New research is dismantling the long-standing myth of the "pristine" Amazon. A reconstruction of 10,000 years of Amazonian pyrogeography, based on 1,361 radiocarbon (¹⁴C) dates across 303 sites - including soil charcoal and burned archaeological material - shows that fire in the rainforest is almost exclusively a human-driven phenomenon, not a natural one. Over the last two millennia, human-ignited fire has driven vegetation change on a scale comparable to major climatic shifts, such as deglaciation or the extinction of Pleistocene megafauna. The research has been published in the open-access, peer-reviewed Frontiers of Biogeography journal.

Amazonian fires rarely, if ever, ignite without human input. In the pre-human evolutionary history of these wet forests, fire was an exceptional rarity.

Glacial-aged paleoecological reconstructions from sites like the Hill of Six Lakes in Brazil and the Serra Sul dos Carajás reveal that charcoal was either entirely absent or present in only minuscule amounts before human arrival. Even more striking, the Campo Libre sediment core on the Andean slopes of Ecuador showed a total absence of fire for 30,000 years, ending only when humans appeared on the landscape around 4,500 years ago.

In their paper, the researchers, describes the arrival of humans as the introduction of fire to a "naïve landscape." Because Amazonian plants are evolutionarily fire-sensitive, the introduction of regular burning by a fire-using species fundamentally altered a system that had been stable since the late Pleistocene.

By compiling and analysing 1,361 (¹⁴C) radiocarbon-dated charcoal fragments and archaeological materials, researchers mapped a history of human-driven fire across Amazonia that unfolded over three phases of the Holocene.

Between 10,000 and 6,000 years ago, fires were highly restricted, occurring primarily within the basin's peripheral areas and along the main channel of the Amazon River. This localised footprint shifted dramatically between 6,000 and 4,000 years ago, as the geographic spread of fire and occupation sites accelerated sharply across most regions - a development that coincided with the onset of early maize cultivation in northwestern and southwestern Amazonia.

Finally, between 3,000 and 2,000 years ago, fire reached the deep interior of the basin: though central Amazonia had remained a relatively fire-free refuge for thousands of years while the periphery burned, it was ultimately transformed as expanding human influence and fire-use reached the very heart of the forest.

This human-driven fire history is marked by a dramatic, two-phase decline over the last 700 years.

First, an initial decrease in fire frequency 600 to 700 years ago which supports the "early abandonment" of lands several centuries before European arrival. Physical evidence from lake sediments shows a significant "pollen surge" during this window, signaling massive reforestation and a major pre-Columbian shift in land use or site abandonment.

The second and larger decline followed the "Great Dying" after A.D. 1541, when disease, warfare, and enslavement killed an estimated 90-95% of Indigenous peoples in the Americas. As ignitions vanished with the population, the forest entered a second, more extensive phase of recovery.

These changing fire patterns - particularly over the last two millennia - led to an increase in human-caused fires, which spread across all regions and accelerated changes in vegetation. Ultimately, this left a profound ecological imprint that has strongly shaped today’s plant communities by selectively favoring fire-tolerant species, such as palms, over fire-sensitive vegetation.

The restructuring of Amazonian pyrogeography over the last 2,000 years has likely played a large role in shaping modern forests. The intensification of fire during this period induced rates and magnitudes of vegetation change that are comparable to major climatic shifts. The impact was subtle, favoring species that were already there but showed the most fire tolerance, such as some palms, but this pressure has undoubtedly changed the configuration of Amazonian plant communities.

- the team explained in their research article

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