A report to be released has found the eucalypt forests of south-east Australia - stretching from Queensland through NSW and Victoria and into Tasmania - store the equivalent of 25.5 billion tonnes of greenhouse gases.

Brendan Mackay, professor of environmental science at the Australian National University, said that was far more than had been thought.

"That's an awful lot of carbon we do not want emitted into the atmosphere," Professor Mackay said.

Trees consume carbon dioxide when they grow, which they store. If the trees are chopped down, the carbon is released as carbon dioxide.

Prof Mackay said the global community should pay closer attention to the value of native forests in tackling climate change. Globally, deforestation created the same amount of greenhouse pollution as transport.

"We need to look at (forests) through fresh eyes," Prof Mackay said.

Australia's emissions trading scheme, due to start in 2010, will not include carbon emissions from logging native forests.

Prof Mackay said the federal government had not thought it through.

"The policy can no longer be blind to the green carbon that's in these natural forests," he said.

"We need to start factoring in the carbon value of these forests when deciding what to do with them."

The ANU collated field and satellite data, and found the international standard for the carbon storage potential of temperate forests was a long way out when it came to Australia.

The Intergovernmental Panel on Climate Change estimates such forests held 217 tonnes of carbon per hectare, but the ANU report found Australia's forests stored an average of 640 tonnes per hectare.

In some areas, forests stored 2000 tonnes of carbon per hectare.

That's because the forests contain such big, old trees - some 80m tall.

The research will be released in a report, "Green carbon: the role of natural forests in carbon storage", at the ANU in Canberra.