Prescribed burns and logging won’t protect homes in bushfires

Samantha Donovan reported this story on Thursday, January 19, 2012 08:18:00

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TONY EASTLEY: The first study to look at prescribed burning and what impact it has on saving houses during a bushfire has concluded it’s not how much burning is done, but where.

Australian and Californian researchers studied the relative positions of 500 homes destroyed in Victoria’s Black Saturday catastrophe.

With more here’s Samantha Donovan.

SAMANTHA DONOVAN: More than 2,100 homes were destroyed in the Black Saturday fires.

The fact they were on all types of terrain including cleared land, areas of prescribed burns and state forest gave Australian and Californian researchers a unique opportunity to assess what contributed to the loss of so many buildings.

After the disaster many residents questioned the adequacy of prescribed burning in some areas.

The Australian National University’s Dr Philip Gibbons says the research showed that prescribed burning was only half as effective at protecting houses as clearing vegetation around buildings.

PHILIP GIBBONS: So prescribed burning is not the silver bullet that some people suggest it is. So when the weather gets up to the extremes that we experienced on Black Saturday then we know that prescribed burnings, the effect of prescribed burning becomes diminished.

But it was surprising that clearing vegetation, trees and shrubs close to your house, was twice as effective as prescribed burning on Black Saturday.

SAMANTHA DONOVAN: Dr Gibbons also found prescribed burning was most effective when done close to homes.

PHILIP GIBBONS: And prescribed burning is typically done distant from houses. And so the average distance from a house of prescribed burning on Black Saturday was eight kilometres. But we found that at that distance from houses prescribed burning had virtually no effect in terms of protecting houses.

SAMANTHA DONOVAN: The researchers also considered the effect the logging of native forest has on protecting homes in a bushfire.

Philip Gibbons:

PHILIP GIBBONS: Yeah well another issue that came up after Black Saturday was raised by a few commentators including Wilson Tuckey was that really we should think less about locking up our forest into national parks but logging more of our forests so that we reduce bushfire risk.

Now we found that indeed a house that is close to forest is at greater risk. But it didn’t matter if that forest was national park or state forest that was managed for logging. In other words logging had no effect in terms of protecting houses on Black Saturday.

They take out all the really big logs. They take out the trunks of trees and they leave the leaves on the ground. They leave the fine fuels, okay. So they’re the ones that contribute to the intensity of the fire.

And also if you log an area heavily you end up with a young forest that’s very dense and that can also add to the fuel in a forest. It’s like having a big thick layer of shrubs in the forest and the crowns are all connected.

SAMANTHA DONOVAN: The research is being published today by the Public Library of Science.

TONY EASTLEY: Samantha Donovan reporting there.

Read the transcript or listen to the podcast on Radio National AM, HERE

The original study, Land Management Practices Associated with House Loss in Wildfires, is available HERE

• Jon Sumby: Broadscale fuel reduction burns are not the best method ...

I just read an interesting article about bushrire risk mitigation that indicates broadscale fuel reduction burns (e.g. burning a national park) may not be the best method. Instead, ensuring a 40 m buffer zone around houses and doing fuel reduction burns on the margins of properties to within 500 m of properties may be a better strategy!

Below is the results from the abstract:

Land Management Practices Associated with House Loss in Wildfires
Philip Gibbons1, Linda van Bommel 1, A. Malcolm Gill 1, Geoffrey J. Cary 1, Don A. Driscoll 1, Ross A. Bradstock 2, Emma Knight 3, Max A. Moritz 4, Scott L. Stephens 4, David B. Lindenmayer 1

1 TheFennerSchoolofEnvironmentandSociety,TheAustralianNationalUniversity,Canberra,AustralianCapitalTerritory,Australia,
2 CentreforEnvironmentalRisk Management of Bushfires, University of Wollongong, Wollongong, New South Wales, Australia,
3 Centre for Mathematics and its Applications, The Australian National University, Canberra, Australian Capital Territory, Australia,
4 Ecosystem Sciences Division, Department of Environmental Science, Policy and Management, University of California, Berkeley, California, United States of America

From the abstract:
Significant fuel variables in a logistic regression model we selected to predict house loss were (in order of decreasing effect):
(1) the cover of trees and shrubs within 40 m of houses,
(2) whether trees and shrubs within 40 m of houses was predominantly remnant or planted,
(3) the upwind distance from houses to groups of trees or shrubs,
(4) the upwind distance from houses to public forested land (irrespective of whether it was managed for nature conservation or logging),
(5) the upwind distance from houses to prescribed burning within 5 years, and
(6) the number of buildings or structures within 40 m of houses.

All fuel treatments were more effective if undertaken closer to houses. For example, 15% fewer houses were destroyed if prescribed burning occurred at the observed minimum distance from houses (0.5 km) rather than the observed mean distance from houses (8.5 km). Our results imply that a shift in emphasis away from broad-scale fuel-reduction to intensive fuel treatments close to property will more effectively mitigate impacts from wildfires on peri-urban communities.

Download the full analysis: