UAXACTÚN, Guatemala — Deep in the jungle, where the forest canopy bends sunlight into a lattice of overlapping greens, where jaguars glide and the throaty cries of howler monkeys resound over the bird song, sits a sawmill that slices giant mahogany logs.

Ominous as the scene may look, the mill is part of a conservation strategy to preserve the forest.

The forest’s survival, indeed the endurance of forests across the tropics, whether in Brazil, the Congo Basin or Indonesia, offers benefits far beyond national borders. By absorbing carbon dioxide and trapping carbon, forests play a vital role in reducing greenhouse gas emissions.

On that, there is little disagreement. Yet it has been much harder to reach a consensus over how to fend off the threats encircling them. Cattle ranchers, farmers, illegal loggers and drug traffickers all lay waste to forestland, virtually immune to government efforts to protect it.

The experiment here in the Maya Biosphere Reserve in Guatemala’s northern Petén region suggests one solution: The most effective way to protect forests is to give control of them to the communities who already live there.