Jair Bolsonaro will merge Brazil’s environment and agriculture ministries, a senior aide has confirmed, raising fears the ultra-right leader will ramp up conversion of Amazon rainforest into farmland.

After his election victory on Sunday, the president-elect is putting together a cabinet that he says will “make Brazil great”, though many conservationists fear it will put short-term business interests ahead of the world’s biggest terrestrial carbon sink, indigenous communities and rich eco-systems.

During the campaign, the former army captain initially promised he would merge the two ministries to ensure production takes priority over protection. “We won’t have any more fights over this,” he said.

He later hinted he might reconsider, but any suggestion of a softening of position was thrown out on Tuesday at a meeting of his inner circle to form what aides called “a combat vanguard”.

“Agriculture and environment will be in the same ministry, as we’ve said from the beginning,” said Onyx Lorenzoni, who is expected to become chief of staff when the new government takes power in January.

The move will be cheered by Brazil’s influential agribusiness and mining lobbies, who were among the strongest backers of Bolsonaro because they want to open up the Amazon, Cerrado and other protected areas.

But the country’s current environment and agriculture ministers expressed surprise and concern over the plan.

“The new ministry that would emerge from the fusion … would have difficulties operating that could result in damages to both agendas,” said the environment minister, Edson Duarte.

“How will a minister of agriculture comment on an oil field or mineral exploration?” asked the agriculture minister, Blairo Maggi.

Marina Silva, a former environment minister and presidential candidate warned it would destroy Brazil’s reputation as a force for good in climate and biodiversity talks.

“We are entering a tragic time in which environmental protection will amount to nothing. The Bolsonaro government hasn’t even started and the backsliding is already incalculable,” she tweeted.

If the Amazon deforestation rate – already running at a rate of 52,000 square kilometres per year – accelerates, the global implications could also be immense.

The Amazon absorbs huge amounts of carbon, regulates weather systems, is home to more species than any other ecosystem on earth and pumps water to the economically important cities of São Paulo and Rio de Janeiro

“To increase deforestation and greenhouse gas emissions is to leave each and every one of us more vulnerable to an increasing risk of climate extremes,” said Carlos Rittl, executive secretary of the Brazilian Climate Observatory.

Bolsonaro has flipped back and forth on the Paris climate accord, which aims to reduce carbon emissions to ensure global warming remains within the band of 1.5C t0 2C.

He initially said he would pull Brazil out, then said it would stay in as long as there were no restrictions on his government’s plans to open up the “AAA” corridor, referring to the huge band of land stretching from the Andes, through the Amazon to the Atlantic.

He has also opposed any further demarcation of indigenous land, which would probably mean the resumption of stalled mega-dam projects in the Amazon that have been held up by the environment and indigenous affairs agencies.

More land and environmental defenders have been killed in Brazil than any other country.

Indigenous leaders said Bolsonaro’s policies and incendiary language would embolden farms, illegal miners and land grabbers to use more violence against forest dwellers.

“He is a threat to humanity,” said Dinamã Tuxá, coordinator of Brazil’s Association of Indigenous Peoples. “Those who invade indigenous lands and kill our people will be esteemed. He represents an institutionalisation of genocide in Brazil.”