In the vine-entangled forests of the Aguarague National Park, crude that seeped for decades out of abandoned wellheads saturates the soil and has stained the bedrock of creeks that provide water to the indigenous Guarani who live nearby.

The petroleum stench is overpowering as David Benitez, who lives in the park and grazes his cattle among the wells, sifts tainted soil between his fingers.

"The odor is much stronger in the summer, when there's no water to wash the oil downstream," says the 47-year-old farmer.

Pope Francis is expected to raise concerns about the environmental costs of development next week when he meets with Bolivian President Evo Morales and his counterpart in Ecuador, Rafael Correa, on the first two stops of a three-country tour. Francis' weeklong trip follows his landmark encyclical demanding dramatic measures to halt climate change and ensure future generations aren't living in "debris, desolation and filth."

The Guarani for years have fought to protect their native lands in and around this narrow 70-mile-long park in the southeastern Chaco region that flanks Bolivia's richest natural gas fields. Francis has called on governments to better engage such indigenous peoples, calling them nature's best caretakers because the land, for them, is sacred.

Respecting native peoples, working to alleviate the poverty and living less wasteful lives are part of Francis' calls to action. But his critics say such prescriptions are unrealistic for developing economies like those of Ecuador and Bolivia that rely on mining and oil and gas extraction.

Morales, an environmental hero to many for demanding rich nations do more to halt global warming, is assailed by conservationists at home who say he puts extraction ahead of clean water and forests.

After taking office in 2006, Morales renegotiated contracts to give Bolivia a bigger share of natural gas revenues, which account for half its exports, helping him cut the poverty rate nearly in half.

But with demand outpacing production, Morales has pushed to expand oil and gas drilling. A decree issued in May will permit drilling in in all 22 of Bolivia's "protected" wilderness areas despite objections from indigenous communities.

Lacking major industries, Bolivia has no other option, he argues.

"If we don't drill for gas, what will Bolivia live off?" he told state oil workers last year.

The Guarani, the nation's third-largest indigenous group, believe the drilling only will make them poorer. Aguarague park is the sole water source for the roughly 150,000 people in Bolivia's hottest, driest region.

They point to the legacy of drilling by the state-owned YPFB oil company along the narrow ridge on which the park sits.

Oil began oozing from wellheads in the 1980s after drilling ended, but nothing was done until 2010 when Guarani protests spurred the government to promise a cleanup. Even so, the work didn't begin in earnest until this year, and the job is not done. Tons of petroleum-soaked soil need to be hauled away. Wells remain unsealed.

Officials defending the stepped-up extraction say new technology will keep production clean. But the Guarani are skeptical. Environmental protection is weak in Bolivia. Highlands mines dump toxic tailings into rivers unhindered while fines have been set so low that polluters would rather pay than clean up, environmentalist say.

Bolivia's environment and energy ministries did not respond to Associated Press requests via email and phone calls for current data on polluters and fines levied. It's not known, for example, whether a fine was ever levied against the operator of a gas pipeline across Aguarague after a 2006 spill into the Pilcomayo river.

"There's no information. No one knows," said Marco Ribera, a biologist with the Environmental Defense League, or LIDEMA.

Benitez said there's also less wildlife in the park, which was established as a natural reserve in 2000 and is habitat for jaguar, foxes and anteaters. With few rangers patrolling the area, there's little to stop illegal logging and hunting.

As for working with local natives, as Pope Francis has urged, that's not happening, according to Celso Padilla, a top leader of the Guarani, who are nominal co-administrators of Aguarague park.

"We're in an emergency," he said. "The government is doing away with Mother Earth."

Pope Francis will have an opportunity to hear that message directly in the nearby city of Santa Cruz during his tour, which takes him first to Ecuador and later to Paraguay.

The Argentine pontiff is well-versed in regional environmental issues and will raise them in private with both Morales and Correa, said Peruvian Archbishop Pedro Barreto, who coordinates a Roman Catholic Church network launched last year to fight deforestation and contamination in the pan-Amazon region.

Barreto said the pope would give each a copy of his encyclical, which accuses politicians of listening more to the oil industry than Scripture, common sense or the cries of the poor.

Both Morales and Correa have moved recently to restrict environmental groups.

In December 2013, Ecuador shuttered the non-governmental group Pachamama, which fought Correa's decision to drill for oil in Yasuni National Park and defended indigenous groups opposed to Canadian and Chinese-owned mining projects in the Amazon. The government accused it of inciting violent protests.

That same month, Morales expelled the Danish non-governmental group IBIS, accusing it of creating divisions among indigenous groups.

And on June 18, the same day Francis released his environmental treatise, Morales threatened to expel any group "that works against natural resource exploration."

Speaking at the inauguration of an oil well in the Chapare region, he accused rich nations of unfairly imposing protected wilderness areas on countries such as Bolivia.

They destroyed their own forests, he said, so now they want to be stewards of ours.

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Associated Press writers Carlos Valdez and Paola Flores in La Paz, Bolivia, contributed to this report