The fate of one of the hotspots of global diversity is hanging by a thread as conservation and indigenous groups in Ecuador race to raise a petition of over half a million names which would force a national referendum on whether foreign oil companies be allowed into the Yasuní national park.

President Rafael Correa of Ecuador appeared to sign the death warrant of the park last week when he unilaterally dissolved a radical conservation plan which guaranteed that the 840m barrels of oil thought to lie below one area of the park would remain unexploited if the international community raised $3.6bn (£2.3bn) over 13 years. Although $336m had been pledged by governments, local authorities, charities and individuals around the world, only $13m is said to have been deposited in the two trust funds administered by the UN.

Correa's decision to allow oil companies to drill below one of the most biodiverse places on the planet, where at least one tribe lives in voluntary isolation, was met by demonstrations in Quito and condemnation by international conservation organisations.

The only chance of stopping the companies now is to raise a petition of 5% of the country's 10m voters to force a referendum. If the names can be collected, Correa is likely to be defeated because recent polls suggest a large majority of Ecuadoreans remain in favour of the Yasuní-ITT initiative. This week marches were being planned in cities including Quito, Machala, Cuenca, Puyo and Guayaquil.

"The government doesn't have the right to dissolve the Yasuní-ITT initiative because this doesn't belong to them," said Esperanza Martinez, the president of the Acción Ecológica environmental group, which is part of the coalition. "The initiative was a proposal that came from civil society."

Correa has gone on the offensive, accusing ecologists and his critics of being naive, and saying poverty destroys nature faster than the oil industry. "The real dilemma is this: do we protect 100% of the Yasuní and have no resources to meet the urgent needs of our people, or do we save 99% of it and have $18bn to defeat poverty?" he said. "There are groups that are politicising the Yasuní-ITT issue to finally 'beat' the government, and especially to manipulate young folk."

Rafael Correa (@MashiRafael) ...solamente digitales para ahorrar papel y evitar tanta tala indiscriminada de árboles. Veremos quién es quién. No se dejen engañar...

He raised the stakes by threatening to force newspapers to go entirely digital. In a series of tweets he said that if the necessary signatures were gathered and there was a referendum, he would propose that newspapers be published in digital format only "to save paper and avoid so much indiscriminate cutting of trees."

Rafael Correa (@MashiRafael) ...Ahora los mayores "ecologistas" son los diarios mercantilistas. Bueno, si vamos a consutla popular propondremos también diarios ...

Environment minister Lorena Tapia promised minimal environmental impact if the oil companies went in. "The park will stay as it is, as much as the government can do. We will use the best technology and the strictest control," she said.

But conservationists said oil would inevitably lead to destruction, not just from pollution of waterways and industry infrastructure, but from tens of thousands of people flooding in to the area in search of land and work, as they have done everywhere else in Ecuador where oil has been exploited. The area north of the Tapo river, just a few miles from Yasuní, was exploited in the 70s and is now a heavily populated, highly polluted area of towns, farms and with little original forest left.

"The greatest fear is that roads will be biuilt and people will enter the park. If that happens Yasuní could be like other oilfield areas in Ecuador. Correa says the bulldozers could be starting work within weeks," said Kelly Swing, professor of environmental science at the Universidad San Francisco de Quito and director of the Tiputini research station on the edge of the Yasuní park.

Leonardo DiCaprio (@LeoDiCaprio) Disappointing news from Ecuador: Correa OKs drilling in one of most bio-diverse region in world. http://t.co/9paN6TbWE3 #noquenelyasuni

Hollywood stars this week joined international conservationists. Actor Leonardo di Caprio, in a series of tweets, said: "Sad day, but fight is not over. Correa abandoned Yasuní, but people of Ecuador have not."

Leonardo DiCaprio (@LeoDiCaprio) MT @AmazonWatch Thx for ur tweets. Sad day, but fight is not over. Correa abandoned Yasuni, but people of Ecuador have not #NoToquenElYasuni

Leading environmenatal activists accused Correa of "failing the world". Nnimmo Bassey, drector of Environmental rights action in Nigeria and former chair of Friends of the Earth International, said: "Life is more valuable than crude oil. No-one can buy the planet and all she has to offer. All who value the planet, no matter where we are located, must defend Yasuní. The Ecuadorian constitution recognizes the right of nature. Let us tell President Correa that opening up Yasuní ITT to the claws of the oil predators is a blatant abuse of nature and her rights."

He added: "Now, the only hope that remains is the reaction from the people of Ecuador. This act brings to the fore the critical struggle that we must wage around the world to ensure that elected officials do not usurp our sovereignty after being sworn into office. And the protests that greeted the announcement is a sign that the people of Ecuador are clear about the fact that the decision to allow the assault on Yasuní is not with the consent of the people."

Uncertainty surrounds the money that has already been contributed. The Ecuadorian government created both an international and a national trust which together collected about $13m. According to one source in government, deposits below $ 50,000 will not be returned.

Correa's abandonment of the Yasuní initiative is a blow to both global climate change and biodiversity. It is estimated that protection of the park would have avoided 407m metric tons of CO2 emissions and 800m metric tons of CO2 from avoided deforestation.