The squatters are mainly peasants who have come in search of farmland. But the population of Petén has grown to more than 500,000 from 25,000 in the 1970s, according to a Unesco report. Not all of the residents are illegal, and many seek no more than subsistence.

Willingly or not, they often become pawns of the drug lords. The squatters are numerous, frequently armed and difficult to evict. In some cases, they function as an advance guard for the drug dealers, preventing the authorities from entering, warning of intrusions and clearing land that the drug gangs ultimately take over.

A recent State Department report said that “entire regions of Guatemala are now essentially under the control” of drug trafficking organizations, mainly the Mexico-based Zetas. Those groups enjoy a “prevailing environment of impunity” in “the northern and eastern rural areas” of Guatemala, the report said.

The drug organizations have bought vast cattle ranches in the Petén to launder drug profits, as well as to conceal a trafficking hub, including remote, jungle-shrouded landing strips. Cattle ranching in the Petén has quadrupled since 1995, with herds totaling 2.5 million cattle, according to Rudel Álvarez, the region’s governor.

“Organized crime and drug traffickers have usurped large swaths of protected land amid a vacuum left by the state, and are creating de facto ranching areas,” Mr. Álvarez said. “We must get rid of them to really have conservation.”

Deforestation has led to soil erosion at Yaxchilán, a Mayan city across the border in Mexico, which in turn has swollen rivers that erode limestone temples, said Norma Barbacci, regional director for the World Monument Fund. Ash from the squatters’ burns to clear fields for planting cause acid rain that wears at temples.