In the latest case "a large number" of trees was taken around Castlemaine and Kyneton, authorities say.

Equipment has been seized after a joint police and Parks Victoria investigation into the trees cut down and removed from Fryers Ridge Nature Conservation Reserve, Lauriston Nature Conservation Reserve and Castlemaine Diggings National Heritage Park.

Parks Victoria and police plan to press charges after the months-long investigation resulted in a search warrant at a residential property.

It is a "very welcome" development, La Trobe ecologist Jim Radford said.

It is hard to get exact figures on how much Victorian firewood has been taken illegally over the years, he said.

"Anecdotally, and from what you see in the forests, you can see it's quite substantial."

Firewood theft has been rife not only through the Castlemaine and Kyneton region but in parks and reserves right across the state, Dr Radford said.

"I think there's certainly been a rise in the amount of illegal felling and fallen timber collection to supply to the Melbourne market as open wood fires become more and more popular as a luxury heating element," he said.

"You just have to look at what people are prepared to pay for a trailer-load of redgum or box. It is highly profitable, particularity when you are stealing that resource from the public estate."

Victoria's conservation regulator is currently investigating "a number" of organised groups and individuals illegally taking firewood for resale, chief regulator Kate Gavens said.

"The groups often comprise well organised teams," she said.

"A recent investigation in the Enfield State forest area involved the seizure of five vehicles, ten chainsaws along with 14 cubic metres of processed firewood. Charges have been laid against two individuals."

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Groups commonly take firewood from redgum forests in the riverland as well as small, isolated reserves of box and ironbark, Ms Gavens said.

"While these are valued firewood species, they come from slow growing forests where these illegal and destructive activities impact on valuable habitat for animals and birds," she said.

It is not only removing live trees that impacts wildlife, Dr Radford said.

"It's dead standing trees too. If they are felled they can easily be cut up and taken," he said.

"They are ecologically valuable for the hollows they provide for owls, cockatoos, gliders and goannas."

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