The already endangered greater glider is on a fast track to extinction after the NSW environmental watchdog watered down logging protections, experts say.
WWF-Australia and other conservation groups have accused the Environment Protection Authority of reckless changes making it easier for the state's Forestry Corporation to log forests.
The EPA has ditched a requirement for the government-owned corporation to search for glider den trees before logging amid ongoing EPA investigations into the suspected illegal destruction of glider habitat in two state forests.
In both cases, it issued stop-work orders and questioned if habitat searches had been competently carried out.
After officers found a dead glider close to one harvesting site, the Forestry Corporation admitted searching for den trees during the day when the nocturnal animals were asleep in hollows.
Conservation groups hoped the EPA would enforce new rules to achieve better surveys, such as mandating night-time searches but it instead dumped the requirement altogether.
Forestry Corporation will have to retain more large, hollow-bearing trees per hectare - 14 instead of the current eight in high-density glider areas, and 12 instead of the current eight in low-density areas.
Experts are furious and say the change will fast-track the glider's slide towards extinction, given they each use a network of between six and 20 den trees and also need food trees nearby.
WWF ecologist Kita Ashman was briefed on the changes by EPA chief Tony Chappel.
"He said, 'we acknowledge it is a marginal improvement but it is still an improvement', to which I responded, 'Let me be clear, this is a step backwards'," she said.
"I told him that as an expert on this species, the EPA would be locking in this animal's extinction."
Wilderness Australia greater glider ecologist Andrew Wong said the Forestry Corporation would be able to log right up to the base of retained trees but under the old rules, a 50-metre buffer zone of bush had to be left.
Mr Wong said the new rules, due to come into effect next Friday, would not leave gliders with useful habitat and were a cruel blow for a species already on the brink.
"Everyone you talk to is basically saying they are going extinct," he said.
Mr Chappel said in a statement the changes would better protect gliders and exclusion zones would still apply around "known recorded locations of greater glider dens".
"Instead of depending on unreliable point-in-time surveys to find the habitat of the gliders, we will assume the species is present and conserve their habitat.
"We have reviewed extensive research, sought expert views and believe this change strikes the right balance, resulting in significant ecological and regulatory improvement to the current arrangements."
Forestry Corporation said it worked with the EPA on the changes and they struck the right balance between conservation and renewable timber production.
"Forestry Corporation is confident the changes will still enable us to supply the current contracted timber volumes," it said in a statement.
"We are also establishing a landscape monitoring program for Southern Greater Gliders across the state using thermal drones and spotlight surveys."
NSW Environment Minister Penny Sharpe said the new rules were "a first step, not the final step".
"These new rules are an upgrade in protections for greater gliders and protect more habitat than the previous rules," she told AAP.
"The EPA will continue to refine and update protections and work with all stakeholders to do this to ensure that greater gliders survive."
There was no comment from federal minister Tanya Plibersek, who moved the greater glider from vulnerable to endangered status after the Black Summer bushfires wiped out more than a third of its habitat.
