Owen F. Price

Prescribed burning: how can it work to conserve the things we value?

Prescribed burning is a commonly applied management tool, and there has been considerable debate over the efficacy of its application. We review data relating to the effectiveness of prescribed burning in Australia. Specifically, we address two questions: (1) to what extent can fuel reduction burning reduce the risk of loss of human life and economic assets posed from wildfires? (2) To what extent can prescribed burning be used to reduce the risk of biodiversity loss? Data suggest that prescribed burning can achieve a reduction in the extent of wildfires; however, at such levels, the result is an overall increase in the total area of the landscape burnt. Simulation modelling indicates that fuel reduction has less influence than weather on the extent of unplanned fire. The need to incorporate ecological values into prescribed burning programmes is becoming increasingly important. Insufficient data are available to determine if existing programs have been successful. There are numerous factors that prevent the implementation of better prescribed burning practices; most relate to a lack of clearly defined, measurable objectives. An adaptive risk management framework combined with enhanced partnerships between scientists and fire-management agencies is necessary to ensure that ecological and fuel reduction objectives are achieved.

Wildfires, fuel treatment and risk mitigation in Australian eucalypt forests: Insights from landscape-scale simulation

Wildfires pose significant risks to people and human infrastructure worldwide. The treatment of fuel in landscapes may alter these risks but the magnitude of this effect on risk is poorly understood. Evidence from Australian Eucalyptus forests suggests that mitigation of risk using prescribed burning as a fuel treatment is partial because weather and fuel dynamics are conducive to regular high intensity fires. We further examine the response of risk to treatment in eucalypt forests using landscape simulation modelling. We model how five key measures of wildfire activity that govern risk to people and property may respond to variations in rate and spatial pattern of prescribed fire. We then model effects of predicted climate change (2050 scenarios) to determine how the response of risk to treatment is likely to be altered in the future. The results indicate that a halving of risk to people and property in these forests is likely to require treatment rates of 7-10% of the area of the landscape per annum. Projections of 2050 weather conditions under climate change further substantially diminished the effect of rate of treatment. A large increase in rates of treatment (i.e. circa. 50% over current levels) would be required to counteract these effects of climate change. Such levels of prescribed burning are unlikely to be financially feasible across eucalypt dominated vegetation in south eastern Australia. Despite policy imperatives to expand fuel treatment, a reduction rather than an elimination of risk will result. Multi-faceted strategies will therefore be required for the management of risk.

The efficacy of fuel treatment in mitigating property loss during wildfires: Insights from analysis of the severity of the catastrophic fires in 2009 in Victoria, Australia.

Treatment of fuel (e.g. prescribed fire, logging) in fire-prone ecosystems is done to reduce risks to people and their property but effects require quantification, particularly under severe weather conditions when the destructive potential of fires on human infrastructure is maximised. We analysed the relative effects of fuel age (i.e. indicative of the effectiveness of prescribed fire) and logging on remotely sensed (SPOT imagery) severity of fires which occurred in eucalypt forests in Victoria, Australia in 2009. These fires burned under the most severe weather conditions recorded in Australia and caused large losses of life and property. Statistical models of the probability of contrasting extremes of severity (crown fire versus fire confined to the understorey) were developed based on effects of fuel age, logging, weather, topography and forest type. Weather was the primary influence on severity, though it was reduced at low fuel ages in Moderate but not Catastrophic, Very High or Low fire-weather conditions. Probability of crown fires was higher in recently logged areas than in areas logged decades before, indicating likely ineffectiveness as a fuel treatment. The results suggest that recently burnt areas (up to 5-10 years) may reduce the intensity of the fire but not sufficiently to increase the chance of effective suppression under severe weather conditions. Since house loss was most likely under these conditions (67%), effects of prescribed burning across landscapes on house loss are likely to be small when weather conditions are severe. Fuel treatments need to be located close to houses in order to effectively mitigate risk of loss.

Fire-Stick Forestry: A Matrix Model in Support of Skilful Fire Management of Callitris intratropica R. T. Baker by North Australian Aborigenes

The response of a monospecific stand of Callitris intratropica R. T. Baker & H. G. Smith to a range of fire intensities and inter-fire periods were simulated using a stage based matrix model. The model used published values for life history parameters and incorporated linear density dependence in fecundity and growth. Mild fires (i.e. those that killed to mature trees) with mean period between 2 to 8 years maintained a healthy stand structure. More frequent or more intense fires resulted in damage or extinction of the stand, whereas decreasing frequency or intensity yielded stands which were heavily stocked with saplings, few of which were recruited into the larger size classes. These results were largely insensitive to modification of life history parameters. We conclude that stands of C. intratropica on sites without topographic fire-protection must have been maintained by Aboriginal fire management. Observed damage and decline of C. intratropica stands is consistent with a reversion to uncontrolled fire regimes in the recent past.

The 'wilderness effect' and the decline of Callitris intratropica on the Arnhem Land Plateau, northern Australia

An aerial survey along a transect from eastern side of the Arnhem Land Plateau where Aboriginal people still lead a semi-traditional lifestyle, to the unoccupied western side of the Plateau, revealed systematic differences in the proportion of living and dead Callitris intratropica trees. Multiple regression analysis showed that the highest proportion of dead C. intratropica stems occurred on unoccupied, level terrain dominated by open Eucalyptus forests, with a minor or complete absence of Allosyncarpia ternata closed-canopy forests. A detailed study of one population of C. intratropica in western Arnhem Land adjacent to a small patch of A. ternata forest, known as Round Jungle, showed that the population had a unimodal size-class distribution, reflecting a low density of stems less than 10 cm in diameter at breast height (dbh). A computer simulation model was developed on the basis of estimates of annual fecundity, mortality and growth rates derived from observations of the stand. Sensitivity analyses suggested that a well-stocked stand could be transformed to one similar to that observed at Round Jungle after 50 years, if annual mortality rate of the immature stems (i.e. 12 cm dbh) mortality and fecundity had much less effect on the predictions of the model than the rate of mortality of the smallest size class. The model suggests that C. intratropica populations can rapidly fluctuate in response to changes in fire regime, while extinction is a gradual process and is consequently unlikely if some seedlings can escape burning, for instance by establishing in fire-protected microsites. This conclusion is consistent with the observed greater mortality of C. intratropica on sand sheets that have little topographic variability at the micro- or mesoscale, compared with other habitat types in areas that are currently unoccupied by Aboriginal people. Our study shows that predicting the fate of individual populations will require careful consideration of local factors such as the presence of micro-topographically safe sites for seedling establishment, as well as the surrounding pattern of vegetation and landforms that mediate the impact of fire on C. intratropica. However, we suggest that rather than refining details of the adjustment of C. intratropica in response to changed fire regimes associated with European colonisation, subsequent research should focus on the effect and significance of these changes for other organisms.

The effect of fuel age on the spread of fire in sclerophyll forest in the Sydney region of Australia

We investigated the effect of fuel age on the truncation of spread of unplanned fires using a set of 1473 patches in the Sydney region of Australia. Twenty-two percent of patches derived from prescribed fire experienced a subsequent unplanned fire within 5 years, compared with 42% of patches derived from unplanned fires. Among those encounters, the subsequent unplanned fire stopped at the leading edge of 18% of prescribed patches and 11% of unplanned patches. In comparison, the subsequent fire stopped somewhere in the patch for 44% of both prescribed and unplanned fires. Overall, there was a 10% chance that a prescribed burn patch would experience an unplanned fire that stops within the patch. Statistical modelling revealed that the presence of a road barrier was the best predictor of the likelihood of stopping on the leading edge, but fuel age and weather also had an influence. Stopping on the trailing edge was less influenced by the variables analysed. In extreme weather, even 1-year-old patches have a low likelihood of stopping unplanned fires. Fuel age had little influence on the spread of unplanned fires. Consequently, prescribed fires will be most effective when sited at the urban interface where resultant reduced unplanned fire intensity will be a benefit.

Quantifying the influence of fuel age and weather on the annual extent of unplanned fires in the Sydney region of Australia

Planned fire is used globally to minimise the risk of unplanned fire, but it is important to measure the return for effort in terms of the reduction of risk per unit area of planned fire. Here, we use 30 years of fire mapping from four subregions of the Sydney region to compare the annual extent of unplanned fire with previous planned and unplanned fire. Using linear mixed modelling, we were able to discriminate the relative influence of previous fire, seasonal rainfall and weather during the peak fire season. The mean annual area burnt over the period was 4.11%, comprising 0.53% planned and 3.58% unplanned. We found that weather during the fire season was the most influential factor. Annual rainfall had a modest negative relationship with unplanned fire area. Past fire had some influence, but the relationship implied that approximately three units of planned fire are required to reduce the unplanned fire area by one unit. Managers would need to burn 5.4% per year to halve unplanned fire extent, a ten-fold increase on recent levels. This would increase the total area burnt, and have other effects that need to be considered (from smoke and greenhouse gas emissions, and changes to biodiversity).

Fine-scale patchiness of different fire intensities in sandstone heath vegetation in northern Australia

We assessed the extent of burning and rockiness in 3712 5 × 5 m quadrats along 9.2 km of transects sampling five different fires in sandstone heaths where contemporary fire regimes are thought to be reducing the populations of many plants. All fires were patchy, with means of 64% burnt for early dry season and 84% for late dry season fires. Rockiness was strongly related to the presence of unburned patches, and some late dry season fires leave no patches in the absence of rocks. Half of the unburned patches were 10 m or less in length and of the 83 patches identified only three were still detectable when data were amalgamated into quadrats of 500 m2. Thus, very few patches could be recognised from satellite images. The results suggest that fires are much more patchy than satellite-derived fire maps indicate. This has important implications for understanding how populations of fire sensitive plants will respond to different fire regimes.

Forest fire management, climate change, and the risk of catastrophic carbon losses

Approaches to management of fireprone forests are undergoing rapid change, driven by recognition that technological attempts to subdue fire at large scales (fire suppression) are ecologically and economically unsustainable. However, our current framework for intervention excludes the full scope of the fire management problem within the broader context of fire−vegetation−climate interactions. Climate change may already be causing unprecedented fire activity, and even if current fires are within the historical range of variability, models predict that current fire management problems will be compounded by more frequent extreme fire-conducive weather conditions (eg Fried et al. 2004). Concern about climate change has also made the mitigation of greenhouse-gas (GHG) emissions and increased carbon (C) storage a priority for forest managers.

Divergent responses of fire to recent warming and drying across south‐eastern Australia

The response of fire to climate change may vary across fuel types characteristic of differing vegetation types (i.e. litter vs. grass). Models of fire under climatic change capture these differing potential responses to varying degrees. Across south-eastern Australia, an elevation in the severity of weather conditions conducive to fire has been measured in recent decades. We examined trends in area burned (1975-2009) to determine if a corresponding increase in fire had occurred across the diverse range of ecosystems found in this part of the continent. We predicted that an increase in fire, due to climatic warming and drying, was more likely to have occurred in moist, temperate forests near the coast than in arid and semiarid woodlands of the interior, due to inherent contrasts in the respective dominant fuel types (woody litter vs. herbaceous fuels). Significant warming (i.e. increased temperature and number of hot days) and drying (i.e. negative precipitation anomaly, number of days with low humidity) occurred across most of the 32 Bioregions examined. The results were mostly consistent with predictions, with an increase in area burned in seven of eight forest Bioregions, whereas area burned either declined (two) or did not change significantly (nine) in drier woodland Bioregions. In 12 woodland Bioregions, data were insufficient for analysis of temporal trends in fire. Increases in fire attributable mostly to warming or drying were confined to three Bioregions. In the remainder, such increases were mostly unrelated to warming or drying trends and therefore may be due to other climate effects not explored (e.g. lightning ignitions) or possible anthropogenic influences. Projections of future fire must therefore not only account for responses of different fuel systems to climatic change but also the wider range of ecological and human effects on interactions between fire and vegetation.