Cool burns can cut forest CO2 emissions

Cool burns can cut forest CO2 emissions

18 March 2010

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USA —  Prescribed burning programmes in natural forests may significantly reduce carbon emissions long term and contribute to climate change strategy, the findings of recent studies on forest fire impacts conclude.

A study of western US forests published in the journal Environmental Science & Technology found that controlled, cooler burning can reduce forest undergrowth and lessen the risk of uncontrolled wildfire that destroys a forest’s biggest trees. Because the big, mature trees hold most of the forest carbon, preventing high-intensity wildfires can protect the bulk of a forest’s carbon stores.

Using satellite data and computer models of emissions, scientists concluded that widespread prescribed burns can reduce fire emissions of carbon dioxide in the western US by an average of 18 to 25 per cent, and by as much as 60 per cent in certain forest systems.

“If we reintroduce fires into our ecosystems, we may be able to protect larger trees and significantly reduce the amount of carbon released into the atmosphere by major wildfires,” said Christine Wiedinmyer, the lead author on the study from the US National Center for Atmospheric Research (NCAR) in Colorado. More frequent, less severe fires result in lower tree mortality by keeping fuel levels low in the forests, adds Matthew Hurteau of Northern Arizona University, a co-author of the study.

The study modelled would happen if widespread prescribed burning were carried across eleven western US states. The results showed that carbon emissions could be reduced in total by an annual average of 14 million tonnes. The authors cautioned that it may not be difficult to carry out prescribed burns to the extent modeled.

In the western US, as in other industrialised countries, the last century has seen land management reduce the incidence of fire in forests. At the same time, climate change is producing hotter, drier conditions for many forests. This has delivered a two-pronged boost to the incidence of wildfire, increasing carbon emissions along the way. So prescribed burns can be an important piece of a climate change strategy, Wiedinmyer concluded.

The findings are backed up by another study of giant sequoias in California’s Sierra Nevada by the University of Arizona’s Laboratory of Tree-Ring Research. It found that during what’s known as the Medieval Warm Period from 800 to 1300 AD, fires were frequent in the sequoia forests, every three to ten years. Since 1860, human intervention has reduced fires frequency substantially.

Published in the journal Fire Ecology in February, the study found that the giant trees appeared to benefit from the higher fire frequency of fire during medieval times. Now the climate is warming again, introducing regular, low-intensity fires could be crucial to helping the sequoias survive, lead author Thomas Swetnam said.

A lack of prescribed burning in forest reserves is one potential contributing factor being examined by the inquiry into the ‘Black Saturday’ wildfires that killed 183 people in Australia’s south-eastern state of Victoria in early 2009. An incredibly intense firestorm razed whole towns and completely destroyed 450,000 hectares of forest. High forest fuel loads are believed to have contributed to the catastrophic intensity of the fires.

The Victorian government has been criticised for not employing prescribed burning programmes as aggressively as neighbouring Australian states. By one estimate, the fires resulted in the emission of more than 100 million tonnes of greenhouse gases into the atmosphere, increasing the country’s total annual carbon footprint by as much as 20 per cent in just a few days. The inquiry has yet to hand down its final report.

In Australia’s tropical north, efforts are underway to reintroduce age-old Aboriginal practices of controlled burning of savannah grassland to reduce major wildfire risk. The national science agency CSIRO says by doing so it may be possible to reduce carbon emissions by five million tonnes a year and create carbon offset market revenues of $A50 million for indigenous people.

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