Australia's forests key to fighting global warming

Ancient Australian forests are key to fighting climate change and contain the world's most dense carbon store, eclipsing tropical rainforests as efficient greenhouse gas absorbers, according to scientists.

Towering Mountain Ash forests covering Victoria state's cool highlands hold four times more carbon, or around 1,900 metric tons of carbon per hectare, than tropical forests, scientists at the Australian National University said.

"The trees in these forests can grow to a very old age, at least 350 years, and they can grow very large, very tall, and they grow very dense, heavy wood," said Brendan Mackey, a professor of environment science.

The researchers studied biomass data from 132 forests around the world to discover regions storing the most carbon, with results published in the US-based Proceedings of the National Academy of Sciences.

The Australian forest was compared to old growth tracts on the US Pacific Coast, Siberia, the central Amazon, Thailand and Cambodia, Venezuela, Finland and elsewhere.

The findings overturn conventional thinking about the carbon density of different forest types that until now held that tropical rainforests were the most carbon-dense, remarked Mr Mackey.

The Victorian forest, part of the water catchment for Australia's second biggest city Melbourne, was a large store because the area had been protected from logging, highlighting the link between old growth forest felling and global warming.

"Part of the reason these trees store so much is that they have reached mature growth. You are just never going to store the same amount of carbon if you are turning the forest over every 40 years," said Mr Mackey.

"This reinforces the point that we need to think about the carbon value of these forests, which we've just been thinking of until now as wood supply," he said.

A second reason for Mountain Ash's carbon efficiency was that plant growth rates were balanced by rates at which biomass decayed, with the cool Victorian forests conducive to high growth and slower rates of decomposition.

That placed Australia's living and dead biomass carbon among Mountain Ash forest at 1,900 metric tons per hectare against 650 tones per hectare in temperate US Pacific forests and between 140 and 250 metric tons in most rainforests globally.