A woman chained herself to a tree at Wolli Creek in south-west Sydney on Thursday, as the clearance of remnant bushland to make way for the WestConnex project continued.

Environmentalists said the site was significant because it was one of the few remaining sections of critically-endangered Cooks River/Castlereagh ironbark bioregion left in the city.

On Thursday, around two dozen people opposed to the land clearing held a vigil at the site after a large part of the permitted 1.4 hectares of forest was felled the previous day.

Around two dozen protesters gathered to voice their opposition to the clearing of bushland at Wolli Creek. ( ABC: Bill Code )

The trees were being removed ahead of the construction of a parking facility for vehicles working on the construction of the WestConnex project.

Until the clearance, the forest was also the last piece of remnant bushland for several kilometres in either direction and a treasured local parkland.

President of the Wolli Creek Preservation Society Deb Little said she had enjoyed the bushland since she was a child, and said the State Government could have put the parking space on an adjacent golf course.

Birds affected by felling, Preservation Society says

As a large number of the trees were felled on Wednesday, Ms Little said she saw birds including black-faced cuckoo shrikes, which she said had likely fled the forest as the trees were cut down.

"They really looked like they were looking for a nest," she said, as a group of black cockatoos flew overhead.

Deb Little has enjoyed spending time in the forest at Wolli Creek since she was a child. ( ABC: Bill Code )

"There were also New Holland honeyeaters coming out.

"We've been here for a week, sitting around observing the birds, and haven't seen them.

"They [the honeyeaters] were certainly making what seemed like distress noises.

"They would have been smashed to smithereens the way the vegetation was just bashed down. It was sickening."

Wildlife Rescue group Wires told the ABC it had been stationed on site but as yet had not been called upon to care for any animals in the forest, which was also home to the powerful owl — listed as vulnerable.

Lost forest to be offset: Government

Speaking to 702 ABC Sydney to mark Threatened Species Day, NSW Environment Minister Mark Speakman downplayed the significance of the site.

"That ironbark forest is 1.4 hectares, there are over 1,000 hectares of that ironbark forest left in the Sydney basin," he said.

Police arrive with bolt cutters to remove a woman chained to a tree. ( ABC: Bill Code )

Mr Speakman added that Roads and Maritime Services were also required to "offset" the removal of the forest.

"That site next to the M5 isn't a stellar example of the forest because it's fairly small and has got a lot of edges, so we'll probably end up with a better biodiversity outcome finding an offset somewhere else," he said.

But Ms Little disputed Mr Speakman's take.

"If there's critically-endangered Cooks River/Castlereagh woodland out in western Sydney, shouldn't it be protected in its own right, not used as an offset?" she said.

"It's just crazy to say, 'we won't clear this bit, in offset for that?' It's also critically-endangered."