As little as one-third of this pre-Columbian Eden - home to bubbling springs, monkeys, jaguars and towering trees supposedly imbued with spiritual powers - is still intact.

After decades of crop burning, forest fires, insufficient environmental protection and a recent invasion by displaced indigenous people, the prognosis for this natural wonder in southern Chiapas state is alarming: 15 years of life.

"In the last 14 years the forest area has diminished by 41 per cent," said Alejandro Lopez Portillo, head of a government programme that administers resources in the Montes Azules Reserve in the heart of the jungle. "That's equivalent to 33,500 hectares per year in the Lacandon jungle."

The Lacandon region comprises some 1.9 million hectares, of which two-thirds is now pastureland or cultivated for crops.

"Given this tendency, in 2015 the trees and jungle could disappear," Lopez said, eyeing one of the gaping holes in the dense forest from the windows of a helicopter.

During an aerial tour of the region, Martin Gonzalez of the Federal Prosecutor's environmental protection wing Profepa said deforestation has been a problem for decades but has accelerated in the last few years. In 1998 alone, an abnormally strong season of forest fires destroyed some 25,000 hectares.

The government in 1978 declared about 600,000 hectares a "protected zone," giving the land to the Lacandon indigenous group, considered to be the purest descendants of the Mayas.

The heart of the protected area is known as Montes Azules (Blue Woodlands) and is an ancient region of virgin forest. Even its abrupt ravines and inaccessible areas have not saved it from settlement by other indigenous groups.

Montes Azules is home to 26 communities - 700 families with an average of seven members each - who invaded the forest illegally, a government report says. Many were fleeing violence between pro-government paramilitary groups and the armed rebel group Zapatista National Liberation Front (EZLN), which declared war against the government in 1994 to demand improved rights for the Mayan Indians. Others came to escape poverty.

Profepa estimates that the groups have devastated some 600 hectares within Montes Azules.

"What worries us most is that the invasions are not being halted; on the contrary, in the last year they've increased," Lopez said as smoke rising from agricultural fires obscured the helicopter view of the area.

Montes Azules, with just 0.16 per cent of Mexico's land, shelters 28 per cent of its mammal species, 32 per cent of its bird species, 14.4 per cent of fish and 12 per cent of reptiles.

(Agencies via Xinhua)