Some show the head-high water mark from when the Goulburn River breached its banks in spring, inundating nearby Shepparton and Mooroopna.

Many were ringbarked by the Forests Commission in the 1930s, while others are centuries old and bare scars of Aboriginal cultural heritage.

Then there are also those that have been cut off at the stump, harvested for firewood and sold on Facebook Marketplace.

Patrolling the national park in a 4WD is Greg Chant, Hume regional manager at the Conservation Regulator, and Parks Victoria's enforcement operations manager Chris Mercier.

The two authorities, along with Forest Fire Management have been tasked with protecting local wildlife, habitat and trees of cultural significance.

Ground-dwelling animals likes bush stone curlews and lace monitors (tree goannas) are declining in the national park, while the once prominent Murray Darling carpet python has all but disappeared.

"There's been so much habitat loss here," Mr Mercier says.

He and Mr Chant can tell by the stumps which trees have been illegally felled or removed by authorities in flood works and other activities.

"You've got people that operate at a commercial level," Mr Chant says as the 4WD rocks over the uneven track.

"You've got people that just do it ... to keep their families warm at night, or ... on behalf of an elderly relative or friend who can't access firewood.

"We're all now under pressure with rising interest rates, rising costs for everything. People are going to access the cheapest available method to keep their houses warm in winter."

Victoria's autumn round of legal firewood collection runs from March until the end of June, but Shepparton's nearest collection point is about a 45-minute drive to Benalla.

The national park's proximity to the regional city makes it Victoria's biggest illegal firewood hotspot.

"It's quick access to the resource, but also you've got a ready-made market at your doorstep," Mr Chant says.

The firewood is sold on sites like Facebook Marketplace, which requires no seller identity verification and enforcement generally comes via targeted surveillance or catching perpetrators in the act.

"Trying to shut them down on social media is a difficult thing," Mr Mercier says.

"It takes a lot of investigation and that's something that we need to look at, frankly, as a whole government."

While those taking wood for personal use tend to be frustrated but co-operative when confronted by enforcement officers, Mr Mercier says commercial thieves can be aggressive or try to escape, fearing the seizure of their saws, trailers and vehicles.

"Last year, we had somebody who was coming in the opposite direction to one of our local rangers ... with four cubic metres in the trailer, tried to do a runner, broke the axle, and left it," Mr Mercier says.

Others have collided with trees or abandoned their trailers trying to escape prosecution.

Last year the Conservation Regulator laid 625 charges and issued 85 infringement notices for firewood offences in Victoria.

Many perpetrators have existing criminal records, Mr Chant says, and magistrates aren't holding back when handing out penalties of almost $10,000 and jail time if the matter goes to court.

"People we're dealing with have often been violent offenders too, so we need to be aware of that," Mr Chant says.

"Sometimes things can go wrong and we need to plan accordingly."

Trees of Aboriginal cultural significance, such as scar trees and canoe trees, have also been destroyed by firewood thieves, though perhaps unintentionally.

"Cultural heritage trees can sometimes be hard for the average person to define," Mr Mercier says.

Greater Shepparton was historically home to eight different clans of the Yorta Yorta nation.

The Conservation Regulator is currently raising awareness of cultural heritage trees and the importance of hollows for habitat, which can take 80 years to develop after a branch breaks.

Other hotspots for firewood theft include Gippsland in Victoria's southeast and the Grampians in the west.

One man living adjacent to the state forest in Gippsland was caught using a feller buncher - effectively an excavator with an attached chainsaw arm - to extract and cut hundreds of tonnes of timber at an industrial level.

Mr Mercier, who has worked in Victoria's national parks for more than two decades, says rangers are increasingly encountering fringe groups in state forests and national parks.

One man recently called Parks Victoria to declare himself above regulations, claiming he had the right to harvest firewood on public land.

"He quoted the Magna Carta and all sorts of other things," Mr Mercier says.

"The world has changed since COVID."

"Having said that," Mr Chant replies with a grin, "I've never had better reception on my phone since getting the third jab."

Jokes, confrontations and chases aside, the pair love their jobs.

"We've been doing this for a long time and I couldn't think personally what else I'd rather be doing," Mr Mercier says.

Mr Chant agrees.

"It's a privilege to be entrusted to actually do this job, to protect it for the current generations, but future generations as well," he says.

"Some of these bigger trees, once they're gone, it's going to take a long time for them to be replaced, if ever."

Australian Associated Press