Hundreds of thousands of hectares of land have been cleared in Queensland, a new study has found, after a surge led by cattle graziers under relaxed laws that the state government is seeking to overturn.

A state science department study on land cover released on Sunday found 296,000 hectares of land was cleared in 2014-15, more than a third of it in Great Barrier Reef catchments.

The deputy premier, Jackie Trad, said this was an “alarming” trend that demanded immediate action to “protect the reef from this reckless clearing”.

A Labor bill to restore clearing restrictions scrapped by the former Newman government in December 2013 is due to be debated in parliament this month. The government needs the support of uncommitted independents Billy Gordon and Peter Wellington to pass the bill, which prompted a protest march on state parliament by hundreds of farmers last week.

The Liberal National opposition defended the level of clearing by farmers – 91% of which was for cattle pasture – saying it had reached a similar level of 261,000 hectares in the final year under Labor’s previous restrictions.

The government has countered by saying the 2012-13 clearance rate followed Newman’s announcement he was “taking an axe” to vegetation management laws and the government signalled it would not prosecute clearing cases leading up to its amendments.

By comparison, an average of 542,100 hectares was cleared in the Brazilian Amazon in 2014 and 2015, according to Brazil’s National Institute of Space Research.

Tree clearing has been the single decisive factor in fluctuating carbon emissions in Queensland, which was Australia’s largest carbon polluter with 27.9% of all emissions in 2014, according to the Australian National Greenhouse Accounts released in May.

Excluding emissions from tree clearing, Queensland’s carbon pollution rose 27.3% from 2000. But emissions overall dropped 4.8% in that time because tree clearing rates fell between 2005 and 2011.

Tree clearing is the only state sector, along with the waste industry, to show a real reduction in carbon emissions this century. Emissions from tree clearing made up more than a third of Queensland’s carbon pollution in 2000 but contributed just under 13% in 2014.

The Slats (Statewide landcover and trees study) report showed the rate of clearing in 2014-15 steady at what Trad said was an “unacceptable level”, almost double that of 2011-12.

The Slats figures showed clearing in reef catchments had risen 46% since 2011-12, while clearing of highest conservation value remnant vegetation had more than doubled to 114,000 hectares, making up 38% of clearing in 2014-15.

Andrew Cripps, the opposition spokesman for natural resources, accused the government of “fudging the figures to suit their own political agenda” and said clearing levels were “stable” and “sustainable”.

He said the Slats analysis appeared to conflate activities such as fodder harvesting and vegetation thinning – the “selective removal of some trees in a paddock to allow more sun for pasture growth for cattle” – with broadscale land clearing.

Cripps said 62% of all clearing in 2014-15 “ involved farming families managing regrowth on previously cleared land – a practice essential to maintain pasture to feed livestock”.

“We urge Queenslanders to see through Labor’s manipulation of data and understand that farmers need to manage vegetation to protect pasture growth, build fences and feed livestock during drought,” he said.

“Annastacia Palaszczuk and Labor claim farmers are environmental vandals, but they’re not. They look after their land to make sure it’s productive for future generations.”

Tim Seelig of the Queensland Conservation Council said the new Slats figures showed “a high clearing rate is now entrenched in Queensland, and suggested this won’t come down without swift legislative action”.

Tree clearing on this scale has a devastating effect on native wildlife, poses a big threat to the Great Barrier Reef Tim Seelig, Queensland Conservation Council

“This is the second year in a row where just under 300,000 hectares – roughly equivalent to 300,000 football pitches – has been destroyed through tree clearing in 12 months,” he said.

“Tree clearing on this scale has a devastating effect on native wildlife, poses a big threat to the Great Barrier Reef, risks worse drought and erosion, and is a major source of carbon emissions in Queensland.”

Martin Taylor of WWF called on state MPs to support the bill restoring clearing controls if they were “serious about preventing global warming, saving the reef and saving Queensland wildlife from extinction”.

Taylor said sediment flowing into the reef – of which land clearing for grazing was a “major cause” – had tripled since European colonisation of Queensland, according to an estimate by the Great Barrier Reef Marine Par Authority in 2014.