Rangers have discovered a half-hectare site still recovering from the 2003 bushfire was destroyed by a four-wheel-drive over the weekend.
ACT Parks and Conservation's ranger-in-charge James Overall said rangers had found the site on Saturday morning in Pierces Creek Forest, just near the Lower Cotter Catchment.
"I've never seen anything like it," Mr Overall said.
Mr Overall suspected it was the work of a stolen car because of the damage it would have caused to the vehicle.
He said the destruction could have been done on Friday night or early Saturday morning.
A ranger for about seven years, Mr Overall said he was pretty despondent about the incident and now the area would need to be rehabilitated again.
"These sites that were so badly torched in 2003 have really little topsoil, so things grow very slowly out here," he said.
"That 15-year-old tree stock is now back to ground zero.
"It's been a waste of money and time."
He said hundreds of shrubs and trees had been wiped out by what seemed to be a pretty methodical attempt to create a new clearing.
Just nearby is a small bog which rangers have repeatedly tried to shut off to anti-social four-wheel-drivers who use the bog to test their vehicles.
"They keep winching out the logs and rocks just so they can get in there," Mr Overall said.
But the damage is also disruptive to native wildlife. The damaged section of native trees is sandwiched between old pine forest which native animals tend to avoid.
"They don't like moving through pine forest at all," Mr Overall said.
"It doesn't provide them with their food sources, doesn't provide them with their habitat, shelter, all those sorts of things."
"These native corridors are so important in the landscape for that reason."
Rangers were also concerned people could return to the site and get their vehicles stuck, forcing them to abandon them.
"Then they get torched," Mr Overall said.
"We've had a spate of vehicles being torched in this landscape."
In November, an abandoned car was set alight, which started the 204-hectare Pierces Creek bushfire.
Just across the road from the damaged section is the Lower Cotter Catchment, which provides Canberra with its drinking water.
While a recent report from ACT Environment Commissioner Kate Auty recommended closing sections of the catchment to cars for this reason, Mr Overall said parks was hesitant to shut sections of Pierces Creek Forest.
Mr Overall said he didn't want to tar all four-wheel-drivers with the same brush but said rangers always had to balance access.
"If anything, it would be making sure those roads in the network that are supposed to be closed, are closed," he said.
Mr Overall said ACT Policing was investigating and he hoped members of the four-wheel-drive community would out the culprits.
Sign up for our newsletter to stay up to date.