From the air you can appreciate the vast scale of the Petn jungle - a sea of virgin rain forest stretching in all directions. North of the frontier town of Flores, the rolling green canopy continues uninterrupted deep into neighboring Mexico and Belize. There are no paved roads and only a handful of dirt tracks and villages interspersed between the overgrown ruins of Guatemala's ancient Mayan cities.
But moving south, more and more plumes of smoke rise above the jungle floor, a telltale sign that yet another poor peasant family has arrived in the Petn. Swaths of burned earth and ragged, eroded pastures are left in their wake, consuming the jungle at an alarming rate.
With thousands of Mayan Indians desperate for land arriving from the highlands every month, many fear that North America's largest rain forest may not survive the invasion.
"The Petn will turn to desert if it is deforested; it's a scientific fact," says Carlos Soza Manzanero, director of the Flores-based environmental group Pro-Petn. "The soil can't support highland-style agriculture and erodes away, but nobody can stop the newcomers."
Hundreds of thousands of uprooted Mayan peasants - many of them former guerrilla fighters - have been on the move since the end of Guatemala's 30-year civil war. Believing falsely that the peace settlement signed in December sanctions the seizure of uninhabited lands, many have come to the Petn, a sparsely populated wilderness that makes up a third of Guatemalan territory.
This remote northwestern area has seen its population increase 22-fold to 360,000 in the past 30 years. With the annual growth rate now estimated at 10 to 15 percent and growing, the population is expected to reach 500,000 by the end of the decade.
Arriving in the wilderness, newcomers typically clear the forest using slash-and-burn tactics. But the soils are so poor that the new fields are exhausted within a year or two, and the farmers move on to clear more land to feed their families.
"The immigrants come from a culture of corn production, so they try to farm by clear-cutting just as they would in the highlands," says Hermogenes Roldan Morales, a Ministry of Agriculture and Forestry official working in Petn. "Of course these tactics don't work in tropical lowlands, with bad results for both farmers and the land." More than 40 percent of unprotected forests in the region have been "severely degraded" according to government estimates.
Even the 3.9 million acres of legally protected jungle that make up the Maya Biosphere Reserve are under threat. The government is avoiding confrontations with squatters in the reserve for fear of upsetting the peace process or donor nations. Some immigrants have reportedly cut farms inside national parks in the reserve that are designed to protect ancient Mayan structures, many of which have not been excavated.
In March, armed squatters in the reserve took 29 government officials hostage near the village of Laguna del Tigre when the officials tried to enforce a court order to move them from the protected lands. The officials were later released, but the squatters stayed.
"The peace process is misunderstood and mismanaged in this region," says Pro-Petn's Mr. Soza. "Only international pressure and assistance can protect the reserve. If it is left as an internal matter, there will only be chunks of jungle left."
The government's hand is very weak in Petn. With few roads, phone lines, or settlements, authorities have difficulty policing the frontiers.
Diplomatic sources in the capital say the Petn has become a major transshipment route for US-bound narcotics and illegal immigrants.