A new study in Nature Communications reveals that the so-called “Lost City of the Amazon,” a vast archaeological landscape in Ecuador’s Upano Valley, left ecological legacies that continue to shape modern forests.
The Upano Valley is home to more than 300 km² of pre-Columbian mound complexes, roads, and plazas, identified in recent years by LiDAR surveys that mapped over 7,000 structures. Archaeologists have long debated the scale of these settlements and the reasons for their eventual abandonment.
To provide an independent record of human impact, researchers led by Mark B. Bush of the Florida Institute of Technology analyzed a sediment core from Lake Cormorán, less than 10 kilometers from the mound complexes. The record spans the past 2,770 years and preserves fossil pollen, phytoliths, and charcoal.
Their results show that maize cultivation began as early as 570 BCE, accompanied by forest clearance and enrichment of alder (Alnus) stands, a tree valued for construction timber, firewood, and soil fertility. Evidence of slash-and-burn and slash-and-mulch techniques appears during different phases of occupation. The period between 500 BCE and 200 CE shows the strongest signals of human disturbance, aligning with the main construction and use of the Upano mounds.
Rather than ending abruptly, as some archaeologists suggested based on a debated volcanic ash layer, the record indicates a gradual decline in cultivation and burning between 200 and 550 CE, followed by forest recovery. The site was later reoccupied around 1500 CE, when maize farming resumed, leaving ecological imprints still visible in today’s forests.
The study shows that modern forests around Lake Cormorán - which appear pristine - may be as young as 120 years in composition, shaped by a combination of past cultivation, climate shifts, and succession. Palms such as Dictyocaryum, now dominant in the canopy, expanded only after human activity ceased, favored by wetter and warmer conditions in the past two centuries.
“Modern Amazonian forests are not untouched wilderness but mosaics of ecological legacies,” the authors conclude, noting that human activity left enduring footprints on vegetation even after centuries of abandonment.
The findings highlight that the Upano Valley, once larger than Machu Picchu or Kuelap, was not only an archaeological giant but also an ecological force that reshaped the forests of the eastern Andes.
Written with the help of a news-analysis system.