"This research leads the academy to expect substantial negative impacts on species and ecosystems within the park arising from the provisions of the Heritage Bill," the letter said.

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The creation of a community advisory panel that had no requirement for members with scientific qualifications meant science-based advice would be "all but removed from the management" of the horses, it added.

‘Right balance’

Despite the criticism, the bill was passed by the Legislative Council late on Wednesday.

Fairfax Media approached Environment Minister Gabrielle Upton for comment about the academy's letter.

In her speech offering "strong support" for the bill, Ms Upton said the new law struck "the right balance between protecting the environment and the heritage value of the brumbies that have been in the area for nearly 200 years".

Ms Upton conceded in her speech that "the introduction of the species has affected the park over time", and said "there will need to be a reduction in the overall size of the brumby population to achieve that balance with the fragile alpine environment".

But added that "it is not a question of protecting only the heritage values of the horses or of the environment – both are important".

'Out of the blue'

Joe Hughes, who runs 4BP Horses a company that finds new homes for brumbies around the country, said the brumbies bill had "come out of the blue", and contradicted a 2016 draft plan that would have reduced their numbers from an estimated 6000 in the national park to 600 over 20 years.

"It's just insane – there's no science, no community input" on the new plan, Mr Hughes said. "I love horses but I certainly don't want them to be in a national park."

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Mr Hughes' 4BP group found homes for about 200 wild horses last year and about half that the year before.  He said many of the trapped horses couldn't be transported because they were in such poor health, and were released back in the park.

"You're releasing horses already starving back into a starving environment," Mr Hughes said.

The animals were eating out many of the edible grasses and straying into bogs and other wetlands desperate to find fodder, he said.

Mehreen Faruqi, the Greens environment spokeswoman, said there was "no lack of scientists expressing concern about this bill".

"Yet the Liberal-National government is not just pushing through with it but actually undermining the National Park’s plan of management and locking out scientific expertise and experience from the Advisory Panel," Dr Faruqi said.

The Greens along with Labor were seeking to introduce amendments to the bill, including to ensure the National Parks and Wildlife Act and National Park Management Principles prevailed over any wild horse management plan.