Pope Francis denounced the illegal logging and exploitation of Madagascar's unique natural resources on Saturday as he opened a visit to the Indian Ocean nation with a plea for the government to fight the corruption that is ravaging the island's environment and keeping its people in "inhumane poverty."

Francis urged President Andry Rajoelina to provide Madagascar's people with jobs and alternative sources of income so they aren't forced to cut down trees to find fertile soil, poach the island's wildlife and engage in contraband and illegal exportation of its diverse flora, fauna and mineral resources.

"The deterioration of that biodiversity compromises the future of the country and of the earth, our common home," Francis warned Rajoelina and other government authorities as he began the second leg of his week-long trip to southern Africa.

Madagascar is home to 5 per cent of the world's plant and animal species, with around 95 per cent of its reptiles and 89 per cent of its plant life existing nowhere else on Earth, according to the World Wildlife Fund. Yet it is also one of the world's poorest countries, with 75 per cent of its 25.5 million people living on less than USD 2 a day.

Environmental groups and Transparency International have long highlighted the illegal logging of Madagascar's rosewood forests and other endangered tree species as evidence of the rampant corruption that has made multimillionaires out of a few "rosewood barrons" who have plundered the island's northeastern forests.

"Your lovely island of Madagascar is rich in plant and animal biodiversity, yet this treasure is especially threatened by excessive deforestation, from which some profit," Francis said. He cited forest fires, poaching and the "unrestricted cutting down of valuable woodlands" as particular threats.

More so than any pope before him, Francis has made environmental concerns a pillar of his papacy, linking global warming to the persistent exploitation of the world's poor by the wealthy.

He has issued an entire encyclical on the need to care for God's creation and next month will preside over a meeting of bishops from the Amazon, where an outbreak of rainforest fires have once again focused international attention on the need to preserve what he calls the "lungs of the planet."

Francis has also frequently called attention to the devastation wrought on the poor by corruption, often calling public officials to account on his foreign trips.

Transparency International, which ranks Madagascar among the most corrupt countries, has accused local public officials of complicity or negligence in the illegal logging, mining of gold and sapphires and the poaching of tortoises, turtles and exportation of lemurs.

In his speech Saturday, Francis urged Rajoelina, who came to power on a campaign to fight corruption, to make good on his pledges.

"I would encourage you to fight with strength and determination against all endemic forms of corruption and speculation that increase social disparity, and to confront the situations of great instability and exclusion that always create conditions of inhumane poverty," he said.

Francis, the world's first pope from the global south, acknowledged that some of the island's poor have no choice but to cut down forests to find soil or extract minerals in illegal ways that damage the environment.

"So it is important to create jobs and activities that generate income, while protecting the environment and helping people to emerge from poverty," he said.

Philip Boyle, British ambassador to Madagascar, estimated that 200,000 hectares (about 495,000 acres) of forest a year are lost in Madagascar and by some projections most of the damp, moist forest will be lost by 2040.

"Unless there are measures to prevent mass deforestation and mass reforestation then possibly the most unique habitat on earth will be lost," he said on the sidelines of the pope's speech.