The former Greens leader and two other activists were found guilty of trespassing after refusing to leave a logging coupe in Tasmania's Eastern Tiers on November 8, 2022.
The trio, who came before Hobart Magistrates Court on Wednesday for sentencing, have said they were defending habitat of the critically endangered swift parrot.
Magistrate Jackie Hartnett said people had a right to protest but this wasn't unfettered, even if what was occurring was against their beliefs.
She fined Brown $500 but opted not to record a conviction, partly based on his clean record apart from one conviction in the 1990s.
Ms Hartnett had previously described Brown's evidence during the court hearing as argumentative and unimpressive.
Speaking outside court, Brown said he would appeal the conviction.
"We maintain from the outset (the forestry activity) was illegal and none of us should have been convicted," he said.
Bob Brown argued his foundation had reported swift parrots in the coupe to forestry operator. (HANDOUT/AUSTRALIAN NATIONAL UNIVERSITY)
"I am not overly impressed with the magistrate's failure to understand that upholding the law means protecting critically endangered creatures.
"The magistrate has come down on the side of commerce rather than the planet."
Brown argued in court his foundation had reported swift parrots in the coupe to forestry operator Sustainable Timber Tasmania via a letter on November 2, 2022 and logging should have been paused as per protocols.
Under Tasmanian forestry plans, tree felling must cease within 500m of sightings of swift parrots or their nests until the site has been assessed.
Ms Hartnett said the letter didn't establish parrots were there and the court would have to "engage in speculation" about whether co-ordinates of the sightings were within 500m of logging on the day.
Protester Kristy Alger, with Bob Brown, was fined $16000. (Ethan James/AAP PHOTOS)
Kristy Alger, who attached herself to the boom of an excavator, was fined $1600 for "substantially" impeding forestry operations.
Ms Hartnett said Alger, a 42-year-old mother-of-three, had modest financial means but noted she had been fined twice previously for trespassing.
The third activist, Karen Weldrick, who is expected to be sentenced in November, had attached herself to an excavator with "some form of concealed mechanism".
The court was previously told search and rescue crews had to be deployed to free Weldrick and Alger.
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