Contrasting human influences that shaped the vegetation of the Upano Valley, Ecuador.

Long histories of human occupation are emerging for the wet forests of the Andean flank, even ones that are apparently ‘pristine’. The past habitations were societally and temporally complex with sophisticated cultures emerging, flourishing, and disappearing. The Upano River in eastern Ecuador supported such cultures, and yet the timing of occupation and whether their impact on the local ecosystem resulted in lasting ecological changes is not known. Here, using paleoecological reconstructions from Lake Cormorán, located immediately adjacent to the Upano Valley and within 5 km of abandoned mound complexes, we provide a timeline of human influence spanning the last 2770 years. We document the onset of maize cultivation c. 570 BCE, changes in land use within the occupation phase, with evidence of slash-and-burn, slash-and-mulch and silviculture. A gradual decline in forest exploitation presaged an apparent abandonment of the site c. 550 CE. A much later wave of land use that began about 1500 CE, coupled with a regional transition to a wetter climate, produced a distinctive forest composition unique to the last 120 years.