RIO DE JANEIRO—Pope Francis took on the defence of the Amazon and the environment near the end of his weeklong trip to Brazil, as he donned a colorful indigenous headdress Saturday and urged treating the rainforest as a garden.

The pontiff met with a few thousand of Brazil’s political, business and cultural elite in Rio de Janeiro’s municipal theatre, where he also shook hands with aboriginal people from a tribe that has been battling ranchers and farmers trying to take over their land in northeastern Bahia state.

In a separate speech to bishops, the pope called for “respect and protection of the entire creation which God has entrusted to man, not so that it be indiscriminately exploited but rather made into a garden.”

He also urged attention to a 2007 document by Latin American and Caribbean bishops that he had been in charge of drafting, which underscored dangers facing the Amazon environment and its native people. The document also called for new evangelization efforts to halt a steep decline in Catholics leaving for other faiths or no faith.

“The traditional communities have been practically excluded from decisions on the wealth of biodiversity and nature. Nature has been, and continues to be, assaulted,” the document reads.

Several indigenous people in the audience hailing from the Amazon region said they hoped the pope would help them protect land designated by the government as indigenous reserves, which farmers and ranchers illegally invade to cut timber and graze cattle. Grazing has been the top cause of deforestation in Brazil in recent years.

“We got credentials for his speech and attended so we could tell the pope what’s happening to our people,” said Levi Xerente, a 22-year-old member of the Xerente tribe in Tocantins state in the Amazon. “We hope that he will help intervene with the government and stop all the big public works projects that are happening in the region.”

Xerente, speaking in broken Portuguese, said the biggest threats to native peoples in the region were big agribusiness invading land and the government’s own massive infrastructure projects, including the damming of rivers for hydroelectric power generation, and roads being carved out of the forest, often to reach giant mines.

Francis thanked Brazilian bishops for maintaining a church presence in the rugged and vast Amazon, an area equivalent to the United States west of the Mississippi River. But he pushed church leaders to refocus their energies on the region.

“The church’s work needs to be further encouraged and launched afresh” in the Amazon, the pope said in prepared remarks, urging an “Amazonian face” for the church.

He cited the church’s long history of working in the region.

“The church’s presence in the Amazon basin is not that of someone with bags packed and ready to leave after having exploited everything possible,” he said. “The church has been present in the Amazon basin from the beginning ... and is still present and critical to the area’s future.”

Catholic priests and nuns have taken up the causes of Indians and of poor subsistence farmers in the Amazon, often putting themselves in danger. Violent conflicts over land rights are common in the region, where wealthy farmers and ranchers are known to hire gunmen to intimidate people into leaving land the government has set aside as reserves for their use.

Francis also issued a blistering criticism Saturday of the Brazilian church’s failure to keep its flock from straying to evangelical churches, challenging the region’s bishops to be closer to their people to understand their problems and offer them credible solutions.

In a five-page speech he read to the 300 or so bishops gathered for lunch in the auditorium of the Rio archbishop’s residence, Francis drove home a message he has emphasized throughout his first international trip at World Youth Day: the need for priests and young Catholics to shake up the status quo, get out of their stuffy sacristies and reach the faithful on the margins of society.

He took a direct swipe at the “intellectual” message of the church that so characterized the pontificate of his predecessor, Benedict XVI. He said ordinary Catholics simply don’t understand such lofty ideas and need a simpler message of love, forgiveness and mercy.

“At times we lose people because they don’t understand what we are saying, because we have forgotten the language of simplicity and import an intellectualism foreign to our people,” he said. “Without the grammar of simplicity, the church loses the very conditions which make it possible to fish for God in the deep waters of his mystery.”

According to Brazilian census data, the number of Catholics dipped while the number of evangelical Protestants and Pentecostals has nearly doubled.

The Vatican noted that the talk was both the longest and most important to date of Francis’ pontificate.

Later Saturday, Francis was presiding over an evening vigil service on Copacabana beach expected to draw more than 1 million young people. He returns to Rome on Sunday.