Simulation of prescribed burning strategies in south-west Tasmania, Australia: effects on unplanned fires, fire regimes, and ecological management values

Bradstock

2010

Int. J. Wildland Fire

Self Cite

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. Abstract. 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.Additional keywords: bushfire risk, fire management, prescribed burning.

Section: <0001supporting

confidence: 49%

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

Bradstock

2010

Int. J. Wildland Fire

Self Cite

“…The results of simulation studies often reach the opposite conclusion to those empirical studies: that small amounts of treatment result in large reductions in area burnt by unplanned fires (Finney 2007;King et al 2006;Loehle 2004). Loehle (2004) coined the term leverage to mean the area of unplanned fire reduction (from an untreated state) obtained per unit of treatment.…”

Section: Introductionmentioning

confidence: 66%

“…Finney (2007) found that treating 1% of the landscape per annum in an optimised design reduced the probability of burning by about 60%. King et al (2006) found that treating 5% of the landscape reduced the area burnt by about 50%. Given these disparities, there is a need for synthesis.…”

Section: Introductionmentioning

confidence: 99%

The Drivers of Effectiveness of Prescribed Fire Treatment

2012

Forest Science

Prescribed burning for fuel reduction is a major strategy for reducing the risk from unplanned fire. Although there are theoretical studies suggesting that prescribed fire has a strong negative influence on the subsequent area of unplanned fire (so-called leverage), many empirical studies find a more modest influence. Here, I develop a series of simulations to explore the landscape drivers of leverage. Leverage declines with treatment level in a nonlinear, "decay" relationship, implying diminishing effectiveness. The spatial configuration of the prescribed fire treatment has a major effect: long linear (gridded) barriers are far more effective than patch barriers, but gaps in the grid lead to large reductions in leverage. However, the extent of unplanned fires in the landscape has the largest influence such that a landscape with 3% annual extent has only one-fifth of the leverage of a landscape with 28%. Leverage decreases with the probability of spread, suggesting that treatment is less effective when fire weather is severe. For gridded designs, leverage increases with the size of individual fires, but this is not the case for patch designs. These results agree well with recent empirical studies finding that prescribed burning has only a modest effect on subsequent unplanned fire in many biomes. They also help to explain why those empirical studies report lower effectiveness than many simulation studies. In practice, leverage values >1 (replacement of unplanned with planned fire) are hard to achieve. The drivers of effectiveness of prescribed fire treatment AbstractPrescribed burning for fuel reduction is a major strategy for reducing the risk from unplanned fire. While there are theoretical studies suggesting that prescribed fire has a strong negative influence on the subsequent area of unplanned fire (so called leverage), many empirical studies find a more modest influence. Here, I develop a series of simulations to explore the landscape drivers of leverage. Leverage declines with treatment level in a non-linear, 'decay' relationship, implying diminishing effectiveness. The spatial configuration of the prescribed fire treatment has a major effect: long linear (gridded) barriers are far more effective than patch barriers, but gaps in the grid lead to large reduction in leverage. However, the extent of unplanned fires in the landscape has the largest influence such that a landscape with 3% annual extent has only one fifth of the leverage of a landscape with 28%. Leverage decreases with the probability of spread, suggesting that treatment is less effective when fireweather is severe. For gridded designs, leverage increases with the size of individual fires, but this is not the case for patch designs. These results agree well with recent empirical studies that find prescribed burning has only a modest effect on subsequent unplanned fire in many biomes. They also help to explain why those empirical studies report lower effectiveness than many simulation studies. In practice, leverage values above 1 (repla...

“…It is likely that the strategic spatial arrangement of the EDS areas has enhanced the return for effort above parity. Such an effect has been demonstrated in simulation studies (Finney 2001;King, Cary et al 2006). However, there are other potential causes for the large reduction in LDS, including a reduction in LDS ignitions due to improved community awareness brought about by the WALFA program.…”

Section: Discussionmentioning

confidence: 96%

“…This result is similar to that found by (Price and Bradstock 2011) for the forests of the Sydney region in eastern Australia, where there was no evidence of nonlinearity and an empirical study in Jarrah forests of Western Australia (Boer, Sadler et al 2009), which found a weak concave relationship. However, there was a marked concave relationship in a simulation study of Tasmanian forests (King, Cary et al 2006). A linear relationship implies that there will be a certain level of treatment at which wildfires are eliminated.…”

Section: Discussionmentioning

confidence: 99%

The influence of prescribed fire on the extent of wildfire in savanna landscapes of western Arnhem Land, Australia

Russell‐Smith

Watt

2012

Int. J. Wildland Fire

Fire regimes in many north Australian savanna regions are today characterised by frequent wildfires occurring in the latter part of the 7-month dry season. A fire management program instigated from 2005 over 24 000 km2 of biodiversity-rich Western Arnhem Land aims to reduce the area and severity of late dry-season fires, and associated greenhouse gas emissions, through targeted early dry-season prescribed burning. This study used fire history mapping derived mostly from Landsat imagery over the period 1990-2009 and statistical modelling to quantify the mitigation of late dry-season wildfire through prescribed burning. From 2005, there has been a reduction in mean annual total proportion burnt (from 38 to 30%), and particularly of late dryseason fires (from 29 to 12.5%). The slope of the relationship between the proportion of early-season prescribed fire and subsequent late dry-season wildfire was ~-1. This means that imposing prescribed early dry-season burning can substantially reduce late dry-season fire area, by direct one-to-one replacement. There is some evidence that the spatially strategic program has achieved even better mitigation than this. The observed reduction in late dry-season fire without concomitant increase in overall area burnt has important ecological and greenhouse gas emissions implications. This efficient mitigation of wildfire contrasts markedly with observations reported from temperate fire-prone forested systems.