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|  Australian Forests Best in World Carbon Sink
Seems the Victorian Euc regnans are the best carbon sinks on the planet. Australian forests lock up most carbon › News in Science (ABC Science) Quote: | Australian forests lock up most carbon
Mountain ash forests in Australia are the best in the world at locking up carbon, a new study has found.
And one of the authors says climate change negotiations should give more attention to protecting forests like these.
Environmental scientist, Professor Brendan Mackey of the Australian National University and colleagues report their findings in today's issue of the Proceedings of the National Academy of Science.
"Currently everyone is focussed on how to reduce emissions from deforestration and degradation in developing countries," says Mackey.
"But what this points to is that we can't forget about emissions from natural forests in economically developed countries like Australia."
In the first study of its kind, Mackey and colleagues compared the amount of carbon per unit area locked up in 132 forests around the world.
Forests ranged from the Amazon in the tropics to temperate moist forests, such as stands of mountain ash (Eucalyptus regnans) in Victoria's Central Highlands.
They calculated the total biomass locked up in living and dead plant material and the soil of each forest.
Surprise findings
Mackey and colleagues found the highest amount of carbon was contained in a forest located in Victoria's Central Highlands, which held 1900 tonnes of carbon per hectare.
This most "carbon-dense" forest was a stand of unlogged mountain ash over 100 years old. Mountain ash live for at least 350 years, says Mackey.
He says similar but lower carbon densities were found for other temperate moist forests in New Zealand, Chile and the Pacific coast of North America.
By comparison, the average tropical forest had somewhere between 200 and 500 tonnes of carbon per hectare, says Mackey.
"The common understanding is that tropical forests store the most carbon because they're the most biologically productive and have the most plant growth," says Mackey.
But, he says, researchers have missed the fact that nearly half of the carbon locked up in temperate forests like the mountain ash, is in fallen trees and other dead plant material.
In tropical forests, dead plant material is rapidly decomposed and carbon dioxide is released into the atmosphere through respiration.
By contrast, moist temperate forests are warm enough to encourage good growth rates, dead plant material decays much more slowly and carbon-rich dead biomass lasts much longer.
Policy implications
Mackey says the findings reinforce the role of forests in storing carbon and in mitigating climate change.
He says the research especially underscores the importance of protecting carbon-dense forests in developed countries.
Under the Kyoto Protocol, countries are not required to account for carbon lost through degradation and deforestation of their native forests, says Mackey.
He says, the upcoming Copenhagen climate change negotiations should rectify this.
Forest industry
The forest industry argues logging old growth forests is important to reduce the risk of bushfire, which releases CO2 emissions.
"If we lock up and leave these forests, what we're actually doing is increasing the risk that these forests will burn down," Allan Hansard, CEO of the National Association of Forest Industries, told ABC Radio today.
"This is important from a climate change perspective because if you actually have a look at the amount of emissions from these fires it's actually quite substantial."
But Mackey says most of the carbon is in the woody biomass and soil, which is not burnt in fires.
And he says logging actually increases the risk of fire by opening up the forest, increasing the amount of fuel on its floor, and drying the forest out.
Growing forests?
Mackey says another common misunderstanding is that younger growing forests sequester more carbon than mature forests.
He says while growing forests have a greater rate of carbon uptake, it's more important to look at the total amount of carbon stored in a forest.
Since carbon is emitted much more rapidly than it is sequestered, Mackey says the best way to sequester carbon forests is to protect existing old forests.
"If you take one of these mature [mountain ash] forests with 1900 tonnes of carbon in it and trash it … it's going to take hundreds of years to grow back that amount of carbon."
|  Why our trees are greener than most Quote: | Why our trees are greener than most
The world's most carbon-dense forest is in Australia, researchers at the Australian National University say.
The findings that a mountain ash forest north-east of Melbourne is a more efficient carbon sink than any other that has been measured should be factored in to global climate talks in Copenhagen later this year, one of the research team members said.
"Governments should recognise the carbon value of natural forests and offer incentives to people who own them to protect and restore them," said Professor Brendan Mackey.
"Our findings reinforce the significant role of Australia's natural eucalyptus forests in carbon storage and we need to recognise the value of these forests in climate change mitigation."
Professor Mackey and his colleagues at the Fenner School of Environment and Society studied biomass data from 132 forests around the world to compare their carbon-storing ability.
While it has been commonly thought that tropical forests were the most efficient carbon sinks because of their rapid growth rates in warm conditions, the team discovered that in fact the moist temperate Eucalyptus regnans forest in the central highlands of Victoria did better.
Although plants in tropical forests grow quickly they also have high rates of respiration and decay. In the mountain ash forest, these decay rates are much slower.
"The amount of carbon stored in an ecosystem depends on the rate that plants photosynthesise and grow, but that's countered by the rate biomass respires and decays," Professor Mackey said. "[In the Victorian forest] it's wet and hot enough for photosynthesis to trundle along very happily but . . . it's cool enough so that trees hang around a lot longer."
There were other factors which contributed to the superior performance of the Victorian forest. Mountain ash trees live for a very long time - at least 350 years - growing very big and tall. They contain great volumes of wood which is also particularly dense, enhancing carbon storage.
Another important factor is that this particular forest, which is at the headwaters of the Yarra River, is part of the catchment area for Melbourne's water supply so has been protected from logging or any other human interference for at least a century. And while bushfires have flared over the years, it has evolved to adapt to the fire regime.
"If they get an intense fire that kills the tree, you haven't lost all of the carbon - most of it is in the trunk, branches and roots, and much of it remains after a fire, even as deadwood," Professor Mackey said.
He believed the research showed that how important it was to conserve and protect existing forests in developed countries, rather than simply focusing on deforestation in developing countries or on planting new trees to offset emissions.
The findings are published today in the US-based Proceedings of the National Academy of Sciences.
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19th June 2009, 06:37 PM
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