During a press briefing at the 2018 AAAS Annual Meeting, researchers described how they can use a sensing technology known as LiDAR to uncover the secrets of ancient tropical forests. | National Center for Airborne Laser Mapping (NCALM) - http://ncalm.cive.uh.edu/
Using airborne mapping, researchers are discovering new archeological sites that show pre-Columbian Mesoamerica was “significantly more densely populated at the time of European contact” than previously thought.
The findings, which were announced during the 2018 AAAS Annual Meeting in Austin, Texas, have implications for understanding the region’s history of migration, land use and conservation and even early climate changes, participants said.
Christopher Fisher, professor of anthropology at Colorado State University, pointed to two sites he has studied in the Mosquitia Rainforest of Honduras and the city of Angamuco in the Mexican state of Michoacán. Thousands of Mayan people lived in complex cities with central plazas, pyramids, reservoirs, canals and terraced farmlands in this area 1,000-2,000 years ago.
Sometime in the 1530s, Europeans discovered these cities and brought new diseases that killed an estimated nine out of 10 people of the city’s residents within a generation, Fisher said. There is evidence that the cities’ remaining residents ritually de-sanctified their religious sites before abandoning the cities, which were subsequently forgotten and hidden by dense tropical forests.
Traditional methods of on-the-ground archeological surveys would take 20 years to assemble as much data as two days of LiDAR ranging and the earlier surveys still miss important features, Fisher said. The vegetation is so dense in these forests, for instance, that after comparing his previous on-the-ground survey tracks with LiDAR data, Fisher realized he had walked within 10 meters of one of its largest pyramids on the Angamuco site without seeing it.
Sheryl Luzzadder-Beach, left, Juan Carlos Fernandez-Diaz, Christopher Fisher and Timothy Beach described how intensive and sophisticated agricultural practices by Mayan farmers have been discovered using remote sensing technology. | Professional Images Photography
That is what makes the use of LiDAR, the light detection and ranging technology, so exciting, said Juan Carlos Fernandez-Diaz, laser operator and electronics engineer at the National Center for Airborne Laser Mapping, based at the University of Houston, Texas. LiDAR uses lasers mounted on airplanes to pass through the vegetation and map the contours of the features below.
“We are finding sites in areas that we used to think were not ideal for human habitation,” Fernandez-Diaz said. “Perhaps the most important thing is we’re amassing a huge amount of data,” which can be used to document and study these sites and protect their resources.
As good as the LiDAR data are, there is still on-the-ground work to be done after compiling a LiDAR map, said Timothy Beach, professor of geography and the environment, University of Texas at Austin. He said he and his colleagues dig down as much as four meters below the surface to study the soil stratigraphy, chemistry and collect pollen and items for radiocarbon dating to understand how the sites evolved.
“There’s a lot of archeological work to be done to sort out how the populations fluctuated and how these cities grew over time,” said Beach’s collaborator, Sheryl Luzzadder-Beach, professor of geography, University of Texas at Austin.
Another aspect that Beach is studying is whether Mayan practices of clearing upland wetland land for farming and using central reservoirs and canals “could be part of this broader increase of methane that has occurred over the later Holocene.” If so, it could support the hypothesis by William Ruddiman of the University of Virginia, that agricultural practices, beginning with rice paddy farming in Asia, may have increased atmospheric methane and caused a period of global warming period that began 7000 years ago. “It’s a great hypothesis,” Beach said.
“LiDAR records are the ultimate conservation records,” since they do not degrade and are comprehensive, Fisher said. He predicts that data, which includes information about features like the vegetation, will be analyzed by scientists in the future with yet-undiscovered tools to yield more discoveries. Documenting these sites now is critical, Fisher said, because “accelerating rates of global change are threatening our patrimony in ways we’ve never seen before.”
[Associated image: National Center for Airborne Laser Mapping (NCALM) - http://ncalm.cive.uh.edu/]