Brown and six supporters spent Sunday night at a logging site in the Styx Valley after harvesting machines moved in about a week ago.

Tasmania Police were called on Monday and Brown has been charged with trespass, alongside two supporters who locked themselves onto machinery.

Brown said they could be jailed for defending Australia’s natural treasures and that “onerous” bail conditions mean he can’t set foot in more than a million hectares of state forest until the matter goes to court on April 29.

He told AAP at least four or five enormous trees had been felled in a logging coupe that comes within 200 metres of the World Heritage area.

But he fears it could be many more than that and the coupe should never have been excluded from the protected zone.

“But we haven’t been over that whole coupe,” Brown said.

“One of those trees is 3.3m in diameter.

“The World Heritage Convention requires that areas of potential World Heritage value shouldn’t be logged.”

The area is home to the largest flowering plants in the world – eucalyptus regnans, which can grow to a height of 100m.

“I was sitting on one of the tree stumps, in amongst the carnage,” Brown said.

“Last week there was a brilliant ancient forest dating right back to the dinosaurs.

“This week it is a squalid … graveyard of a forest. It’s appalling.”

He says the logging could end tomorrow if the state and federal governments mustered the political will.

Veteran protester Colette Harmsen spent three months in prison last year over environmental protest action.

The veterinarian was among those charged on Monday and says native forests are worth the risk.

“The coupe we were protesting in, the size of the trees was mind-blowing,” she said.

“I’ll be going back there. We need to protect these places before they’re gone forever … even if that means spending more time in prison.”

Tasmania’s public forestry company trades as Sustainable Timber Tasmania.

It says the felled trees were not giants according to its definition, including that they must be taller than 85m, or greater than 4m in diameter at a point about 1.3m above ground level.

“Two giant trees have been identified and protected in this coupe and excluded in informal reserves,” said Suzette Weeding, who is in charge of conservation and land management.

“The area will be regenerated to native forest using seed that has been collected from the local area.”

Brown and Harmsen were granted police bail, ahead of their April court date.

Harmsen has also been banned from state forests as a condition of bail.

The third person arrested, Ali Alishah, was remanded in custody. Brown said he was arrested at the same protest site on Friday.

Four others involved in the overnight action will be issued with infringement notices, police said.

– AAP