A jarrah tree, believed to have been hundreds of years old, has been cut-down illegally in Western Australia's south-west, prompting outrage from environmentalists and a state government investigation.

The tree, near Gelorup, was found by a member of the public in an area earmarked for the controversial multi-million-dollar Bunbury Outer Ring Road and bypass.

It has angered community members, including local action group Friends of the Gelorup Corridor, which is fighting against development in the area.

Community activist Johnny Prefumo said it was sad news for local wildlife.

"Well you've got your cockatoos, your different types of parrots, all kinds of animals, require these trees," he said.

"They take at least 150 years to develop."

Locals think the tree was felled for firewood. ( Supplied: Friends of the Gelorup Corridor )

Mr Prefumo said it was likely the tree was cut down for firewood.

"It doesn't surprise me, people are keen to get a load of firewood," he said.

Another local, Terri Sharp said she regularly walked in the area and went to see the tree for herself.

"There's a whole pile of larger branches stacked on the other side of the fire break and there's a lot of wood missing. You can see where they've actually cut and taken bits off," she said.

"They must have loaded them into the trailer because there's old tracks there and there's no way you could carry that much wood by hand."

Authorities deny involvement in felling

Authorities say they weren't responsible for cutting down the tree. ( Supplied: Friends of the Gelorup Corridor )

The State Government department in charge of the Bunbury Outer Ring Road project has denied any involvement in the tree being cut down, with a Main Roads spokesman calling the incident 'a mystery'.

Work is yet to begin on the bypass road.

The Department of Water and Environmental Regulation will investigate the incident and whether the tree removal was in accordance with the Environmental Protection Act.

Environment Minister Stephen Dawson said he would be eagerly awaiting the outcome of the review.

"I have only just become aware that the Department of Water and Environmental Regulation has received a complaint concerning the removal of a jarrah tree in the state's south-west," he said.

"I look forward to hearing of the outcome of the investigation."

Not an isolated incident

The Walpole South Coast Environment Group was appalled at the discovery of the damaged tree. ( Supplied: Kasey Hill )

The incident came less that two months after a giant Karri tree on WA's south coast was ringbarked in an area flagged for a road-widening project in Walpole.

It is believed the vandal used a chainsaw and axe to cause the damage.

South-west Greens MP Diane Evers speculated that people could be vandalising the trees out of protest.

"I think it's some sort of violent protest to say 'get on with it' without realising the damage they are causing," she said.

"You've got a number of people trying to hold on to something they see as precious and other people who take what I would call 'violent action' to cut down this tree, knowing what upset it's going to cause."

Community members said the incident has bought back memories of old jarrah trees that were cut down by authorities south of Perth ahead of the previous state government's controversial Roe 8 project.

Another Gelorup resident Rosina Mogg said these kinds of trees need to be protected.

"We have ancient trees housing animals on the brink of extinction in line for the bulldozers," Mrs Mogg said.

"These trees should be afforded heritage listing protection."