Deep within a rainforest in Belize, scientists using lasers beamed from an airplane to peer beneath the dense foliage have discovered evidence of a vast network of ancient Maya farms that date back thousands of years.

The findings, part of more than 20 years of research in this part of Central America, show how the ancient Maya civilization, which reached its peak at around 250 A.D. to 900 A.D., adapted their farming practices in the face of environmental challenges.

The farms were used to grow maize, beans, squash and avocados, most likely after a series of droughts starting 1,800 years ago forced Maya farmers to expand agriculture from the region’s dry slopes into the forest’s low-lying wetlands, said Tim Beach, a University of Texas geoarchaeologist and the lead author of a paper about the finding published Oct. 7 in the journal Proceedings of the National Academy of Sciences.

“The lines of evidence suggest the wetland fields were starting as early as 2,000 years ago, and really exploding around 1,200 years ago,” Beach said. “If the uplands are dry, we speculated that this would be a natural place to expand into for a resilient culture.”

For the new research, the scientists used a remote-sensing technology known as light detection and ranging, or lidar, which involves bouncing laser pulses off surfaces to measure their contours. Over the course of two days in early July 2016, a plane flying less than 2,000 feet above the ground scanned a 100-square-mile patch of the rainforest with more than 6.5 billion laser pulses.

Maya artifacts had been previously found in the region, but the lidar measurements revealed the full scope of the farms and canals, including one area that the scientists had never seen before.

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“The beauty of lidar is it allows us to peer underneath the forest,” said study co-author Sheryl Luzzadder-Beach, a professor of geography at the university. “It allows us to get an accurate map of the ground.”

The study demonstrates the benefits of combining high-tech tools like lidar with traditional archaeological practices, according to Katharine Johnson, a University of Connecticut geographer who has used airborne lidar to unearth remains of historic sites hidden beneath dense forests in New England.

“Lidar is certainly a revolutionary tool in the field of archaeology but is best used in combination with complementary information,” Johnson said in an email. “The work in this study to date the fields and explore their uses/crops provides a fascinating look into past land use in this region, and gives a sense of the scale and magnitude at which it was occurring.”

In addition to wetland fields, the researchers found a vast network of canals.

“They run for, in some cases, a kilometer long when you add them up together,” Beach said. “They’re broken up in these patterns that look almost like a spider’s web, or like a net that you could see draped across the landscape.”

But in addition to overcoming environmental changes, it’s likely that the Maya caused some of their own when they expanded agriculture into the rainforests of northwestern Belize, according to the researchers.

Through their farming practices, which included burning the fields before planting, the Maya likely contributed to a slight regional rise in atmospheric levels of the greenhouse gases carbon dioxide and methane.

“It’s not that the ancient Maya were a source of global warming,” Beach said. “The point we want to make is that these very small changes in greenhouse gases may have been significant and may have caused some level of climate warming, which should give us cause to worry even more about what’s going on now.”

Emily Hammer, a University of Pennsylvania archaeologist who wasn’t involved with the study, said the findings provide a broader framework to understand how human activities have contributed to climate change.

“This important study and others like it are demonstrating that large-scale ancient modification of land surfaces in tropical zones across the world likely contributed to the early beginnings of a period in which humans became a significant transformative force in the Earth system,” Hammer told NBC News MACH in an email.

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