Bolivian wildfires have destroyed two million hectares (almost five million acres) of forest and grassland since August, according to officials.
Almost half of the losses are in "protected" areas, known for high biodiversity.
Scientists at the College of Biologists in La Paz estimate that regeneration of the local ecosystem will take about 300 years.
The government is under pressure to declare a national emergency.
Defence Minister Javier Zavaleta blamed people for starting the fires, calling them "saboteurs" who are playing a "macabre game".
"We put out the fires and there are people behind us that are starting them again… We cannot control wildfires like this," he said.
High temperatures and strong winds also stoked the flames over the weekend.
Civic groups in Santa Cruz - the worst-affected region - have imposed a Tuesday deadline for the emergency declaration, insisting it would help channel firefighting efforts and international aid.
The fires began in May and intensified in August, while blazes also raged in neighbouring Brazil.
In Bolivia, the Chiquitanía - a transition zone between the Amazon and the Gran Chaco lowlands - is the worst hit.
On Monday, Amnesty International sent a letter to the government, asking President Evo Morales to suspend his July decree, which authorised "controlled burning" in the affected areas to help farmers create bigger plots for crops.
María José Veramendi Villa, South America researcher for Amnesty International, said: "Brazil is not the only country suffering from the terrible forest fires in the Amazon ... Instead of making contradictory and baseless public declarations, Bolivian authorities must scientifically and independently investigate the origin of this serious crisis."
The president initially dismissed international help in fighting the fires, but as domestic pressure and international attention grew, he later backtracked, unlike his Brazilian counterpart who linked the offer to colonialism.
Mr Morales later agreed to hire a US "supertanker" plane - the biggest of its kind in the world - to drop water on the fires.
Russia has since sent a plane, too. "The State is only paying the operating expenses, it is not a rental," Mr Morales confirmed when it arrived on Monday.
In a series of tweets that day, he said the fires were painful for all to see and he thanked the armed forces for their work to extinguish them.
In August, he briefly suspended his controversial re-election campaign to address the issue.
Mr Morales is currently bidding for a fourth consecutive term, having gone to the courts to abolish term limits. Elections will take place on 20 October.