable in these desert environments. We present an approach for measuring and reporting on fire management outcomes to account for spatio-temporal rainfall variability. The purpose is to support Indigenous groups to assess perfor-mance against their management targets, and lay the groundwork for developing an accredited method for valuing combined social, cultural and biodiversity outcomes. We reviewed fire management plans of desert Indigenous groups to identify spatial fire pattern indicators for right-way fire in spinifex deserts. We integrated annual rainfall surfaces with time-since fire mapping (using Landsat imagery) to create a new spatial dataset of accumulated rainfall-since-last-fire, that better represents post-fire vegetation recovery as categorised by local Indigenous people. The fire pattern indicators were merged into a single score using an environmental ac-counting approach. To strengthen interpretation, we developed an approach for identifying a control area with matching vegetation and fire history, up to the point of management. We applied these methods to a 125,000 ha case study area: Durba Hills, managed by the Martu people of Western Australia. Using a 20-year time series, we show that since right-way fire management at Durba Hills was re-introduced (2009), the fire pattern indicators have improved compared to those in the matched control area, and the composite result is closer to the fine-scaled mosaic of right-way fire pattern targets. Our approach could be used by Indigenous groups to track performance, and inform annual fire management planning. As the indicators are standardised for rainfall variation, results from multiple sites can be aggregated to track changes in performance at larger scales. Finally, our approach could be adapted for other fire-prone areas, both in Australia and internationally with high spatio-temporal rainfall variability, to improve management planning and evaluation.

Fire-vegetation feedbacks potentially maintain global savanna and forest distributions. Accordingly, vegetation in savanna and forest ecosystems should have differential responses to fire, but fire response data for herbaceous vegetation have yet to be synthesized across biomes. Here, we examined herbaceous vegetation responses to experimental fire at 30 sites spanning four continents. Across a variety of metrics, herbaceous vegetation increased in abundance where fire was applied, with larger responses to fire in wetter and in cooler and/or less seasonal systems. Compared to forests, savannas were associated with a 4.8 (±0.4) times larger difference in herbaceous vegetation abundance for burned versus unburned plots. In particular, grass cover decreased with fire exclusion in savannas, largely via decreases in C4 grass cover, whereas changes in fire frequency had a relatively weak effect on grass cover in forests. These differential responses underscore the importance of fire for maintaining the vegetation structure of savannas and forests.

Fuel properties influence the behaviour of forest fires, so understanding how these change with time since fire is important for appraising the bushfire threat and planning and implementing bushfire mitigation operations. A space-for-time study in mature karri forests with fuel ages ranging from 1 to 92 years demonstrated that total fine-fuel weight (TFFW) increased with time since fire for about 30 years then plateaued at a mean value of about 50 t ha(-1). For fuels older than four years, on average, 74% of TFFW was in the surface fuel layer (the litterbed) and 17% was in the near-surface layer (up to 1 m above the surface layer). Live understorey vegetation contributed only about 6% to TFFW. Predicting TFFW from time since fire was improved by including karri tree basal area. Mean understorey height (Uht) increased with time since fire, peaking at 6 m after about 30 years, then declining to about 4 m after 92 years. Mean understorey hazard (Uhaz), derived from U-ht plus the proportion (%) of dead fuel in each fuel layer, followed a similar trend, peaking at 20-30 years post-fire, then declining. Although U-haz had declined by 36% from the maximum value by 60+ years post-fire, it was 27% higher than the U-haz value for young fuels (1-<5 years old). For a mean prescribed-burn interval of eight years, 50% of the forest fuel will be <= four years old and so will be carrying about not less than 19 t ha(-1) of fine fuel (<= 38% of the maximum value), with a Uhaz value of about <3.56 (<50% of the maximum value). Fuel weight and Uhaz directly influence fire intensity, flame size, spotting potential and rate of spread. Therefore, prescribed burning, done strategically and at the appropriate temporal and spatial scales, will make bushfires less damaging and easier and safer to suppress.

•Resprouting is essential to crown development in eucalypts.•Natural even-aged stands of eucalypts are very small, isolated and rare.•Mild burning throughout the landscape can protect carbon storage in biomass.•Timber harvesting can increase carbon sequestration inside and outside forests.•Black Summer indicated that Australia must shift its forest management paradigm.

. In fire-prone environments, prescribed burning is important for achieving many public land management objectives including protecting communities and the environment from damaging bushfires. There is evidence that in some biomes, reducing the size of burnt patches and creating a fine-scale mosaic of vegetation at different times since last fire (seral stages) may benefit biodiversity. However, planning and implementing an ongoing burning program to achieve this is problematic. To advance an understanding of the factors affecting burn patch size and seral diversity metrics, a novel experimental management trial that aimed to create and quantify a fine-scale fire mosaic was implemented in a south-west Australian forest landscape. The 10-year trial demonstrated that the fire mosaic characteristics, including diversity of seral stages, burnt patch size, patch distribution and patch connectedness, can be managed to a large extent by ignition frequency, which affects landscape fuel flammability, and the timing of the introduction of fire with respect to weather conditions. In this trial, the frequent introduction of fire under low to moderate Forest Fire Danger Indices resulted in a landscape comprising a quantifiably higher diversity of seral stages and smaller burnt patches than adjacent areas treated by fuel reduction prescribed burns and by a high intensity bushfire.

A risk-based framework for targeting investment in prescribed burning in Western Australia is presented. Bushfire risk is determined through a risk assessment and prioritisation process. The framework provides principles and a rationale for programming fuel management with indicators to demonstrate that bushfire risk has been reduced to an acceptable level. Indicators provide targets for fuel management that are applicable throughout the state and can be customised to meet local circumstances. The framework identifies eight bushfire risk management zones having broad consistency of land use, fire environment and management approach, which combine to create a characteristic risk profile. Thirteen fuel types based primarily on structural attributes of the vegetation that influence fire behaviour are recognised and used to assign models for fuel accumulation and fire behaviour prediction. Each bushfire risk management zone is divided into fire management areas, based on the management intent. These are areas where fuels will be managed primarily to minimise the likelihood of fire causing adverse impacts on human settlements or critical infrastructure, to reduce the risk of bushfire at the landscape scale or to achieve other land management outcomes. Indicators of acceptable bushfire risk are defined for each fire management area and are modified according to the distribution of assets and potential fire behaviour in the landscape. Risk criteria established in the framework can be converted to spatially represented targets for fuel management in each zone and can be reported against to measure the effectiveness of the fuel management program. In areas where the primary intent is to reduce the risk of bushfire at the landscape scale, managers have flexibility to apply prescribed fire in ways that maintain and enhance ecosystem services, nature conservation and landscape values through variation in the seasonality, intensity and scale of planned burning.

People proliferated across Australia, which was then a part of Sahul, from about 40 000 years ago when megafauna finally disappeared long before the Last Glacial Maximum. The so called ‘blitzkrieg’ hypothesis proposes that megafauna were extinguished by Aboriginal hunting. It is argued, either that there were some changes in vegetation and fire regimes as a consequence, or that fire regimes and vegetation were largely unaffected by human arrival. However, there is an alternative view that Aboriginal burning changed the vegetation so that megafauna had insufficient food resources to sustain them. We aimed to resolve this debate by examining the published palaeological and historical evidence. This evidence indicates that Aboriginal burning initially turned much biomass into charcoal, reducing browse, changing vegetation and causing megafaunal extinctions. It created ecosystems whose health and safety depend on constant human input of mild fire. Mild burning of these anthropogenic landscapes consumes relatively little biomass and produces relatively little charcoal. Although burning by people has typically been regarded as an ecological disturbance, the historical evidence, together with traditional Aboriginal knowledge, suggests that it is actually maintenance, essential to sustain our natural environment. We conclude that people can reinstate resilient, healthy and safe landscapes irrespective of climate change.

A survey was undertaken in the Great Sandy Desert, Western Australia, to document changes in total plant species richness and the richness of plants of significance to Aboriginal people, with time since fire. Species richness was highest in the early post-fire seral stages, then declined with time as ‘fire ephemerals’ completed their life cycle. Culturally significant plants, which comprised ~42% of all plants recorded, were found in all seral stages but were most abundant in the early stages post fire. A fine-scale mosaic of seral stages created by frequent patch burning provides a higher variety of plant resources per unit area, increasing harvesting efficiency of culturally important plants.

Prescribed burning is an important management tool in jarrah (Eucalyptus marginata Sm.) forests of southwest Western Australia to reduce the risk of damaging bushfires. In 1986 to 1987, we established long-term study sites in dry (mean annual rainfall ~700 mm) and moist (mean annual rainfall ~1000 mm) jarrah forests to assess the effects of prescribed burning, as well as other fire treatments including fire exclusion, on the composition, richness, and relative abundance of forest understory vegetation. Over almost 30 years, species assemblages within all fire treatments changed significantly through time, but the changes were independent of treatment. The pattern of change in composition of fire response types over elapsed time was different between sites. At the dry site, changes in species assemblages were initially relatively large in the first decade or so of the study, but slowed thereafter. At the moist site, compositional change driven by obligate seeding shrubs occurred faster and more uniformly with time across all treatments. Species richness was also independent of fire treatment at both sites. Species richness decreased with elapsed time on the moist site but increased with elapsed time on the dry site. The stronger elapsed-time effect rendered the time since fire effect on loss of species richness on the moist site to be insignificant, but there was an inverse relationship with time since fire at the dry site. Within each site, there were clear patterns of changing abundance based on life form and fire response groups, but this was not consistent between sites. At the scale of the current study, jarrah forest plant communities displayed resilience to imposed experimental fire regimes. Over time, either elapsed time or time since fire, species assemblages across all treatments changed regardless of fire treatment, but changes were mostly associated with specific plant life forms and fire response traits, suggesting that the process is both deterministic and stochastic. While many species changed in abundance over time, no species were lost as a result of the fire treatments. Within the fire frequency and intensity ranges investigated in this study, there was flexibility in the application of prescribed fire to achieve management objectives without loss of plant diversity.

ABSTRACT Flammable spinifex grasslands of arid Western Australia cover about 98 million hectares of the state, and large wildfires in this environment threaten biodiversity, life, property and cultural values. Understanding fire behaviour in spinifex grasslands informs prescribed burning and wildfire suppression activities. Unmanned aerial systems (UAS) are aiding in improving fire behaviour prediction by providing comprehensive and accurate measurements of vegetation cover, volume and height, the fuel characteristics of vegetation that influence fire behaviour. Classification of spinifex cover derived from UAS image capture has been compared to field transects. Data from UAS align better with Landsat satellite imagery than fuel cover measures from field transects. A good correlation was found between UAS-derived vegetation cover and Landsat imagery, which means satellite imagery can be used with confidence to estimate and map fuel cover at a range of temporal and spatial scales. UAS have also proven useful in the development of a spectral index describing spinifex cover. The rapid development of affordable UAS instruments and software has enabled the production of point clouds, which provide further vegetation structure information not available from previous image captures. These developments in UAS application together with satellite imagery will enable fire managers to more efficiently and accurately map fuel characteristics at a range of scales, greatly enhancing their ability to forecast fire danger and to predict fire behaviour without having to carry out costly ground-based field measurements.

Inappropriate fire-regimes brought about by patterns of human settlement and land-use threaten plant diversity in Mediterranean-type climate (MTC) regions. In south-west Western Australia (SWWA), where there are many threatened plant species distributed across a range of human-modified landscapes, there is a need for approaches to identify where the threat is greatest. This requires knowledge of contemporary fire regimes, how they vary across landscapes, and the sensitivity of threatened species to these regimes. Currently, this information is lacking, and this limits strategic fire management. In this study we compiled fire response information for SWWA’s threatened plant species and undertook a bioregional assessment of variation in fire interval over the last 40 years. We determined the fire response traits of 242 (60%) of the region’s 401 extant threatened species. Over half of the 242 species were obligate seeders and will therefore have population dynamics particularly sensitive to fire interval. Our study highlights large differences in fire interval across nine bioregions in SWWA. The differences were greatest for the heavily cleared and fragmented bioregions compared with more continuously vegetated bioregions. We discuss how variations in the frequency of fire life-history traits and fire interval interact to determine the nature and relative level of threat posed by fire in these landscapes. Survival of many populations of threatened flora in this biodiversity hotspot will depend on developing appropriate fire regimes that match the regeneration requirements of each species.

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.

Fire behaviour characteristics define the impacts on society and the environment. While wildland fire science has expanded to include the analysis of fire activity and effects across the globe, an understanding of global fire behaviour patterns and its drivers remains incomplete. We utilized the literature and unpublished datasets as sources for compiling a worldwide fire environment and fire behaviour database consisting of field-based experimental fires, planned-ignition prescribed fires and wildfires. Analysis of the database allows for the assessing of the influences of fuel and weather descriptors on fire behaviour characteristics at various scales, namely climate zone, biome, ecoregion, and vegetation type. The database comprises nearly 6000 fires. Fire spread rate and fireline intensity vary by five orders of magnitude (seven in the former case if smouldering is considered). Variation in fire-spread rate is dominated by fuel moisture content within Koppen-Geiger climates, except in tropical wet and hot desert climates, where wind speed prevails. Fuel structure is less important than weather-related variables, but it explains 35 and 30% of the variability within monsoon-influenced humid subtropical and hot summer Mediterranean climates, respectively. Fuel structure and load metrics increase in importance in regards to fireline intensity, being the dominant influence (66-91%) in hot semi-arid, temperate oceanic, and hot summer Mediterranean climates. Fuel moisture content exerts by far the major control in the variation in fire spread rate within broad vegetation types (forest, woodland, shrubland, grassland), while fuel structure metrics dominate the variation observed in fireline intensity, except in woodlands, where fuel moisture content is slightly more influential. Efforts to understand potential fire activity and fire regime shifts in relation to global change, and the formulation of policies for adaptive fire management will benefit from the results of this study.

The Waroona bushfire burnt 69,000 ha south of Perth in January 2016. During the first two days of the fire, there were two pyrocumulonimbus (pyroCb) events and two destructive evening fire runs. Over 160 homes were destroyed and there were two fatalities. This case study examines in detail the links between the meteorological observations and the fire behaviour reconstruction.The first pyroCb developed on Wednesday 6 January 2016, when the fire made an unexpectedly fast run in light prevailing winds. The pyroCb produced lightning strikes that ignited a new fire downwind of the main head fire. A second pyroCb developed on Thursday morning, against normal diurnal thunderstorm trends. Similar to the previous evening, the fire spread faster than expected, given the near-surface meteorological conditions.On both evenings there were destructive ember storms over the towns of Waroona (Wednesday) and Yarloop (Thursday). Examination of the meteorological observations has linked these ember showers to the onset of downslope winds, locally known as `scarp winds'. As downslope winds are associated with strong localised turbulence, they provide a mechanism for transport of large numbers of firebrands.The periods of extreme fire behaviour at Waroona were against normal diurnal expectations and did not coincide with the highest observed Fire Danger Index (FDI) values, which occurred at around 1600 LT. This study links both pyroCb events to accelerated fire spread, which presents a hazard to firefighters that is not accounted for in traditional, surface based methods of fire prediction. Downslope winds similar to those that impacted the Waroona fire occur at many locations. They provide a highly localised mechanism for destructive evening ember showers.This investigation into the Waroona fire describes the potential impacts of fireatmosphere feedback processes. Consequently, it highlights the need for predictive methods and tools that anticipate fire behaviour which is not steady-state. Planned simulations using a coupled fire-atmosphere model will allow further insights into features of this case study.

A fire sensitive plant, Banksia quercifolia R.Br., that often occurs as thickets embedded in forest landscapes in south-west Australia was exposed to repeated broad-scale fires at short intervals. Fire severity and patchiness was mapped using satellite imagery and the response of the B. quercifolia population monitored. Over the study period, the mean interval of fire in the landscape in which B. quercifolia occurred was 1.7 yr—almost half the juvenile period of the species—and the landscape fire frequency was six fires per decade. The population increased in response to episodes of fire escape and fire-caused mortality and consequent regeneration. Unlike surrounding vegetation, immature B. quercifolia thickets were not flammable under conditions of mild weather and moist fuels, so they burnt at a lower frequency than more flammable vegetation in the surrounding landscape, enabling the species to persist. When the thickets had developed sufficiently to burn, the plants had reached maturity and regenerated readily from seed. However, the juvenile period increased by 58 % following a period of 16 % below average rainfall, which has implications for fire management in a drying climate.