Pope Francis is opening a divisive meeting on preserving the Amazon and ministering to its indigenous peoples, as he fends off attacks from conservatives who are opposed to his ecological agenda.

Francis was to celebrate an opening Mass on Sunday with global attention newly focused on the forest fires that are devouring the rainforest, which scientists say is a crucial bulwark against global warming. On hand are more than 180 cardinals, bishops and priests from the region who have gathered at the Vatican for three weeks of debate.

Among the most contentious proposals on the agenda is whether married elders could be ordained priests to address the chronic priest shortages in the region. Currently indigenous Catholics in remote parts of the Amazon can go months without seeing a priest or having a proper Mass.