UPDATE: FEDERAL Environment Minister Tony Bourke has continued his attack on the NSW Government over a grazing trial.

Mr Burke said he was still investigating whether or not he has the power to stop a trial which allows livestock to return to national parks.

''All I've seen so far is a media release from the NSW Minister so I want to get to the bottom of exactly what they're proposing,'' Mr Burke told weeklyimesnow.

"I will have to check what legal powers I have; the legal authority I had in Victoria was a bit different because they were doing it at a site that had a national heritage listing on it which gave me a wider ambit of legal power.

"But the principle of this is really simple. I believe national parks are there for our native species. I don't believe national parks are there for people to be using them as a site that ordinarily would be how you use a farm, not a national park,'' Mr Burke said.

"A national park is meant to be a place where people can go and enjoy nature but increasingly we're seeing a very different view of national parks from the Liberal Party.

"They reckon in the background, instead of hearing Australian birds, you should either hear cows mooing or gunfire. It's an unusual approach to a national park.''

Environment Minister Robyn Parker yesterday announced the scientific trial in yet-to-be-determined river red gum and cypress forests in the Riverina area, saying it would only be conducted on land where permits had been issued by the former Labor government.

Ms Parker said existing grazing permits would be extended to 2016, "but no new land will be opened up ... for the trial''.

She said former Nationals MP Richard Bull would determine which of the forests would be subject to the scientific trial.

"This is a trial of the active management of forests recommended before the creation of the river red gum and cypress forest reserves by the previous government in 2010 and 2011,'' Ms Parker said.

''The trial will only be conducted on land where grazing permits were issued when the areas were State Forests.

"The trial will examine the social, economic and ecological impacts and benefits of grazing."

Labor opposition and Greens said the trial would devastate native animals and vegetation.

Opposition environment spokesman Luke Foley said the grazing trial was "the latest in a long line of attacks'' on the state's national parks, following decisions to allow hunting and horse riding.

He accused Ms Parker of bowing to the demands of the National Party and farmers, and said grazing would "have a devastating impact on our native animals and plants.''

The Victorian Government has attempted to introduce cattle grazing in the Alpine National Park, only to be overuled by Environment Minister Burke.

The Weekly Times understands the trial will include cattle grazing in the Millewa National Park even though they will be still excluded across the river in Victoria's Barmah Forest.

Member for Murray Darling John Williams said he was ecstatic at the decision.