Bushfire greenhouse gas emissions – from mild to wild

Published in the University of Melbourne VOICE magazine – Volume 11 Number 1 January 12 – February 8 2015 by Nerissa Hannink

A study in Australia’s eucalypt forests has revealed that levels of carbon and greenhouse gases released in wildfire could be reduced by fuel reduction burning, or planned burns conducted prior to the bushfire season in high risk forests.

Funded by the Bushfire CRC, the work was led by researchers at the University of Melbourne and is published in the International Journal of Wildland Fire and the Forest Ecology and Management journal.

The results will inform land management decisions as well as government policy regarding planned burning, and enable more accurate estimations of the contribution that bushfires make to Australia’s National Greenhouse Gas Inventory.

This new capability is timely given that Australia is a signatory to phase 2 of the Kyoto Protocol and must account for greenhouse gas emissions from managed forests for the 2013 to 2020 commitment period.

Project scientists Chris Weston and Luba Volkova measured forest carbon before and after planned burning in eucalypt forests across Australia’s south-eastern states.

When a high intensity wildfire occurred three months after a fuel reduction burn they had measured in a Gippsland forest, Drs Weston and Volkova teamed up with the CSIRO’s Mick Meyer to compare greenhouse gas emissions from low intensity planned burning and high intensity bushfire. The mild to wild bushfire comparison could then begin.

“With bushfires expected to increase in intensity and frequency due to climate change, we wanted to produce some baseline greenhouse gas emissions estimates to inform the debate over whether fuel reduction burns are effective in reducing emissions,” Dr Volkova says.

“Current estimates of bushfire emissions are conservative because they are based mainly on fine fuels monitoring data, derived for the purpose of bushfire spread predictions. This approach has not been able to adequately determine the contribution to emissions from logs and other large or coarse fuels.

“We measured all major fuel types including litter, small plants and bark as well as dead trees and large woody debris on the forest floor, to calculate the carbon and greenhouse gases emitted,” Dr Volkova says.

The team studied the fuel types in three scenarios; before and after planned burns alone, before and after a planned burn and wildfire in the same area three months apart, and before and after an extremely severe wildfire in a long-unburnt forest.

They found that fuel reduction burning in forests reduced emissions from subsequent wildfire by around 40 per cent.

Low fire intensity planned burns reduced total forest carbon by around 6 per cent whereas really high intensity wildfire reduced forest carbon by around 30 per cent, showing that when it comes to fire and greenhouse gas emissions mild is definitely better than wild.

“We find that wildfires generate more smoke and burn a lot more of the heavy fuels such as dead trees, producing more methane which is a much more potent greenhouse gas than carbon dioxide,” Dr Weston says.

“Fuels are also usually much drier at the time of wildfire and so burn more completely than fuels in the planned burns that are conducted in cooler and more controlled conditions.

“It was encouraging to see wildfire intensity reduced by the prior fuel reduction burn, suggesting there is significant potential to mitigate greenhouse gas emissions from forests at high risk from bushfires through fuel reduction burning,” he says.

The next step for the team is to generate a model of forest fire emissions over decades and centuries to compare emissions from mild and wild fires that occur at different frequencies.

The results of this analysis will encompass more intense and more frequent fire during the transition to a changed climate and improve strategic burning decisions and adaptive forest management in the future.

The model will also indicate whether planned burns are likely to reduce total emissions over the longer time period.

“We hope these results will help land managers develop predictive tools to enhance the management of our forests and allow Australia to better plan for emissions targets in our changing climate,” Dr Volkova says.

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