As ski enthusiasts make their way to Australia's premier alpine resorts this winter, few are probably aware of the ecological disaster hidden in plain view.

The Monaro region of New South Wales is the gateway to the Snowy Mountains and a mysterious dieback has attacked its dominant tree species, the eucalyptus viminalis or ribbon gum.

A map of the affected area in the Monaro Plains. ( Supplied: Cris Brack )

Hundreds of thousands of the trees are already dead in an area covering 2,000 square kilometres, roughly the size of the Australian Capital Territory.

The trees are being attacked by a native weevil, which eats out their canopy depriving them of their ability to produce energy from the sun. They literally starve to death.

Normally the hardy species can defend itself but for some unknown reason its immune system is fatally compromised.

The weevil feeds on the young shoots of eucalypts trees. ( Landline )

Forestry scientist Cris Brack from the Australian National University, said the cause of the stress was still unknown more than 15 years after the first trees started dying.

He said the full extent of the dieback was mapped about five years ago but scientists were still baffled by what was stressing the trees.

"We think maybe it's the way the rainfall is falling, so it's falling at different times of the year and the trees aren't managing to access the moisture in the soil," Associate Professor Brack said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 3 minutes 39 seconds 3 m 39 s Dr Cris Brack explains the ribbon gum dieback on the Monaro Plains. ( Bill Brown )

"The other big story is possibly changing the fire regime, maybe something to do with the Aboriginal burning and how that's changed the patterns."

He said the species played a crucial role as habitat for koalas and other small marsupials as well as birds, reptiles and insects.

"The trees have a huge role in the environment, not only providing shade, they provide habitat for animals, they have micro-changes, they pull nutrients out of the soil through the leaves back onto the leaf litter," he said.

"So they have a very large environment engineering role simply by being there, and once that goes that role disappears so there can be quite major changes to the environment."

Greening Australia is now coordinating a recovery strategy started by local land care groups.

It is planting thousands of ribbon gums on eight different properties in a research trial looking at whether ribbon gum collected from other parts of eastern Australia are resistant to the dieback.

David Bush from the CSIRO's Australian Tree Seed Centre in Canberra said the provenances being trialled came from as far away as northern NSW, Tasmania and South Australia.

"It's likely that there's going to be quite a lot of variation adaptation to different climates in that sort of collection, so we're hopeful that maybe something that's come from somewhere a bit hotter and drier or even somewhere that's got different soil types might be more resistant to the dieback," Mr Bush said.

Farmers burn the leaf litter in a stand of ribbon gums. ( ABC South East NSW: Bill Brown )

Other similar tree species such as eucalyptus benthamii, the Camden white gum, were also being trialled in case the viminalis are permanently lost to the region.

According to Greening Australia's project manager Nicki Taws, the near $500,000 recovery strategy was long overdue.

"It's not a commercially valued species, the tree itself is not a threatened species although the community that it forms is a threatened species," Ms Taws said.

"It largely occurs on private land, people have seen it, lots of people travel up and down that highway every year going to the snow fields but it really has taken a big effort to get some action taken.

"I think we can certainly restore habitat and provide connections across the landscape, whether it's with the eucalyptus viminalis, the ribbon gum, I don't know, that's still to be seen down the track when we look at the results of the trials we are doing here.

"We can certainly do something and part of the issue here is that nothing has been done for quite some time while this problem has gone on, it's gone under the radar.

"Greening Australia has been really fortunate to gain some funding from the NSW Environmental Trust which has enabled us to work with all the people we need to, the scientists, the landholders, landcare groups, the Indigenous people of the region.

"... It's a whole community problem and it really needs everyone on board to address the issue and start on ground actions to restore the landscape."

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